EXCHANGE COUPLING IN HOMODINUCLEAR HETERODINUCLEAR COMPLEXES CUIIM [M = CR(III), MN(III), MN(II), FE(III), CO(III), CO(II), NI(II), CU(II), ZN(II)] - SYNTHESIS, STRUCTURES, AND SPECTROSCOPIC PROPERTIES

A series of heterodinuclear complexes Cu(II)M, where M = Cr(III) (1), Mn(III) (2), Mn(II) (3), Fe(III) (4), Co(II) (5), Co(III) (6), Ni(II) (7), Cu(II) (8), and Zn(II) (9), containing the oximato dianion (Dopn2-) as bridging ligand and 1,4,7-trimethyl-1,4,7-triazacyclononane (L) as one of the two capping ligands have been synthesized by using the [Cu(DopnH)]+ cation (H2Dopn = 3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime) as a ligand for the different ML(n+) centers. The compounds have been characterized on the basis of IR, electronic, and EPR spectroscopy and variable-temperature (2-295 K) magnetic susceptibility measurements. The dinuclear complexes are quasi-isostructural with the copper(II) ion in a distorted square pyramidal environment, CuN4O, and the M ion, except for that in 8, is six-coordinate with the MN3O3 or MN3O2Cl coordination sphere. For M = Cu (8), the coordination geometry of M with the CuN3O2 chromophore is also square pyramidal. The crystal and molecular structures of the compounds [(Dopn)Cu(II)(OH2)Cr(III)(OCH3)L](ClO4)2.H2O (1) and [(Dopn)Cu(II)(mu-CH3COO)-Mn(III)L](ClO4)2.2H2O (2) have been established by X-ray diffraction. 1 crystallizes in the monoclinic system space group P2(1)/n, with cell constants a = 13.096(3) angstrom, b = 17.933(4) angstrom, c = 15.994(3) angstrom, beta = 113.49(3)-degrees, V = 3444.9(13) angstrom3, and Z = 4. The structure consists of oximato-bridged Cu(II)Cr(III) dications and noncoordinated perchlorate anions, with a Cu...Cr distance of 3.86 angstrom. The crystal data for 2 are as follows: orthorhombic, space group P2(1)2(1)2(1), a = 12.275(4) angstrom, b = 14.171(9) angstrom, c = 19.780(3) angstrom, V = 3441(2) angstrom3, Z = 4. The structure consists of a six-coordinate Mn(III) center, MnN3O3, and the copper(II) center has an N4O donor set. An acetate group bridges the manganese and copper ions with a Cu...Mn separation of 3.54 angstrom. A low-quality X-ray structure determination for the Cu(II)Fe(III) complex is also reported. Analysis of the susceptibility data yields a strong antiferromagnetic interaction (2J = -596 cm-1) between adjacent Cu(II) ions in 8, showing once again that bridging oximes are good mediators for exchange interactions. The strength of the effective antiferromagnetic interaction decreases with increasing number of unpaired electrons in this series, 8 > 7 > 5 > 4 approximately 3. Moderately strong ferromagnetic interactions have been observed for Cu(II)Mn(III) (2) (2J = + 109 cm-1) and Cu(II)Cr(III) (1) (2J = + 37 cm-1). A qualitative rationale has been provided for the difference in magnetic behaviors. The X-band EPR spectra (3-77 K) have been measured to establish the ground states of the dinuclear complexes. Well-resolved S = 2 EPR spectra for different heterometal systems have been observed.