Hydrogen N-( phosphonomethyl ) imino-diacetato ] ( 1 , 10-phenanthroline ) copper ( II ) trihydrate : a low-temperature redetermination

# 2005 International Union of Crystallography Printed in Great Britain – all rights reserved The room-temperature crystal structure of the title compound, [Cu(H2pmida)(phen)] 3H2O [where H2pmida is hydrogen N-(phosphonomethyl)iminodiacetate, C5H10NO7P 2 , and phen is 1,10-phenanthroline, C12H8N2], was recently determined by Pei Lu, Ke, Li, Qin, Zhou, Wu & Du [Struct. Chem. (2004), 15, 207–210]. We report here a redetermination, at 180 (2) K, with greatly improved precision. Hydrogen bonds lead to the formation of one-dimensional tapes which run along the [100] direction of the unit cell. Adjacent tapes are interconnected via – offset stacking (between the 1,10phenanthroline ligands) and by hydrogen bonds involving the water molecules of crystallization.

Although the crystal structure of this compound has recently been reported (Pei et al., 2004), we redetermined it at 180 (2) K, with a final R value of 0.0376, to gain more precise data for our studies of the magnetic properties of such crystalline hybrid materials. The low-temperature redetermination allowed the direct location of all H atoms associated with the protonated carboxylic and phosphonic acid groups, and with the three water molecules of crystallization, thus giving a much better insight into the hydrogen-bond network present in the crystal structure of (I).
The unit-cell volume decreased by ca 13 Å 3 , consistent with determination at a lower temperature. The asymmetric unit composed of a complete [Cu(H 2 pmida)(phen)] complex ( Fig. 1) plus three water molecules of crystallization (O1W, O2W and O3W). The crystallographically unique Cu 2+ atom is coordinated by one phen residue via the two N-donor atoms, leading to a bite angle of 82.18 (9) , which is in good agreement with that reported by Pei et al. [82.06 (16) ], and also with those typically found in related compounds as revealed by a search in the Cambridge Structural Database (CSD, Version 5.26; Allen, 2002;Allen & Motherwell, 2002). The remaining four positions of the Cu 2+ coordination are occupied by the N-and O-donor atoms from the H 2 pmida 2À anionic ligand, leading to a typical Jahn-Teller distorted octahedral coordination geometry, {CuN 3 O 3 }. In general, the Cu-N and Cu-O bond lengths and angles (Table 1) are not significantly different from those obtained from the roomtemperature determination (Pei et al., 2004). Each [Cu(H 2 pmida)(phen)] complex is connected to adjacent molecules via a series of hydrogen bonds between the protonated carboxylic and phosphonic acid groups (donors), and the coordinated carboxylate groups (acceptors) of a neighbouring complex ( Fig. 2 and Table 2). Such a regular arrangement of hydrogen bonds between adjacent complexes leads to the formation of two graph-set motifs, viz. R 2 2 (16) and R 4 4 (24) (Fig. 2), which are recursively repeated along the [100] direction of the unit cell, creating a one-dimensional hydrogen-bonded tape. The intermetallic Cu1Á Á ÁCu1 i distance across the O7Á Á ÁO1 hydrogen-bond bridge is 7.571 (2) Å , while across the O2Á Á ÁO5 bridge, Cu1Á Á ÁCu1 ii is 9.162 (2) Å [symmetry codes: (i) À1 + x, y, z; (ii) 1 À x, 1 À y, Àz]. The one-dimensional tape is formed in such a way that the coordinated phen molecules are external to the hydrogen-bonded core (Fig. 2). Therefore, the aromatic residues are engaged in offsetstacking along the [100] direction of the unit cell, thus linking neighbouring hydrogen-bonded tapes (Fig. 3). Further connections between tapes are made by hydrogen bonds involving the water molecules of crystallization ( Fig. 4 and Table 2), thus leading, along with the above-mentionedinteractions, to a three-    Hydrogen bonding in (I) represented as green-filled dashed bonds giving a one-dimensional tape running along the [100] direction of the unit cell with a schematic diagram showing the two graph-set motifs, viz. R 2 2 (16) and R 4 4 (24). [Symmetry codes: (i) 1 À x, 1 À y, Àz; (ii) 1 + x, y, z; (iii) À1 + x, y, z; (iv) Àx, 1 À y, Àz; (v) 2 À x, 1 À y, Àz.] offset interactions, running along the [100] direction of the unit cell between 1,10-phenanthroline residues belonging to adjacent onedimensional hydrogen-bonded tapes (see Fig. 2). Hydrogen bonds are represented as green-filled dashed bonds.

Experimental
Chemicals were readily available from commercial sources and were used as received without further purification, i.e. N-(phosphonomethyl)iminodiacetic acid hydrate (H 4 pmida, 97% Fluka), 1,10phenanthroline monohydrate (phen, >99.0% Fluka) and copper(II) hydroxide [CuCO 3 ÁCu(OH) 2 , 55% in Cu, Panreac]. The title compound was synthesized from a mixture containing 0.19 g of CuCO 3 ÁCu(OH) 2 , 0.38 g of H 4 pmida and 0.23 g of phen in ca 6.7 g of distilled water. The mixture was stirred at ambient temperature for 30 min, yielding a homogeneous suspension with a molar composition of ca 1.0:1.9:1.4:433, which was transferred to PTFE-lined stainless steel reaction vessels (ca 40 ml). Reactions took place over a period of 3 d, under autogeneous pressure and static conditions, in a preheated oven at 373 K. The vessels were left to cool to ambient temperature before opening. The mother liquor was filtered off and allowed to stand in the open air for approximately 2 d, yielding a large amount of a dark-green single-crystalline phase. Individual single crystals were washed with copious amounts of distilled water (3 Â ca 50 ml), and then air-dried at ambient temperature to give the title compound.
H atoms associated with the three water molecules of crystallization, and with the protonated carboxylic and phosphonic acid groups (H2C and H7A), were clearly visible in difference Fourier maps, and were included in subsequent least-squares refinements. For the water molecules, the O-H and HÁ Á ÁH distances were restrained to 0.95 (1) and 1.55 (1) Å , respectively, to ensure a chemically reasonable geometry for these groups. For the hydroxyl groups, the O-H distances were restrained to 0.90 (1) Å . These H atoms were further refined with an isotropic displacement parameter fixed at 1.5U eq of the parent O atoms. H atoms bound to carbon were placed in idealized positions and allowed to ride on their parent atoms with relative isotropic displacement parameters (U iso ) fixed at 1.2U eq of the parent C atom and C-H = 0.95 Å .

Special details
Experimental. (Please see the Experimental Section in the main paper) Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.