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

M A Halcrow, L M Rodriguez-Martinez, E K Brechin, J E Davies, I J Scowen, M McPartlin

Research output: Contribution to journalArticlepeer-review

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 degrees C affords L-1 in 10-50% yield after an aqueous quench. The complexes [M(L-1)(4)](BF4)(2) (M=Ni, I; M=Cu, 2; M=Pd, 3) have been prepared by complexation of hydrated M(BF,), (M=Ni, Cu), or [PdCl2(NCPh)(2)] + 2AgBF(4), by four equivalents of L-1 in MeCN. Diffusion of Et2O into MeCN solutions of 2 affords two crystalline polymorphs of this complex, both containing square planar [Cu(L-1)(4)](2+) dications [Cu-N = 2.005(7)-2.042(6) Angstrom]. The major, monoclinic form contains axial Cu...NCMe contacts of 2.394(7) and 2.859(5) A, while the minor, triclinic form exhibits long axial Cu...FBF3 bonds (Cu...F = 2.478(5), 2.551(5) Angstrom). In both structures, the Cu...N(nitroxyl) distances are 9.5-9.7 Angstrom. The e-band EPR spectrum of 2 in 10:1 MeCN:toluene solution at 293 K is a broad featureless line, suggesting \J(Cu-L)1\ greater than or equal to 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. (C) 1999 Elsevier Science S.A. All rights reserved.

Original languageEnglish
Pages (from-to)171-179
Number of pages9
JournalJournal of organometallic chemistry
Volume573
Issue number1-2
Publication statusPublished - 31 Jan 1999

Keywords

  • spin-label
  • nickel
  • copper
  • palladium
  • crystal structure
  • superexchange
  • RU(II) POLYPYRIDYL COMPLEXES
  • ORGANIZED SYSTEMS
  • EPR PROBES
  • TRANSITION-METALS
  • NITROXIDE
  • CHEMISTRY

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