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A method for topological analysis of high nuclearity coordination clusters andits application to Mn coordination compounds†

George E. Kostakis,*a Vladislav A. Blatov*b and Davide M. Proserpio*c

Received 25th November 2011, Accepted 10th January 2012DOI: 10.1039/c2dt12263d

A novel method for the topological description of high nuclearity coordination clusters (CCs) wasimproved and applied to all compounds containing only manganese as a metal center, the data onwhich are collected in the CCDC (CCDC 5.33 Nov. 2011). Using the TOPOS program packagethat supports this method, we identified 539 CCs with five or more Mn centers adopting 159topologically different graphs. In the present database all the Mn CCs are collected and illustrated in sucha way that can be searched by cluster topological symbol and nuclearity, compound name and Refcode.The main principles for such an analysis are described herein as well as useful applications of thismethod.

Introduction

The coordination chemistry of polynuclear coordination clusters(CCs) represents one of the most successful, productive anddynamic scientific field of Inorganic Chemistry. Over the lasttwo decades, chemists’ interest in this scientific field has growntremendously either modeling bioinorganic systems such asPhotosystem II1 or synthesizing finite CCs which can behave assingle molecule magnets (SMMs).2 The improvement of the X-ray facilities for the structure determination represents one majorparameter which acts as a source of inspiration for inorganic che-mists, thus, during only the last decade, the synthesis, structuralcharacterization and properties of several high nuclearity CCssuch as Mn84,

3 Ni32,4 Cu44,

5 Fe168,6 Mo368,

7 have been reported.The description of high nuclearity CCs relied on the abilities

of each author to understand the stipulation of the CC based onthe representation of a classic Platonic polyhedron. In somecases when robust polytopic ligands are employed into a directedself-assembly process then CCs are isolated which can bedescribed in terms of (n × n) square grids,8 or a limited class ofCCs can described adopting the metallacrown approach; amethod introduced by Pecoraro et al. 15 years ago.9 However, in

both cases the abilities of these methods are restricted to thedescription of a few examples. The recently reported high CCssuch as Fe168,

6 Er60,10 Co36,

11 Cu17Mn28,12 Cu24Dy8,

13 orNi54Gd54

14 revealed the limits of this platonic descriptionbecause their cores are very difficult to be described in terms ofPlatonic polyhedra. The massive utilization of flexible or semi-flexible organic ligands for the construction of high nuclearityCCs15 implies that a plethora of polynuclear CCs will bereported in the future, thus a worldwide system of nomenclature,classification, identification, and reclamation of these CCs isneeded. Being motivated by the idea of describing coordinationnetworks and metal organic frameworks (MOFs) in terms ofconnected nets as the ones found in zeolites16–18 we have devel-oped an approach to describe high nuclearity CCs utilizing eachmetal center as a node and every monoatomic bridge (O, N, S)as a linker.19 This approach seems to be a very useful tool forunderstanding the growth of high nuclearity CCs.20

In this article, we present a further development of this ideaby employing the methods of topological analysis that areimplemented into the TOPOS program package.21 The improve-ment of our structural analysis based on TOPOS revealed somedifferences with our recent review of Manganese CCs22 that wediscuss herein. In the present work we prepare a database with539 Mn CCs, collected and illustrated in such a way that canbe searched by cluster topological symbol and nuclearity, yearcompound name and RefCode. In addition we describe in detailthe six most frequently observed CCs and some useful examplesof structural–graphical comparison and how the database canbe used to understand the growth of high nuclearity clusters. Wedo not compare the magnetic properties of similar nuclearitycompounds; however we believe that the better understandingof the high nuclearity growth will assist synthetic chemists inthe construction of molecular clusters with better magneticproperties.

†Electronic supplementary information (ESI) available: A database inexcel format containing all the 539 CCs (analyzed with references,refcodes, space group, year and all the topological information (motifnames, nuclearity, independent nodes, dimensionality) and a descriptionof the CC 2,4M5-1 added as an example. See DOI: 10.1039/c2dt12263d

aInstitute of Nanotechnology, Karlsruhe Institute of Technology,Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen,Germany. E-mail: george.kostakis@kit.edubSamara State University, Ac. Pavlov St. 1, Samara 443011, Russia.E-mail: blatov@ssu.samara.rucUniversità degli Studi di Milano, Dipartimento di Chimica Strutturale eStereochimica Inorganica (DCSSI), Via G. Venezian 21, 20133 Milano,Italy. E-mail: davide.proserpio@unimi.it

