Effect of Coordinating Solvents on Solution Speciation and the Crystallisation via ROP of a Triphos-Silver Coordination Cage

Abstract

There is a general lack of understanding of how coordination polymers (metal-organic frameworks) form. Some insight can be gained from observations of formal ROP (ring-opening polymerisation) relationships between coordination polymers and their discrete soluble precursors. Most ROP examples reported previously have involved bidentate bridging ligands. Here we present an unusual example of a ROP relationship based on a tripodal ligand. In particular, 1,3,5-tris(diphenylphosphino)benzene (L1) is found to form a symmetrical coordination cage of stoichiometry Ag3(L1)2 in solution in acetonitrile. This contrasts with previous observations in less-coordinating solvents in which higher nuclearity cages are also formed, and shows that the coordinating acetonitrile solvent reduces anion-templating effects. On crystallization from acetonitrile a one-dimensional polymeric structure [Ag3(L1)2(NCCH3)(OTf)3] n is obtained. The structure is noteworthy in being a ROP isomer of the trinuclear cage observed in solution. The structure also exhibits solvent-filled channels (maximum diameter 6.1 A) but the material is not stable to desolvation. The structure of the polymer contrasts with that obtained from less-coordinating solvents, the latter being a stable hexagonal 2-dimensional structure with nanoporosity.