Dinuclear Spin-Crossover Complexes Based on Tetradentate and Bridging Cyanocarbanion Ligands

Spin-crossover (SCO) Fe­(II) dinuclear complexes of formula [Fe2(tmpa)22-tcpd)2]·0.8­(CH3OH) (1·MeOH) and [Fe2(andmpa)22-tcpd)2]·2CH3OH (2·MeOH) (tmpa = tris­(2-pyridylmethyl)­amine, andmpa = bis­(2-pyridylmethyl)­aminomethyl)­aniline, (tcpd)2– = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide) have been synthesized and characterized by infrared spectroscopy, X-ray diffraction, and magnetic measurements. The crystal structure determinations of the two complexes (1·MeOH and 2·MeOH) and the desolvated complex 1 (from 1·MeOH) revealed a neutral centrosymmetrical dinuclear structure in which the (tcpd)2– cyanocarbanion acts as a double μ2-bridging ligand between two [FeL]2+ (L = tmpa (1), andmpa (2)) units involving two free coordination sites in the cis configuration. Examination of the shortest intermolecular contacts in 1·MeOH and 1 reveals no significant hydrogen bonding between the dinuclear units, while in 2·MeOH these units are held together by significant hydrogen bonds between one of the uncoordinated nitrile groups and the anilate function, giving rise to 1D supramolecular structure. The three dinuclear complexes 1, 2·MeOH, and 2 exhibit SCO behaviors which have been evidenced by the thermal evolutions of the χmT product and by the average values of the six Fe–N distances for 1 and 2·MeOH, that reveal a gradual conversion with transition temperatures (T1/2) at ca. 352 K (1), 196 K (2), and 180 K (2·MeOH). For the solvated 1·MeOH, the sharp SCO transition observed around 365 K was induced by the desolvatation process above 330 K during the magnetic measurements.