4634 | Dalton Trans., 2012, 41, 4634–4640 This journal is © The Royal Society of Chemistry 2012

Analysis of CCs with TOPOS

TOPOS analysis of metal–organic complexes (molecular orpolymeric ones as well as CCs) consists of the following steps:

1. Determination of all interatomic contacts with the methodof spherical sectors.23 This method is based on the Voronoi par-tition of the crystal space, and determines both strong and weakcoordination and metal–metal interactions. As a result, the com-plete representation of the structure is obtained, from which allsimpler partial representations can be derived.18 For the MnCCs only valence contacts were considered.

2. Generation of all partial representations by successiveremoval of weakest contacts. Since Mn–X–Mn bridges wereexceptionally assumed to form the intracluster links, only Mn–Xcontacts were treated at this step, where X is any is any electro-negative p element. In most cases, only the complete represen-tation corresponded to the chemically reasonable structure, i.e.all Mn–X contacts were of like strength. Nonetheless, the struc-tures exist where the finite clusters can be separated only with

some Mn–X contacts ignored. At this step we had revealed allsuch cases.

3. Determination of dimensionality of the cluster groups. Atthis step the target finite (0D) CCs of any nuclearity were separ-ated from the polymeric 1D, 2D, or 3D structural groups,however when such a CC can be found in a multidimensionalpolymeric compound then such information was given in thedatabase as well. Only those 0D clusters were considered thatcontain exclusively Mn as metal atoms. The possible motifs (interm of graphs) of mono-, di-, tri- and tetranuclear CCs arelimited and can be very easily described, thus we considered onlyrather complicated clusters that contained five or more Mn atoms.

4. Simplification of the CCs graphs. All non-Mn (X) atomswere excluded from the 0D clusters with the TOPOS simplifica-tion procedures to obtain the graphs of Mn skeletons. 1-coordi-nated X atoms (Mn–X) were removed, 2-coordinated X atoms(Mn–X–Mn) were transformed into edges Mn–Mn, while highercoordinated atoms were contracted to the Mn atoms keeping thecluster connectivity (Fig. 1). Only monoatomic bridges were

Fig. 1 A simplification of the CC [MnIII6(μ3-O)2(μ3-1-(2-oxyphenyl)propanoneoximato)4(μ2-1-(2-oxyphenyl)propanoneoximato)2(H2O)2(EtOH)4(naphthalene-2-carboxylato)2] (refcode: AGABOA)

24 (a) removing terminal aqua, ethanol, and naphthalene-2-carboxylato (n-2-c) ligands, (b) remov-ing μ2-1-(2-oxyphenyl)propanoneoximato ligands (μ2) with breaking two-atom Mn–N–O–Mn bridges, into graph edges (red dashed lines), (c, d) suc-cessively contracting two pairs of μ3-1-(2-oxyphenyl)propanoneoximato ligands to the Mn atoms (μ3) with transforming one-atom oxy-bridges intograph edges (red dashed lines) and breaking two-atom Mn–N–O–Mn bridges, (e) contracting μ3-oxo ligands to the Mn atoms with transforming one-atom oxo-bridges into graph edges, (f ) the resulting 2,3,4M6-1 graph of the Mn skeleton.

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considered as Mn–Mn edges in the resulting Mn skeleton; if thebridge Mn–{X}n–Mn consisted of several X atoms (n > 1) it wasbroken. In particular, all two-atom Mn–N–O–Mn bridges ofoximato groups in [MnIII6(μ3-O)2(μ3-1-(2-oxyphenyl)propano-neoximato)4(μ2-1-(2-oxyphenyl)propanone-oximato)2(H2O)2(Et-OH)4(naphthalene-2-carboxylato)2] (Fig. 1) are not treated as thegraph edges. The choice for this selection is manifold. First, itleads to a simpler and clearer classification. Indeed, the mono-atomic bridges provide the most rigid CC skeleton that is hencetopologically more distinct. The polyatomic bridges (e.g. carbox-ylates) can then be considered connecting several skeletons intoa more complicated species. Second, the special attention to themonoatomic bridges has a physical reason since the process oftransferring magnetic information through monoatomic bridgesis very well studied and understood, and many Mn CCs definedin this way possess pronounced magnetic properties (seeexamples below). It is worth stating that the algorithm underconsideration can be easily extended to CCs containing anykinds of bridges.

