Record Two-Halide Exchange in Cu(2,5-dmpz)Br$_{2}$: Theory and Experiment

Cu(2,5-dmpz)Br$_{2}$ (2,5-dmpz = 2,5-dimethylpyrazine) is an antiferromagnetic rectangular lattice, with the S=1/2 copper ions bridged along one axis through the pyrazine molecules and through Cu-Br. . . Br-Cu contacts in a transverse direction. Large orbital overlap is obtained by the very short Br-Br distances plus the linear arrangement of the copper and bromine atoms. The magnetic susceptibility corresponds to an exchange strength of J/k$_{B} \quad \approx $ 160 K, a record for exchange for two bromide contacts. Numerical techniques have been developed for calculating two-halide contact magnetic exchange interactions from first principles [1,2]. They predict the same exchange strength for Cu(2,5-dmpz)Br$_{2}$ based only on the structural parameters of the compound. We present the magneto-structural correlations in Cu(2,5-dimethylpyrazine)Br$_{2}$ and compare this to two other known pyrazine complexes; Cu(pyrazine)CuBr$_{2}$ and Cu(2,3-dimethylpyrazine)Br$_{2}$. 1. M. Deumal \textit{et al}, \textit{Polyhedron }\textbf{22 } 2235-2239 ( 2003). 2. M. Deumal \textit{et al}, \textit{Euro. J. Inorg. Chem.} \textbf{2005}, 4697-4706.