Encapsulating Hydrides and Main-Group Anions in d10-Metal Clusters Stabilized by 1,1-Dichalcogeno...

REVIEW PAPER

Encapsulating Hydrides and Main-Group Anionsin d10-Metal Clusters Stabilized by 1,1-DichalcogenoLigands

Camille Latouche • C. W. Liu • Jean-Yves Saillard

Received: 28 September 2013 / Published online: 19 December 2013

� Springer Science+Business Media New York 2013

Abstract Cu(I) and Ag(I) can form with 1,1-dithio(seleno) ligands various types

of clusters, the framework of which being maintained by the metal–chalcogen bonds

provided by the bridging ligands. The metal centers are generally tricoordinated and

consequently possess an accepting orbital of valence s and/or p character. There is

no formal metal–metal bonding, but only weak d10–d10 interactions which favor the

overlap between the metal accepting orbitals. Their bonding combinations are

generally suited for interacting with the occupied valence orbitals of an encapsu-

lated anion. Thus, many of these clusters are able to encapsulate anions, a situation

which tends to stabilize the whole structure through building of significant host–

guest bonding. Not only is the anion encapsulation effect to stabilize the cluster

cage, but it can also significantly modify its structure, or act as a template in the

stabilization of species which would not exist as empty clusters. This paper reviews

the synthesis, structure and bonding of all the known clusters of d10 metals deco-

rated with 1,1-dichalchogeno ligands and containing entrapped atomic anions. Their

structures are analyzed with respect to size and shape. The photoluminescence

properties of some of them are discussed.

Keywords Anion encapsulation � d10-metal clusters � Diseleno ligands �Structure � Bonding

C. Latouche � J.-Y. Saillard (&)

Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Universite de Rennes 1, Rennes,

France

e-mail: [email protected]

C. W. Liu (&)

Department of Chemistry, National Dong Hwa University, Hualien 97401, Taiwan, Republic of

China

e-mail: [email protected]

123

J Clust Sci (2014) 25:147–171

DOI 10.1007/s10876-013-0671-3

Introduction

The field of molecular transition-metal chalcogen clusters represents an area of

increasing activity in chemical and material science research [1]. Indeed,

chalcogeno ligands offer the peculiarity of combining the properties of: (i) providing

strong overlap (covalency) with many transition metals although not being p-

acceptor, (ii) having the ability to bridge several metals, (iii) possessing high-lying

lone pairs which can be involved in the optical and photophysical behavior of the

cluster, and (iv) induce magnetic behavior of dn complexes (0 \ n \ 10) by

reducing the HOMO–LUMO gap through lone pair p-donor effect. Besides of that,

chalcogeno metal clusters can be used as molecular precursors in the preparation of

semi-conducting metal chalcogenide nanomaterials [2].

Closed-shell d10 metals such as Cu(I), Ag(I) or Zn(II) are known to form clusters

of various sizes with various types of bridging 1,1-dichalcogeno ligands [1]. In these

species, there is no formal bonding between the metal centers. Thus, the stability of

the metallic framework is mainly ensured by the chelating effect of the ligands,

although weak d10–d10 bonding interaction between the metal centers is also often

present. This type of weak bonding is generally attributed to dispersion forces [3],

mixing of empty metallic valence s- or p-bonding orbitals into occupied d-type

combinations [4–6], relativity effects (for the heavier elements) [7] or a

combinations of several of these factors. Although it provides to the cluster with

some additional stability, it is not strong enough for inducing significant rigidity

within the cluster cage. As a result, the polynuclear metallic framework is rather

flexible and can easily adjust its size and shape for encapsulating various types of

atomic anions.

Not only such cluster cages have favorable structural flexibility for atom

encapsulation, but also they possess suitable bonding ability for making significant

ionic and covalent interactions with an encapsulated anion. In particular, significant

ionic bonding is present when the empty cages are cationic. On the other hand,

considering the local metal coordination mode and not taking into account the weak

M��M bonding, the d10 metal centers adopt generally an approximately trigonal

planar 16-electron configuration and therefore possess an accepting valence p-type

(or sp-hybrid) vacant orbital. Because of their diffuseness and of the relative

proximity of the metal centers (favored by d10–d10 interactions), these orbitals

overlap somewhat, splitting into bonding and antibonding combinations, all of them

being unoccupied. The bonding combinations can be involved in the photolumi-

nescence properties of some of these clusters because they favor the existence of

relatively stable (metal–metal bonding) excited triplet states. They also constitute a

nice set of accepting orbitals perfectly suited for interacting with the occupied

orbitals of an encapsulated hydride or main-group anion, thus inducing significant

cage-host covalent bonding. This general feature is analyzed in details for the

specific case of the octanuclear species discussed just below.

In the followings we will review a series of Cu(I), Ag(I), and to a lesser extent

Zn(II) clusters, stabilized by 1,1-dichalcogeno ligands and containing encapsulated

hydrides and main-group atoms, with a particular emphasis on structure and

bonding. Whereas some of the discussed species exhibit properties which could be

148 C. Latouche et al.

123

used in anion recognition, hydrogen storage or the design of photoluminescent

materials, we think that they present a fundamental interest per se, through their

peculiar and novel structural chemistry. The first compounds described below are

octanuclear clusters. Subsequently, clusters of lower nuclearity, the structure of

which can be described as deriving from those of the octanuclear family, will be

discussed. Finally, clusters of nuclearities larger than eight will be discussed.

Octanuclear Species

1,1-Dichalcogeno octanuclear Cu(I) clusters of the type [Cu8(E\E)6]q (E = S, Se;

q [ 0, = 0,\0) have been known for decades [8–16]. Ag(I) relatives have also been

characterized only for the i-MNT ([S2CC(CN)2]2-) ligand [17]. The idealized

structure of these empty species is of Th symmetry (Scheme 1) and can be described

as made of a regular M8 cube, the edges of which are bridged by a chalcogen atom

in such a way that each E\E ligand adopts a (l2, l2) coordination mode (an

acetonitrile adduct [Cu8{S2P(OEt)2}6(MeCN)2]2? has been reported, in which two

Cu(I) atoms in solid diagonal positions are each further connected to a N atom from

acetonitrile, thus becoming four-coordinated, see [18]).

In such a situation, each metal center is bonded to three chalcogen atoms in a

threefold and approximately planar coordination mode. This is a stable 16-electron

configuration for the metal atoms which do not require the building of formal

metal–metal bonds by sharing electrons covalently. As a matter of fact, the observed

M��M distances are consistent with only weak d10–d10 bonding interaction

(typically ranging between 2.7 and 2.9 A for M = Cu, for example).

