A NOVEL METAL THIAMINE COMPLEX WITH A CYCLIC DIMER FORMED BY METAL-BRIDGED 2 THIAMINE LIGANDS - CRYSTAL-STRUCTURE OF [MN(THIAMINE)CL2(H2O)]2[THIAMINE]2CL4.2H2O

The crystal structure of [Mn(thiamine)Cl2(H2O)]2[thiamine]2Cl4.2H2O has been determined by X-ray diffraction methods. The compound contains a cyclic dimer of a complex cation with two thiamine ligands bridged by two Mn(II) ions across a crystallographic center of symmetry. Each Mn(II) is coordinated by two chloride atoms, a water molecule, a N(1') atom of the pyrimidine from a thiamine and an O(53) atom of the hydroxyethyl side chain from another thiamine. There are two free-base thiamine molecules related by a center of symmetry in the unit cell, which form a base-pair through the hydrogen bonds. Both the independent thiamine molecules in the asymmetric unit assume the common F conformation with phi-T = 10.0(9) and 3.6(10) and phi-P = 85.6(7) and 79.6(7), respectively. The compound provides a possible model for a metal-bridged enzyme-coenzyme complex in thiamine catalysis. Crystallographic data: triclinic, space group P1BAR, a = 12.441(4), b = 13.572(4), c = 11.267(3) angstrom, alpha = 103.15(2), beta 89.03(3), gamma = 115.64(2)-degrees, Z = 1, D(calc) = 1.524 g cm-3, and R = 0.050 for 3019 observed reflections with I > 3-sigma(I).

N-H insertion reactions of rhodium carbenoids. Part 1. Preparation of  -amino acid and  -aminophosphonic acid derivatives.

Rh(II) acetate-catalyzed decompn. of diazophenylacetates PhC(N2)CO2Me 1 and PhC(N2)CO2R* 3 [R*OH = (-)-borneol, (+)-menthol, (-)-8-phenylmenthol] in the presence of a range of N-H compds. results in an N-H insertion reaction of the intermediate carbenoids and formation of N-substituted phenylglycine derivs. PhCH(NR1R2)CO2Me 2 [R1 = R2 = Et; R1 = 4-MeOC6H4, COCH2CHMe2, CO2CH2Ph, (S)-CH(CO2Me)CH2Ph, (S)-CHMePh, R2 = H; 64-83% yields] and PhCH(NR1R2)CO2R* 4 (R1 = R2 = Et; R1 = COMe, CO2Me, R2 = H; same R*; 37-71% yields). The corresponding reactions of di-Me ?-diazobenzylphosphonate PhC(N2)P(O)(OMe)2 5 with primary amines constitute a simple route to aminophosphonates PhCH(NHR)P(O)(OMe)2 6 (R = COMe, COEt, CO2CH2Ph, CO2CMe3, 4-ClC6H4, 4-MeC6H4, 4-MeOC6H4; 13-96% yields).

Asymmetric rhodium carbenoid insertion into the Si-H bond.

Buck, Richard T.; Doyle, Michael P.; Drysdale, Martin J.; Ferris, Leigh; Forbes, David C.; Haigh, David; Moody, Christopher J.; Pearson, Neil D.; Zhou, Qi-Lin. Dep. Chemistry, Loughborough Univ., Loughborough, Leicestershire, UK. Tetrahedron Letters (1996), 37(42), 7631-7634. Publisher: Elsevier, CODEN: TELEAY ISSN: 0040-4039. Journal written in English. CAN 125:328854 AN 1996:644681 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) Abstract Decompn. of Me 2-diazophenylacetate in the presence of dimethylphenylsilane and a chiral dirhodium(II) catalyst results in Si-H insertion of the intermediate carbenoid to give PhCH(SiMe2Ph)CO2Me with varying degrees of enantioselectivity (up to 47% ee; 47% using (S)-Rh2L4, LH = I).

