Structural and Chemical Bonding Dependence of Mechanical Properties in a Family of Metal-Formate Coordination Polymers

Mechanical properties of a family of three-dimensional ammonium metal-formate coordination polymers ([AmineH(n)][M(HCOO)(3)](n), n = 1-4), in relation to their organic amine cation sizes, framework topologies, hydrogen bonding modes, and metal cation radii have been systematically studied via single crystal nanoindentation experiments. Our findings demonstrate that the moduli and hardnesses of these formate frameworks are primarily dominated by their solvent accessible volumes (SAVs), where formates with high SAVs exhibit low framework rigidity. More importantly, we reveal that the SAVs of these formates decrease largely when their network topologies evolve from the uninodal acs net (4(9).6(6)) to binodal (4(9).6(6))(n) (4(12).6(3)) (n = 1-3) net, then to uninodal (4(12).6(3)) net, hence implying the intimate correlations between their topologies and mechanical properties. In addition, we disclose that the framework stiffness of these formates can also be influenced by hydrogen bonding (between organic amine cations and anionic formate frameworks) and metal cation radii. Our study demonstrates the possibility that mechanical robustness of coordination polymers and metal-organic frameworks could be tuned via facile alteration of organic guests, hydrogen bonding fashions, and metal ions.