A hybrid organic/inorganic material is obtained with calcium as the structural building block. The structure of this new oligomeric complex was confirmed by a single crystal X-ray diffraction, which shows the bridging position of the calcium ions between four dioxazaphosphocane moieties.
Methylenebisphosphonates, also known as geminal bisphosphonates, are analogues of pyrophosphates and are also characterized by a PϪCϪP bond. These compounds with various side chains linked to the central carbon atom, like Etidronate or Clodronate, have been extensively studied and widely used in treating various diseases of bone and calcium metabolism. [1Ϫ3] Whereas monophosphonates have been reported to be inactive with respect to calcium related disorders, [4] the presence of a potential donor group adjacent to the phosphonate moiety (as in α-acylphosphonates or α-hydroxyiminophosphonates) restores this activity. [5] Despite the large number of bis-phosphonates investigated for their biological activity or even used clinically, structural studies of their calcium complexes are very limited. However, a common feature of the few structural studies reported is that the Ca ion forms bidentate chelates with two oxygen atoms. [6Ϫ7] In this field, we have synthesized, in the past few years, new eight-membered cyclic hydrogenophosphonates named dioxazaphosphocanes. These cyclic and nonionizable phosphodiesters, with two donor groups (carbonyl and phosphoryl) in the same molecule, display interesting complexing properties towards alkaline earth metal cations. [8] The complexing properties of the dioxazaphosphocane moiety have been demonstrated in the solid state by an Xray structure determination. It revealed an original polymeric arrangement which is in accordance with the previously claimed stoichiometry and the data obtained by classical physical methods (NMR and IR spectroscopy).
[a] Synthe `se et Physicochimie de Mole ´cules dЈInte ´re ˆt Biologique,