On the Magnetic Coupling and Spin Crossover Behavior in Complexes Containing the Head-to-Tail [Fe2II (μ-SCN)2] Bridging Unit: A Magnetostructural Experimental and Theoretical Study

A new dinuclear complex [{Fe(tpc-OBn)(NCS)(mu-NCS)}(2)] (1) based on the tripodal tpc-OBn ligand (tpc-OBn = tris(2-pyridyl)benzyloxymethane), containing bridging mu-kappa N:kappa S-SCN and terminal kappa N-SCN thiocyanate ligands, has been prepared and characterized by single crystal X-ray diffraction, magnetic studies, and DFT theoretical calculations. This complex represents the first example of dinuclear Fe(II )complex with double mu-kappa N:kappa S-SCN bridges in a head-to-tail configuration that exhibits ferromagnetic coupling between metal ions (J(FeFe )= +1.08 cm(-1)). Experimental and theoretical magnetostructural studies on this kind of infrequent Fe(II )dinuclear complex containing a centrosymmetrically [Fe-2(mu-SCN)(2)] bridging fragment show that the magnitude and sign of the magnetic coupling parameter, J(FeFe), depend to a large extent on the Fe-N-C (alpha) angle, so that J(FeFe )decreases linearly when alpha decreases. The calculated crossover point below which the magnetic interactions change from ferromagnetic to antiferromagnetic is found at 162.3 degrees. In addition, experimental results obtained in this work and those reported in the literature suggest that large N-tripodal-Fe(II )distances and bent N-bound terminal kappa N-SCN ligands favor the high spin state of the Fe(II )ions, while short N-tripodal-Fe(II )distances and almost linear Fe-N-C angles favor a stronger ligand field, which enables the Fe(II )ions to show spin crossover (SCO) behavior.