Article,

Coordination alternatives in dinuclear bis(pyridin-2-ylalkyl)benzylamine copper(II) complexes with OH-, RO-, F-, or Cl- bridges: Experimental structures and DFT preferences

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European Journal of Inorganic Chemistry, (2007)
DOI: 10.1002/ejic.200700637

Abstract

L1Cu(m-OH)2CuL1(ClO4)2 (1), L2Cu(m-OH)2CuL2(ClO4)2 (2), L3Cu(m-OH)2CuL3(ClO4)2 (3), L3Cu(m-OMe)2CuL3(ClO4)2 (4), L3Cu(m-F)2CuL3(BF4)2 (5), L4Cu(m-Cl)2CuL4(ClO4)2 (6), and Cu(m-L5)2Cu(ClO4)2 (7), where L1 = bis(pyridin-2-ylmethyl)benzylamine, L2 = (6-methylpyridin-2-ylmethyl)(pyridin-2-ylmethyl)benzylamine, L3 = bis(6-methylpyridin-2-ylmethyl)benzylamine, L4 = (pyridin-2-ylethyl)(pyridin-2-ylmethyl)benzylamine, and L5 = (6-oxidomethylpyridin-2-ylmethyl)(6-methylpyridin-2-ylmethyl)benzylamine, were prepd., structurally characterized and studied by low-temp. EPR spectroscopy. The formation of compd. 5 involved fluoride abstraction from BF4- and that of 7 involved O2-assisted C-H (methyl) activation/monooxygenation of L3. Whereas the dications of 1-4 and 7 possess a square-pyramidal configuration at the copper(II) centers with hydroxide or alkoxide bridges in equatorial positions, the dications of 5 and 6 exhibit equatorial/axial arrangements for the bridging halide ions. In the dication of 5, the tridentate ligand binds in a meridional fashion and includes two adjacent five-membered chelate rings. Such a situation was obsd. previously only with chloride, alkoxide, or aqua bridges. In contrast to the syn configuration of the dication of 2, the dications of complexes 1, 3, 4, and 7 adopt an anti configuration with respect to the binding of Ln. The dications of 1, 2, and 7 have the pyridinyl or 6-methylpyridinyl groups in the axial position, whereas those of 3 and 4 feature the tertiary amine N atom at that site. DFT calcns. of various configurations of the dications of 1-6 reproduce the exptl. obsd. structural alternatives in complexes 1-4, but they do not predict the axial/equatorial structure of 5 as the lowest-energy configuration. The systematic overestimation of repulsive forces and thus of distances by DFT may result in an underestimation of the p-p interaction between the largely coplanar mer-L3 ligands sepd. by $\sim$3.6 \AA in 5, which probably affects its structure. By incorporating these and previous results, the syn vs. anti, equatorial/equatorial vs. equatorial/axial, and axial pyridine vs. axial amine structural alternatives are discussed. on SciFinder(R)

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