Syntheses, Structure, Magnetic Properties and 57Fe Mossbauer Spectroscopies of Two Iron(II) Complexes: Room-temperature Spin Crossover Behavior Observed in [Fe(dpq)(MePy)2(NCS)2]

Two new complexes [Fe(dpq)(MePy)(2)(NCS)(2)] (1) and [Fe(Medpq)(MePy)(2)(NCS)(2)] (2) (dpq=2-dipyrido[3,2-f:2',3'-h]quinoxaline, Medpq=2-methyldipyrido[3,2-f:2',3'-h]quinoxaline, MePy=4-methylpyridine) have been synthesized. The crystal structure of 2 was characterized by X-ray diffraction at room temperature. It crystallizes in orthorhombic space group l2(l)2(l)2(l), with a=15.057(3) angstrom, b=14.569(3) angstrom, c=13.180(3) angstrom, alpha-90.00 degrees, beta=90.00 degrees, gamma=90.00 degrees, and V=2891.2(11)angstrom(3). The distorted [FeN6] octahedron in 2 is formed by six nitrogen atoms from Medpq, two trans-MePy molecules and two cis-NCS- anions. Variable-temperature magnetic susceptibilities and Mossbauer spectroscopies of 1 and 2 reveal the occurrence of a gradual spin transition. The transition for I spans the 200-450 K temperature range with a T-1/2 of 340 K, while for 2, the transition in low temperature is incomplete.