The local planar ML3 16-electron configuration is associated with a low-lying

vacant 4pz (Cu) or 5pz (Ag) orbital perpendicular to the local coordination plane and

therefore pointing towards the middle of the cube (Fig. 1). Because of their diffuse

character and the relatively short non-bonding M��M contacts, these orbitals

overlap somewhat each other. The interaction between these eight vacant pz orbitals

gives rise to the unoccupied combinations shown in the middle of Fig. 1 [19].

The ag and tu bonding combinations have the proper symmetry and nodal properties

to interact in a stabilizing way with the occupied valence s and p orbitals of a main-

group anion which would be placed in the middle of the cage. Actually, 1,1-

dichalcogeno octanuclear Cu(I) clusters in the middle of which a main-group anion,

such as F-, Cl-, Br-, S2-, Se2-, is encapsulated are also known for decades [19–36],

as exemplified by the first structurally characterized dichalcogenophosphato example,

namely {Cu8(l8-Cl)[S2P(OEt)2]6}? synthesized in 1988 [23]. In this cluster, a chloride

anion is encapsulated in a {Cu8[S2P(OEt)2]6}2? cage. Note the cationic charge of the

empty cage which is also important in favoring ionic bonding with the negatively

charged chlorine. Cationic cages should be made of formally monoanionic (not

dianionic) 1,1-dichalcogeno ligands, such as dithiocarbamato S2CNR�2� �

, dichalco-

geno-diphosphato or -diphosphino ligands E2P ORð Þ�2 or E2PR�2 ; E ¼ S; Se� �

.

[Cu8(E\E)6]2? empty cages can be prepared quite easily by the reaction of four

equiv. of copper salts and three equiv. of 1,1-dichalcogeno ligands in common

Encapsulating Hydrides and Main-Group Anions 149

123

organic solvents under anaerobic conditions (Scheme 2). The avoidance of any

chlorinated impurities existing in the common laboratory solvent is crucial to isolate

the empty Cu8 cube. Though this methodology can be applied to both

diselenophosph(in)ates and dithiophosph(in)ates, surprisingly, it is not practical

for the dithiocarbamates (dtc). Indeed the compound, [Cu8(S2CNPr2)6]2? was only

available from the disproportionation reaction between the copper(II) complexes,

Cu(ClO4)2 and Cu(S2CNPr2)2 for which the green copper(III) compounds,

[Cu(S2CNPr2)2][ClO4], were certified as the side products [37]. On the other hand,

M

M

M

M

M

M

M

M

=E

E

Th

µ2

µ2

Scheme 1 The cubicarchitecture of the 1,1-dichalcogeno octanuclearclusters [M8(E\E)6]q

(M = Cu(I), Ag(I); E = S, Se;q [ 0, = 0, \0). The twelveedges of the metal cube arebridged by the six (l2, l2) 1,1-dichalcogeno ligands

pz

au

tg

tu

ag

d levels

d-block

HOMO

HOMO

Th

pz

tu (np)

ag (ns)

Xn-

au

tg

HOMO

Fig. 1 Simplified MO diagrams of a 1,1-dichalcogeno octanuclear clusters [M8(E\E)6]q (M = Cu(I),Ag(I); E = S, Se; q [ 0, =0,\0) and of its interaction with an encapsulated main-group saturated anionXn-


123

a copper cube with four negative charge, [Cu8(i-MNT)6]4- (i-MNT = iso-

maleonitriledithiolate = 1,1-dicyanoethylene-2,2dithiolate, [S2CC(CN)2]2-), can

be yielded if the spectator ligand is [S2CC(CN)2]2-.

Surprisingly, in the case of silver dicationic empty cages of the type

[Ag8{E2P(OR)2}6]2? or [Ag8(E2PR2)6]2? are synthetically unavailable probably

due to their unstable nature, and only one 1,1-dichalcogeno octanuclear Ag(I) clus-

ters in cubic geometry is known, namely [Ag8(i-MNT)6]4-, first made by Birker and

Verschoor [17].

Fluoride-, chloride-, and bromide-centered cubic copper clusters of the type

[Cu8(X){Se2P(OR)2}6]? can be obtained upon reaction of [Cu8{Se2P(OR)2}6]2?

with one equiv. of Bu4NX (X = F, Cl, Br) in acetone in more than 80 % yield

(Scheme 3).

In spite of the lack of silver analogues of a dicationic, empty copper cube, halide-

centered silver homocubanes can still be fabricated in a decent yield from silver(I)

salts, dichalcogenophosph(in)ates, and halide sources. Thus in a typical experiment,

the reaction of [Ag(CH3CN)4](PF6) with (NH4)[S2P(CH2CH2Ph)2] in an 8:6 molar

ratio for 10 min in THF solvent followed by the addition of 1 equiv. of halide source

under stirring leads to the formation of discrete halide-centered AgI8 clusters,

[Ag8(X){S2P(CH2CH2Ph)6}] (PF6) (X = F, Cl, Br) (Scheme 4).

More recently, it has been shown that it is possible to incorporate a hydride inside

such octanuclear cages. Hydride-centered Cu8 clusters, [Cu8(H){Se2P(OR)2}6]?, can

be synthesized in a similar fashion as their halide analogs (see Scheme 3) by using

BH�4 (or BD�4 ) in lieu of ammonium halides in THF. It appears that both 31P NMR and77Se NMR spectroscopy are excellent indicators for the compound formation since the

observed resonance frequencies of anion encapsulated species (H and X) shift

downfield in the 31P NMR spectrum and upfield in the 77Se NMR spectrum in

comparison with the empty cubane. The hydride-centered octanuclear silver relatives

can be isolated in decent yield from the reaction of BH4- with a pentanuclear extended

Scheme 2 The synthesis of [Cu8{E2P(OiPr)2}6](PF6)2 (E = Se, S)

Scheme 3 The synthesis of [Cu8(X){Se2P(OiPr)2}6](PF6) X = F, Cl, Br


123

1-D polymeric compound of the type [Ag5{E2P(OR)2}4]n(PF6)n (E = S, Se), where

hydride acts as a template. A series of cationic complexes formulated as [Ag8(H)

{E2P(OR)2}6]? have been well characterized by various spectroscopies [32, 33].

