Natural abundance 13C and 15N solid-state NMR analysis of paramagnetic transition-metal cyanide coordination polymers

Abstract

The ¹³C and ¹⁵N MAS NMR spectra of a series of well-characterized paramagnetic metal cyanide coordination polymers are acquired at natural abundance, without the need for polarization transfer methods such as cross-polarization or INEPT. For systems where the paramagnetic centre is outside of the cyanide framework, well-resolved ¹³C and ¹⁵N spectra of cyanide ligands are obtained. Chemical shifts deviate from typical diamagnetic cyanide ranges and depend only partly on the cyanide coordination type, being dominated by their proximity to the paramagnetic center. A combination of the observed isotropic chemical shifts, their temperature dependence, and transverse relaxation time constants (T₂) provides valuable local structural information and lays the foundation for the structural elucidation of unknown paramagnetic metal–cyanide coordination polymers. Toward this end, we apply these solid-state NMR techniques to a pair of compounds without a priori knowledge of the structures.