Magnetocaloric Effect in 1D-Polymers Bearing 15-Metallacrown-5 {GdCu5}3+ Units and Anionic Oxalate Complexes

International audienceTwo complexes {[GdCu5(GlyHA)5(H2O)7Cr(C2O4)3]·11.02H2O}n (1) and {{[GdCu5(GlyHA)5(H2O)6]μ2-[Cu(C2O4)2(H2O)]}2μ4-[Cu(C2O4)2]·15.8H2O}n (2), were obtained as outcomes of the reactions between the cationic hexanuclear {GdCu5(GlyHA)5}3+ 15-metallacrown-5 complex (where GlyHA2- = glycinehydroxamate) and the anionic oxalate complexes K3[Cr(C2O4)3] or K2[Cu(C2O4)2]. Both 1 and 2 possess polymeric 1D-chain structures according to X-ray structural analysis. As a consequence of the geometric orientations of the donor atoms in the oxalates from [Cr(C2O4)3]3-, the Cu5 mean planes of neighboring 15-metallacrown-5 units {GdCu5(GlyHA)5}3+ are angled at 75.5° to each other, which leads to formation of a zig-zag motif in the 1D-chains of complex 1. The centrosymmetric complex 2 contains two structurally different bis(oxalato)cuprate anions μ2-[Cu(C2O4)2(H2O)]2-, for one of which, coordination to two adjacent {GdCu5(GlyHA)5}3+ units leads to formation of linear 1D-chains in 2, while the second type, μ4-[Cu(C2O4)2]2-, is coordinated to four {GdCu5(GlyHA)5}3+ units, causing the cross-linking of single 1D-chains into a double-chain 1D coordination polymer. Studies of χMT vs. T data for 1 and 2 in a 2-300 K temperature range revealed the presence of both ferromagnetic and antiferromagnetic interactions amongst paramagnetic centres. The experimental χMT vs. T data for 1 were fitted using a model which takes into account exchange interactions between adjacent copper(II) ions, the Gd-Cu exchange interactions within {GdCu5(GlyHA)5}3+ units and additionally Gd-Cr exchange interactions. Fitting of the χMT vs. T data for 2 was not possible, since coordination of μ4-[Cu(C2O4)2]2- to {GdCu5(GlyHA)5}3+ led to the non-equivalence of several Cu-Cu exchange interactions within the metallacrown units and hence a superfluity of fittable parameters. Complexes 1 and 2 are the first examples of 15-metallacrown-5 complexes demonstrating a magnetocaloric effect (-ΔSM at 13 T reaches 24.26 J K-1 kg-1 at 5 K and 19.14 J K-1 kg-1 at 4 K for 1 and 2, respectively)

Nickel(II) Complexes with Dithiadiiminoamine and Dithiabis(thiosemicarbazone) Ligands

4,7-Dithiadecane-2,9-dione (Dtdk) serves as a starting point for generation of multidentate nitrogen/sulfur chelating agents. Condensation with ethylenediamine or diethylenetriamine yields the neutral hexadentate ligands 1,14-diamino-4,11-dimethyl-6,9-dithia-3,12-diazatetradeca-3,11-diene (Dtdida) and 15-amino-9-methyl-4,7-dithia-10,13-diazapentadec-9-en-2-one (Dtidak) respectively, while the diketone\u27s bis(thiosemicarbazone), itself a neutral ligand, may be deprotonated to form the hexadentate dianion Dtdtz2-. Blue/violet nickel(II) complexes with these ligands have been prepared, viz. Ni(Dtdida)(CIO4)2·0.5H2O 1, Ni(Dtidak)(ClO4)2·0.5CH3CN 4, Ni(DtdtzH2)(ClO4)2 2, and Ni(Dtdtz) 3; they are all S = 1 pseudo-octahedral systems. Although diamines such as ethylenediamine or diethylenetriamine are in principle capable of forming macrocyclic ligands with Dtdk, the products obtained were acyclic. In the case of Ni(Dtidak)2+, a keto-group and a primary amine residue co-exist within the cation, entailing an unusual example of a complex with a non-conjugated ketone coordinated to nickel(II). The coordination spheres of all four complexes have parallel N2S2X2 donor sets, with the ligands similarly folded. The properties of Ni(Dtdtz) evidence significant contribution from the imino-thiolate resonance form of the thioamide moiety. One consequence of this is the relative facility of oxidation of Ni(Dtdtz) to the nickel(III) form, at +0.24 V vs. SCE. © The Royal Society of Chemistry 2000

The 1,8-bis(2′-pyridyl)-3,6-dithiaoctane Complex of Nickel(II): X-ray Crystal Structure and Borohydride Adduct Formation