It was first thought to be synthetically impossible to add a hydride at the center of

a copper/silver [M8(E\E)6]q cluster which bears four negative charges (q = -4)

because it is disfavored from the point of view of ionic bonding. However two

penta-anionic clusters, [M8(H)(i-MNT)6]5-, (M = Cu, Ag) were subsequently

isolated and structurally characterized [34]. The reaction of AgNO3 and [nBu4N]2[i-

MNT] in an 8:6 molar ratio in THF at -20 �C for 3 h, followed by the addition of

one equivalent of (nBu4N)(BH4), produced [nBu4N]5[Ag8(H)(i-MNT)6]. It also can

be produced by the reaction of pre-formed [nBu4N]4[Ag8(i-MNT)6] with borohy-

dride in THF (Scheme 5). The presence of hydride inside the octanuclear silver

cluster is unequivocally certified by both 1H and 109Ag NMR spectroscopies.

From the structural point of view, the hydride-containing octanuclear clusters are

significantly different from their isolated halide- or chalcogenide-containing relatives.

Indeed, upon hydride insertion, the cubic cage affords a strong tetrahedral distortion

from Th ideal cubic symmetry to a tetracapped tetrahedron of T symmetry (Scheme 6).

The experimental structure of [Cu8(H){Se2P(OiPr)2}6]?, the first octanuclear

group 11 cluster containing an encapsulated hydride, is shown in Fig. 2 [30]. The

small size of hydride is not innocent in this tetrahedral distortion, but calculations

have shown that it also increases the accepting ability of the ag (a in T symmetry)

frontier orbital of the empty cage which interacts with the occupied 1 s orbital of the

Scheme 4 The synthesis of [Ag8(X){S2P(OCH2CH2Ph)2}6](PF6) (X = F, Cl, Br)

Scheme 5 The synthesis of (Bu4N)5[Ag8(H)(i-MNT)6] (from Ref. [34])


123

hydride, thus reinforcing the covalent component of the bonding between the

hydride and its cage [36].

On the other hand, this distortion lowers the accepting ability of tu (t in

T symmetry) frontier orbitals of the empty cage which are susceptible to interact

with the occupied p valence orbitals of a main-group anion (Fig. 1). Thus, the

tetrahedral distortion does not favor sp3 hybridization of the encapsulated main-

group atom. Beside of the size effect, this is the reason why encapsulated elements

from the third and fourth period (Cl, Br, S, Se) prefer the cubic Th symmetry for the

whole cluster. However, calculations have shown that a tetrahedral distortion should

also occur when a fluoride or an oxide ion is incorporated in the octanuclear cage

[36]. However, the distortion amplitude is predicted to be weak in the case of

fluoride and intermediate in the case of oxide. A distortion index (DI) can be defined

for evaluating the strength of the Th ? T distortion. Assuming that DI = 0 in the

undistorted Th cubic structure and DI = 1 in a tetracapped tetrahedron of

M

M

M

M

M

M

M

M H-

M

M

M

M

M

M

M

M + H-

=

( (

=E

E

µ2

µ2

Scheme 6 The tetrahedral distortion induced by an hydride encapsulation in a [M8(E\E)6]q cage(M = Cu(I), Ag(I); E = S, Se) (from Ref. [36])

Fig. 2 The X-ray structure of [Cu8(H){Se2P(OiPr)2}6]? with isopropyl groups omitted for clarity (fromRef. [30])


123

T symmetry in which both types of edges (tetrahedron–tetrahedron and cap-

tetrahedron) are equal, DFT calculations on model clusters of the type

[M8(X)(E2PH2)6]q (M = Cu(I), Ag(I); E = S, Se) predicts DI *81–92 % for

X = H, DI *19–36 % for X = F and DI *36–59 % for X = O. It turns out that

most of the known experimental structures of hydride-containing octanuclear

species fall within the predicted DI range [30–36]. A detailed re-examination of the

known X-ray structures of fluorine-containing octanuclear species indicates that half

of them exhibit the predicted small tetrahedral distortion, whereas the other half

affords other types of weak distortion. The explanation comes from the fact that the

calculated stabilization energy associated with the small tetrahedral distortion is

also small (a few kcal/mol), then of the same order of magnitude as the energies

associated with steric of crystal packing forces. Thus, the weak tetrahedral distortion

predicted in the gas phase for the simple calculated model can be hidden within

other types of distortions in the solid state. About at the same time a tetrahedral

distortion was predicted by DFT calculations for the hypothetical oxo-containing

[M8(O)(E\E)6] species, the related mixed copper/silver cluster Cu4Ag4(O)[E2-

P(OEt)2]6 was isolated (Fig. 3) [36]. Its X-ray structure clearly exhibits the

predicted one, i.e., an oxygen atom lying in the middle of a copper tetrahedron, the

faces of which are capped by silver atoms.

The question of the possibility of encapsulating nitride or carbide has also been

anticipated, although no compound of that type has been prepared so far. DFT

calculations predict that the encapsulation of these main-group anions should induce

a distortion of the cube towards the formation of a bicapped octahedral arrangement

of S6 symmetry, as exemplified in Fig. 4.

Finally, mention should be made of the dynamical behavior of the

[M8(H)[E2P(OR)2]6]? species. In the case of M = Ag, NMR experiments indicate

that the eight metal atoms are equivalent at the considered time scale. From DFT

calculations one can exclude the unstable Th structure as a transition state

connecting two tetracapped tetrahedra of T symmetry, which would exchange their

four tetrahedral and four capping metal atoms through this symmetrical structure.

Indeed, several vibrational imaginary frequencies are computed for the Th structure.

Meta-dynamics calculations indicate that the exchange mechanism goes through a

much unsymmetrical pathway in which the hydride goes through l1, l2 and l3

coordination modes [36].

Heptanuclear Species

Some octanuclear Cu(I) and Ag(I) clusters of the type [M8(H)(E\E)6]? (E\E = dtc,

E2P(OR)2, E2PR2; E = S, Se) have been shown under some circumstances to react

with BH4- to yield heptanuclear clusters [M7(H)(E\E)6], the structure of which

being derived from that of their [M8(H)(E\E)6]? parents by the simple removing of

one capping M? atom (Scheme 7) [38–40].

