Influence of ligands’ peripheral substituents on the structure, magnetochemical and...

Available online at www.sciencedirect.com

www.elsevier.com/locate/ica

Inorganica Chimica Acta 361 (2008) 2032–2044

Influence of ligands’ peripheral substituents on the structure,magnetochemical and electrochemical behaviourof complexes containing a Cu2O2 butterfly core

Nataliya E. Borisova a,*, Marina D. Reshetova a, Tatiana V. Magdesieva a,Victor N. Khrustalev b, Grigori G. Aleksandrov c, Maxim Kuznetsov a, Roman S. Skazov b,

Alexandr V. Dolganov a, Vladimir N. Ikorskiy d,1, Vladimir M. Novotortsev c,Igor L. Eremenko c, Iliya I. Moiseev c, Yuri A. Ustynyuk a

a Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory 1/3, 119992 Moscow, Russiab A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 ul. Vavilova, 119991 Moscow, Russia

c N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninsky Prosp., 119991 Moscow, Russiad International Tomography Center, SD RAS, 3a, Institutskaya Str. 630090 Novosibirsk, Russia

Received 18 August 2007; received in revised form 17 October 2007; accepted 17 October 2007Available online 24 October 2007

Abstract

New polydentate open structure ligands H3L1 and H3L2 were synthesized by the condensation of 2,6-diformyl-4-tert-butylphenol andcorresponding N-R-o-phenylenediamines (R = Ac and R = Boc). Treating of the ligands with copper trimethylacetate leads to binuclearcopper complexes with dissimilar Cu2O2 cores, the structures of which were solved by X-ray diffraction analysis. The electrochemicalproperties of both complexes were studied; the observed redox transitions were assigned to specific redox-active sites of the molecule.These assignments were confirmed by DFT calculations of the electronic structure of binuclear complexes. Both complexes exhibit anti-ferromagnetic behaviour, as confirmed by variable-temperature magnetic studies.� 2007 Elsevier B.V. All rights reserved.

Keywords: Schiff bases; Binuclear complexes; CVA; DFT calculations; Magnetochemistry

1. Introduction

An interest in binuclear systems has been focused pri-marily on magnetic exchange interaction between twoparamagnetic ions. Such interactions in biomolecules havereceived increased attention since the time when binuclearcopper centres were proposed to be the part of an activesite of several multicopper-containing proteins [1,2]. Binu-

0020-1693/$ - see front matter � 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.ica.2007.10.020

* Corresponding author.E-mail address: [email protected] (N.E. Borisova).

1 Professor Ikorskiy died suddenly in January 2007. He made themagnetochemical measurements and contributed actively until hisuntimely passing.

clear copper oxygenases can be divided into two groupsdependent on magnetic interaction between two Cu(II)ions, e.g. antiferromagnetically coupled centres or uncou-pled ones [2]. Namely, Laccase contains a pair of antifer-romagnetically coupled Cu(II) ions, which are capable ofacting as a two-electron oxidant [1]. However, magneto-structural correlations in biological systems are rare dueto the scarcity of crystallographic results [2]. Magneticinteractions in binuclear artificial complexes form an areaof research actively pursued by many laboratories. Themagnetochemical investigations, together with crystallo-graphic results, allow the estimation of several magneto-structural correlations in exchange-coupled systems. Theobjects of particular interest are dicopper complexes with

mailto:[email protected]

N.E. Borisova et al. / Inorganica Chimica Acta 361 (2008) 2032–2044 2033

a Cu2O2 motif. Several reports of magnetic measurementsfor many Cu2O2-containing complexes with macrocyclicas well as acyclic ligands synthesized from a 2,6-difor-myl-4-substituted phenol building block are published.Among them, the magnetostructural correlations in theseries of CuN2OB complexes with dissimilar Cu2OBbridges 1 (Scheme 1) are well documented by the originalworks of O’Connor [3,4], Kahn [5], Fenton [6] and others[7–10].

The detailed studies of these systems (for B = OH–,N3–, ONC–, Cl– or Br–) showed that the majority ofthem are antiferromagnetically coupled and this couplingstrongly depends on the nature of bridging group B [3,5].The Cu–O–Cu bridging angle is the most important fac-tor determining the magnetic interaction between copperions in unsymmetrical Cu2O2 motif (B = OH or OR). As

Table 1Magnetic and structural parameters for complexes 1 (formula (Cu2LOH)2+)

ON N

N N

Cu CuOH

O OCl

O O

ClO4-

1a

ON N

N N

Cu CuOH

OH2 NO3

NO3-

OH2

1b

ON

N

CuOH

OC

O

O

CO

1c

ON N

N NN N

Cu CuOH

N

1f

2(BF4-)

N

N

N

ON N

N N

Cu CuOH

NH

NH1g

2(Cl-)

Complex 2J, cm�1 Cu–O–Cu (�)

1a �364 99.181b �499 99.901c �367 97.41d �493 98.31e �525 101.41f �420 101.91g �516 100.91h � 0 91.71i 99.9

Scheme 1.

illustrated in Table 1, the geometry of the acyclic phenol-based ligand also contributes to the S–T energy gap. Allpresented complexes are cationic species. For perchlorate(1a) and nitrate (1b) complexes of copper, the mainstructural parameters (e.g. Cu–O–Cu angles or Cu� � �Cuseparation) are very similar, but the S–T energy gaps dif-fer as much as 1.5 times. The ligands with additionalacidic groups capable of covalent bonding with two cop-per ions allow the creation of complexes without coun-ter-ions. It is of special interest to obtain coordinativelyunsaturated neutral binuclear species with dissimilarbridges. However, to the best of our knowledge, the onlyneutral dicopper complex 1i with an acyclic unsymmetri-cal ligand of type 1 was obtained and characterized byX-ray crystallography, but no magnetochemical dataare available for it [11]. One of the possible routes to thistype of complex is the insertion of the OH groups intothe ligand as acid groups (Scheme 2). Five complexesof type 2 (2a–e) have been obtained and characterizedby X-ray and magnetochemical data (Table 2). We devel-oped polytopic ligand 3 based on a 2,6-diformylphenolbuilding block and bearing acidic N–H amide groupscapable of forming neutral dicopper complexes (Scheme3). The current paper deals with the synthesis, as wellas structural, magnetochemical, electrochemical andtheoretical DFT study of new neutral dicopper com-plexes of 3.

N

NCu

O

O

lO

lO

ON N

NH2 H2N

Cu CuOH

O O

O

ClO O

O

ClOO

1d

ON N

N N

Cu CuOH

OH2

NH

NH1e

BF4-

SiF6-

Cl

ON N

N N

Cu CuOH

OH2H2O

2(ClO4-)

1h

ON NN N

S NH

NH

S

Cu Cu

O

1i

Cu–OH–Cu (�) Cu� � �Cu (A) Reference

100.44 2.947 [3]102.2 2.991 [3]99.3 2.924 [5]99.3 2.957 [6]

102.5 3.05 [7,8]103.6 3.053 [4]101.3 3.014 [9]96.5 2.872 [10]

103.0 2.982 [11]

Scheme 2.

