Common Structural Features in Calcium Hydroxyphosphonoacetates. A High-Throughput Screening

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• 作者：Rosario M. P. Colodrero ; Aurelio Cabeza ; Pascual Olivera-Pastor ; Maria Papadaki ; Jordi Rius ; Duane Choquesillo-Lazarte ; Juan M. Garc铆a-Ruiz ; Konstantinos D. Demadis ; Miguel A. G. Aranda
• 刊名：Crystal Growth & Design
• 出版年：2011
• 出版时间：May 4, 2011
• 年：2011
• 卷：11
• 期：5
• 页码：1713-1722
• 全文大小：1112K
• 年卷期：v.11,no.5(May 4, 2011)
• ISSN：1528-7505

文摘

R,S-Hydroxyphosphonoacetic acid (H₃HPA) is an inexpensive multidentate organic ligand widely used for the preparation of organo-inorganic hybrid materials. There are reports of several crystal structures and the variability of the resulting frameworks is strikingly high, in contrast with the simplicity of the ligand. In an attempt to investigate and rationalize some salient structural features of the crystal structures, we have carried out a systematic high-throughput study of the reaction of H₃HPA with Ca²⁺ in aqueous solutions (pH values ranging 1.0鈭?.5) at room temperature and hydrothermally at 180 掳C. The tested synthetic conditions yielded five crystalline single-phase Ca鈭扝₃HPA hybrids: Ca₃(O₃PCHOHCOO)₂路14H₂O (1), Ca(HO₃PCHOHCOO)路3H₂O (2), Ca₅(O₃PCHOHCOO)₂(HO₃PCHOHCOO)₂路6H₂O (3), CaLi(O₃PCHOHCOO) (4), and Ca₂Na(O₃PCHOHCOO)(HO₃PCHOHCOO)路1.5H₂O (5). Four new crystal structures, 2鈭?b>5, are reported (three from powder diffraction data and one from single-crystal data), which allowed us to unravel some key common structural features. The Ca鈭扝₃HPA hybrids without an extra alkaline cation, 1鈭?b>3, contain a common structural motif, which has been identified as a linear Ca鈭扝₃HPA鈭扖a鈭扝₃HPA鈭扖a trimer. This inorganic motif has a central Ca²⁺ in a distorted octahedral environment, whereas the two side Ca²⁺ cations are in an eight-coordinated oxygen-rich environment. The H₃HPA ligands are chelating the central Ca²⁺ through two pairs of carboxylate and phosphonate oxygen atoms forming six-membered rings, Ca鈭扥鈭扖鈭扖鈭扨鈭扥鈭扖a. This coordination mode allows the peripheral Ca(II) ions to bind the ligand through the 鈭扥H group and the other carboxylate oxygen, forming a five-membered ring, Ca鈭扥鈭扖鈭扖鈭扥鈭扖a. The presence of alkaline cations, Li⁺ and Na⁺, disrupt this common structural feature leading to highly dense frameworks. Finally, similarities (and differences) between Ca鈭扝₃HPA and Cd鈭扝₃HPA hybrids are also discussed.