Rhodium carbenoid O-H insertion reactions with phenols; a facile method for the synthesis of trialkyl 2-aryloxyphosphonoacetates and their use in the preparation of 2-aryloxy-3-phenylpropanoates

Substituted phenols undergo a facile Rh carbenoid-mediated O-H insertion reaction with (EtO)2P(O)C(:N2)CO2R (I; R = Et, Me) to give 44-86% 2-aryloxyphosphonoacetates II (R1 = e.g., H, 4-Me, 4-Cl, 2-OH, 4-PhCH2O). Phenols contg. strongly electron withdrawing groups, bulky ortho-substituents or certain ortho-heteroatom substituents show reduced or variable yields. Catechol affords a mono-adduct which cyclizes to lactate III. Aniline inserts preferentially and exclusively over phenol in a competition reaction with I (R = Et) to give (EtO)2P(O)CH(NHPh)CO2Et. II are versatile intermediates in a prepn. of 2-aryloxy-3-phenylpropenoates IV by Wadsworth-Emmons reaction with benzaldehydes R2C6H4CHO (R2 = PhCH2O, 2-Cl, H). Dissolving Mg metal redn. provides a mild method for the conversion of propenoates IV into the corresponding propanoates.

The synthesis, characterisation and reactivity of 2-phosphanylethylcyclopentadienyl complexes of cobalt, rhodium and iridium

2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C5R'(4)(CH2)(2)PR2] (R = Et, R' = H or Me, R = Ph, R' = Me), have been prepared from the reaction of spirohydrocarbons C5R'(4)(C2H4) with LiPR2. C5Et4HSiMe2CH2PMe2, was prepared from reaction of Li[C5Et4] with Me2SiCl2 followed by Me2PCH2Li. The lithium salts were reacted with [RhCl(CO)2]2,[IrCl(CO)3] or [Co-2(CO)(8)] to give [M(C5R'(4)(CH2) 2PR2)(CO)] (M = Rh, R = Et, R' = H or Me, R= Ph, R' = Me; M = Ir or Co, R = Et, R' = Me), which have been fully characterised, in many cases crystallographically as monomers with coordination of the phosphorus atom and the cyclopentadienyl ring. The values of nu(CO) for these complexes are usually lower than those for the analogous complexes without the bridge between the cyclopentadienyl ring and the phosphine, the exception being [Rh(Cp'(CH2)(2)PEt2)(CO)] (Cp' = C5Me4), the most electron rich of the complexes. [Rh(C5Et4SiMe2CH2PMe2)(CO)] may be a dimer. [Co-2(CO)(8)] reacts with C5H5(CH2)(2)PEt2 or C5Et4HSiMe2CH2PMe2 (L) to give binuclear complexes of the form [Co-2(CO)(6)L-2] with almost linear PCoCoP skeletons. [Rh(Cp'(CH2)(2)PEt2)(CO)] and [Rh(Cp'(CH2)(2)PPh2)(CO)] are active for methanol carbonylation at 150 degrees C and 27 bar CO, with the rate using [Rh(Cp'(CH2)(2)PPh2)(CO)] (0.81 mol dm(-3) h(-1)) being higher than that for [RhI2(CO)(2)](-) (0.64 mol dm(-3) h(-1)). The most electron rich complex, [Rh(Cp'(CH2)(2)PEt2)(CO)] (0.38 mol dm(-3) h(-1)) gave a comparable rate to [Cp*Rh(PEt3)(CO)] (0.30 mol dm(-3) h(-1)), which was unstable towards oxidation of the phosphine. [Rh(Cp'(CH2)(2)PEt2)I-2], which is inactive for methanol carbonylation, was isolated after the methanol carbonylation reaction using [Rh(Cp'(CH2)(2)PEt2)(CO)].

Universal tight binding model for chemical reactions in solution and at surfaces. II. Water

A revised water model intended for use in condensed phase simulations in the framework of the self consistent polarizable ion tight binding theory is constructed. The model is applied to water monomer, dimer, hexamers, ice, and liquid, where it demonstrates good agreement with theoretical results obtained by more accurate methods, such as DFT and CCSD(T), and with experiment. In particular, the temperature dependence of the self diffusion coefficient in liquid water predicted by the model, closely reproduces experimental curves in the temperature interval between 230 K and 350 K. In addition, and in contrast to standard DFT, the model properly orders the relative densities of liquid water and ice. A notable, but inevitable, shortcoming of the model is underestimation of the static dielectric constant by a factor of two. We demonstrate that the description of inter and intramolecular forces embodied in the tight binding approximation in quantum mechanics leads to a number of valuable insights which can be missing from ab initio quantum chemistry and classical force fields. These include a discussion of the origin of the enhanced molecular electric dipole moment in the condensed phases, and a detailed explanation for the increase of coordination number in liquid water as a function of temperature and compared with ice-leading to insights into the anomalous expansion on freezing. The theory holds out the prospect of an understanding of the currently unexplained density maximum of water near the freezing point. 