Scheme 3.

2034 N.E. Borisova et al. / Inorganica Chimica Acta 361 (2008) 2032–2044

2. Experimental

2.1. Materials and physicochemical measurements

NMR spectra were measured on a BRUKER AVANCE400 MHz NMR spectrometer at 24 �C. IR spectra wererecorded on a Nicolet FT-IR spectrometer in Nujol orKBr. Mass spectra were obtained on a MALDI-TOFReflex 3 instrument (BRUKER) in the positive ion mode(UV laser, 337 nm). For full mass spectra see electronicSupplementary material. Electrochemical oxidation andreduction potentials were measured with an IPC-Winpotentiostat at a stationary Pt electrode with a workingsurface area of 5.14 mm2, with n-Bu4NPF6 as a supportingelectrolyte in anhydrous organic solvents (dimethylsulfox-ide and methylene dichloride) in an argon atmosphere at20 �C in a special electrochemical cell at a potential sweeprate of 50–500 mV/s. Platinum wire served as an auxiliaryelectrode, and a chlorsilver electrode Ag/AgCl/KCl in

Table 2Magnetic and structural parameters for complexes 2 (formula (Cu2LOR))

ON NN

C6H13 O C6H13O

Cu Cu

O

MeOH

HOMe2a

ON

OtBu

But

Cu

O

ON

OtBu

But

Cu

2

Cl

ON N

S SO O

Cu CuOO

OOO

H2d

Complex 2J, cm�1 Cu–O–Cu (�)

2a �336 99.22b �384 99.12c �630 99.32d �402 99.52e �405 97.7

water was used as a reference. To start with, 2,6-difor-myl-4-tert-butylphenol [17], N-acetyl-o-phenylenediamine[18] and N-(tert-butoxycarbonyl)-o-phenylenediamine [19]were synthesized by literature methods. Other reagentsand solvents were obtained from commercial sources.

2.2. Magnetic susceptibility measurements

Magnetic susceptibility data for complexes 4 and 5 weremeasured using SQUID magnetometer MPMS-5S (Quan-tum Design) in the temperature range 2–300 K in the mag-netic field 397.89 kA mK1. No dependence of magneticsusceptibility on magnetic field was observed.

2.3. Quantum-chemical calculations

All calculations were performed using the resources ofthe Joint Supercomputer Center (JSC) supercomputer

N

OtBu

tBu

Cu

N

O

tBu

tBuCu

b

ON NN

Ph O

N

PhO

Cu CuO

2c

Cl

ON N

P PO O

Cu CuOO

OOO

H2e

H2O

OH2

Cu–OR–Cu (�) Cu� � �Cu (A) Reference

103.3 2.947 [12]99.6 2.945 [13]

101.8 3.572 [14]98.2 2.940 [15]

100.8 2.965 [16]


MVS-1000M (www.jscc.ru). The calculations have beendone at the DFT level of theory. The geometry optimiza-tions have been carried out using the PBE generalized gra-dient functional [20]. Geometries have been optimizedusing the TZ2P [21] valence basis set and SBKJC effectivecore potentials for Cu, C, N and O atoms [22–24]. Vibra-tion frequencies have been used to characterize the station-ary point as minima. All calculations were performed usingthe PRIRODA program [25,26]. Atomic coordinates and ener-gies are given in electronic Supplementary material.

2.4. X-ray crystallographic study

Crystallographic data for 4 and 5 were collected by thestandard procedure [27] using a Bruker AXS SMART1000 diffractometer equipped with CCD detector (graph-ite-monochromated Mo Ka radiation, k = 0.71073 A,T = 120 K, x and / scan mode, scan step – 0.3�, time offrames collection – 30 s). The semiempirical absorptioncorrection was applied [28]. The structures were solved bydirect methods using the SHELXS97 [29] program and refinedusing the SHELXL97 package [30] by least-squares method inthe full-matrix anisotropic (atoms of solvate methanol mol-ecules in 4 were specified isotropic, the positions of the Hatoms were fixed by standard rigid procedure)approximation.

2.5. Synthesis of 2,6-bis((2-(acylamino)phenylimino)

methyl)-4-tert-butylphenols (3a and 3b)

A solution of N-acyl-o-phenylenediamine (9.7 mmol) inanhydrous methanol (7 mL) was added dropwise for anhour to a solution of 2,6-diformyl-4-tert-butylphenol (1 g,4.85 mmol) in anhydrous methanol (7 mL). The reactionmixture was stirred for 8 h at room temperature, afterwhich a precipitate of product was filtered off and washedwith ether. An additional portion of the substance wasobtained by the partial evaporation of the mother liquor.

Compound 3a: (2.24 g, 98% yield). M.p. 193–194 �C(MeOH). Anal. Calc. for C28H30N4O3: C, 71.47; H 6.43;N, 11.91. Found: C, 71.44; H, 6.48; N, 11.94%. IR(KBr)/cm�1: 1624 m(C@N), 1668 m(C@O), 3326, 3377,3226 m(OH); IR (Nujol)/cm�1: 1622 m(C@N), 1668m(C@O), 3321, 3390, 3172 m(OH). 1H NMR ((D3C)2CO):1.42 s (9H, CH3), 2.17 s (6H, CH3), 7.17 t (2H, CH), 7.28t (2H, CH), 7.34 d (2H, CH), 8.19 s (2H, CH), 8.25 d(2H, CH), 8.98 br s (2H, NH), 9.04 s (2H, CH@N), 13.51s (1H, OH). 13C NMR ((D3C)2CO): 23.50, 30.05, 34.04,117.86, 121.31, 121.68, 124.24, 127.17, 130.97, 133.41,135.96, 139.85, 141.96, 159.42, 167.88. m/z (EI) 469 (100,M�H+), 440 (35, M�2CH3

þ), 427 (75, M�3CH3þ), 383

(20, M�2Ac�H+).Compound 3b: (1.58 g, 70% yield). M.p. 210–212 �C

(MeOH). Anal. Calc. for C34H42N4O5: C, 69.60; H, 7.22;N, 9.55. Found: C, 69.57; H, 7.11; N, 9.45%. IR (Nujol)/cm�1: 3385 m(OH), 1685 m(C@O), 1630 m(C@N). 1HNMR ((D3C)2CO): 13.85 s (1H, OH), 8.97 s (2H, HC@N),

8.56 s (2H, NH), 8.09 s (2H, CH), 7.67 d (2H, CH), 7.31 t(2H, CH), 7.25 d (2H, CH), 7.18 t (2H, CH), 1.43 s (18H,CH3), 1.36 s (9H, CH3). 13C NMR ((D3C)2CO): 159.61,153.24, 141.58, 141.33, 133.13, 130.86, 127.44, 124.93,122.58, 121.72, 118.66, 79.61, 31.43, 28.42. m/z (MALDI-TOF): m/z (%) = 587 (100, M+H+).