Thus, the starting tetracapped tetrahedral arrangement generates a tricapped

tetrahedral structure, the local connectivity of the remaining M atoms being

unchanged in the heptanuclear product (see for example [Cu7(H){S2P(OEt)2}6] in


123

Fig. 5). These results have inspired a theoretical investigation on various related

hypothetical heptanuclear clusters [40]. The geometry optimization of the empty

cages {M7[E2P(OH)2]6}? (M = Cu, Ag) yielded an almost perfect cubic structure

with a missing vertex. Thus, the presence of an encapsulated hydride induces a

tetrahedral distortion, both in the octanuclear species (tetracapped tetrahedron) and

the heptanuclear species (tricapped tetrahedron).

As in the octanuclear case, DFT calculations indicate that encapsulating a third-

or fourth-row main-group anion in the heptanuclear cage does not modify its cube-

derived architecture. This prediction was confirmed by the synthesis and charac-

terization of [Cu7(X){Se2P(OEt)2}6] (X = Cl, Br) [40] (see Fig. 6). Whereas no

heptanuclear fluorine species is known so far, the corresponding predicted structure

Fig. 3 The X-ray structure ofCu4Ag4(O)[S2P(OEt)2]6 withethyl groups omitted for clarity(from Ref. [36])

M

M

M

M

MM

M

M

S6

Fig. 4 Left A M8 cube prepared for a bicapped octahedral distortion. Right the computed bicappedoctahedral architecture of the [Cu8(l6-N)(S2PH2)6]- model of S6 symmetry (from Ref. [36])


123

is still cube-derived (no tetrahedral distortion as in the octanuclear relatives).

However, the fluoride ion does not sit in the middle of the uncompleted cube, but

closer to the metal located on the C3 axis, generating a kind of trigonal pyramidal

tetracoordination. On the other hand, the hypothetical {Cu7(O)[S2P(OH)2]6}- is

found to exhibit a moderate tetrahedral distortion.

Finally, it is worthwhile mentioning that the hydride-centered heptanuclear

silver(I) clusters such as [Ag7(l4-H){Se2P(OiPr)2}6] and [Ag7(l4-H){S2P(OEt)2}6]

T

MM

M

M

MM

M

M

H-E E

=

µ2

BH4-

M+

C3

[M8(H)(E E)6]+

MM

M

MM

M

M

E E

µ2

E Eµ2 µ1

M7(H)(E E)6

(E = S, Se)

Scheme 7 Tetracapped tetrahedral octanuclear and tricapped tetrahedral heptanuclear clustersencapsulating hydride (from Ref. [40])

Fig. 5 The X-ray structure of [Cu7(H){S2P(OEt)2}6] (from Ref. [38]). Left the tricapped tetrahedralCu7H core. Right the whole cluster with ethyl groups omitted for clarity


123

display photoluminescence at 77 K in CHCl3 glass with kemmax at 626 and 575 nm,

respectively [39]. The excitation wavelength is at 410 and 380 nm. DFT

calculations indicate that these transition are best described as of MLCT type in

the case of the former and mainly 4d(Ag) ? 5 s/5p(Ag) in the case of the later.

Hexanuclear Species

To our knowledge, no anion incorporation inside hexanuclear Cu(I) or Ag(I) cages

stabilized by 1,1-dichalcogeno ligands has been reported so far. One should note

however that a cluster exhibiting an encapsulated hydride inside an octahedral

Cu(I) skeleton, namely [Cu6(H)(TMTC)3Cl4]? (TMTC = trimethyltriazacyclohex-

ane), has been reported [41]. On the other hand, empty Cu(I) and Ag(I) clusters of

the type M6(E\E)6 (E\E = dtc, E2P(OR)2; E = S, Se) are known [14, 42, 43]. Two

distinct structural types, both of them having the metals in an approximate trigonal-

planar coordination mode, but differing from each other by their ligand connec-

tivity, are reported. One of them, exemplified by Cu6[S2P(OEt)2]6 [14], exhibits an

arrangement of ideal S6 symmetry which can be viewed as derived from that of the

Th octanuclear [Cu8(E\E)6]q structure discussed above by removing two of the eight

Cu(I) vertices, those lying on a solid diagonal of the cube. Actually, there are three

different ways for removing two cube vertices, leading to the three possible

Cu6(E\E)6 topologies shown in Scheme 8. Only the S6 one, noted S6(A) in

Scheme 8, is known so The other reported M6(E\E)6 structural type, exemplified by

Ag6[{E2P(OiPr)2]6 (E = S, Se) [25, 42], has also an S6 ideal symmetry (noted

S6(B) in the followings) and its ligand topology is better seen as related to that of

Fig. 6 The X-ray structure of [Cu7(Br){S2P(OEt)2}6] (from Ref. [40]). Left the cube-derived Cu7Br core.Right the whole cluster with ethyl groups omitted for clarity


123

[Cu6(H)(TMTC)3Cl4]? [41], with a metallic arrangement displaying an approximate

octahedron. Contrarily to S6(A), the S6(B) structure cannot be related to the

octanuclear Th arrangement. Nevertheless, it provides similar tricoordination to the

six metal centers.

The possibility for mono-anion incorporation inside these four different

Cu6(E\E)6 structures has been explored through DFT calculations on

[Cu6(X)(S2PH2)6]- (X = H, F, Cl, Br) models. Interestingly, the (in fact slightly

distorted to C1) C2 structure of Scheme 8 is preferred over the two other cube-

derived ones (S6(A) and Cs) in the case of hydride. Indeed, only this C2 cage allows

the tetrahedral distortion which permits the hydride to sit in the middle of a

bicapped tetrahedron. However, this distortion requires some energy cost, so that the

S6(B) structure is found to be more stable, despite it allows less cage-host covalent

bonding [40]. On the other hand, chloride and bromide prefer to be encapsulated in

the middle of the S6(A) cage. Fluoride is also computed to (slightly) prefer the

S6(A) cage, but, as in the heptanuclear case (see above), its equilibrium position is

not in the middle of the octahedron. It is shifted along the C3 axis in such a way it

lies in a pyramidal tricoordinated bonding mode. The core structures of the

computed [Cu6(X)(S2PH2)6]- (X = H, Cl, F) global minima are displayed in Fig. 7.

Tetranuclear Species

The formal continuous removal of metal vertices from an M8 cube, in order to

generate Mn species of lower nuclearity does not stop at n = 6 (Scheme 9).

