Crystal formation of 1D coordination polymers based on chiral, achiral and racemic 1,2-cyclohexane scaffolds

Abstract

Enantiomerically pure ligands (1a and 1b) and meso1c based on trans-1,2-cyclohexanediol and cis-1,2-cyclohexanediol, respectively, were used for the formation of zigzag 1D coordination polymers, when combined with bent HgCl₂. A racemic mixture or 1a/1b in a 1/1 ratio has also been studied. Four 1D coordination polymers have been obtained and their structures have been analysed using X-ray diffraction on single crystals and also on powder. 1a-HgCl₂ (and isostructural 1b-HgCl₂) crystallizes in the non-centrosymmetric P2₁2₁2₁ space group, 1c-HgCl₂ in the non-centrosymmetric P2₁2₁2 space group and 1a_0.51b_0.5-HgCl₂ crystallises in the centrosymmetric P2₁/n space group. The analysis of network energies, evaluated using a partial charges calculation method (PACHA) used here for the first time for 1D coordination networks, allows evaluation of energetical parameters like the packing energy (PE) of each crystalline compound, as well as their cooperativity index (CI), illustrating the influence of chirality on the packing of this series of 1D coordination polymers. It has been shown that the use of the achiral ligand 1c requires the highest cooperativity between chains.