Extracting structural trends from systematic variation of phosphonate/phosphonate monoester coordination polymers

Abstract

Here we report on three new barium-phosphonate coordination polymers of systematically varied ligand features – a linear diphosphonatebis(monoisopropylester), a trigonal planar triphosphonate, and a trigonal planar triphosphonatetris(monoisopropylester). These coordination polymers are compared to a known prototypical pillared layered barium-diphosphonate, based on a linear diphosphonate, and to each other in order to develop systematic structural trends as a result of the varied ligand features. The findings here indicate that in going from linear cores to trigonal planar cores, there is a disruption in barium-phosphonate coordination, resulting in increased hydration on the cation to compensate and fill the barium coordination sphere. Furthermore, addition of the monoisopropyl ester produces significant steric effects, resulting in truncated structures compared to the acid analogues, along with the formation of bilayers featuring the hydrophobic esters on the periphery. Changing of the ligand geometry and the addition of the monoester operate orthogonally and in conjunction if both changes are present.