2.6. Synthesis of complexes (L1Cu2OMe Æ MeOH) 4 and

(L2Cu2OH) 5

A solution of 3a or 3b (0.55 mmol) in anhydrous metha-nol (15 mL) was added dropwise with vigorous stirring foran hour to a solution of copper trimethylacetate dihydrate(0.298 g, 1.1 mmol) in anhydrous methanol (15 mL). Thereaction mixture was stirred for 5 h, and a precipitate ofthe complex was filtered off. An additional amount of thecomplex was obtained after evaporation of the motherliquor. The precipitate was washed with a small amount(3–5 mL) of cold anhydrous methanol (twice) and twicewith the same amount of diethyl ether. Slow evaporationof a solution of complexes in a methanol–methylene dichlo-ride mixture gave crystals suitable for X-ray determination.

Compound 4 (0.303 g, 85% yield). Decomposed >235 �C. Anal. Calc. for C28H27Cu2N4O3 Æ MeO Æ MeIH: C,54.79; H, 5.21; N, 8.52. Found: C, 54.54; H, 4.94; N,8.82%. IR (Nujol)/cm�1: 1625 m(C@N), 1690 m(C@O),3300, 3263 m(MeOH). IR (KBr)/cm�1: 1629 m(C@N),1689 m(C@O), 3301, 3266 m(MeOH). m/z (ESI(+) [MeCN]):673.9 (55, LCu2CuO+), 1204.8 (100, L2Cu4OH+). m/z

(ESI(+) [acetone]): 674.1 (10, LCu2CuO+), 1205.0 (100,L2Cu4OH+). m/z (MALDI-TOF(+)): 658 (30, LCu2Cu+),674 (100, LCu2CuO+).

5 (0.352 g, 88% yield). Decomposed > 197 �C. Anal.

Calc. for C34H40Cu2N4O6: C, 56.11; H, 5.54; N, 7.70.Found: C, 56.42; H, 5.71; N, 7.52%. IR (Nujol)/cm�1:1622 m(C@N), 1710 m(C@O), 3230 m(OH).

3. Results and discussion

3.1. Syntheses of ligands and dicopper complexes

The condensation of N-acetyl-o-phenylenediamine with2,6-diformyl-4-tert-butylphenol occurs readily when thestarting compounds react in a ratio of 1:2 in anhydrousmethanol and affords 3a in high yield (Scheme 4). The sub-stance thus formed is well soluble in the majority of polarorganic solvents. The structure of 3a is confirmed byNMR, mass and IR spectrometry data.

The C@N bond frequencies in IR spectrum of ligand 3a

(1622 cm�1 (Nujol) or 1624 cm�1 (KBr)) indicate thestrong hydrogen bonding. The position of signal of pheno-lic OH group in 1H NMR spectrum (d 13.51 ppm) alsoconfirms the formation of an intramolecular hydrodgenbond between the OH group of the phenol and azomethinenitrogen atom.

Schiff’s base 3a reacts easily with copper trimethylace-tate dihydrate in methanol at room temperature to

http://www.jscc.ru

Scheme 4.


form binuclear copper complex 4 with bridging methoxygroup and coordinated methanol molecule in 85% yield(Scheme 5). This light green complex is highly soluble inpolar organic solvents, but its solutions in halogenatedhydrocarbons are unstable. Dilute HCl in methanoldecomposes this complex to ligand 3a, which is furtherhydrolyzed to form 2,6-diformyl-4-tert-butylphenol andN-acetyl-o-phenylenediamine hydrochloride.

Complex 4 was characterized by the data of mass spec-trometry ESI-MS, MALDI-TOF and IR spectroscopy.The IR spectrum of 4 contains intense bands m(C@N) at1629 cm�1 and m(C@I) at 1690 cm�1. The intense m(IH)absorption bands at 3301 and 3266 cm�1 (KBr) indicatethe presence of a solvate methanol molecule and are attrib-uted to the free hydroxy group (3266 cm�1) and hydroxygroup bonded to the acetyl group through a hydrogenbond (3301 cm�1).

The mass spectrum of positive ions (ESI(+)-MS, ace-tone) of complex 4 exhibits ions with m/z = 1204.9(100%) and 674.0 (10%) with the isotopic patterns thatmatch the cationic species [(L1Cu2)2OH]+ (L1 is trianionof 3a) and [(L1Cu2)CuO]+; the latter originates from thedimeric species by elimination of one L1H ligand andone copper atom. The fragmentation of the [(L1Cu2)2OH]+

ion was proved by the tandem ESI-MS experiment. Thehigh intensity of the peak of the dimeric complex probablyindicates that 4 is prone to dimerization in solution, as wasfound for binuclear cobalt complex of 2,6-bis(1,2-dicyano-2-aminovinyliminomethyl)-4-tert-butylphenol [31]. Thepeak intensity of the fragment ion [(L1Cu2)CuO]+ 673.9rises to 52% when a concentrated solution of 4 in acetoni-trile is measured. Contrary to the ESI-MS spectra of 4, the

Scheme

spectrum detected by laser ionization contains no ion ofdimeric species, but two fragmentation peaks[(L1Cu2)CuO]+ 674 (100%) and [(L1Cu2)Cu]+ 658 (25%)are observed.

In order to create a binuclear copper complex withhydroxy-bridging metal ions, we used the method of ‘‘finetuning’’ of volume and electronic properties of the periph-eral substituent – acyl group. To prevent coordination ofthe methanol molecule to the copper ion and to generatethe hydroxy-bridged complex instead of the methoxy-bridged one, we utilized bulky tert-butoxycarbonyl-grouplinked to the nitrogen atom of the o-phenylenediaminering.

The acyclic ligand 3b was obtained using the same pro-cedure as for 3a, by treating 2,6-diformyl-4-tert-butylphe-nol with N-tert-butoxycarbonyl-o-phenylynydiamine(Scheme 4). The resulting yellow substance is highly solublein the majority of organic solvents, including halogenatedones. The treatment of solution of 3b with acids results inligand degradation followed by hydrolysis of mono-Bocderivative. Both acetyl-substituted ligands 3a and 3b arecapable of strong intramolecular hydrogen bondingbetween the OH group of phenol-ring and azomethinenitrogen atom.

The treatment of 3b with copper trimethylacetate inmethanol leads to binuclear complex 5 with 85% yield(Scheme 5). Complex 5 contains neither counter-ions normolecules of solvent, coordinated to copper atoms. Thiscomplex was characterized by IR spectra and elementalanalysis.

