Rc. Holz et al., SYNTHESIS, MOLECULAR-STRUCTURE, AND REACTIVITY OF DINUCLEAR COPPER(II) COMPLEXES WITH CARBOXYLATE-RICH COORDINATION ENVIRONMENTS, Inorganic chemistry, 37(6), 1998, pp. 1219-1225
The dinucleating ligand -methyl-1,3-xylylene)bis(N-(carboxymethyl)glyc
ine) (CH(3)HXTA) has been used to synthesize the dinuclear Cu(II) bis(
pyridine) complex Na[Cu-2(CH(3)HXTA)(Py)2]. 1.5(1,4-dioxane) (Na(1)):
triclinic space group P (1) over bar (a = 12.550(3) Angstrom, b = 13.4
13(3) Angstrom, c = 13.540(4) Angstrom, alpha = 117.12(2)degrees, beta
= 104.70(2)degrees, and gamma = 92.13(2)degrees). The structure shows
two distinct distorted square pyramidal Cu(IT) centers with each Cu(I
I) ion bound by two carboxylate oxygen atoms, one amine nitrogen atom,
a phenolate oxygen atom, and one pyridine nitrogen atom. The Cu--Cu s
eparation is 3.531 Angstrom, and the Cu1-O1-Cu2 angle is 123.7 degrees
. The phenyl ring of the CH(3)HXTA ligand is twisted relative to the C
u1-O1-Cu2 plane, and the resulting dihedral angle is 44.2 degrees. The
electronic absorption spectrum of 1 in aqueous solution at pH 3 sugge
sts a shift toward trigonal bipyramidal Cu(II) coordination in solutio
n. Spectral titration of Na[Cu-2(CH(3)HXTA)(H2O)(2)] with L (where L =
pyridine or sodium cyanide) results in complexes with terminal L grou
ps. These exogenous ligands appear to bind in a positive cooperative s
tepwise fashion. Variable-temperature magnetic susceptibility data for
1 indicate that the Cu(II) ions are antiferromagnetically coupled (-2
J = 168 cm(-1)). X-band EPR spectra of an aqueous solution of 1 shows
isotropic signals with g = 2.14, while a powdered sample of 1 provides
no EPR spectrum. A Delta M-s= 2 transition at g = similar to 4.5, exp
ected for weakly magnetically coupled Cu(IT) ions, is not observed for
powdered samples but is observed for a methanolic solution sample of
1. On the basis of these data, the two Cu(II) ions are antiferromagnet
ically coupled in the solid state but due to a coordination geometry c
hange become weakly ferromagnetically or antiferromagnetically coupled
in solution. H-1 NMR studies on a methanol solution of 1 are consiste
nt with weak spin-coupling in solution.