5. Determination of the topology of the Mn skeletons. Thetopology of the graph is described by three types of indicesattributed to each Mn atom: (i) coordination sequence, which isthe set of numbers atoms in the subsequent coordination shells;(ii) point symbol, which collects the numbers and sizes of thesmallest cycles and corresponds to the ‘Schläfli symbol’ that weused before;18,25 (iii) vertex symbol, which extracts so-calledrings (they are the cycles that are not sums of two smallercycles) from the point symbol (Fig. 2).25 We assumed two Mnclusters topologically equal if all atoms in their Mn skeletonscould be matched by indices (i)–(iii). The clusters with the sameset of the indices were assigned to the same topological type,which, according to the TOPOS rules, was designated by theNDk-m symbol,18 where N is a sequence of coordinationnumbers of topologically non-equivalent Mn atoms (they havedifferent sets of the indices), D is dimensionality; D = M forfinite (molecular) clusters, k is the number of Mn atoms in thecluster, and m is an ordering number to distinguish topologicallydifferent clusters with the same NDk symbol. For example, thecluster in Figs 1 and 2 has the symbol 2,3,4M6-1, i.e. this is thefirst type of 6-atom cluster with three topologically non-equival-ent atoms of coordination 2, 3, and 4. We call a Mn skeletonn-nodal (uninodal, binodal, or trinodal for n = 1, 2, or 3) if it hasn topologically non-equivalent Mn atoms. For example, the

cluster in Figs 1 and 2 is trinodal. If several Mn skeletons wereunited in more complicated 0D species by polyatomic bridges itwas indicated in the database, for example, (1,3,3,3,4,5M12-1)2for dimers in COFYEC or [(2,4M6-1)2(2M3-1)2] for complextetramer in KESCAN (see the ESI†).

6. Identifying common cores of different Mn skeletons withthe TOPOS procedure of searching for a particular subgraph tofind structural similarities between lower and higher nuclearityCCs (see examples below).

Examples

The topological analysis of all manganese based CCs found inthe CCDC (CCDC 5.31 Nov. 2011) according to the algorithmdescribed above resulted in 539 entries and 159 topologicallydifferent graphs (motifs). The whole database can be found inthe ESI.† The distribution of the graph topologies shows that theseven most frequent motifs (with 248 entries) cover almost halfof the database (46.0%). We will describe herein these six mostpopular motifs (see Fig. 3) named as (a) 3,4,6M12-1 (78examples), (b) 3,5M6-1 (53 examples), (c) 2,3,4M6-1 (59examples), (d) 2,3,4M9-1 (19 examples), (e) 3,6M7-1 (15examples) and (f ) 2,3M6-1 (12 examples); the 2,4M5-1 type(12 examples) is presented in the ESI.† The other CCs areobserved in 8 or fewer structures while 90 CCs were uniquelyobserved.

(a) Motif 3,4,6M12-1. This motif corresponds to a compoundwhich was initially reported by Lis in 1980 formulated as[MnIV4MnIII8O12(O2CMe)16(H2O)4] (1) (AQACMN).26 Thiscompound was magnetically investigated after 12 years27 and itwas found to possess a ground spin state of S = 10 behaving asSMM, thus several compounds possessing the same motif havebeen reported (78 entries in total can be found in the ESI,†14.5% of the whole database). This trinodal motif is composedof an inner tetrahedron which is surrounded by eight manganesenodes and consists of four 3-, 4- and 6-coordinated nodes,respectively.

(b) Motif 3,5M6-1. The hexanuclear CC shown in Fig. 3 rep-resents the second popular motif in the Mn chemistry. This typeof CC consists of two tetrahedra sharing a common edge, madeup by four 3-coordinated nodes and two 5-coordinated nodes.This skeleton was initially reported in 1986 in a mixed valencecompound formulated as MnIII2MnII4O2(piv)10(pivH)4 (2)(pivH = pivalic acid) (FACYUD),28 while the complex showsantiferromagnetic interactions with a magnetic moment (per Mnatom) of 4.81 μB at 296 K and a Weiss constant of 34 K. Oursurvey resulted in 53 compounds that possess the same skeletonand compose 9.8% of the database, with varying MnII and MnIII

oxidation states.(c) Motif 2,3,4M6-1. Our survey for this motif resulted in 59

compounds. This fragment is widely known in Mn chemistry,due to the fact that one of those compounds (CEYMAV),29 for-mulated as [MnIII6O2(Etsao)6{O2CPh(Me)2}2(EtOH)6] (3),(Etsao2− = dianion of 2-hydroxyphenylpropanone oxime), wasfound to possess a ground state S = 12 and record values of theeffective energy barrier to magnetisation reversal (Ueff ) and TBfor a 3d-metal-based SMM. Thus several research groups syn-thesized compounds with similar topology in order to investigatethe SMM behavior. The topology of this motif can be described

