A one-dimensional copper(II) phenylenediphosphonate: catena-poly[[(1,10-phenanthroline-κ2 N,N′)copper(II)]-μ3-[m-phenylenediphosphonato-κ3 O:O′:O′′]]

The title compound, [Cu(1,3-HO3PC6H4PO3H)(C12H8N2)]n, is a coordination polymer of the metal–diphosphonate family. The chain structure is constructed from ‘4+1’ square-pyramidally coordinated copper(II) atoms bonded to chelating phenanthroline (phen) ligands and linked through 1,3-phenyldihydrogendiphosphonate ligands. The basal plane of the Cu(II) site is defined by the phen nitrogen donors and phosphonate oxygen atoms from two diphosphonate ligands, while the apical position is occupied by an oxygen donor from a third diphosphonate ligand. The chains propagate along the a-axis direction. Inversion-related phen groups engage in π-π stacking with a mean distance of 3.376 (2) Å between the ring planes. O—H⋯O hydrogen-bonding interactions between the protonated {P—OH} groups of one chain and the {P=O} groups of adjacent chains stabilize the crystal packing.

The title compound, [Cu(1,3-HO 3 PC 6 H 4 PO 3 H)(C 12 H 8 N 2 )] n , is a coordination polymer of the metal-diphosphonate family. The chain structure is constructed from '4+1' square-pyramidally coordinated copper(II) atoms bonded to chelating phenanthroline (phen) ligands and linked through 1,3phenyldihydrogendiphosphonate ligands. The basal plane of the Cu(II) site is defined by the phen nitrogen donors and phosphonate oxygen atoms from two diphosphonate ligands, while the apical position is occupied by an oxygen donor from a third diphosphonate ligand. The chains propagate along the a-axis direction. Inversion-related phen groups engage instacking with a mean distance of 3.376 (2) Å between the ring planes. O-HÁ Á ÁO hydrogen-bonding interactions between the protonated {P-OH} groups of one chain and the {P O} groups of adjacent chains stabilize the crystal packing.

Comment
Metal organophosphonate materials are prototypical organic-inorganic hybrid composites, often exhibiting layered or pillared-layer structures (Clearfield, 1998;Finn et al., (2003)). A variety of transition metal compounds of organophosphonic ligands have been investigated for their catalytic, ion exchange, sensor and non-linear optical properties (Bakmutova et al. (2008);Konar et al.,(2007);Vermeulen, (1997);Turner et al. (2003)). In the specific case of copper-organophosphonate materials, layered structures are the most common, adopting the prototypical 'pillared' layer motif (Arnold, et al. (2002)). In the course of our extensive studies of metal-organophosphonate chemistry (Armatas et al. ring. The alternating ring structure is similar to that observed for the previously reported [Cu(2,2'-bipyridine)(1,3,5-(HO 3 P) 2 C 6 H 3 PO 3 H 2 )] (DeBurgomaster, et al. (2010)). Charge-balance requirements dictate that the diphosphonate ligand must be doubly protonated, that is (HO 3 PC 6 H 4 PO 3 H) 2-. The P2-O5 bond distance of 1.574 (2) Å, compared to distances of 1.509 (2)Å and 1.517 (2)Å for P2-O4 and P2-O6, establishes O5 as one protonation site, an observation confirmed by the appearance of a peak consistent with the O5 proton on the difference Fourier map. The location of the second proton is less clear with O2 and O3 as possibilities. Based on the appearance of a peak consistent with an O2 proton in the difference Fourier, oxygen atom O2 was deemed the site of protonation. The pendant {P = O} and {P-OH} groups of adjacent chains engage in hydrogen-bonding to link the chains into a three-dimensional framework (Fig. 3).

Refinement
Hydrogen atoms of the phenanthroline ring and the phosphonate protons were located on the difference Fourier and were subsequently positioned geometrically with C-H = 0.95 Å and O-H = 0.84 Å. These latter hydrogen atoms were constrained to ride on their parent atoms with U iso (H) = 1.2 x U iso (C) and U iso (H) = 1.5 x U iso (O). Fig. 1. The asymmetric unit of the title compound, showing the atom-labeling scheme and displacement ellipsoids at the 50% probability level. Color scheme: copper, blue; phosphorus, yellow; nitrogen, light blue; oxygen, red; carbon, black; hydrogen, pink.  Crystal data [Cu(C 12

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.