Although no pentanuclear [M(I)]5(E\E)6 or[M(I)]5(X)(E\E)6 (M = d10) spe-

cies is known so far, tetranuclear complexes of the type [Zn(II)]4(X)(E\E)6

(X = O, S, Se) are well documented [44–48]. The structure of these tetrahedral

species can be derived from that of the octanuclear cubic ones by removing the

four blue vertices, as sketched in Scheme 9. In these compounds, the bonding

between the oxide ion and its guest cage can be considered as localized, with a

sp3-hybridized oxygen and four tetrahedrally coordinated (ZnXE3) 18-electron

metal centers. The Zn4 tetrahedron is surrounded by six edge-capping 1,1-

dichalcogenophosphate ligands.

M

M

M

M

M

M

M

MM

M

M

M

M

M

M

M

M

M

S6(A) C2 Cs

= Vacancy

Scheme 8 The three possibilities for a cube-derived M6 framework. The symmetry groups are that of thefull M6(E\E)6 clusters (from Ref. [40])


123

Nonanuclear Species

When going to nuclearities larger than 8, one leaves the cubic filiation. Furthermore,

in most of the cases the size of the encapsulating cage becomes larger and therefore it

is less favorable for accommodating a small anion such as hydride or fluoride. To our

knowledge, no report of anion incorporation in a nonanuclear dichalcogeno-stabilized

Cu(I) or Ag(I) cluster has been reported so far. Very recently, the compound

(Na)[Ag9(S){S2P(OEt)2}8] was isolated by one of us (C. W. Liu, H.-W. Chang, et al.,

unpublished result). It can be synthesized in 76 % yield from the reaction of

[Ag(CH3CN)4](PF6), NH4S2P(OEt)2, and NaSH in 9:8:1 molar ratios at -20 �C.

Preliminary structural investigations indicate that the Ag9S core of the [Ag9(S){-

S2P(OEt)2}8]- anion can be described as a highly distorted tricapped trigonal prism

containing a sulfide atom which is heptacoordinated to the six silver atoms

constituting the distorted trigonal prism as well as one of the capping metals (Fig. 8,

left). The corresponding Ag–S distances are comprised between 2.49 and 2.82 A.

Discarding these Ag–(l7–S) bonds as well as the weak Ag(I)��Ag(I) interactions

(Ag��Ag range 3.13–3.81 A), all the silver atoms are in a local trifold coordination

mode and therefore possess an accepting orbital susceptible to participate to the

bonding with the encapsulated anion. Preliminary DFT calculations indicate

delocalized bonding between the encapsulated sulfide and its metal cage. They also

indicate that the strength of the various Ag–(l9–S) interactions is only loosely related

to the corresponding internuclear distances, due to the strong asymmetry of the cluster

which is induced by the metal/ligand ratio and the various bonding modes of the

ligands (l2, l2), (l2, l1) and (l1, l1) (C. W. Liu, H.-W. Chang, et al., unpublished

result). Finally, it should be mentioned that (Na)[Ag9(S){S2P(OEt)2}8] displays

yellow emission at 77 K (kemmax = 573 nm) in CH2Cl2 glass.

Decanuclear Specie

The first structurally characterized decanuclear cluster containing an encapsulated

anion, namely [Ag10(S)(S2PPh2)8], was reported by Fenske and coauthors [49] some

Fig. 7 The Cu6–X cores of the isomers of lowest energy computed for the [Cu6(X)(S2PH2)6]- (X = H,Cl, F) models


123

Scheme 9 Mn (n = 8–4) cluster cubic derivations for real or hypothetical [M(I)]n(E\E)6 (M = d10)species susceptible to encapsulate monoatomic anions (from Ref. [40])


123

years ago. Its X-ray structure exhibits two highly unsymmetrical and quite different

independent molecules. In these molecules, the silver atoms are involved in three

metal–dithiophophane bonds and the central sulfide is described as hexacoordinated,

lying in a distorted trigonal prismatic environment, with Ag–S distances ranging

between 2.39 and 2.92 A [49].

The selenide-containing decanuclear species [Ag10(Se){Se2P(OR)2}8] (R = Et,iPr) are one of the products which can be obtained from the reaction of

Ag(CH3CN)4PF6 with NH4Se2P(OR)2 in diethyl ether at -20 �C [50]. Note that

the general formula of these clusters differs from the nonasilver species discussed

just above simply by the number of Ag(I) metals. The crystal structure of the ethyl

derivative has been determined. Its Ag10 core can be viewed as a highly distorted

bicapped tertragonal prism, with Ag��Ag distances comprised between 2.96 and

3.38 A (Fig. 8, right). The encapsulated selenide is in bonding contact with the ten

metal centers. However, two Ag–(l10–S) distances are relatively long (3.17 and

3.18 A) as compared to the others (range 2.63–2.98 A). Theoretical calculations

confirm significant covalent interaction for these longer contacts (C. W. Liu et al.,

unpublished result). As in the case of the related nonanuclear clusters discussed just

above, the bonding between the encapsulated sulfide and its metallic cage is highly

unsymmetrical. It is noteworthy that the corresponding covalent interactions are

similar in both types of clusters, whereas the ionic component is slightly stronger in

the decanuclear case, due to the higher positive charge of the hosting cage.

Undecanuclear Species

Two idealized metallic arrangements (Scheme 10) have been reported in the case of

undecanuclear species encapsulating anions: The hexacapped trigonal bipyramid

[51] and the pentacapped trigonal prism [52–59]. Actually, these two different

topologies are not unrelated, for there is a continuous transit which can interconvert

them. Therefore, one can assume that such a cage is able to adjust its shape to the

size of the encapsulated anion.

The hexacapped trigonal bipyramidal structure is adopted by the hydride-

containing [Ag11(H)(S2CNPr2)9]? cluster [51]. It can be prepared by the reaction of

Fig. 8 The Ag9S (left) and Ag10Se (right) cores of [Ag9(S){S2P(OEt)2}8]- and [Ag10(Se){Se2P(OEt)2}8](from Ref. [50, C. W. Liu, H.-W. Chang, et al., unpublished result], respectively)


123

Na(S2CNnPr2) with AgNO3 in the presence of NaBH4 in 9:11:1 molar ratios in

MeCN at -20 �C for 3 h. A similar reaction carried out in the presence of NaBD4

instead of NaBH4 produces [Ag11(D){S2CNnPr2}9](NO3). In the X-ray structure, the

adjacent Ag��Ag distances range between 2.82 and 3.12 A and the hydride is

located close to the middle of the bipyramid. DFT calculations on the

[Ag11(H)(S2CNH2)9]? model found an optimized geometry in quite good agreement

with X-ray (Fig. 9).