Fig. 2 (left) The coordination sequence (numbers of coordinationshells are shown), (right) cycles (grey and green triangles and their sumas 4-cycle), and rings (grey and green triangles) for a Mn atom in thecluster 2,3,4M6-1. The target Mn atom is yellow. The 4-cycle is not aring since it is a sum of two smaller cycles.

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in terms of 4 fused triangles resulting in a trinodal motif bearing2-, 3- and 4-coordinated nodes.

(d) Motif 2,3,4M9-1. 19 compounds were found to possess atrinodal skeleton with 2-, 3- and 4-coordinated nodes. All thesecompounds are derived from rigid organic ligands with varyingMnII and MnIII oxidation states and can be alternativelydescribed in terms of a 3 × 3 square grid. The first example ofthis motif can be found in a compound formulated as [MnII9(2-POAP–2H)6](ClO4)6·3.57MeCN·11H2O (4) (KANBOQ)30

(2POAP–2H = 2,6-bis(4-amino-4-(2-pyridyl)-2,3-diaza-buta-1,3-dien-1-olato)pyridyl). Magnetic studies showed dominantantiferromagnetic exchange.

(e) Motif 3,6M7-1. The most popular motif in Mn7 chemistryis this one presented in Fig. 3 (lower middle). 15 compoundswere found to possess this disk-like binodal motif with six 3-coordinated nodes and one 6-coordinated node, with varyingMnII and MnIII oxidation states. The first reported examplein our survey was [MnIII3MnII4(OH)3(hmp)9Cl3](Cl)(ClO4)(IPULUA) (5), (hmpH = 2-(hydroxymethyl)pyridine).31 Fittingof the magnetic data by matrix diagonalization, incorporatingonly axial anisotropy (DSz

2), gave equally good fits with S = 10,g = 2.13, D = −0.14 cm−1 and S = 11, g = 1.94, D =−0.11 cm−1.

(f ) Motif 2,3M6-1. The third most popular motif in Mn6chemistry consists of 11 examples, found in our survey, posses-sing the 2,3M6-1 topology that can be described by two tri-angles jointed through one node Fig. 3 (bottom right). The firstskeleton that was found in our survey was identified in a com-pound formulated as {[Mn3O(O2CCH2Cl)6(Py)2(H2O)]}2 solv

(6) (TUYDAS).32 Magnetic studies of this compound revealedthat the complex exhibits weak antiferromagnetism.

Database

At this point we would like to point some useful commentsregarding the handling of our database.

(A) The automated topological analysis of all Mn CCs showssome differences in comparison with our previous study.22

For example, compound [MnIII10O6(OH)2(BTA)8(py)8F8] (7)(Fig. 4, left) was previously identified as a 7-nodal CC with 3-,5- and 6-coordinated nodes and total point symbol(32.4)2(3

3)2(34.43.53)(34.45.5)(35.44.5)2(3

7.45.53)(37.47.5), whilethe present analysis shows that the correct description of the

Fig. 3 The graph representation of the six most frequent motifs observed in Mn CCs.

Fig. 4 Mn skeletons in (left) 3,6M10-1 [MnIII10O6(OH)2(BTA)8(py)8F8](JAMWEA) (7) and (right) 2,3,3,3,5,5,5,5,6,6,6,7,7M26-1 [MnIII26O16

(OH)10(OMe)6(F)10(BTA)20(BTAH)2(MeOH)13(H2O)] (MULTOC) (8)containing the same super-tetrahedron (T2) motif of JAMWEA.

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skeleton of compound 7 is a super-tetrahedron (T2) motif withtotal symbol 3,6M10-1. This mismatch is probably due to thesubstantial distortion from the ideal super-tetrahedron geometryof the decorated core of 7. Overall, the systematic search withTOPOS was able to find other 194 compounds that correspondto 81 motifs that were overlooked before.

