Paramagnetic Pyrazolylborate Complexes Tp(2)M And Tp*M-2: H-1, C-13, B-11, And N-14 Nmr Spectra And First-Principles Studies Of Chemical Shifts

The paramagnetic pyrazolylborates Tp(2)M and Tp*M-2 (M = Cu, Ni, Co, Fe, Mn, Cr, V) as well as [Tp(2)M](+) and [Tp*M-2](+) (M = Fe, Cr, V) have been synthesized and their NMR spectra recorded. The H-1 signal shift ranges vary from similar to 30 ppm (Cu(II) and V(III)) to similar to 220 ppm (Co(II)), and the C-13 signal shift ranges from similar to 180 ppm (Fe(III)) to similar to 1150 ppm (Cr(II)). The B-11 and N-14 shifts are similar to 360 and similar to 730 ppm, respectively. Both negative and positive shifts have been observed for all nuclei. The narrow NMR signals of the Co(II), Fe(II), Fe(III), and V(III) derivatives provide resolved C-13,H-1 couplings. All chemical shifts have been calculated from first-principles on a modern version of Kurland-McGarvey theory which includes optimized structures, zero-field splitting, and g tensors, as well as signal shift contributions. Temperature dependence in the Fe(II) spin-crossover complex results from the equilibrium of the ground singlet and the excited quintet. We illustrate both the assignment and analysis capabilities, as well as the shortcomings of the current computational methodology.