Sergiu Shova

Hetero di- and trinuclear Cu-Gd complexes with trifluoroacetate bridges: synthesis, structural and magnetic studies.

The synthesis, structural determinations and magnetic properties of an original dinuclear Cu-Gd and two trinuclear Cu-Ln-Cu complexes (Ln = Gd or Dy) made with a Schiff base ligand and carboxylate ligands are reported. In each complex, the copper and gadolinium or dysprosium ions are linked by a double phenoxo bridge and a eta1:eta1:mu trifluoroacetato bridge. The dinuclear Cu-Gd complex exhibits the usual ferromagnetic interaction while the trinuclear (Cu-Gd-Cu) complexes can not be fitted with a simple Hamiltonian that only takes into account the Cu-Gd interaction. Introduction into the Hamiltonian of a Cu-Cu interaction between the terminal copper ions gives a nice fit in the case of a ferromagnetic Cu-Cu interaction (J(Cu-Cu) = 8.3 and 9.8 cm(-1)). For the first time, the occurrence of a ferromagnetic interaction between the copper ions of the trinuclear entities is evidenced and supported by the field dependence of the magnetization. As there is no direct proof for the existence of an interaction between two centers through a third magnetic center located in between them, we can conclude that the existence of pi-pi stacking interactions through the phenyl rings of the ligands are responsible for the presence of these interactions.

An original 1D Cu-Co heterometallic compound: synthesis, structure and magnetic properties

A novel heterobimetallic system, 1∞[LCuIICoII(NCS)2] (1), was obtained by reacting the neutral mononuclear complex [LCu] with cobalt(II) acetate in the presence of potassium thiocyanate (L is the dianion of the Schiff base resulting from the 2 ∶ 1 condensation of 3-methoxysalicylaldehyde with 1,3-propanediamine). The crystallographic investigation of 1 reveals a one-dimensional alternating zig-zag chain-like structure, made of dinuclear {LCuCo} units linked by thiocyanate bridges. The copper(II) ion is pentacoordinate to the N2O2 donor set of the Schiff base ligand in the basal plane, with the apical position occupied by the sulfur atom. The cobalt ion displays a strongly distorted (4 + 2) octahedral geometry. The distance between the phenoxo-bridged metal ions is 3.149(1) A. The Cu⋯Co distance for the NCS− bridged ions is equal to 6.125(1) A. The magnetic properties of 1 were investigated in the temperature range 2–300 K and they are explained by a strong antiferromagnetic Cu(II)–Co(II) exchange interaction through the phenoxo bridges and a weak ferromagnetic Cu(II)–Co(II) interaction through the thiocyanato bridges. Several theoretical models are proposed to fit the magnetic data of 1, the most appropriate one being the full matrix diagonalization for a closed-chain of four dinuclear units [CuIICoII], taking into account two different exchange parameters and a D term, which yielded the following results: J = −101.2 cm−1, j = 2.8 cm−1, D = −0.11 cm−1, g = 2.38.

The first example of a hetero-tetranuclear [(VO)Gd]2 complex: synthesis, crystal structure and magnetic properties of [VOLGd(hfa)2CH3OH]2·2CH3OH·2(CH3)2CO

A cyclic tetranuclear [V(IV)O-Gd(III)](2) complex with VO and Gd ions alternately arrayed, behaves, from the magnetic point of view, as two independent dinuclear entities each having a S= 4 ground state, as a consequence of an active and ferromagnetic VO-Gd interaction through the double phenoxo bridge and a magnetically inactive VO-Gd interaction through the amide bridge.

Synthesis and Structural Characterization of the Mononuclear Cobalt(II) Complex: {5,5′-Dihydroxy-2,2′-[o-phenylene-bis(nitrilomethylene)]diphenolato}cobalt(II) Dihydrate

The Schiff base ligand H2L·C2H5OH derived from the condensation reaction between o-phenylenediamine and 2,4-dihydroxybenzaldehyde as well as its mononuclear complex [CoL]·2H2O have been synthesized and characterized by X-ray crystallography, IR, 1H NMR and UV–Vis analyses, and density functional theory (DFT B3LYP) calculations. The CoII ion has a slightly distorted square-planar coordination provided by tetradentate dianionic N2O2 ligand L2−. The spin state of the complex was determined as being Sxa0=xa01/2. On the basis of DFT calculations, the UV–Vis absorption bands of the ligand can be assigned to the 1A1xa0→xa01B2 (two) and 1A1xa0→xa01A1 transitions, while for complex they correspond to the 2A2xa0→xa02B1 (two) and 2A2xa0→xa02A2 ones.Graphical AbstractIndex Abstract The Schiff base ligand H2L·C2H5OH derived from the condensation reaction between o-phenylenediamine and 2,4-dihydroxybenzaldehyde as well as its mononuclear complex [CoL]·2H2O have been synthesized and characterized by X-ray crystallography, IR, 1H NMR and UV–Vis analyses, and density functional theory (DFT B3LYP) calculations.