Mireille Perec

Synthesis and characterization of zinc(II) oxydiacetate (oda) complexes. Crystal structures of [{Zn(oda)·0.3H2O}n], [Zn(oda)(bipy)(H2O)]·2.5H2O and [Zn(oda)(phen)(H2O)]·1.5H2O (bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline)

Three novel zinc(II) oxydiacetate (oda) compounds [{Zn(oda)·0.3H2O}n]1, [Zn(oda)(bipy)(H2O)]·2.5H2 O 2(bipy = 2,2′-bipyridine) and [Zn(oda)(phen)(H2O)]·1.5H2O 3(phen = 1,10-phenanthroline) have been synthesized and their structures determined by single-crystal X-ray diffraction methods. Compound 1 consists of polymeric sheets formed by ZnO5 units bridged by carboxylate groups in anti-syn conformation along the z axis; 2 and 3 are mononuclear with the zinc atoms in distorted octahedral ZnN2O4 co-ordination geometries. Thermal decomposition of the compounds under an oxygen atmosphere affords ZnO at ca. 500 °C.

Magnetism and structure in chains of copper dinuclear paddlewheel units.

An anhydrous copper carboxylate compound of formula [Cu(trans-2-butenoate)(2)](n) has been characterized. X-ray analysis reveals a structure built by paddlewheel units bridged by pairs of Cu...O axial bonds to give infinite chains arranged in a new topological motif. Susceptibility measurements in the 10-300 K temperature range, and isothermal magnetization curves at 2, 5, 10, and 50 K with fields up to 5 T, were obtained. Electron Paramagnetic Resonance (EPR) spectra of powder samples were measured at 33.9 GHz at 300 K, and at 9.60 GHz at temperatures in the range 90 <or= T <or= 350 K. Fitting the susceptibility data to a chain model of alternating paddlewheel and [Cu(mu-O)(2)Cu] dinuclear units yielded exchange interactions J(1) = -330.6(1) cm(-1) and J(2) = 5.9(2) cm(-1). The EPR spectra reflect the usual antiferromagnetic dinuclear behavior, with zero field splitting parameters of the excited spin triplet, D = -0.329(3) cm(-1) and E approximately 0, plus a central peak not expected for isolated dinuclear units. We interpret this peak as arising from the stochastic spin dynamics of the chain introduced by exchange couplings between spins in neighbor dinuclear units, which averages out the zero field splitting. Interactions of the units with the rest of the chain acting as a spin bath give rise to a quantum transition between localized dinuclear states and states of the spin chain. This effect competes with the condensation of the antiferromagnetic dinuclear units into the singlet ground state, producing a characteristic temperature dependence of the shape of the powder EPR spectra. We interpret these features in terms of basic theories of magnetic resonance in coupled spin systems applied to the chain array of dinuclear units.

SYNTHESIS AND X-RAY CRYSTAL DETERMINATION OF FOUR NOVEL LANTHANIDE(III) OXYDIACETATE COMPLEXES

Abstract Four newlanthanide oxydiacetates [{Y(Hoda)3}·H2oda·H2O] (1), [{Y2(oda)3(H2O)4·2H2O}n] (2), [{LaGd(oda)3(H2O)3·6H2O}n] (3) and [{LaY (oda)3(H2O)3·6H2O}n] (4) (oda = O2CCH2OCH2CO2) have been synthesized and their structures determined by singlecrystal X-ray methods. Compound 1 is monometallic with distorted YO9 units formed via coordination of three tridentate Hoda ligands. Compound 2 consists of polymeric sheets of YO9 units formed via coordination of three tridentate oda ligands bridged through carboxylate groups to YO8 units. Compounds 3 and 4 are isomorphous heterobimetallic three-dimensional networks of LnO9 units (Ln Gd or Y) formed via coordination of three tridentate oda ligands bridged to the larger radius La (III) in LaO9 units through carboxylate groups.

X-ray study on the nickel(II)-oxydiacetic system and its 1,10-phenanthroline and 2,2′:6′,2′′ terpyridine complexes

Abstract Three new metal–organic coordination complexes have been prepared and their crystal structures determined: [Ni(oda)(H2O)3]·1.5H2O, [Ni(oda)(phen)(H2O)]·1.5H2O and [Ni(oda)(terpy)]·2H2O (oda=oxydiacetate, phen=1,10-phenanthroline, terpy=2,2′:6′,2′′ terpyridine). The oxydiacetate ligand is tridentate in these compounds, being hinged in the first and nearly planar in the other two. Hydrogen-bonding and π–π interaction is extensive in the solids.