(B) In the ESI† useful comments have been introduced inorder to distinguish the dimensionality of the decorated com-pound. For example compound (DUFNIC)33 is a heptadecanuc-lear mixed valence compound with NDk-m symbol3,5,6,6,10M17-1, while as is mentioned in the ESI,† this com-pound forms an infinite chain (1D) through azide linkers. Simi-larly, when for a compound the symbol 2D or 3D is present, itindicates that the CCs are connected to form an extendednetwork in two or three dimensions.

(C) As is already stated above, we chose to consider only themonoatomic bridges as linkers; however we are in the process ofalso including the di- or tri-atomic bridges. For this reason, inour survey when we have detected that two CCs are jointthrough a diatomic or triatomic bridges, then we have markedthe final topology as a “dimer” etc. For example, in compoundCOFYEC34 two discrete dodecanuclear CCs are linked througha triatomic bridge, therefore we have identified this compound as(1,3,3,3,4,5M12-1)2 and added the comment “dimer”.

Applications

In this part we illustrate the usefulness and the possibilities of anautomatic search for common cores of the Mn skeletons (step 6of the TOPOS analysis, see above).

(A) In 2004, Brechin, Collison and coworkers35 reported twopolynuclear Mn clusters with benzotriazole (BTAH) ligands;compound 7 (JAMWEA) which was described above and[MnIII26O16(OH)10(OMe)6(F)10(BTA)20(BTAH)2(MeOH)13(H2O)](8) (MULTOC). The metallic skeleton of 7 is a distorted super-tetrahedron (T2) with the 3,6M10-1 motif (Fig. 4, left), which isnot so obvious, from the first view, due to the distortion of thecentral core. The comparison of those two metallic cores withTOPOS shows that 8 has been built up around the Mn10 super-tetrahedron (T2). Both compounds were obtained by similar syn-thetic routes; the difference was in the utilization of pyridine for“blocking” the extension of the super-tetrahedron.

(B) Two different synthetic procedures have been followed forthe synthesis of two Mn25 CCs formulated as [MnIII22MnII3O20

(N3)6(O2CPh)26(MeCN)2]·solv (9) (RUBVOA)36 and [MnIV6-MnIII18MnIIO18(OH)(OMe)(hmp)6(pdm)6(pdmH)6](N3)2(ClO4)6·solv (10) (YEVQEW).37 An isostructural core (BETCOT) of thelatter was reported in 2004.38 At the first glance (Fig. 5, top) butalso by comparison the two figures that the authors recorded intotheir articles, it seems that the two cores are not related.However, applying the TOPOS subgraph search we are able tofind that the two Mn25 CCs consist of a similar inner Mn13 corewhich is surrounded by twelve Mn nodes in a different way, dueto different organic ligands. In Fig. 5 (middle and bottom) thetwo cores are highlighted in order to show the similar internalMn13 core.

(C) Recently, two polynuclear manganese CCs derived from2-(hydroxymethyl)pyridine (hmpH) in the presence of benzoateformulated as [MnIII2MnII6O2(O2CPh)10(hmp)4(MeOH)2] (11)

and [MnIII10MnII6O8(OH)2(O2CPh)12(hmp)10(H2O)2] (O2CPh)2(12), were reported.39 The experiment revealed that similar syn-thetic procedures were followed; however Et3N was additionallyused to obtain 12. Employing the TOPOS subgraph search it isvery easy to understand that the hexadecanuclear cluster (Fig. 6bottom) is a dimer of the octanuclear cluster (Fig. 6, top).

(D) Several high nuclearity clusters have been isolated frompolyalcoholic ligands.15 Among all of those examples, we reportherein two which show interesting structural features. In 2007,Brechin and coworkers40 reported a Mn22 CC formulated as[MnIV2MnIII18MnII2O6(OCH3)14(O2CCH3)16(Br–mp)8(HIm)2]·2C6H14·5CH3OH (13) (LIMQAA) where Br–mpH3 is 2-(bromo-methyl)-2-(hydroxymethyl)-1,3-propanediol, the topological rep-resentation of which is presented in Fig. 7, left. More recently,Murray et al.41 obtained an almost planar decanuclear cluster in[Mn10O3(O2CCH3)6(tea)(teaH)3(teaH2)3][NO3]2· 3H2O (14)(SOPSAS), (Fig. 7, right) where teaH3 is triethanolamine; aligand which is closely related to Br–mpH3. A comparison of

Fig. 5 Mn skeletons in (left) [MnIII22MnII3O20(N3)6-(O2CPh)26(MeCN)2]·solv (9) (RUBVOA) 3,4,5,5,5,5,6,6,6,7,8,8,8, 12M25-1 and(right) [MnIV6MnIII18MnIIO18(OH)(OMe)(hmp)6(pdm)6- (pdmH)6−](N3)2(ClO4)6·solv (10) (YEVQEW) 5,5,7,9,12M25-1. In red and blueare the common Mn13 cores.

