ABSTRACT
Transformations of anionic Cu(II) chlorocomplexes have been studied under conditions of catalytic exchange reactions between carbon tetrachloride and n-alkanes. It was shown that chlorocuprates are just precursors and are easily reduced to the genuine catalysts, that is, to the respective Cu(I) complexes. Both the composition and the geometric structure of the precursor (CuCl(4)(2-)) and, probably, the active site (CuCl(3)(2-)) have been investigated by several techniques (UV-vis spectroscopy, electron spin resonance (ESR), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), and static magnetic measurements). The dependence of the metathesis velocity on the [Cl-]/[Cu] ratio was found to exhibit a maximum most likely corresponding to the highest content of trichlorocuprite CuCl(3)(2-).
ABSTRACT
Heterospin complexes [Cu(SQ)2Py].C7H8, Cu(SQ)2DABCO, and [Cu(SQ)2NIT-mPy].C6H6, where Cu(SQ)2 is bis(3,6-di-tert-butyl-o-benzosemiquinonato)copper(II), DABCO is 1,4-diazabicyclo(2,2,2)octane, and NIT-mPy is the nitronyl nitroxide 2-(pyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, have been synthesized. The molecules of these complexes have a specific combination of the intramolecular ferro- and antiferromagnetic exchange interactions between the odd electrons of Cu(II) and SQ ligands, characterized by large exchange coupling parameters |J| approximately 100-300 cm(-1). X-ray and magnetochemical studies of a series of mixed-ligand compounds revealed that an extra ligand (Py, NIT-mPy, or DABCO) coordinated to the metal atom produces a dramatic effect on the magnetic properties of the complex, changing the multiplicity of the ground state. Quantum chemical analysis of magnetostructural correlations showed that the energy of the antiferromagnetic exchange interaction between the odd electrons of the SQ ligands in the Cu(SQ)2 bischelate is extremely sensitive to both the nature of the extra ligand and structural distortions of the coordination unit, arising from extra ligand coordination.
ABSTRACT
Crystallization of heterospin bischelate NiL(2), where L is deprotonated nitroxide 4-(3',3',3'-trifluoromethyl-2'-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl, with alcohols allows a logical assembly of layered [NiL(2)(CH(3)OH)(2) (1) and NiL(2)(C(2)H(5)OH)(2) (2)] or frame compounds [NiL(2)(HO(CH(2))(4)OH) (3) and NiL(2)(HO(CH(2))(5)OH) (4)]. The structures of complexes 1, 2, and 4 have been determined. Crystal data: 1, monoclinic, space group P2(1)/c, a = 8.929(2) Å, b = 15.773(3), c = 11.518(2), beta = 118.84(1) degrees, Z = 2; 2, monoclinic, space group P2(1)/c, a = 9.923(5) Å, b = 15.992(5) Å, c = 11.486(2) Å, beta = 120.63(3) degrees, Z = 2; 4, monoclinic, space group C2/c, a = 21.028(4) Å, b = 10.943(2), c = 14.405(3), beta = 110.61(3) degrees, Z = 4. The structure of 3 is very close to the structure of 4 and has been reported earlier. Robust H-bonding between the OH groups of the coordinated alcohols and the >N-(*)O groups of the neighboring fragments NiL(2) leads to the formation of polymeric layers in the solid. At the same time, hydrogen bonds form effective channels for magnetic interactions >N-(*)O.H-O(R)-Ni(2+)-(R)O-H.O(*)-N<. The magnetic phase transition to the weak ferromagnetic state below 7 K is inherent in 1-4. For 2 and 4, this transition is induced by the external magnetic field that correlates with the elongation of Ni-(R)O and (R)O.O(*)- distances in the exchange channels >N-(*)O.H-O(R)-Ni(2+)-(R)O-H.O(*)-N< in solids 2 and 4 compared to 1 and 3. It has been found that magnetic ordering occurs only within the polymeric layers formed due to multiple hydrogen bonds. Investigation of the anisotropy of magnetic susceptibility performed on large single crystals of 1-4 revealed an essentially different ordering of the magnetic moments of magnetic sublattices in 1, 2 and in 3, 4.
