Study Phosphonic Acid Supramolecular Isomerism And Special Hydrogen Bonds Based On 2-carboxyethyl-ethylphenyl Times

Among the broad family of metal–organic coordination polymers, carboxylate, phosphonateand sulfonate are the most widely used ligands for moderate or strong ligation, whereasphosphinate （R-1R2PO2） has rarely been employed for the construction of coordination polymers.Phosphinate can be viewed as a tetrahedra （P atom in the center, four vertices are occupied by twoO atoms and two C atoms）. The oxygen atom of phosphonic acid can not only show strongcoordination abilities, but also be apt to form strong hydrogen bond interactions. Compared withthe mono-organic-group-attached carboxylate or phosphonate moieties, the phosphinate group isfurther bonded to an additional organic group, which can allow a better modulation of thestructure of the resultant metal complexes.In our current studies, we selected （2-carboxyethyl）（phenyl）phosphinic acid （H2L） as themain ligand, and1,10-phenanthroline （phen） as the auxiliary ligand. Our research efforts affordeda series of a novel metal phosphinates, namely,[Mn（L）（phen）（H₂O）]·2（H₂O）（1）,[Mn（L）（phen）（H₂O）]（2）,[Cu（L）（phen）（H₂O）]·3（H₂O）（3）,[Cd（L）（phen）]（4）,[Cd（L）（phen）]·3（H₂O）（5）,[Cd（L）（phen）]·13/6（H₂O）（6）, of which1and2, as well as4,5and6,can be regarded as isomers, and3bears a strong structural analogy to1, although the metalspecies in them are different.1and3show discrete dimer structures, while2,4,5and6featuredifferent double-chain arrays.The addition of strong base such as sodium hydroxide or potassium hydroxide to the aqueoussolution of （2-carboxyethyl）（phenyl）phosphinic acid afforded two novel monovalent metalcarboxylate–phosphinates, namely, NaH（（Ph-PO₂-C₂H₄-COOH）₂）2（7） and[KH（（Ph-PO₂-C₂H₄-COOH）₂）2]·H₂O （8）. The former shows a layer architecture while the latterfeatures a chain array. Compounds7and8containing short, symmetric or almost symmetricO···H···O hydrogen bonds.Through the studies on the supramolecular isomerism and hydrogen bonding characteristicsof these coordination polymers, we have a more in-depth understanding on the assembly of metalphosphinate coordination polymers.