Alkaline earth metal–organic frameworks supported by ditopic carboxylates

Abstract

Hydrothermal reactions of alkaline earth metal nitrates with two ditopic carboxylic acids, trans-1,4-cyclohexanedicarboxylic acid (H₂CDC) and 1,4-phenylenedipropionic acid (H₂PDP), generate two 3-D metal–organic frameworks (MOFs) with empirical formulas [Ca(CDC)(H₂O)₂]·H₂O (1) and [Sr(PDP)(H₂O)] (2), respectively. Compound 1 consists of Ca–COO–H₂O chains cross-linked through the –C₆H₁₀– spacers of the CDC anions, showing slightly open 1-D channels along the crystallographic c axis that accommodate the guest water molecules. Compound 2 exhibits a MOF consisting of wavy 2-D Sr–COO–H₂O nets linked by –CH₂CH₂C₆H₄CH₂CH₂– tethers, and the condensed structure appears to arise from conformational flexibility of the ligand spacer.

Keywords:

• Calcium complexes
• Strontium complexes
• Coordination polymers
• Metal–organic frameworks

Acknowledgements

The authors gratefully acknowledge support for this study from the donors of The Petroleum Research Fund, administrated by the ACS, and the University of Colorado Denver. We thank Dr Banglin Chen and Hadi Arman of the University of Texas at San Antonio for assistance in acquiring the single crystal X-ray diffraction data. We also thank Drs Daqiang Yuan and Xiaoying Huang for helpful discussions.