Metal-metal communication in copper(II) complexes of cyclotetraphosphazene ligands.
Copper(II) chloride and bromide react with the pyridyloxy-substituted cyclotetraphosphazene ligands, octakis(2-pyridyloxy)cyclotetraphosphazene (L(1)), and octakis(4-methyl-2-pyridyloxy)cyclotetraphosphazene (L(2)), to form the dimetallic complexes, [L(CuX2)2] (L = L(1), X = Br; L = L(2), X = Cl or Br), and [{L(1)(CuCl2)2}n]. Single crystal X-ray crystallography shows the complex [{L(1)(CuCl2)2}n] to be a coordination polymer propagated by interligand "Cu(mu-Cl)2Cu" bridges whereas [L(2)(CuCl2)2] forms discrete dimetallic cyclotetraphosphazene-based moieties. The variable temperature magnetic susceptibility data for [{L(1)(CuCl2)2}n] are consistent with a weak antiferromagnetic exchange interaction between the copper(II) centers occurring via the bridging chloride ions. [L(2)(CuCl2)2] and [L(CuBr2)2] (L = L(1) and L(2)) exhibit normal Curie-like susceptibilities. The abstraction of a chloride ion, using [Ag(MeCN)4](PF6), from each copper site in [L(2)(CuCl2)2], affords the new complex, [L(2)(CuCl)2](PF6)2, in which the two copper(II) ions are separated by "N-P=N-P=N" phosphazene bridges. Electron spin resonance and variable temperature magnetic measurements indicate the occurrence of weak antiferromagnetic coupling between the unpaired electrons on the copper(II) centers. Density Functional Theory (DFT) calculations on the [L(2)(CuCl)2](2+) dication and the related cyclotriphosphazene complex, [L(4)(CuCl2)2] (L(4) = hexakis(4-methyl-2-pyridyloxy)cyclotriphosphazene), have identified "electron-density-bridge" molecular orbitals which involve Cu 3d orbitals overlapping with the non-bonding N-based molecular orbitals on the phosphazene rings as the pathway for this interaction.
Ainscough
Eric W
EW
Chemistry-Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North, New Zealand 4442. e.ainscough@massey.ac.nz
Brodie
Andrew M
AM
Davidson
Ross J
RJ
Moubaraki
Boujemaa
B
Murray
Keith S
KS
Otter
Carl A
CA
Waterland
Mark R
MR