Département de chimie moléculaire

The isolation, structural characterization, and electronic properties of high-spin mononuclear five-coordinated Mn(II) complexes, [Mn(terpy)(X)2] (terpy = 2,2':6',2''-terpyridine; X = I- (1), Br- (2), Cl- (3), or SCN- (4)), are reported. The x-ray structures of the complexes reveal that the Mn ion lies in the center of a distorted trigonal bipyramid for complexes 1, 2, and 4, while complex 3 is better described as a distorted square pyramid. The electronic properties of 1-4 were studied by high-field and high-frequency EPR spectroscopy (HF-EPR) performed between 5 and 30 K. The powder HF-EPR spectra were recorded in high-field-limit conditions (95-285 GHz) (D « g$\beta$B). The spectra are thus simplified, allowing an easy interpretation of the exptl. data and an accurate detn. of the spin Hamiltonian parameters. The magnitude of D varies between 0.26 and 1.00 cm-1 with the nature of the anionic ligand. Thanks to low-temp. EPR expts., the sign of D was unambiguously detd. D is pos. for the iodo and bromo complexes and neg. for the chloro and thiocyanato ones. A structural correlation is proposed. Each complex was characterized by a significant rhombicity with E/D values between 0.17 and 0.29, reflecting the distorted geometry obsd. around the Mn. Finally, the authors compared the spin Hamiltonian parameters of the authors' five-coordinated complexes and those previously reported for other analogous series of dihalo four- and six-coordinated complexes. The effect of the coordination no. and of the geometry of the Mn(II) complexes on the spin Hamiltonian parameters is discussed. [on SciFinder(R)]