NMR studies of solid organometallic polymers

Abstract

A series of solid organometallic polymers is known, consisting of octahedrally coordinated M(CN)(_6) [M=Co, Fe, Ru, Os] centres linked by trigonal bipyramidal connecting rods of the form R(_3)X [R=Me, Et, Bu] and derivatives thereof. These polymers have open structures with large cavities and channels and therefore could potentially be used as molecular sieves or ion-exchangers. Functionalisation of the rods could also lead to them being used as catalysts. The polymers are, however, insoluble in water and commonly used solvents making it impossible to use solution-state analytical techniques. Single-crystals are also difficult to grow and therefore X-ray crystallographic studies have only been possible for a few of them. The research described here is the analysis of the polymers using solid-state nuclear magnetic resonance (NMR) spectroscopy. It has been possible to probe theirstructures via a number of different nuclei since each polymer contains at leastthree spin-active nuclei ((^13)C, (^119)Sn or (^207)Pb, (^15)N). Spectra have been obtained at ambient temperatures and for 13ºC also at lowered and elevated temperatures. A two dimensional spin-exchange experiment has been used to investigate an interesting exchange process. For those polymers whose structures are known the NMR chemical shift and anisotropy and asymmetry data have been correlated with structural features. This information has then been used to predict the structures of those polymers where X-ray crystallography has not yet been possible.