3.2. The structures of dicopper complexes

The structures of complexes 4 and 5 were determined byX-ray structural analysis. The crystallographic parametersand most important bond lengths are given in Tables 3and 4.

Two Cu(II) atoms in molecule 4 are linked together viatwo bridging oxygen atoms from methoxy and phenoxygroups (Fig. 1). The four-membered metallocycle Cu2O2

forms a butterfly core with dihedral CuO2/CuO2 angleequal to 13.2�. The distorted square-planar environmentof one copper atom (Cu(1)) is formed by the additionalcoordination with two nitrogen atoms of pentadentate

5.

DF

Td

ata

for

5c

(Ao

r�)

Bo

nd

len

gth

or

angl

eX

-ray

dat

afo

r5

b(A

or

�)D

FT

dat

afo

r5

b

(Ao

r�)

Sin

glet

Tri

ple

tS

ingl

etT

rip

let

3.13

23.

035

Cu

(3)��C

u(4

)3.

0368

(10)

3.11

13.

015

2.03

12.

020

Cu

(3)–

O(7

)1.

982(

3)2.

090

2.04

92.

037

1.98

6C

u(4

)–O

(7)

1.96

5(3)

2.00

31.

931.

894

1.93

5C

u(3

)–O

(12)

1.88

1(3)

1.88

31.

981

1.89

41.

934

Cu

(4)–

O(1

2)1.

877(

3)1.

878

1.91

21.

937

1.95

9C

u(3

)–N

(5)

1.92

7(3)

1.94

21.

965

1.94

31.

970

Cu

(3)–

N(6

)1.

942(

3)1.

942

1.96

91.

939

1.95

7C

u(4

)–N

(7)

1.92

8(3)

1.92

91.

955

1.94

41.

948

Cu

(4)–

N(8

)1.

932(

3)1.

942

1.95

42.

402

2.38

0O

(12)

–H��O

(10)

2.18

1.90

41.

944

100.

798

.5C

u(4

)–O

(7)–

Cu

(3)

100.

60(1

3)98

.896

.911

1.5

103.

4C

u(4

)–O

(12)

–Cu

(3)

107.

84(1

4)11

1.6

103.

474

.078

.2O

(12)

–Cu

(3)–

O(7

)75

.47(

12)

73.7

77.8

73.8

77.3

O(1

2)–C

u(4

)–O

(7)

75.9

6(12

)75

.879

.9


ligand L1. The other two nitrogen atoms of this ligand arebound to the second copper atom (Cu(2)). The last oneexhibits a tetragonal-pyramidal environment due to theadditional interaction with the oxygen atom O(5) of themethanol molecule (Cu(2)–O(5) 2.314(8) A). Symmetricalbonding of the ligand with two copper atoms leads to theformation of two five- and two six-membered metallocyclesconnected with each other (Fig. 1). Two six-memberedneighbouring metallocycles in 4 are planar. On the con-trary, the planarity of five-membered metallocycles is sub-stantially distorted, due to the hindrance of bulky acetylsubstituents at nitrogen atoms N(1) and N(4). The dihedralangles CuN2/N2C2 for these moieties are equal to 18.5� and24.8�. Formally, the conformation of the complex (withouttaking into account the coordinated methanol molecule)could be considered as ‘‘flat concave lens’’ (Fig. 2).

The distances between the donor atoms and Cu(2) atomare somewhat longer than the corresponding values forCu(1). This is undoubtedly a consequence of the formationof an additional Cu(2)–O(5) bond with the methanol mol-ecule. The long Cu–O(5) distance (2.314(8) A) is in agree-ment with published data for this type of complex withthe apical oxygen atom (2.300(2) A) [32]. The Cu(1)–Cu(2) distance (3.027(2) A) also lies within the interval ofthe values observed for the copper complexes of a similar

Table 3Crystallographic data and structural parameters for complex 4 and 5

4 Æ 2.5MeOH 5 Æ MeOH

Formula C32.50H44Cu2N4O7.50 C35H44N4O7Cu2

Formula weight 738.81 759.82Temperature (K) 120(2) 120(2)Wavelength (A) 0.71073 0.71073Crystal system, space

grouptriclinic, P�1 triclinic, P�1

Unit cell dimensions

a (A) 9.708(4) 14.409(4)b (A) 13.203(5) 16.631(5)c (A) 13.509(5) 17.324(5)a (�) 100.122(11) 108.749(5)b (�) 97.128(12) 112.028(5)c (�) 97.524(13) 98.127(5)

V (A3) 1670.6(11) 3478.1(18)Z 2 4Dcalc (g/cm3) 1.469 1.451Absorption coefficient

(mm�1)1.327 1.276

F(000) 772 1584Crystal size (mm) 0.64 · 0.32 · 0.13 0.30 · 0.24 · 0.08h Range for data

collection (�)1.55–26.06 1.35–27.13

Absorption correction semi-empirical fromequivalents

semi-empirical fromequivalents

Maximum and minimumtransmission

0.987 and 0.453 0.905 and 0.701

Refinement method full-matrix least-squares on F2

full-matrix least-squares on F2

Data/parameters 6248/421 15162/865Goodness-of-fit on F2 1.003 1.000Final R indices [I > 2r(I)] R1 = 0.0729,

wR2 = 0.2403R1 = 0.0537,wR2 = 0.1093

Tab

le4

Dat

ao

nin

tera

tom

icd

ista

nce

san

dan

gles

for

com

ple

xes

4an

d5

(X-r

ayd

iffra

ctio

nan

alys

is)

Bo

nd

len

gth

or

angl

eX

-ray

dat

afo

r4

(Ao

r�)

DF

Td

ata

for

4c

(Ao

r�)

Bo

nd

len

gth

or

angl

eX

-ray

dat

afo

r5

c(A

or

�)

Sin

glet

Tri

ple

t

Cu

(1)��C

u(2

)3.

027(

2)3.

124

3.08

1C

u(1

)��C

u(2

)3.

0299

(10)

Cu

(1)–

O(4

)1.

896(

7)1.

942

1.97

4C

u(2

)–O

(1)

1.98

4(3)

Cu

(2)–

O(4

)1.

939(

7)1.

951

1.98

9C

u(1

)–O

(1)

1.96

3(3)

Cu

(1)–

O(1

)1.

967(

7)2.

046

2.00

7C

u(1

)–O

(6)

1.87

9(3)

Cu

(2)–

O(1

)1.

976(

7)2.

046

2.02

3C

u(2

)–O

(6)

1.87

7(3)

Cu

(1)–

N(2

)1.

901(

8)1.

937

1.95

1C

u(1

)–N

(1)

1.93

2(3)

Cu

(2)–

N(3

)1.