Towards reverse engineering of Photosystem II: Synergistic Computational and Experimental Approaches

ABSTRACT Photosystem II (PSII) of oxygenic photosynthesis has the unique ability to photochemically oxidize water, extracting electrons from water to result in the evolution of oxygen gas while depositing these electrons to the rest of the photosynthetic machinery which in turn reduces CO2 to carbohydrate molecules acting as fuel for the cell. Unfortunately, native PSII is unstable and not suitable to be used in industrial applications. Consequently, there is a need to reverse-engineer the water oxidation photochemical reactions of PSII using solution-stable proteins. But what does it take to reverse-engineer PSII’s reactions? PSII has the pigment with the highest oxidation potential in nature known as P680. The high oxidation of P680 is in fact the driving force for water oxidation. P680 is made up of a chlorophyll a dimer embedded inside the relatively hydrophobic transmembrane environment of PSII. In this thesis, the electrostatic factors contributing to the high oxidation potential of P680 are described. PSII oxidizes water in a specialized metal cluster known as the Oxygen Evolving Complex (OEC). The pathways that water can take to enter the relatively hydrophobic region of PSII are described as well. A previous attempt to reverse engineer PSII’s reactions using the protein scaffold of E. coli’s Bacterioferritin (BFR) existed. The oxidation potential of the pigment used for the BFR ‘reaction centre’ was measured and the protein effects calculated in a similar fashion to how P680 potentials were calculated in PSII. The BFR-RC’s pigment oxidation potential was found to be 0.57 V, too low to oxidize water or tyrosine like PSII. We suggest that the observed tyrosine oxidation in BRF-RC could be driven by the ZnCe6 di-cation. In order to increase the efficiency of iii tyrosine oxidation, and ultimately oxidize water, the first potential of ZnCe6 would have to attain a value in excess of 0.8 V. The results were used to develop a second generation of BFR-RC using a high oxidation pigment. The hypervalent phosphorous porphyrin forms a radical pair that can be observed using Transient Electron Paramagnetic Resonance (TR-EPR). Finally, the results from this thesis are discussed in light of the development of solar fuel producing systems.

Structure-fonction de MARCH1, une E3 ubiquitine ligase régulant la présentation antigénique par le CMH II

