Microwave synthesis, crystal structures, and low-temperature heat capacities of two novel alkaline earth metal coordination polymers featuring O-ferrocecarbonyl benzoic acid

Abstract

Two novel alkaline earth metal coordination polymers [M(O-fcba)2·(H2O)2]n [M = Ca(1), Sr(2), O-ferrocecarbonyl benzoic acid = O-fcbaH] have been microwave synthesized by the corresponding alkaline earth metal chlorates and deprotonated ligand. Both 1 and 2 were characterized by elemental analysis, IR, TG/DTG, PXRD, and X-ray crystallography. The structure study shows that these two compounds are isostructural. The adjacent eight-coordinated M(II) ions are bridged by oxygen atoms of carboxyl groups, resulting in the 1D metal-node-based chains with the unique feature of boat-like configurations appearing alternatively in ac plane and ab plane. With the help of hydrogen bond and π–π stacking, the adjacent 1D chains are self-assembled to the 2D layers, further forming the 3D framework. The results of low-temperature heat capacities show that respective obvious endothermic peaks appear in the temperature ranges of 340–368 K for 1 and in that of 336–372 K for 2, which could be assigned to the dehydration process of the title coordination polymers and be proven by the first mass loss during TG/DTG thermal analysis technique.