954(

9)1.

938

1.95

7C

u(1

)–N

(2)

1.93

4(3)

Cu

(1)–

N(1

)1.

950(

8)1.

957

1.97

2C

u(2

)–N

(3)

1.92

9(3)

Cu

(2)–

N(4

)1.

986(

9)1.

965

1.98

5C

u(2

)–N

(4)

1.95

0(3)

Cu

(2)–

O(5

)2.

314

2.72

62.

715

O(6

)–H��O

(5)

2.27

Cu

(1)–

O(1

)–C

u(2

)10

0.2(

3)99

.599

.7C

u(1

)–O

(1)–

Cu

(2)

100.

31(1

2)C

u(1

)–O

(4)–

Cu

(2)

104.

0(3)

106.

710

2.1

Cu

(2)–

O(6

)–C

u(1

)10

7.55

(14)

O(4

)–C

u(1

)–O

(1)

78.3

(3)

76.7

79.4

O(6

)–C

u(1

)–O

(1)

76.0

5(12

)O

(4)–

Cu

(2)–

O(1

)77

.0(3

)76

.578

.7O

(6)–

Cu

(2)–

O(1

)75

.60(

11)

Fig. 1. Structure of complex 4 according to the X-ray diffraction data.

Fig. 2. Projection of complex 4 along the axis O(4). . .O(1) (solvatemethanol molecule excluded for clarity).

Fig. 3. Structure of complex 5 conformers 5c (a) and 5b (b) according tothe X-ray diffraction data.


structure (2.947(1)–3.572(1) A [33]). The donor oxygenatoms (O(2), O(3)) of the acetyl groups can also beinvolved in coordination with the metal atoms [32,33].However, such intramolecular coordination in the case of3 is impossible, due to the rigidity of the structure.

Compound 5 crystallizes as a methanol solvate in a 1:1ratio. The crystal structure of 5 is shown in Fig. 3, alongwith the atomic numbering scheme. Selected bond lengthsand angles are listed in Table 4. The unit cell of the com-plex contains two crystallographically independent mole-cules of 5 representing different conformers (5b and 5c),which differ only by the mutual arrangement of the termi-nal tert-butoxycarbonyl substituents (Fig. 3a and b).

Similar to molecule 4, molecule 5 consists of the centralfour-membered Cu2O2 ring in a butterfly conformationsurrounded by the pentadentate ligand L2. Each of thetwo Cu(II) atoms has a distorted square-planar coordina-tion environment of two bridging oxygen atoms of thephenoxy and hydroxy groups, and two of the four closestnitrogen atoms of the ligand L2. The Cu� � �Cu distance isalso very similar to that observed for 4 (Table 4). However,contrary to 4, the four-membered Cu2O2 ring in 5 is signif-icantly flattened (the fold angle on the O� � �O line is 6.6� for5c and 3.5� for 5b). Moreover, the whole conformation of 5

is almost planar (Fig. 4): only the presence of the bulkyC(O)OBut groups gives rise to its slight distortion. It is ofinterest to note that the C(O)OBut substituents of the one

molecule of 5 are shifted to the same side of the plane,whereas for the other molecule, these substituents areshifted to different sides of the plane (Fig. 4). The observedconformations of the two independent molecules of 5

are stabilized by the intramolecular hydrogen bondsO–H� � �O (Fig. 3).

Thus, the molecules of 4 and 5 can adopt several confor-mations which differ by the mutual arrangement of theC(O)Me or C(O)OBut fragments, as regards their rotationaround the N–C bonds and bending from the molecularplane. Surprisingly, two of the four possible conformersoccur in the case of compound 5, whereas only one con-former occurs in the case of compound 4. To elucidaterotation isomerism of complexes 4 and 5, quantum-chemi-cal (DFT) calculations were carried out.

Fig. 4. Projection of complex 5 conformers along the axis O(6). . .O(1) or O(7). . .O(12) (hydrogen atoms excluded for clarity).


The theoretical DFT study of the structure of complex 4

revealed the series of minima on the PES both for singletand triplet states (Fig. 5). A methanol molecule iscoordinated to the Cu(1) atom for all studied isomers ofcomplex 4, but in the conformer 4a(1), the methanol mol-ecule is capable of forming an additional hydrogen bondwith the oxygen atom of the nearest acetyl group(rOH� � �O@C = 1.746 A). The complex 4a(1) corresponds tothe global minimum on PES. Several closely arranged localminima corresponding to the conformers with differentmutual orientation of the acetyl groups appear on thePES of the molecule due to the rigidity of the frameworkof the molecule. According to the calculation data, the freeenergy of triplet state 4b, which contains no hydrogen bondwith the oxygen of the acetyl group, is only 0.8 kcal/molhigher than that of the singlet state of 4a(1). The differences

Fig. 5. Conformational dynamics of comp

in free energies of the singlet and triplet states range withinthe accuracy of the method used; therefore, the only state-ment that can be asserted is that the singlet and tripletstates of 4 are very close in energy.

The PES for 4 also contains the local minima of the sin-glet and triplet states of conformer 4c, in which the orien-tation of the acetyl groups is similar to that found in crystalby the X-ray diffraction. The Gibbs energies of the minimaare 0.6 kcal/mol (for the singlet state) and 1.34 kcal/mol(for the triplet state) higher than that of 4a(1). The bondlengths of the nearest coordination sphere of the copperions in triplet complex 4c are in better coincidence withthe X-ray diffraction data than those of singlet complex4c, but the bridging angles in the Cu2O2 metallocycle forsinglet state of 4c are very similar to experimental data(Table 4). This fact is in good agreement with measured

lex 4 according to DFT calculations.


temperature dependence of magnetic susceptibility whichrevealed that complex 4 contains two strongly antiferro-magnetically coupled copper ions (see below).

The PES for complex 5 also contains several minimacorresponding to the singlet and triplet states of conform-ers of 5 (Fig. 6). Contrary to the PES of complex 4, a sin-glet state of complex 5c is the global minima on the PES forcompound 5. The conformer 5b is slightly higher in energy(0.05 kcal/mol) than 5c and 5a is higher in energy(0.52 kcal/mol) than 5c. Both conformers 5b and 5c are sta-bilized by strong hydrogen bonding between the hydrogenatom of the bridging hydroxy group and the oxygen atomof the N-Boc substituent. These conformers with H-bondare quite similar in energy and both of them are presentin crystals of 5 (vide supra). As for complex 4, the struc-tural parameters of triplet states of conformers 5a and 5b

are in better agreement with X-ray data than those of sin-glet states (Table 4). The triplet states of complex 5 con-formers are 2.0 kcal/mol higher in energy thancorresponding singlet states (except for 5c, the energy ofwhich is larger (5.96 kcal/mol)).

