Carborane bis-pyridylalcohols as linkers for coordination polymers : synthesis, crystal structures and guest-framework dependent mechanical properties

We report the synthesis and characterization of six novel coordination polymers (CPs) based on M(II) (M: Zn and Co), di-, tri-, and tetracarboxylate linkers and two novel bis-pyridylalcohol 1,7-bis{(pyridin-n'-yl)methanol}-1,7-dicarba-closo-dodecaboranes (n' = 3, L1; n' = 4, L2) ligands. The polycarboxylates are terephthalic acid (H₂BDC), 1,3,5-benzenetricarboxylic acid (H₃BTB), and 1,2,4,5-tetrakis(4-carboxyphenyl)benzene (H₄TCPB). Structural description of CPs reveals the flexibility of the carborane ligands and their ability to construct extended structures. The CP containing Co(II), BTB, and L2 behaves as a crystalline sponge for a variety of guests, showing a higher affinity for aromatic guest molecules. Single-crystal nanoindentation experiments indicate that a high number of specific interactions between the guests and the CP framework result in a high elastic modulus and hardness values.