4638 | Dalton Trans., 2012, 41, 4634–4640 This journal is © The Royal Society of Chemistry 2012

these two clusters indicates that the Mn22 skeleton is composedof two Mn10 copies via additional bridge Mn atoms.

(E) In 2003, a dodecanuclear CC formulated as [MnIV2-MnIII6MnII4(μ4-O)2(μ3-O)4(μ3-OH)4(μ3-OCH3)2( pko)12](OH)(ClO4)3 (15) (BEDCAP) (pko = di-pyridyl ketone oxime), wasreported.42 In this article the authors attempted to compare thecore of this compound with the core of compound [MnIV4MnIII8O12(O2CMe)16(H2O)4] (1) (see the figures in the originalpaper).27 They mentioned different conformations of 15 and 1but did not draw a final conclusion about their topology. Apply-ing our approach, compound 15 can be represented as a hexano-dal CC with symbol 3,4,4,5,5,8M12-1 that is quite differentcompared to 1 (3,4,6M12-1), so their topological difference isnow evident (Fig. 8).

(F) Another useful application of this approach is the compari-son of compounds with the same nuclearity but crystallizing indifferent space groups. For example, compounds [MnIII22MnII4-O16(OMe)12(pdol)12(N3)6] (16) (UKUMIW)43 and [MnIII22-MnII4O16(OMe)12(pdol)12(MeOH)6](OH)6 (17) (VOLZOM),44

which were solved in the Fd3̄ space group, possess the samedecorated metallic skeleton as the compound [MnIII22MnII4-

O16(OMe)18(pdol)12(OH)2(H2O)]ClO4 (18) (QAVDAT)45 whichwas solved in the P31c space group. This motif can be describedas a “super super-tetrahedron” (T3) with the addition of 6 Mnnodes (in red in Fig. 9) and is classified as tetranodal2,3,7,9M26-1.

Conclusions

We presented herein an improved method for the topologicaldescription of high nuclearity CCs. Using the TOPOS programpackage that supports this method we identify 539 entries and159 different topologies for polynuclear Mn CCs. In the presentdatabase all Mn CCs are collected and illustrated in such a waythat can be searched by cluster topological symbol and nuclear-ity, compound name and Refcode. Our next target is to extendthis classification to other metal centers, such as cobalt46 inorder to establish a worldwide database of nomenclature, classifi-cation, identification, and reclamation of these CCs.

With this approach, it becomes easier for synthetic chemists:(a) to identify any structural similarity of their compounds withthe reported up to now, (b) to find all the CCs of the some nucle-arity, (c) to find structural motifs which are similar varying onlyin the metal center, (d) to compare the skeletons through the

Fig. 7 The simplified cores of the Mn22 (LIMQAA) 2,2,3,4,4,4,6M22-1 (left) and Mn10 (SOPSAS) 2,4,6M10-1 (right) clusters for comparison.

Fig. 6 The simplified cores of the octanuclear 3,4,6M8-2 (top) and thehexadecanuclear 3,4,4,5,5,5,6,9M16-1 (bottom) clusters of 11 and 12.

Fig. 8 The Mn skeletons of 1 (AQACMN) (left) and 15 (BEDCAP)(right) with 3,4,6M12-1 and 3,4,4,5,5,8M12-1 motifs.

Fig. 9 The 2,3,7,9M26-1 motif found in compounds 16–18(UKUMIW, VOLZOM, QAVDAT).

This journal is © The Royal Society of Chemistry 2012 Dalton Trans., 2012, 41, 4634–4640 | 4639

TOPOS subgraph search; the latter represents a useful tool tounderstand structural similarities of lower and higher nuclearityCCs. All the above records and the results presented herein indi-cate the functionality and usefulness of this database approach.

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4640 | Dalton Trans., 2012, 41, 4634–4640 This journal is © The Royal Society of Chemistry 2012