The quadridentate dipyridyl-dithioether ligand 1,8-bis(2′-pyridyl)-3,6-dithiaoctane (Pdto) forms a pseudooctahedral complex with nickel(II). Blue [Ni(Pdto)(OH2)2](ClO4)2 crystallizes in the space group P21/c, with a= 11.677(5), b= 13,255(2), c= 15.804(4) Å, β= 107.45(3)° and Z=4. The ligand is folded about the Ni(II) ion so that the water ligands are cis within an O2S2 plane and the pyridines mutually trans. Reduction by sodium amalgam yields a nickel (I) complex with an axial EPR spectrum, whereas borohydride reduction is very slow. Indeed, the pink adduct [Ni(Pdto)(BH4)]+ has substantial stability in solution. © 1998 Elsevier Science S.A. All rights reserved

Nickel(II), Nickel(I), and Nickel(O) Complexes with 1,8-Bis(2′-pyridyl)-3,6-dithiaoctane

Nickel complexes with 1,8-bis(2′-pyridyl)-3,6-dithiaoctane (Pdto) are synthesized; Ni(Pdto)(H 2O) 2(ClO 4) 2 is studied by X-ray diffraction

Assembly of Dinuclear Cu II Rigid Blocks by Bridging Azido or Poly(thiocyanato)chromates: Synthesis, Structures and Magnetic Properties of Coordination Polymers and Polynuclear Complexes

International audienceReaction of a dinuclear cationic copper(II) complex of 4,4′-[2-(3-hydroxyiminobutyl)imino]biphenyl [CuII2(LH)2]2+ with N3- resulted in the formation of a dinuclear azido [CuII2(LH)2(N3)2(H2O)2] complex or a 2D coordination polymer [CuII2(LH)2(N3)2]n. Reaction of the dinuclear complex with [CrIII(NCS)6]3- or [CrIII(NCS)4(NH3)2]- produced a 2D polymer {[CuII2(LH)2(CH3CN)2]3[CrIII(NCS)6]2}n or a 1D chain, constructed from tetranuclear units {[CuII2(LH)2][CrIII(NCS)4(NH3)2]2}n. Structures of the compounds were determined by X-ray crystallography and complexes were characterised by the temperature dependency of the magnetic susceptibility and by ESR spectroscopy. Magnetic properties of homometallic compounds were fit with the model of a dimer with the Hamiltonian Ĥ = -JŜ1*Ŝ2. For heterometallic complexes χMT curves were fit as the superposition of magnetism resulting from both [CuII2(LH)2]2+ and the adjacent CrIII-containing anion. J values for the complexes lie in the range from -12.74(4) to -17.77(8) cm-1. It was shown that the 4,4′-biphenyl bridge efficiently mediates exchange interactions

Antiferromagnetic ordering in cobalt(II) and nickel(II) 1D coordination polymers with the dithioamide of 1,3-benzenedicarboxylic acid

International audienceA series of 1D coordination polymers [Co(m-dtab)Cl2]n (1), [Co(m-dtab)Br2]n (2) and [Ni(m-dtab)2(Br)2]n (3), where m-dtab = the dithioamide of 1,3-benzenedicarboxylic acid, were prepared. The structures of all complexes were determined by X-ray diffraction . Magnetic properties of the compounds were characterized by molecular susceptibility vs. T dependence in the temperature range from 2 to 300 K. All compounds possess antiferromagnetic exchange interactions, and antiferromagnetic ordering was found in [Co(m-dtab)Br2]n and [Ni(m-dtab)2Br2]n at TN = 2.9 K and 2.6 K, respectively. DFT calculations showed that exchange interactions in [Co(m-dtab)(Hal)2]n could be transferred through two pathways: m-dtab between metal ions or interchain π-π stacking of aromatic rings, so the systems are not 1D from the viewpoint of magnetochemistry. The results of DFT calculations are consistent with the existence of magnetic ordering

Modeling of Ni-Fe-Center of Ni-CO-Dehydrogenases by Nickel Complexes with Thiaazaligands

Three new nickel(II) complexes with ligands 1,8-bis(2′-pyridyl)-3,6-dithiaoctane (Pdto) and dithiosemicarbazone of 4,7-dithiadecane-2,9-dione (DtdtzH 2) of composition Ni(Pdto)(H 2O) 2(ClO 4) 2, Ni(DtdtzH 2)(Cl0 4) 2 and Ni(Dtdtz) were prepared, their molecular structures, spectral and redox-properties were studied. The possibilities of chemical reduction of Ni(Pdto)(H 2O) 2(ClO 4) 2 to nickel(I) and nickel(0) species and the reaction of nickel(I) complex with CO were shown, which may be described as the modeling of one of the stages of reactions with CO on active Ni-Fe-site of Ni-CO-dehydrogenases. It was found that Ni(DtdtzH 2)(ClO 4) reacted with (Et 4N) 2[Fe 4S 4(SBz) 4] (BzSH = C 6H 5CH 2SH) forming adduct. In the row of studied complexes Ni(Pdto) (H 2O) 2(ClO 4) 2 maybe described as the best structural model of Ni-Fe-site of Ni-CO-dehydrogenases on the redox properties