名称:
Coordination of the strong field di-imine 3,3′-bipyridazine. Structural, magnetic and spectroscopic properties of the Fe(II), Co(II) and Ni(II) complexes
摘要:
The di-imine system 3,3'-bipyridazine (L) generates a particularly strong ligand field and this is revealed in the low-spin nature of [FeL2(NCS)2] and of salts of [FeL3]2+, the appearance of a double reversible quartet transition in [CoL3]2+, and the high energy (13 200 cm-1) of the 3A2g --> 3T2g transition in the electronic spectrum of [NiL3]2+. In attempts to prepare bis(ligand) complexes the mixed low-spin cationic, high-spin anionic complexes [FeL3][FeCl4], [FeL3][Fe(NCS)4] and [FeL3][FeCl4]2 were isolated. These were characterised by magnetic and Mossbauer spectral measurements. The structures of both [FeL3][ClO4]2 and [NiL3][ClO4]2 reveal unusually short Fe-N (1.927(3) angstrom) and Ni-N (2.060 angstrom) distances and these, and the high field strength, are believed to result in part from the absence of ortho-hydrogen atoms in the ligand molecules which cause considerable inter-ligand repulsion in complexes of the related di-imine, 2,2'-bipyridine. [FeL3][ClO4]2 crystallises in space group P3BARc1 (Z = 2) with cell parameters a = 10.281(2), b = 10.281(2), c = 15.863(4) angstrom. A total of 430 reflections with I(o) > 3-sigma(I(o)) was observed and a final value of R = 0.045 was obtained. [NiL3][ClO4]2 crystallizes in space group P321 (Z = 1) with cell parameters a = 10.225(3), b = 10.225(3), c = 8.049(3) angstrom. Stacking faults and twinning create an apparent P6BAR2c diffraction symmetry. A total of 266 reflections with I(o) > 3-sigma(I(o)) was observed and a final value of R = 0.042 was obtained.