The Influence of Isomerism on Crystallization in Aluminum Pyridinedicarboxylate Coordination Compounds

The reactions of three isomeric pyridinedicarboxylic acid linkers - 2,4-, 2,6-, and 3,5-pyridinedicarboxylic acid - with various aluminum salts were investigated by high-throughput solvothermal synthesis. Two coordination compounds were obtained from the symmetrical linkers (2,6- and 3,5-pyridinedicarboxylic acid). The former is based on molecular Al-O dimers, similar to those reported in the coordination polymer CAU-16. The latter forms a porous extended framework and is a member of the CAU-10 family of compounds. Full characterization of both compounds is reported. Crystal structures were determined from high-resolution synchrotron powder diffraction data. The number of guest water molecules determined crystallographically is in excellent agreement with the number found by thermogravimetric and elemental analyses. It was found that the CAU-10 analogue undergoes a reversible, displacive phase transition from a non-centrosymmetric to a centrosymmetric space group on loss of guest water molecules, due to guest-framework interactions.