It is of C3 symmetry (the highest symmetry possible considering the ligand

arrangement) with the hydride sitting almost exactly in the middle of the bipyramid

(optimized Ag–H distances: 3 9 1.90 and 2 9 2.28 A). This result is at variance with

the Mn(H)(E\E)6 (n B 8) cube-derived species discussed above which show a

preference for hydride sitting in a tretrahedral site. Therefore, the possibility for the

hydride sitting in the middle of one of the fused tetraheda constituting the hexacapped

bipyramid has also been tested by DFT calculations. Results indicate that this

possibility should be excluded. It is however predicted that the hydride should easily

move vertically away from its equilibrium position, such a displacement requiring

little energy. This finding is consistent with 1H and 2H NMR measurements [51].

Discarding their interactions with the central hydride and the other metals of the

cluster, the three equatorial silvers (black atoms in Scheme 10) are only di-

coordinated (SAgS angle = 91�), whereas all the other metals are tricoordinated, as in

most of the clusters discussed in this review. The resulting 30 Ag–S bonds are provided

by six (l2, l2) and three (l1, l1) dithiocarbamate ligands: the low (l1, l1) coordination

mode resulting from space filling limitations around the hexacapped trigonal

bipyramidal metallic arrangement. It is likely that the particular unsaturation of the

three equatorial metals tends to strengthen their interaction with the hydride and

therefore favors the hydride position in the middle of the equatorial metal triangle.

The related chalcogenide-containing [Ag11(X)(S2CNEt2)9] (X = S, Se) clusters

are also known [60–64]. Due to the larger size of the encapsulated anion, the Ag11

M

M

M

M

M

M M

M

M M

M

M MM

M

MM M

MM

M

M

Scheme 10 The 11-vertex hexacapped trigonal bipyramid (left) and the pentacapped trigonal prism(right). Their interconversion is associated with a change in the size of the blue and black triangles andwith a vertical displacement of the red atoms (Color figure online)


123

polyhedron resembles more to a pentacapped trigonal prism. Nevertheless, as in

[Ag11(H)(S2CNPr2)9]?, the encapsulated anion is pentacoordinated in a trigonal

bipyramidal configuration, being located, not exactly, but close to the center of the

Ag11 polyhedron. Probably because of the more ‘‘spherical’’ shape of this

polyhedron, the three equatorial metal atoms can achieve tricoordination, the 33

Ag–S bonds being provided by six (l2, l2) and three (l2, l1) dithiocarbamate

ligands. DFT calculations on the [Ag11(E)(S2CNH2)9] (E = S, Se) models

reproduce all these structural peculiarities [63]. As for the hydride derivative, a

displacement of the encapsulated chalcogenide along the C3 axis away from the

middle of the equatorial metallic triangle is computed to be almost energy-free over

a few tenths of A. As a matter of fact, the related [Ag11(X)(S2CNPr2)9] (X = S, Se)

derivatives, recently synthesized by one of us [63], exhibit an X-ray structure in

which the chalcogenide, does not lie at the middle of the metal polyhedron, but is

shifted close to one of the axial metals. As a consequence, the entrapped

chacogenide is heptacoordinated with average X–Ag distances of 2.69 and 2.79 A

for X = S and Se, respectively.

In the 1,1-dichalcogenophosphate family of ligands, somehow related clusters

have are also known, namely the [Ag11(S){S2P(OR)2}8]? (R = Et, Pr, iPr) series

[64]. They can be prepared by treatment of [Ag(CH3CN)4]?, S2P(OR)2-, and S2O4

2-

in 11:8:1 ratios (Scheme 11) and these compounds exhibit photoluminescence at

298 K. Upon excitation at k[ 380 nm resulted in a broad emission centered at

*720 in the near-IR region. In the solid state, the metal framework exhibits an

extremely distorted pentacapped trigonal bipyramidal structure. A total of 30 Ag–S

bonds are provided by six (l2, l2) and two (l2, l1) dithiophosphates. Discarding the

bonding with the encapsulated sulfide, eight metals are tricoordinated and three are

dicoordinated. However, the crystal structure reveals two supplementary bonds with

an acetone molecule (used a solvent in the synthesis). These weaker bonds complete

tricoordination for two of the three coordinatively ‘‘unsaturated’’ metals. It is not

excluded that in solution, another coordinated acetone molecule achieves

Fig. 9 X-ray (left) and DFT-optimized metallic skeletons entrapping a hydride in [Ag11(H)(S2CNPr2)9]?

(from Ref. [51])


123

tricoordination for all the metals. The encapsulated sulfide is pentacoordinated (Ag–

S range 2.40–2.65 A) in a particularly irregular fashion [64]. It is likely that the

structural difference between this dithiphosphate species and the dithiocarbamate

derivatives discussed just above is related to their difference in their number of

ligands.

Another class of undecanuclear clusters is composed of the

[M11(X)(X0)3{E2P(OR)2}6]q (M = Cu, Ag; X0 = chalcogen, q = 0; X = halogen,

q = ?1; X = halogen; E = S, Se) family. For example, [Cu11(l9-Br)(l3-

Br)3{S2P(OiPr)2}6](PF6) can be prepared by the reaction of [Cu(CH3CN)4](PF6) with

NH4[S2P(OiPr)2] in an 11:6 ratio in methanol followed by the addition of 4 equiv. of

Bu4NBr at ambient temperature. Treatment of [Cu11(l9-Br)(l3-Br)3{S2P(OiPr)2}6]?

with excess amount of Bu4NI in acetone yields yellow powders of [Cu11(I)(I)3{S2-

P(OiPr)2}6]?, a result of replacement of bromides with iodides. Intriguingly the

reactions of [Cu11(Br)(l3-Br)3{S2P(OiPr)2}6]? and [Cu11(I)(l3-I)3{S2P(OiPr)2}6]?

with Na2S2O3 in acetone produce [Cu11(S)(l3-Br)3{S2P(OiPr)2}6] and [Cu11(S)

(l3-I)3{S2P(OiPr)2}6], respectively [59]. The central bromide/iodide can be replaced

by a sulfide yielded from Na2S2O3. On the other hand, the reaction of

[Ag(CH3CN)4](PF6) with (NH4)[E2P(OiPr)2] (E = S, Se) in an 11:6 ratio for an hour

in methanol solvent followed by addition of four equiv. of Bu4NI, led to the isolation of

air and moisture stable discrete iodide—centered AgI11 clusters, [Ag11(l9-I)(l3-

I)3{E2P(OiPr)2}6](PF6) (E = S, Se) [58]. The metallic framework of these clusters can

be unambiguously described as a pentacapped trigonal prism and the encapsulated

anion is nonavalent, being bonded to all the metal atoms but the two who cap the

triangular faces. The six 1,1-dichalcogeno ligands are in a (l2, l2) coordination mode

and the three halogenide ligands are capping three among the six ‘‘vertical’’ triangular

faces defined by the black metals of Scheme 11. An idealized view of the Ag11(l9-

X)(l3-X0)3 core of such species is shown in Fig. 10. Discarding bonding with the

encapsulated anion, each metal atom is in a local tricoordination mode. The two metals

capping the triangular faces are bonded to three S (or Se) atoms, whereas the other

metals are bonded to two S (or Se) and one X0 atoms. Thus, the 33 metal–ligand bonds

are provided by the six (l2, l2) 1,1-dichalcogenophosphates and three l3-X0 ligands.