Les molécules classiques du CMH de classe II sont responsables de la présentation de peptides exogènes par les cellules présentatrices d’antigène aux lymphocytes T CD4+. Cette présentation antigénique est essentielle à l’établissement d’une réponse immunitaire adaptative. Cependant, la reconnaissance d’auto-antigènes ainsi que l’élimination des cellules du Soi sont des problèmes à l’origine de nombreuses maladies auto-immunes. Notamment, le diabète et la sclérose en plaque. D’éventuels traitements de ces maladies pourraient impliquer la manipulation de la présentation antigénique chez les cellules dont la reconnaissance et l’élimination engendrent ces maladies. Il est donc primordial d’approfondir nos connaissances en ce qui concerne les mécanismes de régulation de la présentation antigénique. La présentation antigénique est régulée tant au niveau transcriptionnel que post-traductionnel. Au niveau post-traductionnel, diverses cytokines affectent le processus. Parmi celles-ci, l’IL-10, une cytokine anti-inflammatoire, cause une rétention intracellulaire des molécules du CMH II. Son mécanisme d’action consiste en l’ubiquitination de la queue cytoplasmique de la chaîne bêta des molécules de CMH II. Cette modification protéique est effectuée par MARCH1, une E3 ubiquitine ligase dont l’expression est restreinte aux organes lymphoïdes secondaires. Jusqu’à tout récemment, il y avait très peu de connaissance concernant la structure et les cibles de MARCH1. Considérant son impact majeur sur la présentation antigénique, nous nous sommes intéressé à la structure-fonction de cette molécule afin de mieux caractériser sa régulation ainsi que les diverses conditions nécessaires à son fonctionnement. Dans un premier article, nous avons étudié la régulation de l’expression de MARCH1 au niveau protéique. Nos résultats ont révélé l’autorégulation de la molécule par formation de dimères et son autoubiquitination. Nous avons également démontré l’importance des domaines transmembranaires de MARCH1 dans la formation de dimères et l’interaction avec le CMH II. Dans un second article, nous avons investigué l’importance de la localisation de MARCH1 pour sa fonction. Les résultats obtenus montrent la fonctionnalité des motifs de localisation de la portion C-terminale de MARCH1 ainsi que la présence d’autres éléments de localisation dans la portion N-terminale de la protéine. Les nombreux mutants utilisés pour ce projet nous ont permis d’identifier un motif ‘‘VQNC’’, situé dans la portion cytoplasmique C-terminale de MARCH1, dont la valine est requise au fonctionnement optimal de la molécule. En effet, la mutation de la valine engendre une diminution de la fonction de la molécule et des expériences de BRET ont démontré une modification de l’orientation spatiale des queues cytoplasmiques. De plus, une recherche d’homologie de séquence a révélé la présence de ce même motif dans d’autres ubiquitines ligases, dont Parkin. Parkin est fortement exprimée dans le cerveau et agirait, entre autre, sur la dégradation des agrégats protéiques. La dysfonction de Parkin cause l’accumulation de ces agrégats, nommés corps de Lewy, qui entraînent des déficiences au niveau du fonctionnement neural observé chez les patients atteints de la maladie de Parkinson. La valine comprise dans le motif ‘’VQNC’’ a d’ailleurs été identifiée comme étant mutée au sein d’une famille où cette maladie est génétiquement transmise. Nous croyons que l’importance de ce motif ne se restreint pas à MARCH1, mais serait généralisée à d’autres E3 ligases. Ce projet de recherche a permis de caractériser des mécanismes de régulation de MARCH1 ainsi que de découvrir divers éléments structuraux requis à sa fonction. Nos travaux ont permis de mieux comprendre les mécanismes de contrôle de la présentation antigénique par les molécules de CMH II.

Copper(II) complexes of N(4)-substituted thiosemicarbazones derived from pyridine-2-carbaldehyde: Crystal structure of a binuclear complex

Ten copper(II) complexes {[CuL1Cl] (1), [CuL1NO3]2 (2), [CuL1N3]2 · 2/3H2O (3), [CuL1]2(ClO4)2 · 2H2O (4), [CuL2Cl]2 (5), [CuL2N3] (6), [Cu(HL2)SO4]2 · 4H2O (7), [Cu(HL2)2] (ClO4)2 · 1/2EtOH (8), [CuL3Cl]2 (9), [CuL3NCS] · 1/2H2O (10)} of three NNS donor thiosemicarbazone ligands {pyridine-2-carbaldehyde-N(4)-p-methoxyphenyl thiosemicarbazone [HL1], pyridine-2-carbaldehyde-N(4)-2-phenethyl thiosemicarbazone [HL2] and pyridine-2-carbaldehyde N(4)-(methyl), N(4)-(phenyl) thiosemicarbazone [HL3]} were synthesized and physico-chemically characterized. The crystal structure of compound 9 has been determined by X-ray diffraction studies and is found that the dimer consists of two square pyramidal Cu(II) centers linked by two chlorine atoms.

Effect of H-bonding on the ambivalence of SCN- towards copper(II)

Condensations of 2-(2-aminoethyl)pyridine with 4-methylimidazole-5-carboxaldehyde and 1-methyl-2-imidazolecarboxaldehyde generate the tridentate N donor ligands L and L' respectively. Reactions of Cu(NCS)(2) with L and L' yield respectively CuL(SCN)(NCS) (1) containing a CuN4S core and CuL'(NCS)(2) (2) having a CuN5 core. Both the cores are square pyramidal with SCN bound in 1 at the axial position through the S end. This differential behaviour of SCN in the two complexes despite the ligands being very similar, is investigated by DFT calculations at the B3LYP/TZV level. It is found that DFT calculations predict isolation of the Cu(ligand)(NCS)(2) species for both the ligands L and L'. Presence of an offsetting intermolecular H-bonding between the N atom of the thiocyanate and the N-H proton of the ligand L of an adjacent molecule makes the binding of SCN via the S end feasible in 1 resulting in the H-bonded-dimer Cu2L2(SCN)(2)(NCS)(2). The strength of the H-bond is estimated as 27.1 kJ mol (1) from the DFT calculations. The question of such H-bonding does not arise with L' as it lacks in a similar H atom. Dimeric 1 represents a case of two non-interacting spins. (C) 2008 Elsevier B. V. All rights reserved.

