The outcome of a synthesis involving a metal ion and a (poly)phosphonic acid depends on a plethora of variables such as solution pH, reactant molar ratios, nature of the metal ion, number of phosphonate groups, and other “functional” moieties present on the ligand backbone. Products are usually coordination polymers of diverse dimensionality. Here we report that the use of a chelating auxiliary ligand (2,2′-bpy) can “disrupt” the polymeric architecture of the copper phosphonate, causing the isolation of a series of molecular complexes (mononuclear or binuclear) that incorporate both the phosphonate and the 2,2′-bpy ligands. Synthetic details, crystal structures, and intermolecular interactions (π–π stacking and hydrogen bonding) are discussed. The structures of the obtained Cu complexes are extended into 2D or 3D networks via multiple hydrogen bonds involving the molecular units and crystallization water molecules. These H-bonded networks have been classified from the topological viewpoint, revealing diverse topologies that also include their undocumented types.

Dissolution of biologically important sparingly soluble salts, such as calcium carbonate and calcium oxalate, is possible by use of carboxyl- and carboxyl/phosphonate-bearing, anionic additives, citrate, malate, carboxyphosphonate, and butane tetracarboxylate. Calcium-containing dissolution products have been identified, characterized, and independently synthesized. These are polymeric materials composed of calcium and the additive as the ligand. Their full characterization was carried out by single-crystal X-ray crystallography and other techniques.

New metal–organic materials were synthesized based on diphosphonates. They possess interesting structural/topological features, and exhibit substantial catalytic activity in the hydrocarboxylation of alkanes.

Phosphonate ligands demonstrate strong affinity for metal ions. However, there are several cases where the phosphonate is found non-coordinated to the metal ion. Such compounds could be characterized as salts, since the interactions involved are ionic and hydrogen bonding. In this paper we explore a number of such examples, using divalent metal ions (Mg2+, Ca2+, Sr2+ and Ni2+) and the phosphonic acids: p-aminobenzylphosphonic acid (H2PABPA), tetramethylenediamine-tetrakis(methylenephosphonic acid) (H8TDTMP), and 1,2-ethylenediphosphonic acid (H4EDPA). The compounds isolated and structurally characterized are [Mg(H2O)6]·[HPABPA]2·6H2O, [Ca(H2O)8]·[HPABPA]2, [Sr(H2O)8]·[HPABPA]2, [Mg(H2O)6]·[H6TDTMP], and [Ni(H2O)6]·[H2EDPA]·H2O. Also, the coordination polymer {[Ni(4,4’-bpy)(H2O)4]·[H2EDPA]·H2O}n was synthesized and characterized, which contains a bridging 4,4’-bipyridine (4,4’-bpy) ligand forming an infinite chain with the Ni2+ cations. All these compounds contain the phosphonate anion as the counterion to charge balance the cationic charge originating from the metal cation.