The ideal symmetry of the whole cluster is C3h. The bonding in these clusters has been

subject of theoretical investigations [52, 58], especially in the case of the [Ag11(l9-

I)(l3-I)3 {E2P(OiPr)2}6]? which is the first characterized compound exhibiting a

nonavalent iodine atom [58]. Calculations indicate that iodide is similarly bonded to its

two types of silver first neighbors. The covalent interaction with the two metals which

cap the triangular faces is much weaker, confirming nonavalency. As a whole, the

covalent bonding between the l9-I atom and its hosting cage is equivalent to the

bonding of one of the l3-I capping ligands with the rest of the cluster.

Finally, mention should be made on the fact that most of the undecanuclear

clusters discussed above exhibit photoluminescence properties in the UV–Vis

region [51–59]. DFT calculations have shown that these properties are associated

with an excited triplet state which correspond to the occupation of a low-lying

orbital (usually the LUMO or LUMO?1) which is a totally symmetrical metal–

metal bonding combination of dominant valence s or p character. Indeed, the


123

16-electron configuration of each metal center of the empty cage induces the

existence of a vacant s/pz hybrid on it. Whatever is the symmetry of these the

11-vertex species, there are several totally symmetrical combinations of these local

hybrids. If one of them (or a combination of) is always mobilized for the bonding

with the encapsulated anion, at least one remains available for occupation in the

excited state. Its metal–metal bonding character tends to stabilize the triplet state

and in turn favors the emissive properties.

Dodecanuclear Species

The dodecanuclear silver clusters [Ag12(l5-X)2{E2P(OEt)2}10] (X = Br, I; E = S,

Se) have been reported recently by one of us [65]. They have been isolated from the

reaction of [Ag(CH3CN)4](PF6) with dichalcogenophosphate ammonium salts and

Scheme 11 The synthesis of [Ag11(S){S2P(OR)2}8](PF6) (R = Et, Pr, iPr) (from Ref. [64])

Fig. 10 The C3h idealizedAg11(l9-X)(l3-X0)3 core of the[M11(X)(X0)3{E2P(OR)2}6]q

(M = Cu, Ag; X = chalcogen,q = 0; X = halogen, q = ?1;X0 = halogen; E = S, Se)


123

halides. They can be viewed as centrosymmetrical dimers of hexanuclear units

[Ag6(l5-X){E2P(OEt)2}5] linked through two Ag–E and two Ag��Ag contacts

(Fig. 11). Within a monomer, the Ag6 core can be viewed as a highly distorted

bicapped tetrahedron (or monocapped trigonal bipyramid). The halide is approx-

imately located at the center of the distorted trigonal bipyramid, giving rise to five

non-equivalent X–Ag bonds. In the case of [Ag12(l5-Br)2{S2P(OEt)2}10] for

instance, they lie in the range 2.70–3.20 A. Discarding the Ag–X bonds, all the

metal atoms are tricoordinated, whereas two and three E2P(OEt)2 ligands are in (l2,

l1) and (l2, l2) coordination mode, respectively. It is interesting to note that the

cluster shape of these ‘‘monomers’’ differs from that of the (centered or empty)

hexanuclear species discussed above, the reason being very likely related to the

different number of dichalcogeno ligands.

The synthesis of [Ag12(l5-X)2{E2P(OEt)2}10] (X = Br, I; E = S, Se) can be

achieved via the reaction of [Ag(CH3CN)4](PF6) with diethyl dichalcogenophosphate

ammonium salts in a 6:5 ratio in methanol at -20 �C for an hour followed by the

addition of one equiv. of Bu4NX (X = Br, I). The reaction can be completed within

5 h. Importantly the utilization of dihalogens as templates in the cluster synthesis

appears to be a new feature in supramolecular chemistry. Unfortunately, all three

dodecanuclear silver compounds are non-emissive in both solid state and solution.

Very recently, compound ½Ag12ðl12 � IÞðl3 � IÞ4 S2P CH2CH2Phð Þ2� �

6� (I) was

synthesized and characterized in our group [66]. It was obtained from

Ag CH3CNð Þ4� �

PF6ð Þ with NH4ð Þ S2P CH2CH2Phð Þ2� �

in a 2:1 molar ratio followed

by the addition of one equivalent of Bu4NI. The X-ray structure exhibits a highly

symmetrical cation ½Ag12ðl12 � IÞðl3 � IÞ4 S2P CH2CH2Phð Þ2� �

6�þ of Td symmetry

in which an encapsulated iodide sits in the middle of an Ag12 cuboctahedron

Fig. 11 The structure of [Ag12(l5-Br)2{S2P(OEt)2}10]. The ethoxy groups are omitted for clarity (fromRef. [65])


123

(Fig. 12a). The 12-coordination of the central iodine is the largest one even recorded

for a main-group atom. Only one other example of such coordination mode is

known, namely TpMo� l3 � Sð Þ4Cu3

� �4

l12 � Ið Þ� ��

(Tp = hydridotris(pyrazol-

1-yl)borate) which also exhibits a Cu(I) cuboctahedron centered by iodide [67]. In

½Ag12ðl12 � IÞðl3 � IÞ4 S2P CH2CH2Phð Þ2� �

6�þ, four supplementary iodide cap

triangular metallic faces and the coordination mode of six dithiophospane ligands

is (l2, l2) (Fig. 12b). As a result, each metal atom is involved in three metal–ligand

bonds (one Ag–I and two Ag–S), discarding the interaction with the central iodide.

Calculations indicate that this later interaction is quite similar to that existing in the

undecanuclear cluster the Ag11 l9 � Ið Þ l3 � Ið Þ3 E2P OiPr� �

2

� �6

h iþ, both in terms

of bonding energy and of the balance between covalent and ionic bonding.

