Modification of the magnetic properties of a heterometallic wheel by inclusion of a Jahn-Teller distorted Cu(II) ion

An investigation into the physical consequences of including a Jahn-Teller distorted Cu-II ion within an antiferromagnetically coupled ring, [R2NH2][Cr7CuF8(((O2CBu)-Bu-t)(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.