Copper(II)-catalyzed [2,3]-sigmatropic rearrangement of N-methyltetrahydropyridinium ylids

A ring-contractive and highly diastereoselective [2,3]-sigmatropic rearrangement occurs when N-methyl-1,2,3,6-tetrahydropyridine is treated with sub-stoichiometric amounts of copper or rhodium salts, in the presence of ethyl diazoacetate, giving ethyl cis-N-methyl-3-ethenyl proline (4).

Synthesis, structural analysis, and magnetic behaviour of three fumarate bridged coordination polymers: five-fold interpenetrated diamond-like net of Ni-II, sheets of Ni-II and Co-II

The hydrothermal reactions of Ni(NO3)(2).6H(2)O, disodium fumarate (fum) and 1,2-bis(4-pyridyl)ethane (bpe)/1,3-bis(4-pyridyl) propane (bpp) in aqueous-methanol medium yield one 3-D and one 2-D metal-organic hybrid material, [Ni(fum)(bpe)] (1) and [Ni(fum)(bpp)(H2O)] (2), respectively. Complex 1 possesses a novel unprecedented structure, the first example of an "unusual mode" of a five-fold distorted interpenetrated network with metal-ligand linkages where the four six-membered windows in each adamantane-type cage are different. The structural characterization of complex 2 evidences a buckled sheet where nickel ions are in a distorted octahedral geometry, with two carboxylic groups, one acting as a bis-chelate, the other as a bis-monodentate ligand. The metal ion completes the coordination sphere through one water molecule and two bpp nitrogens in cis position. Variable-temperature magnetic measurements of complexes 1 and 2 reveal the existence of very weak antiferromagnetic intramolecular interactions and/or the presence of single-ion zero field splitting (D) of isolated Ni-II ions in both the compounds. Experimentally, both the J parameters are close, comparable and very small. Considering zero-field splitting of Ni-II, the calculated D values are in agreement with values reported in the literature for Ni-II ions. Complex 3, [{Co(phen)}(2)(fum)(2)] (phen=1,10-phenanthroline) is obtained by diffusing methanolic solution of 1,10-phenanthroline on an aqueous layer of disodium fumarate and Co(NO3)(2).6H(2)O. It consists of dimeric Co-II(phen) units, doubly bridged by carboxylate groups in a distorted syn-syn fashion. These fumarate anions act as bis-chelates to form corrugated sheets. The 2D layer has a (4,4) topology, with the nodes represented by the centres of the dimers. The magnetic data were fitted ignoring the very weak coupling through the fumarate pathway and using a dimer model.

Structural variations in Ni(II) complexes of salen type di-Schiff base ligands

Three di-Schiff-base ligands, N,N'-bis(salicylidene)-1,3-propanediamine (H(2)Salpn), N,N'-bis(salicylidene)-1,3-pentanedianiine (H(2)Salpen) and N,N'-bis(salicylidine)-ethylenediamine (H(2)Salen) react with Ni(SCN)(2). 4H(2)O in 2:3 molar ratios to form the complexes; mononuclear [Ni(HSalpn)(NCS)(H2O)]center dot H2O (1a), trinuclear [{Ni(Salpen)}(2)Ni(NCS)(2)] (2b) and trinuclear [{Ni(Salen)}(2)Ni(NCS)(2)] (3) respectively. All the complexes have been characterized by elemental analyses, IR and UV-VIS spectra, and room temperature magnetic susceptibility measurements. The structures of la and 2b have been confirmed by X-ray single crystal analysis. In complex la, the Ni(II) atom is coordinated equatorially by the tetradentate, mononegative Schiff-base, HSalpn. Axial coordination of isothiocyanate group and a water molecule completes its octahedral geometry. The hydrogen atom attached to one of the oxygen atoms of the Schiff base is involved in a very strong hydrogen bond with a neighboring unit to form a centrosymmetric dimer. In 2b, two square planar [Ni(Salpen)] units act as bide mate oxygen donor ligands to a central Ni(II) which is also coordinated by two mutually cis N-bonded thiocyanate ligands to complete its distorted octahedral geometry. Complex 3 possesses a similar structure to that of 2b. A dehydrated form of la and a hydrated form of 2b have been obtained and characterized. The importance of electronic and steric factors in the variation of the structures is discussed. (c) 2007 Elsevier Ltd. All rights reserved.

