Determination of magnetic and structural properties in solids containing antiferromagnetically coupled metal centers using NMR methods. Magneto−structural correlations in anhydrous copper(II) n-butyrate

A new approach to the investigation of magneto-structural correlations in solids containing antiferromagnetically coupled transition-metal centers is described that illustrates the potential of NMR spectroscopy in such work. The results of a variable-temperature (VT) /sup 13/C cross-polarization magic-angle-spinning (CP/MAS) NMR investigation of anhydrous copper(II) n-butyrate, (Cu(C/sub 3/H/sub 7/COO)/sub 2/)/sub 2/ are reported. Isotropic shifts are found to be primarily contact in origin, and a statistical analysis of their temperature dependence allows the calculation of singlet-triplet energy level separations (-2J), diamagnetic shifts (delta/sub dia/), and electron-nucleus hyperfine coupling constants (A), which are shown to give insight into the mechanisms of electron delocalization along the superexchange pathway. Signal multiplicity can be related to compound structure, which was determined by using x-ray crystallography. The title compound is triclinic and has a space group of P/anti 1/ with a = 9.035 (2) /angstrom/, b = 5.192 (2) /angstrom/, c = 11.695 (3) /angstrom/, ..cap alpha.. = 85.88 (2)/degrees/, ..gamma.. = 109.32 (2)/degrees/, Z = 1, and V = 515.2 (3) /angstrom//sup 3/; the final weighted R value for 2169 reflections was 0.048. 21 references, 4 figures, 4 tables.