Novel europium and gadolinium compounds in the lanthanide(III) oxydiacetate series

Abstract Three new lanthanide oxydiacetate compounds have been prepared and their structures determined by single crystal X-ray methods: {[Ln2(oda)3(H2O)2]·5H2O}n (Ln=Eu, Gd) and [Eu(oda)(Hoda)(H2O)]·2H2O. The former are orthorhombic and Ama2, with LnO8 and LnO9 cores bridged by anti–anti carboxylate ligands and the latter is mononuclear containing a EuO9 core. Luminescence spectra of the europium complexes in the solid state are presented.

1-D polymers with alternate Cu2 and Ln2 units (Ln = Gd, Er, Y) and carboxylate linkages.

Three isostructural Cu 2Ln 2 1-D polymers [Cu 2Ln 2L 10(H 2O) 4.3H 2O] n where Ln = Gd ( 1), Er ( 2), and Y ( 3) and HL= trans-2-butenoic acid, were synthesized and characterized by X-ray crystallography, electron paramagnetic resonance, and magnetic measurements. Pairs of alternate Cu 2 and Ln 2 dinuclear units are combined into a linear array by a set of one covalent eta (2):eta (1):mu 2 carboxylate oxygen and two H bonds, at Cu...Ln distances of ca. 4.5 A. These units exhibit four eta (1):eta (1):mu 2 and two eta (2):eta (1):mu 2 carboxylate bridges, respectively. Magnetic measurements between 2 and 300 K, fields B 0 = mu 0 H between 0 and 9 T, and electron paramagnetic resonance (EPR) measurements at the X-band and room temperature are reported. The magnetic susceptibilities indicate bulk antiferromagnetic behavior of the three compounds at low temperatures. Magnetization and EPR data for 1 and 3 allowed evaluation of the exchange couplings between both Cu and Gd ions in their dinuclear units and between Cu and Gd neighbor ions in the spin chains. The data for the isolated Cu 2 units in 3 yield g || = 2.350 and g [symbol: see text] = 2.054, J Cu-Cu = -338 (3) cm (-1) for the exchange coupling [ H ex(1,2) = - J 1-2 S1 x S2], and D 0 = -0.342 (0.003) cm (-1) and E 0 = 0.003 (0.001) cm (-1) for the zero-field-splitting parameters of the triplet state arising from anisotropic spin-spin interactions. Considering tetranuclear blocks Gd-Cu-Cu-Gd in 1, with the parameters for the Cu 2 unit obtained for 3, we evaluated ferromagnetic interactions between Cu and Gd neighbors, J Cu-Gd = 13.0 (0.1) cm (-1), and between Gd ions in the Gd 2 units, J Gd-Gd = 0.25 (0.02) cm (-1), with g Gd = 1.991. The bulk antiferromagnetic behavior of 1 is a consequence of the antiferromagnetic coupling between Cu ions and of the magnitude, |J Cu-Gd|, of the Cu-Gd exchange coupling. Compound 2 displays a susceptibility peak at 15 K that may be interpreted as the combined result from antiferromagnetic couplings between Er (III) ions in Er 2 units and their coupling with the Cu 2 units.

Adduct formation between zinc and cadmium oxydiacetates and imidazol. Crystal structures of [Zn(Him)2(oda)]n and [Cd2(Him)4(oda)2(H2O)]2·6H2O (Him=imidazol, oda=oxydiacetate)

Abstract The two new compounds [Zn(Him) 2 (oda)] n ( 1 ) and [Cd 2 (Him) 4 (oda) 2 (H 2 O)] 2 ·6H 2 O ( 2 ) (Him=imidazol, oda=oxydiacetate) have been prepared and their structures determined by single-crystal X-ray diffraction studies. Compound 1 consists of polymeric chains formed by ZnN 2 O 2 tetrahedral units bridged by the carboxylate groups of extended oda ligands; 2 is tetranuclear with the cadmium atoms in pentagonal bipyramidal CdN 2 O 5 coordination geometry. The extended structures and the hydrogen-bonding patterns displayed by both the compounds were examined.

