Synthesis and Characterization of New Calcium Phenylphosphonates and 4-Carboxyphenylphosphonates

Three new calcium phenylphosphonates, CaC6H5PO3·2H2O, Ca3(C6H5PO3H)2(C6H5PO3)2·4H2O, and CaC6H5PO3·H2O, and two calcium 4-carboxyphenylphosphonates, Ca(HOOCC6H4PO3H)2 and Ca3(OOCC6H4PO3)2·6H2O, were
prepared. It was found that CaC6H5PO3·2H2O transformed into previously known Ca(C6H5PO3H)2 via Ca3(C6H5PO3H)2(C6H5PO3)2·4H2O in the presence of phenylphosphonic acid, and vice versa, Ca(C6H5PO3H)2 turned into
CaC6H5PO3·2H2O in a weak basic medium. A similar relationship was found between Ca(HOOCC6H4PO3H)2 and
Ca3(OOCC6H4PO3)2·6H2O; i.e., Ca3(OOCC6H4PO3)2·6H2O transformed into Ca(HOOCC6H4PO3H)2 in the presence
of 4-carboxyphenylphosphonic acid. On the contrary, Ca3(OOCC6H4PO3)2·6H2O is formed from Ca(HOOCC6H4PO3H)2 in the presence of ammonium as a weak base. The structure of Ca(HOOCC6H4PO3H)2 was solved from
X-ray powder diffraction data by an ab initio method using a FOX program. The compound is monoclinic, space
group C2/c (No. 15), a = 49.218(3) Å, b = 7.7609(4) Å, c = 5.4452(3) Å, β = 128.119(3)°, and Z = 4. Its
structure is one-dimensional with [Ca2(HOOCC6H4PO3H)4]∞ ribbons forming basic building blocks. The ribbons are
held together by hydrogen bonds between carboxylic groups.