Michael L. Baker, Stergios Piligkos, Alberto Bianchi, Stefano Carretta, David Collison, Joseph J. W. McDouall, Eric J. L. McInnes, Hannu Mutka, Grigore A. Timco, Floriana Tuna, Prabha Vadivelu, Høgni Weihe, Hans U. Güdel and Richard E. P. Winpenny
Modification of the magnetic properties of a heterometallic wheel by inclusion of a Jahn–Teller distorted Cu(II) ion
Dalton Trans. 40, 8533-8539 (2011)                 

Abstract: An investigation into the physical consequences of including a Jahn–Teller distorted Cu^II ion within an antiferromagnetically coupled ring, [R₂NH₂][Cr₇CuF₈((O₂C^tBu)₁₆)] is reported. Inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR) spectroscopic data are simulated using a microscopic spin Hamiltonian, and show that the two Cr–Cu exchange interactions must be inequivalent. One Cr–Cu exchange is found to be antiferromagnetic and the other ferromagnetic. The geometry of the Jahn–Teller elongation is deduced from these results, and shows that a Jahn–Teller elongation axis must lie in the plane of the Cr₇Cu wheel; the elongation is not observed by X-ray crystallography, due to positional disorder of the Cu site within the wheel. An electronic structure calculation confirms the structural distortion of the Cu site.