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Synthesis, Molecular Structure, and Reactivity of Dinuclear Copper(II) Complexes with Carboxylate-Rich Coordination Environments
Inorganic Chemistry
  • Richard C. Holz, Marquette University
  • John M. Bradshaw, Utah State University
  • Brian Bennett, Marquette University
Document Type
Format of Original
7 p.
Publication Date
American Chemical Society
Original Item ID
doi: 10.1021/ic9707873
The dinucleating ligand N,N‘-(2-hydroxy-5-methyl-1,3-xylylene)bis(N-(carboxymethyl)glycine) (CH3HXTA) has been used to synthesize the dinuclear Cu(II) bis(pyridine) complex Na[Cu2(CH3HXTA)(Py)2]·1.5(1,4-dioxane) (Na(1)):  triclinic space group P1̄ (a = 12.550(3) Å, b = 13.413(3) Å, c = 13.540(4) Å, α = 117.12(2)°, β = 104.70 (2)°, and γ = 92.13(2)°). The structure shows two distinct distorted square pyramidal Cu(II) centers with each Cu(II) ion bound by two carboxylate oxygen atoms, one amine nitrogen atom, a phenolate oxygen atom, and one pyridine nitrogen atom. The Cu--Cu separation is 3.531 Å, and the Cu1−O1−Cu2 angle is 123.7°. The phenyl ring of the CH3HXTA ligand is twisted relative to the Cu1−O1−Cu2 plane, and the resulting dihedral angle is 44.2°. The electronic absorption spectrum of 1 in aqueous solution at pH 3 suggests a shift toward trigonal bipyramidal Cu(II) coordination in solution. Spectral titration of Na[Cu2(CH3HXTA)(H2O)2] with L (where L = pyridine or sodium cyanide) results in complexes with terminal L groups. These exogenous ligands appear to bind in a positive cooperative stepwise fashion. Variable-temperature magnetic susceptibility data for 1 indicate that the Cu(II) ions are antiferromagnetically coupled (−2J = 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 ΔMs = 2 transition at g = ∼4.5, expected for weakly magnetically coupled Cu(II) 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 antiferromagnetically coupled in the solid state but due to a coordination geometry change become weakly ferromagnetically or antiferromagnetically coupled in solution. 1H NMR studies on a methanol solution of 1 are consistent with weak spin-coupling in solution.

Inorganic Chemistry, Vol. 37, No. 6 (March 23, 1998): 1219-1225. DOI.

Brian Bennett and Richard C. Holz were affiliated with Utah State University at the time of publication.

Citation Information
Richard C. Holz, John M. Bradshaw and Brian Bennett. "Synthesis, Molecular Structure, and Reactivity of Dinuclear Copper(II) Complexes with Carboxylate-Rich Coordination Environments" Inorganic Chemistry (1998) ISSN: 0020-1669
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