Syntheses, structures and magnetism of homoleptic complexes of 4-pyrid-4-yloxy-2,2,6,6-tetramethyl-1-piperidinoxyl, a new spin-labelled pyridine

Halcrow, Malcolm A. and Rodriguez-Martinez, Lide M. and Brechin, Euan K. and Davies, John E. and Scowen, Ian J. and McPartlin, Mary (1999) Syntheses, structures and magnetism of homoleptic complexes of 4-pyrid-4-yloxy-2,2,6,6-tetramethyl-1-piperidinoxyl, a new spin-labelled pyridine. Journal of Organometallic Chemistry, 573 (1-2). pp. 171-179. ISSN 0022-328X

Full content URL: http://dx.doi.org/10.1016/S0022-328X(98)00654-8

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Item Type:Article
Item Status:Live Archive

Abstract

Reaction of 4-chloropyridine hydrochloride with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinoxyl in the presence of five equivalents of powdered KOH in DMSO at 30°C affords L1 in 10-50 yield after an aqueous quench. The complexes M(L1)4(BF4)2 (M=Ni, 1; M=Cu, 2; M=Pd, 3) have been prepared by complexation of hydrated M(BF4)2 (M=Ni, Cu), or PdCl2(NCPh)2+2AgBF4, by four equivalents of L1 in MeCN. Diffusion of Et2O into MeCN solutions of 2 affords two crystalline polymorphs of this complex, both containing square planar Cu(L1)42+dications Cu-N=2.005(7)-2.042(6) à . The major, monoclinic form contains axial Cu...NCMe contacts of 2.394(7) and 2.859(8) à , while the minor, triclinic form exhibits long axial Cu...FBF3 bonds (Cu...F=2.478(5), 2.551(5) à ). In both structures, the Cu...N(nitroxyl) distances are 9.5-9.7 à . The Q-band EPR spectrum of 2 in 10:1 MeCN:toluene solution at 293 K is a broad featureless line, suggesting JCu-L1�0.07 cm-1. Variable temperature susceptibility measurements on powdered 2 and 3 show weakly antiferromagnetic behaviour. For 2 these data are well reproduced both by the Curie-Weiss law and by a model describing intramolecular superexchange; for 3, the data could not be fit satisfactorily, suggesting the presence of a significant intermolecular superexchange pathway.

Keywords:Spin-label, Nickel, Copper, Palladium, Crystal structure, Superexchange
Subjects:F Physical Sciences > F100 Chemistry
Divisions:College of Science > School of Chemistry
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ID Code:13070
Deposited On:19 Mar 2014 17:59

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