Fig. 7. Conformational dynamics of complex 5 according to DFTcalculations.

3.3. Magnetochemistry and electrochemistry of complexes 4

and 5

Magnetochemical study of complexes 4 and 5 showedthat both of them are antiferromagnetic. According tothe temperature dependence of the magnetic susceptibility,4 and 5 are paramagnetic in the whole range of the temper-atures (Fig. 7a and b). The value of the effective magneticmoment for 4 (�1.4b at high temperature) is typical forthe strongly antiferromagnetically coupled dicopper(II)systems (Fig. 7a). The sharp rise of the magnetic suscepti-bility at low temperatures indicates the presence of a smallamount of a mononuclear copper(II) impurity.

The magnetic behaviour of the phenoxy-hydroxy-bridged dicopper complex 5 is significantly different from4, despite the relatively similar Cu� � �Cu distances andCu–O–Cu angles. The value of the effective magneticmoment for 5 (Fig. 7b) approaches �2.1b at high temper-ature, which is close to that of two non-interactingunpaired electrons. The data obtained for 5 suggest thatthe copper ions are very weakly coupled centres. Cooling

Fig. 6. Experimental dependence leff(T) (black circles) for 4 (a) and

lower than 20 K increases magnetic susceptibility, thusindicating the presence of a small amount of a mononu-clear copper(II) impurity.

Theoretical analysis of v(T) curves for both complexeswere performed using the Bleaney–Bowers [34] equationfor magnetic susceptibility of a dimer with 1/2 spin (the

5 (b). The curves have been plotted from theoretical modeling.

Fig. 8. CV curve for complex 4 (7.10�4 M): Pt, DMSO, 0.1 M Bu4NPF6,100 mV/s.


first component) and taking into account ‘monomericadmixture’ (the other component):

v ¼ 2Nb2g2

3kT1þ 1

3exp

�2JkT

� �� 1

� ð1� pÞ þ Nb2g2

2kTp þ Na

where �2J is the singlet–triplet energy (H = �2JS1 Æ S2)gap and the other terms have their usual meanings; p rep-resents the mol fraction of mononuclear impurity and Nameans temperature independent paramagnetism. The Blea-ney–Bowers equation is used for two oxygen-bridged cop-per ions even in the case of two dissimilar ions (e.g. twoions in a dissimilar coordination environment) [35–38].Actually, relatively weak apical coordination bonds withcounter-ions or molecules of the coordinated solvents don’taffect the strong interaction between copper centresthrough oxygen bridges.

The optimized values of the parameters g, 2J, p and Nafor complex 4 appeared to be 2.20(5), �352(5) cm�1,0.020(1) and 40(1) · 10�6 cm3 mol�1, respectively. The the-oretical curve corresponding to the parameters mentionedabove is shown by the solid line in Fig. 7a.

The magnetic behaviour of 5 is more complex. Accordingto X-ray data, two conformers of complex 5 exist in a solidstate, but the nearest coordination spheres of copper ions inboth conformers are identical. Thus, the magnetism of 5

could be explained from the same Bleaney–Bowers equationas for complex 4, as it is known that magnetic properties ofthe system depend mainly on geometry of the nearest coor-dination sphere of metal ions [3,5–10]. The optimized valuesof parameters g, 2J, p and Na for complex 5 appeared to be2.1(1), �156(8) cm�1, 0.060(2) and 124(27) · 10�5 cm3

mol�1, respectively. The theoretical curve correspondingto these parameters is shown by the solid line in Fig. 7b.The greater error in the estimation of the parameters ofexchange interaction for complex 5 could be explained bythe greater maintenance of the mononuclear impurityadsorbed on a surface of the sample.

It is well documented that antiferromagnetic couplingis increased when the bridging oxygen atom is bondedto more electronegative organic groups than hydrogen[37,39]. These experimental data have a theoretical expla-nation [40]. According to [37,39,40], complex 4 containingthe methoxy group should possess a greater S–T energygap than complex 5 with the bridging hydroxy group.On the contrary, it is well known that if the Cu2O2 corehas some deviation from the planarity, the interactionbecomes less antiferromagnetic [41]. In complex 4, theCu2O2 core has a butterfly conformation, whereas in com-plex 5, only insignificant distortion from a plane can beobserved. Thus, one can expect that the cooperative influ-ence of these two factors should diminish the differencebetween antiferromagnetic interactions in these com-plexes. Our experimental data show that the S–T energygap is greater for the methoxy-bridging complex 4, whilethe hydroxy-bridging complex 5 possesses one half of thecomplex 4 �2J value.

The electrochemical properties of complexes 4 and 5

were studied by cyclic voltammetry. The measurementswere carried out at a Pt electrode in two solvents: DMSOand CH2Cl2. The cyclic voltammetry (CV) curve for 4 inDMSO is shown in Fig. 8. Two quasi-reversible redox tran-sitions observed in the cathodic region at the potentialsEpc1 = �0.81 V and Epc2 = �1.34 V (vs. Ag/AgCl/KCl)correspond to the successive reduction of 4 to 6 and 7.

LCuIICuII ðOCH3Þ4

þe� ½LCuIICuIðOCH3Þ��6

½LCuIICuIðOCH3Þ��6

þe� ½LCuICuIðOCH3Þ�2�7

From the potential difference between the peaks(Epc1 � Epc2), one can calculate the coproportionation con-stant (Kc) for the equilibrium process presented below:

LCuIICuII

4þ ½LCuICuI�2�

7

�Kc

2 ½LCuIICuI��6

The Kc value obtained for DMSO solution is rather high(4.57 · 109), indicating a high stability of mixed-valencecomplex 6 due to odd electron delocalization between thetwo copper atoms and over the ligand. However, the elec-trochemical criterion is not always unambiguous in thiscase because a whole series of different factors can affectthe experimental peak potential values of the redox transi-tions. In particular, a high peak separation between thereduction and the corresponding reoxidation peaks(Epc � Epa), being, in our case, 200–300 mV at a potentialsweep rate of 100 mV/s, indicates that the electron transferis followed by the structural rearrangement of the complex,thus influencing the peak potentials of the forward andreverse redox transitions. It is of interest that the shapeof the CV curve depends on the potential sweep value.After the first electron has been transferred, the CVobtained at a low potential sweep rate (50 mV/s, Fig. 9a)contains only one reoxidation peak (the difference betweenthe forward and backward peak potentials is Epc1 � Epa =


0.30 V), while at high potential sweep rate (500 mV/s,Fig. 9b) there are two reoxidation peaks (Epa1 = �0.75 Vand Epa2 = �0.41 V). However, if the scan direction ischanged after passing the second cathodic peak, only onereoxidation peak is observed even at 500 mV/s.

