New family of thiocyanate-bridged Re(IV)-SCN-M(II) (M = Ni, Co, Fe, and Mn) heterobimetallic compounds : Synthesis, crystal structure, and magnetic properties

The heterobimetallic complexes of formula [(Me2phen)2M(μ-NCS)- Re(NCS)5]·CH3CN [Me2phen = 2,9-dimethyl-1,10-phenanthroline and M = Ni (1), Co (2), Fe (3), and Mn (4)] have been prepared, and their crystal structures have been determined by X-ray diffraction on single crystals. Compounds 1−4 crystallize in the monoclinic C2/c space group, and their structure consists of neutral [(Me2phen)2M(μ-NCS)Re(NCS)5] heterodinuclear units with a Re-SCN-M bridge. Each Re(IV) ion in this series is six-coordinated with one sulfur and five nitrogen atoms from six thiocyanate groups building a somewhat distorted octahedral environment, whereas the M(II) metal ions are five-coordinated with four nitrogen atoms from two bidentate Me2phen molecules and a nitrogen atom from the bridging thiocyanate describing distorted trigonal bipyramidal surroundings. The values of the Re···M separation through the thiocyanate bridge in 1−4 vary in the range 5.903(1)− 6.117(3) Å. The magnetic properties of 1−4 as well as those of the parent mononuclear Re(IV) compounds (NBu4)2[Re(NCS)6] (A1) (NBu4 + = tetra-n-butylammonium cation) and [Zn(NO3)- (Me2phen)2]2[Re(NCS)5(SCN)] (A2) were investigated in the temperature range 1.9−300 K. Weak antiferromagnetic interactions between the Re(IV) and M(II) ions across the bridging thiocyanate were found in 1−4 [J = −4.3 (1), −2.4 (2), −1.8 (3), and −1.2 cm−1 (4), the Hamiltonian being defined as Ĥ = −JŜRe·ŜM]. The magnetic behavior of A2 is that of a magnetically diluted Re(IV) complex with a large and positive value of the zero-field splitting for the ground level (DRe = +37.0 cm−1). In the case of A1, although its magnetic behavior is similar to that of A2 in the high-temperature range (DRe being +19.0 cm−1), it exhibits a weak ferromagnetism below 3.0 K with a canting angle of 1.3°.

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