Anion-directed template synthesis and hydrolysis of mono-condensed Schiff base of 1,3-pentanediamine and o-hydroxyacetophenone in Ni-II and Cu-II complexes

Bis(o-hydroxyacetophenone)nickel(II) dihydrate, on reaction with 1,3-pentanediamine, yields a bis-chelate complex [NiL2]center dot 2H(2)O (1) of mono-condensed tridentate Schiff base ligand HL {2-[1-(3-aminopentylimino)ethyl]phenol}. The Schiff base has been freed from the complex by precipitating the Nil, as a dimethylglyoximato complex. HL reacts smoothly with Ni(SCN)(2)center dot 4H(2)O furnishing the complex [NiL(NCS)] (2) and with CuCl2 center dot 2H(2)O in the presence of NaN3 or NH4SCN producing [CuL(N-3)](2) (3) or [CuL(NCS)] (4). On the other hand, upon reaction with Cu(ClO4)(2)center dot 6H(2)O and Cu(NO3)(2)center dot 3H(2)O, the Schiff base undergoes hydrolysis to yield ternary complexes [Cu(hap)(pn)(H2O)]ClO4 (5) and [Cu(hap)(pn)(H2O)]NO3 (6), respectively (Hhap = o-hydroxyacetophenone and pn = 1,3-pentanediamine). The ligand HL undergoes hydrolysis also on reaction with Ni(ClO4)(2)center dot 6H(2)O or Ni(NO3)(2)center dot 6H(2)O to yield [Ni(hap)(2)] (7). The structures of the complexes 2, 3, 5, 6, and 7 have been confirmed by single-crystal X-ray analysis. In complex 2, Ni-II possesses square-planar geometry, being coordinated by the tridentate mono-negative Schiff base, L and the isothiocyanate group. The coordination environment around Cu-II in complex 3 is very similar to that in complex 2 but here two units are joined together by end-on, axial-equatorial azide bridges to result in a dimer in which the geometry around Cu-II is square pyramidal. In both 5 and 6, the Cu-II atoms display the square-pyramidal environment; the equatorial sites being coordinated by the two amine groups of 1,3-pentanediamine and two oxygen atoms of o-hydroxyacetophenone. The axial site is coordinated by a water molecule. Complex 7 is a square-planar complex with the Ni atom bonded to four oxygen atoms from two hap moieties. The mononuclear units of 2 and dinuclear units of 3 are linked by strong hydrogen bonds to form a one-dimensional network. The mononuclear units of 5 and 6 are joined together to form a dimer by very strong hydrogen bonds through the coordinated water molecule. These dimers are further involved in hydrogen bonding with the respective counteranions to form 2-D net-like open frameworks. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

Anion directed template synthesis of Cu(II) complexes of a N,N,O donor mono-condensed Schiff base ligand: A molecular scaffold forming highly ordered H-bonded rectangular grids

Anion directed, template syntheses of two dinuclear copper(II) complexes of mono-condensed Schiff base ligand Hdipn (4-[(3-aminopentylimino)-methyl]-benzene-1,3-diol) involving 2,4- dihydroxybenzaldehyde and 1,3-diaminopentane were realized in the presence of bridging azide and acetate anions. Both complexes, [Cu-2(dipn)(2)(N-3)(2)] (1) and [Cu-2(dip(n))(2)(OAc)(2)] (2) have been characterized by X-ray crystallography. The two mononuclear units are joined together by basal-apical, double end-on azido bridges in complex 1 and by basal-apical, double mono-atomic acetate oxygen-bridges in 2. Both complexes form rectangular grid-like supramolecular structures via H-bonds connecting the azide or acetate anion and the p-hydroxy group of 2,4- dihydroxybenzaldehyde. Variable-temperature (300-2 K) magnetic susceptibility measurements reveal that complex 1 has antiferromagnetic coupling (J = -2.10 cm (1)) through the azide bridge while 2 has intra-dimer ferromagnetic coupling through the acetate bridge and inter-dimer antiferromagnetic coupling through H-bonds (J = 2.85 cm (1), J' = -1.08 cm (1)). (C) 2009 Elsevier B. V. All rights reserved.