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

摘要

The heterobimetallic complexes of formula [(Me _2phen) _2M(μ-NCS)Re(NCS) _5]·CH _3CN [Me _2phen = 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 [(Me _2phen) _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 Me 2phen 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). The magnetic properties of 1-4 as well as those of the parent mononuclear Re(IV) compounds (NBu _4) _2[Re(NCS) _6] (A1) (NBu _4 ~+ = tetra-n-butylammonium cation) and [Zn(NO _3)(Me _2phen) _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 H = -JSI _(Re)·S _M]. 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 (D ~(Re) = +37.0 cm ~(-1)). In the case of A1, although its magnetic behavior is similar to that of A2 in the high-temperature range (D ~(Re) being +19.0 cm ~(-1)), it exhibits a weak ferromagnetism below 3.0 K with a canting angle of 1.3°.