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 co mpounds have been characterized on the basis of IR, electronic, and EP R spectroscopy and variable-temperature (2-295 K) magnetic susceptibil ity 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 MN3O 3 or MN3O2Cl coordination sphere. For M = Cu (8), the coordination geo metry of M with the CuN3O2 chromophore is also square pyramidal. The c rystal 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](ClO 4)2.2H2O (2) have been established by X-ray diffraction. 1 crystallize s 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 str ucture consists of oximato-bridged Cu(II)Cr(III) dications and noncoor dinated 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 a n N4O donor set. An acetate group bridges the manganese and copper ion s with a Cu...Mn separation of 3.54 angstrom. A low-quality X-ray stru cture determination for the Cu(II)Fe(III) complex is also reported. An alysis of the susceptibility data yields a strong antiferromagnetic in teraction (2J = -596 cm-1) between adjacent Cu(II) ions in 8, showing once again that bridging oximes are good mediators for exchange intera ctions. The strength of the effective antiferromagnetic interaction de creases with increasing number of unpaired electrons in this series, 8 > 7 > 5 > 4 approximately 3. Moderately strong ferromagnetic interact ions 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 pro vided for the difference in magnetic behaviors. The X-band EPR spectra (3-77 K) have been measured to establish the ground states of the din uclear complexes. Well-resolved S = 2 EPR spectra for different hetero metal systems have been observed.