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 consist 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 sulphur 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. Significant 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 H = -JSRe . SM]. 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, its magnetic behavior is similar to that of A2 in the high-temperature range (DRe being +19.0 cm-1) whereas it exhibits a weak ferromagnetism below 3.0 K with a canting angle of 1.3°.