The electron transfer is probably followed by the rear-rangement of the solvate shell of the complex, which affectsthe potential of its reoxidation. This effect can be rathersubstantial for a solvent with high viscosity and good sol-vating ability, which is DMSO. It is known [42] that polarcoordinating solvents stabilize the CuIICuI complexes andinfluence the (Epc1 � Epc2) value. However, it would beearly to draw the final conclusions on the character ofstructural rearrangements, and this will be the subject offurther investigations.

The electrochemical behaviour of complexes 4 and 5 areessentially the same, though the coordination environmentsof the copper atoms are different. The observed reductionpeak potential values for 5 are �0.89 V and �1.43 V, whichare close to those observed for 4. Judging from the poten-tial gap value between two successive electron transfer

Fig. 9. CV for complex 4 (7.10�4) measured in the anodic potential region(Pt, DMSO, 0.1 M Bu4NPF6, 100 mV/s).

steps for complex 5, one can expect high odd electron delo-calization in a mixed valence state, as it was in the case ofcomplex 4. However, magnetic measurements indicate thatin the case of 5, Cu–Cu interaction is smaller due to lesselectronegative hydroxy-group bridging. This observationsupports a conclusion made in [42] that only magnetic mea-surements rather than electrochemical data obtained inpolar coordinating solvents can provide a final answerabout Cu–Cu interaction in a mixed valence state.

The electrochemical oxidation of the binuclear coppercomplexes is much more poorly studied than their reduc-tion. Several examples of reversible metal-centred Cu2+/Cu3+ oxidation are known (see, e.g., [43] and literaturecited therein). However, irreversible oxidation is observedmore often (e.g. [44]), and the nature of a chemical step fol-lowing electron transfer is not discussed. The reversibleligand-centred oxidation of similar complexes has beenreported recently [45–48]. The oxidation of complexes 4

and 5 in DMSO is irreversible, with the loss of two elec-trons at a potential of +1.01 V (Fig. 10) and +0.93 V ver-sus Ag/AgCl/KCl, respectively, followed by a chemicalstep. As indicated by the quantum-chemical calculationdata, the main contribution to HOMO of complexes 4

and 5 is made by orbitals of the donor centres of the ligand.Probably, the oxidation is a ligand-centred process whichweakens the bonding between the copper and the oxygenatoms. As a result, the complex loses its binuclear struc-ture, and one of the Cu(II) atoms leaves the ligand sphere.This is supported by the fact that the reversible redox paircorresponding to Cu2+ reduction can be observed in thereverse scan at a potential of 0.19/0.12 V. The oxidationof free polydentate ligand 3a is also irreversible but atsomewhat more anodic potential (+1.3 V, DMSO) andcorresponds to phenol moiety oxidation.

According to the quantum-chemical simulation data forcomplex 4, the most probable route for the degradation ofthe binuclear complex formed by two-electron oxidation of

Fig. 10. CV for complex 4 (7.10�4) measured in the cathodic potentialregion at sweep rates of 50 mV/s (a) and 500 mV/s (b): Pt, DMSO, 0.1 MBu4NPF6.

Scheme 6.


the ligand is the elimination of copper(II) methoxide sol-vated by DMSO (Scheme 6). In the cationic mononuclearparamagnetic complex 8 with a quinodimethane-like highlyconjugated structure, which is formed in this process, thepositive charge is mainly localized on the metal atom, andthe spin density is distributed equally between the metalcentre and the nitrogen atom that is not involved in coordi-nation. This path of degradation of the starting binuclearcomplex is thermodynamically favourable ðDG0

298 ¼�46:9 kcal=molÞ. Another probable degradation pathwayinvolving the formation of methoxide radical is less favour-able ðDG0

298 ¼ �26:6 kcal=molÞ. Thus, the most probabletransformation of the double-oxidized copper complex 9 isthe elimination of one copper ion from oxidized quinodime-thane-like ligand. The most important structural parametersof complex 8 are presented in electronic Supplementarymaterial.

The study of the electrochemical behaviour of com-plexes 4 and 5 in low-polar CH2Cl2 also showed two redoxtransitions in the cathodic region of the CV curve at thepotentials of Epc1 = �0.73 V and Epc2 = �1.40 V (for 4)and Epc1 = �0.89 V and Epc2 = �1.51 V (for 5). However,the anodic behaviour of 4 and 5 in CH2Cl2 is different fromthat in DMSO. Instead of the one two-electron oxidationpeak observed in DMSO, two separate one-electron oxida-tion peaks are detectable for both complexes in CH2Cl2(for4 Epa1 = 1.16 V and Epa2 = 1.41 V; for 5 Epa1 = 1.13 V andEpa2 = 1.38 V). For the first peak in the reverse scan of CV,the corresponding reduction peak can be observed thoughIpa/Ipc� 1. The second peak is irreversible and likely cor-responds to the ligand oxidation. It should be noted that inCH2Cl2, contrary to DMSO, the redox pair correspondingto Cu2+ reduction was not observed in the reverse scan.That means that after oxidation of the complexes the cop-per ion does not leave the coordination sphere, probablydue to the poor solvation ability of CH2Cl2.

Acknowledgements

The Russian Foundation for Basic Research is grate-fully acknowledged (Projects 05-03-32684 and 05-03-32759). The authors are grateful to the Joint Supercom-puter Center (JSC) for computing time on MVS-1000M.

Appendix A. Supplementary material

CCDC 637640 and 637641 contain the supplementarycrystallographic data for this paper. These data can beobtained free of charge from The Cambridge Crystallo-graphic Data Centre via www.ccdc.cam.ac.uk/data_re-quest/cif. Supplementary data associated with this articlecan be found, in the online version, at doi:10.1016/j.ica.2007.10.020.

References

[1] H.S. Mason, in: K.T. Yasunoba, H.F. Mower, O. Hayaishi (Eds.),Iron and Copper proteins, Plenum, New York, 1976, p. 464.

[2] R.H. Holm, P. Kennepohl, E.I. Solomon, Chem. Rev. 96 (1996) 2239.[3] Ch.J. O’Connor, D. Firmin, A.K. Pant, B.R. Babu, E.D. Stevens,

Inorg. Chem. 25 (1986) 2300.[4] T.W. Sorrell, D.L. Jameson, Ch.J. O’Connor, Inorg. Chem. 23 (1984)

190.[5] T. Mallah, M.-L. Boillot, O. Kahn, J. Gouteron, S. Jeannin, Y.

Jeannin, Inorg. Chem. 25 (1986) 3058.[6] N.A. Bailey, D.E. Fenton, J. Lay, P.B. Roberts, J.-M. Latour, D.

Limosin, J. Chem. Soc., Dalton Trans. (1986) 2681.[7] J.J. Grzybowski, P.H. Merrell, F.L. Urbach, Inorg. Chem. 17 (1978)

3078.[8] R.R. Gagne, M.W. McCool, R.E. Marsh, Acta Crystallogr., Sect. B

36 (1980) 2420.[9] J. Lorosch, W. Haase, Inorg. Chim. Acta 108 (1985) 35.