This dodecanuclear cluster was obtained from the reaction of

[Ag(CH3CN)4](PF6) with (NH4)[S2P(CH2CH2Ph)2] in a 2:1 molar ratio in methanol

followed by the addition of one equiv. of Bu4NI. A distinct quintet peak

(2JPAg = 6.4 Hz) revealed in the 31P NMR spectrum coupled with a triplet peak

(2JPAg = 7.0 Hz) depicted in the 109Ag{1H} NMR spectrum implies that the

molecular cation retains a Td symmetry in solution. The complex displays a yellow

luminescence under UV irradiation in both solid and solution state (kemmax = 533 nm)

with the emission life time in microsecond range. It appears that the ammonium

bis(2-phenethyl)dithiophosphinate ligand is very special in the formation of new

dodecanuclear silver cluster. Attempts to isolate a Ag11(l9-I)(l3-I)3 core of C3h

(vide supra) symmetry with this type of ligands have failed to date for which the

probable reasons cannot not be rationalized.

General Considerations

In principle, increasing the metal nuclearity of the cluster cage should lower its

probability to encapsulate atomic anions, due to the size requirement of the latter.

Fig. 12 a A l12-I—centered cuboctahedral AgI12 skeleton. b Molecular structure of [Ag12(l12-I)(l3-I)4

{S2P(CH2CH2Ph)2}6]? with alkyl groups omitted for clarity (from Ref. [66])


123

This is probably the major reason why encapsulation of main-group atoms in

Cu(I) and Ag(I) clusters stabilized by dichalchogeno ligands has not been reported

so far for nuclearities larger than 12. One should note however that Cu(I) clusters of

nuclearity 16, containing a central halide and stabilized by monothiolato-amino

ligands are known [68]. In these [Cu16L12X]3? (L = (C6H4NMe2)CH =

N(C6H4)S-); X = Cl, Br, I) species, the encapsulated halide is tetrahedrally

bonded to four metals, the other Cu(I) atoms forming a more external sphere. The

whole framework is maintained by the bridging monothiolato-amino ligands [68].

Thus, under some circumstances, a cage of rather large nuclearity can adapt its

shape to the size requirement of the encapsulated atomic anion. It is likely that the

template effect of the ligand is a crucial factor in the stability of these species. This

assertion is consistent with several calculations on the empty cage of anion-

containing clusters with nuclearity larger than 8 which suggest that most of these

empty species are not viable in the meaning of Hoffmann et al. [69], i.e., unlikely to

be isolated as empty clusters.

Anion-containing clusters of nuclearity 16 are also known for derivatives

stabilized by 1,1-dichalcogeno ligands, but this time the encapsulated anions are

molecular species. Compounds [Ag16(EO4){S2P(OEt)2}12]24? (E = S, Se) and

[Ag16(MO4){S2P(OEt)2}12]24? (M = Cr, Mo) have been reported to have a similar

structure, with a tetrahedral sulfate, selenate, chromate or molybdate dianion

entrapped inside a distorted Ag12 icosahedron which is capped by four supplemen-

tary metals. Furthermore, the [Ag16(EO4){S2P(OEt)2}12]2? and [Ag16(MO4){S2-

P(OEt)2}12]2? clusters are dimerized through Ag–S bonds [70]. These examples

stress the fact that the space situated inside large cages needs to be occupied by

stuffing of sufficient volume. This is what happens for example in the chemistry of

large gold clusters in which the cavity space is filled with supplementary gold atoms

[71–74]. However, electrons are necessary to ensure enough Auouter–Auinner

bonding. This is why in this family of clusters the average gold oxidation state is

comprised between 1 and 0. No such behavior is observed in the title clusters in

which the metal oxidation state is always equal to 1. Nevertheless, nano-sized

Cu(I) clusters stabilized by 1,1-dichalcogeno ligands have been shown to exist, as

exemplified by the first structurally characterized example [Cu20(H)11

(S2P(OiPr)2)9], which was isolated, in addition to [Cu7(H)(S2P(OiPr)2)6], from the

reaction of NH4[S2P(OiPr)2], [LiBH4.thf] and Cu(CH3CN)4PF6 [75]. A salient

feature of [Cu20(H)11(S2P(OiPr)2)9] is that it is capable of releasing H2 gas upon

irradiation with sunlight, under mild thermal conditions (65 �C), or in the presence

of acids at room temperature. This cluster contains encapsulated Cu(I) ions and

supplementary hydride ligands which are located close to, but inside, the cage

envelope where they cap triangular or square faces. Supplementary capping

hydrides are located on the outer side of the cage. More precisely, its metal

framework can be described as a Cu18 elongated triangular orthobicupola centered

by a dicopper unit (Fig. 13). The eighteen copper atoms constituting the cage are

maintained together by nine dithiophosphate ligands which cap quadrilateral faces

in a tetrametallic tetraconnectivity. Moreover, six outer hydrides are capping

triangular faces. The content inside the Cu18 orthobicupola can be viewed as a

[Cu2H5]3- unit made of two copper atoms located inside a [H5]5- trigonal


123

bipyramid. Hence, the two copper atoms and two hydrides of the [Cu2H5]3- unit are

located on the cluster C3 axis and the remaining three hydrides are located on the

equatorial plane (Fig. 13). Thus, in these species the glue between the inner and

outer metals is not made by electrons as in the partially reduced gold clusters

discussed just above, but by hydrides which are situated in between both types of

metals. Thus, it is anticipated that the concept of hydride-mediated growth of copper

nanosized clusters as demonstrated in [Cu20(H)11(S2P(OiPr)2)9] will be extended to

other d10 metals such as Ag(I), Au(I), Zn(II), Cd(II), and Hg(II).

Acknowledgments Dr. S. Kahlal is acknowledged for fruitful discussions and criticism of this review.

JYS thanks the Institut universitaire de France for support. CWL thanks National Science Council of

Taiwan (NSC 100-2113-M-259-003-MY3) for financial support.

Fig. 13 The X-ray structure of [Cu20(H)11(S2P(OiPr)2)9]. Color code: elongated triangular orthobicupolaframework (cyan), Cu (purple), H (red), S (yellow), P (blue), O (green) (from Ref. [75]) (Color figureonline)


123

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Encapsulating Hydrides and Main-Group Anions in d10-Metal Clusters Stabilized by 1,1-Dichalcogeno...

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