Crystal Structure of Catena-((μ8-benzene-1,2,4,5-tetracarboxylato)-triaqua-calcium(II)-copper(II))

The construction of some metal-organic framework (MOF) based on alkaline earth metals and aromatic carboxylic acid has been emerging as a research field for more than thirty years.1 The lack of d-orbital electrons in alkaline elements may result in even more coordination geometries in the construction of a MOF material.1 However, by introducing both one transition and alkaline earth metals simultaneously into a MOF structure has been only reported recently.2 The unsaturated coordination and weak coordinated solvent molecules around metal centers can provide some new type of potentially valuable MOF materials.3–6 Based on this design strategy, we have now prepared one Cu(II)-Ca(II) combined coordination complex (I) under the hydrothermal condition (Fig. 1). In (I), these two types of metals are bridged by benzene-1,2,4,5-tetracarboxylic acid (H4BTA). Although no crystallographic void was detected in (I), it can adsorb N2 gas to a certain extent. Herein, we will report the crystal structure of (I). In this research, compound (I) was prepared by dissovling Cu(NO3)2·2(H2O) (0.2 mmol, 48.0 mg), CaCl2 (0.2 mmol, 23 mg) and H4BTA acid (0.2 mmol, 51.0 mg) in 10 mL of water. The mixture was stirred for 10 min at ambient temperature and then heated in a 20-mL capacity Teflon-lined reaction vessel at 160°C for 3 days. After slowly cooling to room temperature at a rate of 5°C h–1, the final plate-blue crystals (51.2 mg), suitable for X-ray structure analysis, could be obtained. The crystal and structure refinement data are summarized in Table 1. 2019 © The Japan Society for Analytical Chemistry