Effect of Ligand Structural Isomerism in Formation of Calcium Coordination Networks

Using different structural isomers (2,5-; 2,4-; 2;6-;
3,4-; 3,5-)
of pyridinedicarboxylic acid, nine calcium-based coordination networks
were synthesized under hydro-/solvothermal conditions and/or were
produced via solvent recrystallization of previously synthesized compounds.
The coordination networks reported were characterized using single
crystal X-ray diffraction and thermal methods. They show diverse structural
topologies, depending on the ligand geometry and coordinated solvent
molecules, with inorganic connectivity motifs ranging from isolated
octahedra to infinite chains, layer and a three-dimensional dense
framework. The as-synthesized and desolvated networks further show
structural transformation to hydrated phases through dissolution/reformation
pathways. The process is likely driven by the high hydration energy
of the calcium metal center.