Spectroscopic characterization of anionic tris(N,N-dialkyldithiocarbamate) complexes of zinc(II) and cadmium(II)

Abstract The infrared and Raman spectra (1500-50 cm−1) of the related complexes Zn(S2CNMe2)2(I), [Bu4N][Zn(S2CNMe2)3] (II), Cd(S2CNMe2)2 (III), [Bu4N][Cd(S2CNMe2)3](IV), Cd(S2CNEt2)2(V) and [Bu4N][Cd(S2CNEt2)3] (VI) have been determined. For complexes with coordination number four, metalsulfur stretching frequencies were assigned at 228 cm−1 for I (ZnS), 180 cm−1 for III (CdS) and 208 cm−1 for V (CdS), whereas for complexes with apparent coordination number six they were assigned at 206 cm−1 for II (ZnS) and in the 150–125 cm−1 range for IV and VI (CdS). Thus, expansion of the coordination sphere of the Zn(II) and Cd(II) metal results in a significant shift towards lower energy of the far IR MS vibrations. Other MS sensitive vibrations in the far IR are found in the 385–350 cm−1 range, and are described as mixed ring bending modes with significant MS stretching contribution.

Structure and magnetic properties of binuclear Cu2(O2CCHCHCH3)4(DMF)2: a carboxylate-bridged Cu(II) spin dimer

Abstract The complex Cu2(O2CCHCHCH3)4(DMF)2 was synthesized from Cu(OH)2, trans-2-butenoic acid, and dimethylformamide. An X-ray structure determination showed that the complex has the familiar Cu2(O2CR)4L2 dimer structure. trans-2-Butenoate groups in molecules related by a center of symmetry have a short contact between the α-carbon atoms (3.611 A), suggesting a study of the solid-state reactivity of this complex. Irradiation of the complex (60Co X-rays, 219 kGy), did not produce any detectable product. Magnetic susceptibility measurements in the range between 2 and 350 K in a powder sample, and EPR measurements in powder and single-crystal samples were performed. The data show the dimeric magnetic structure of the compound, with an antiferromagnetic exchange coupling J/kB=−220 K and a fine structure coupling D/h=−10.04 GHz within the excited spin triplet. Hyperfine structure with the two Cu nuclei is clearly observed. These results are discussed in terms of the structure.

Pyrophosphate-Bridged CuII Chain Magnet: {[Na3Cu(P2O7)(NO3)]·3H2O}n

A Cu(II)...Cu(II) pyrophosphate-bridged compound of formula {[Na(3)Cu(P(2)O(7))(NO(3))].3H(2)O}(n) (1) has been characterized. X-ray diffraction measurements show that it crystallizes in the monoclinic space group P2(1)/m, with unit cell dimensions a = 7.2492(5) A, b = 8.2446(6) A, c = 9.9050(7) A, beta = 107.123(1) degrees, and Z = 2. The structure consists of chains of Cu(II) cations at inversion symmetry sites bound to four equatorial oxygen atoms provided by two pyrophosphate anions halved by a symmetry plane and two axial oxygen atoms of nitrate anions. The molar magnetic susceptibility chi(0) of a powdered sample was measured in the temperature range 2 K < T < 273 K, and an isothermal magnetization curve, M(B(0),T), was obtained at T = 30 K, with the magnetic field B(0) between 0 and 5 T. Fitting a spin-chain model to the susceptibility data, we evaluate an antiferromagnetic exchange coupling 2J = -24.3(1) cm(-1) (defined as H(ex) = -2JS(i)S(j)) between Cu(II) neighbors. For any orientation of B(0), single-crystal electron paramagnetic resonance (EPR) spectra obtained at 9.8 and 33.9 GHz at 300 K display a single signal having a g matrix with orthorhombic symmetry, arising from the merger produced by the exchange interaction of the resonances corresponding to the two rotated Cu(II) sites. The g matrices of the individual molecules calculated assuming axial symmetry yielded principal values g(parallel) = 2.367(1) and g(perpendicular) = 2.074(1) at both frequencies, indicating a d(x(2)-y(2)) ground-state orbital for the Cu(II) ions. The angular variation of the EPR line width suggests exchange narrowing in a system with one-dimensional spin dynamics, as expected from the structure and susceptibility data. The results, discussed in terms of the crystal and electronic structures and of the spin dynamics of the compound, are compared with those obtained in other materials.