[10] G.D. Fallon, K.S. Murray, B. Spethmann, J.K. Yandell, J.H.Hodgkin, B.C. Loft, J. Chem. Soc., Chem. Commun. (1984) 1561.

[11] F.K. Zhovmir, Yu.A. Simonov, V.V. Zelentsov, N.V. Gerbeleu, M.D.Revenko, A.K. Stroesku, A.N. Sobolev, Zh. Neorg. Khim. (Russ.) 33(1988) 2180.

[12] A.S. Antsyshkina, M.A. Porai-Koshits, G.G. Sadikov, V.V. Lukov,V.A. Kogan, S.I. Levchenkov, Zh. Neorg. Khim. (Russ.) 39 (1994)905.

[13] S. Mukherjee, T. Weyhermuller, E. Bothe, K. Wieghardt, P.Chaudhuri, Eur. J. Inorg. Chem. (2003) 863.

[14] M. Sakamoto, S. Itose, T. Ishimori, N. Matsumoto, H. Okawa, S.Kida, J. Chem. Soc., Dalton Trans. (1989) 2083.

[15] P. Guerriero, D. Ajo’, P.A. Vigato, U. Casellato, P. Zanello, R.Graziani, Inorg. Chim. Acta 141 (1988) 103.

[16] P. Guerriero, U. Casellato, D. Ajo’, S. Sitran, P.A. Vigato, R.Graziani, Inorg. Chim. Acta 142 (1988) 305.

[17] L.F. Lindoy, G.V. Meehan, N. Svenstrup, Synthesis (1998) 1029.[18] Z. Shirin, J. Thompson, L. Liable-Sands, G.P.A. Yap, A. Rheingold,

V.A. Borovik, J. Chem. Soc., Dalton Trans. (2002) 1714.[19] N.E. Borisova, M.D. Reshetova, M. Kuznetcov, Yu.A. Ustynyuk,

Synthesis (2007) 1169.

http://www.ccdc.cam.ac.uk/data_request/cif

http://www.ccdc.cam.ac.uk/data_request/cif

http://dx.doi.org/10.1016/j.ica.2007.10.020

http://dx.doi.org/10.1016/j.ica.2007.10.020


[20] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865.[21] D.N. Laikov, Ph. D. Dissertation, Moscow State University, Mos-

cow, 2000.[22] W.J. Stevens, H. Basch, M. Krauss, J. Chem. Phys. 81 (1984) 6026.[23] W.J. Stevens, M. Krauss, H. Basch, P.G. Jasien, Can. J. Chem. (1992)

612.[24] T.R. Cundari, W.J. Stevens, J. Chem. Phys. 98 (1993) 5555.[25] D.N. Laikov, Chem. Phys. Lett. 281 (1997) 151.[26] D.N. Laikov, Yu.A. Ustynyuk, Russ. Chem. Bull. 54 (2005) 820.[27] SMART (control) and SAINT (integration) software, Version 5.0, Bruker

AXS Inc., Madison, WI, 1997.[28] G.M. Sheldrick, SADABS, program for scaling and correction of area

detector data, University of Gottingen, 1997 (based on the method ofR.H. Blessing, Acta Crystallogr., Sect. A 51 (1995) 33).

[29] G.M. Sheldrick, SHELXS97. Program for the Solution of CrystalStructures, University of Gottingen, Germany, 1997.

[30] G.M. Sheldrick, SHELXL97. Program for the Refinement of CrystalStructures, University of Gottingen, Germany, 1997.

[31] N.E. Borisova, Yu.A. Ustynyuk, M.D. Reshetova, G.G. Aleksan-drov, I.L. Eremenko, I.I. Moiseev, Mendeleev Commun. (2003) 202.

[32] K. Anjelkovic, I. Ivanovic, S.R. Niketic, B. Prelesnik, V.M. Leovac,Polyhedron 16 (1997) 4221.

[33] M. Sakamoto, Sh. Itose, T. Ishimori, N. Matsumoto, H. Okawa, S.Kida, J. Chem. Soc., Dalton Trans. (1989) 2083.

[34] B. Bleaney, K.D. Bowers, Prog. Roy. Soc. (London) 25 (1952) 29.[35] A. Hori, M. Yonemura, M. Ohba, H. Okawa, Bull. Chem. Soc. Jpn.

74 (2001) 495.

[36] T. Toki, M. Mikuriya, H. Okawa, I. Murase, S. Kida, Bull. Chem.Soc. Jpn. 57 (1984) 2098.

[37] J. Galy, J. Jaud, O. Kahn, P. Tola, Inorg. Chim. Acta 36 (1979)229.

[38] K.A. Leslie, R.S. Drago, G.D. Stucky, D.J. Kitko, J.A. Breese, Inorg.Chem. 18 (1979) 1885.

[39] D.Y. Jeter, D.L. Lewiss, J.C. Hempel, D.J. Hodgson, W.E. Hatfield,Inorg. Chem. 11 (1972) 1958.

[40] P.J. Hay, J.C. Thibeault, R. Hoffmann, J. Am. Chem. Soc. 97 (1975)4884.

[41] O. Kahn, Molecular Magnetism, Wiley-VCH, New York, Chichester,Weinheim, Brisbane, Singapore, Toronto, 1993, Chapters 6 and 9.

[42] S.K. Mandal, K. Nag, J. Chem. Soc., Dalton Trans. (1984) 2141.[43] S.K. Mandal, L.K. Thompson, K. Nag, J.-P. Charland, E.J. Gabe,

Inorg. Chem. 26 (1987) 1391.[44] W. Mazurek, A.M. Bond, K.S. Murray, M.J. O’Connor, A.G. Weed,

Inorg. Chem. 24 (1985) 2484.[45] F. Michel, S. Torelli, F. Thomas, C. Dubok, C. Philouze, C. Belle, S.

Hamman, E. Saint-Aman, J.-L. Pierre, Angew. Chem., Int. Ed. Engl.44 (2005) 438.

[46] C. Belle, C. Beguin, I. Gautier-Luneau, S. Philouze, J.L. Pierre, F.Thomas, S. Torelli, Inorg. Chem. 41 (2002) 479.

[47] Y. Shimazaki, S. Hirota, O. Yamauchi, Inorg. Chim. Acta 331 (2002)168.

[48] D. Zurita, I. Gautier-Luneau, S. Menage, J.-L. Pierre, E. Saint-Aman, J. Bio. Inorg. Chem. 2 (1997) 46.

Influence of ligands’ peripheral substituents on the structure, magnetochemical and...

Documents

Transcript of Influence of ligands’ peripheral substituents on the structure, magnetochemical and...