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

Spin-crossover (SCO) Fe(II) dinuclear complexes of formula [Fe-2(tmpa)(2)(mu(2)-tcpd)(2)]center dot 0.8(CH3OH) (1 center dot MeOH) and [Fe-2(andmpa)(2)(mu(2)-tcpd)(2)]center dot 2CH(3)OH (2 center dot 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 center dot MeOH and 2 center dot MeOH) and the desolvated complex 1 (from 1 center dot MeOH) revealed a neutral centrosymmetrical dinuclear structure in which the (tcpd)(2) cyanocarbanion acts as a double mu 2-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 center dot MeOH and 1 reveals no significant hydrogen bonding between the dinuclear units, while in 2 center dot 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 center dot MeOH, and 2 exhibit SCO behaviors which have been evidenced by the thermal evolutions of the chi mT product and by the average values of the six FeN distances for 1 and 2 center dot MeOH, that reveal a gradual conversion with transition temperatures (T-1/2) at ca. 352 K (1), 196 K (2), and 180 K (2 center dot MeOH). For the solvated 1 center dot MeOH, the sharp SCO transition observed around 365 K was induced by the desolvatation process above 330 K during the magnetic measurements.