Syntheses, crystal structures, and fluorescence properties of two new copper phosphonates from hydroxy-functionalized bisphosphonic acid ligand.

Exploring metal phosphonates with new crystal structures is of significance for the development of metal-organic frameworks (MOFs). In this work, two new copper phosphonates, [tetraauqa-1,4-phenylenebis(hydroxymethylene))bisphosphonate biscopper(II)] bishydrate [Cu₂(H₂L)(H₂O)₄]·2H₂O (1) and 1,4-phenylenebis(hydroxymethylene))bisphosphonate-(4,4'-bipy) copper(II) [Cu(H₄L)(4,4'-bipy)] (2) (4,4'-bipy = 4,4'-bipyridine), have been synthesized from a hydroxy functionalized bisphosphonate ligand, H₆L = (1,4-phenylenebis(hydroxymethylene))bis(phosphonic acid). The introduction of a hydroxy group can regulate the crystal structures. The bisphosphonate ligand in 1 is hexadentate, binding six copper ions with its six phosphonate oxygen atoms and two hydroxy oxygen atoms, forming a three-dimensional framework structure with rectangle channels running along the b-direction. For 2, the bisphosphonate ligands are double deprotonated and chelate or bridge two copper ions, showing a two-dimensional layered crystal structure. These compounds have interesting fluorescence properties with emission maxima (307 and 410 nm) lying in the blue region. [ABSTRACT FROM AUTHOR]