Ethyl [(2-hydroxyphenyl)(pyridinium-2-ylamino)methyl]phosphonate methanol solvate

In the title compound, C14H17N2O4P·CH3OH, the planes of the pyridinium-2-ylamino and 2-hydroxyphenyl groups form a dihedral angle of 75.6 (1)°, with the pyridinium NH group and the 2-hydroxyphenyl OH group pointing in opposite directions. Three intramolecular hydrogen bonds are observed. Two phosphonate and two methanol molecules are connected by O—H⋯O hydrogen bonds as a centrosymmetric dimeric cluster, and interact further with other dimeric clusters via N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds and C—H⋯π interactions, resulting in a sheet structure.

In the title compound, C 14 H 17 N 2 O 4 PÁCH 3 OH, the planes of the pyridinium-2-ylamino and 2-hydroxyphenyl groups form a dihedral angle of 75.6 (1) , with the pyridinium NH group and the 2-hydroxyphenyl OH group pointing in opposite directions. Three intramolecular hydrogen bonds are observed. Two phosphonate and two methanol molecules are connected by O-HÁ Á ÁO hydrogen bonds as a centrosymmetric dimeric cluster, and interact further with other dimeric clusters via N-HÁ Á ÁO, O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á interactions, resulting in a sheet structure.   Table 1 Hydrogen-bond geometry (Å , ).

Comment
Organophosphorus compounds are of importance because of their growing applications in medicine and agriculture. Aminophosphonates, one family of organophosphorus compounds, have received much attention as phosphorus analogs of naturally occurring aminocarboxylic acids. Many of these types of compounds have antibacterial, anticancer, and enzyme inhibitory properties, and so on (Kafarski & Lejczak, 2001;Liu et al., 2002;Meyer et al., 2004). Many new aminophosphonate compounds have been synthesized and characterized (Palacios et al., 2005;Kaboudin & Moradi, 2005;Kachkovskyi & Kolodiazhnyi, 2007) for these reasons. The title compound was synthesized in order to understand its inhibitory activity on the protein tyrosine phosphatase 1B (PTP1B). Here we describe the crystal structure.
The planes of the pyridinium-2-amino and 2-hydroxyphenyl groups form a dihedral angle of 75.6 (1)°, with the N-H group of pyridinium and O-H of 2-hydroxyphenyl pointing in opposite directions. When the ethyl group and one of the two O atoms bonded to P are substituted by phenyl groups, the dihedral angle between the 2-hydroxyphenyl and pyridine rings is 54.9 (1)°, and the N atom of the pyridine ring and O-H of 2-hydroxyphenyl are close together, forming an intramolecular hydrogen bond (Rohovec et al., 1999). Thus the substitution of functional groups around the P atom influences the arrangement of other function groups. The ethyl (2-hydroxyphenyl)(pyridinium-2-ylamino)methylphosphonate molecule displays three intramolecular hydrogen bonds, two C-H···O and one N-H···O. N1-H1···O3 and C7-H7···O1 lead to the formation of five-membered S(5) ring motifs (Bernstein et al., 1995;Briceño et al., 2007). C9-H9···O1 results in an eight-membered S(8) ring motif. Thus, O1 is involved in a bifurcated hydrogen bond (Jeffrey et al., 1985), which produces a distorted seven-membered ring. Additionally, the solvent methanol is hydrogen bonded to O4, stabilizing the molecular conformation.
The intermolecular interactions of compound (I) are shown in Fig. 2 and in the hydrogen bonding table. Two ethyl (2-hydroxyphenyl)(pyridinium-2-ylamino)methylphosphonate molecules are connected antiparallel as a centrosymmetric dimer via bifurcated hydrogen bonds in which N1 and N2 are donors and O3 is the acceptor, giving rise to two hydrogenbonded R 1 2 (6) rings. In the bifurcated hydrogen bond, the two interactions are unequal; the N···O distance of 2.694 (3) Å and angle of 161° are obviously a stronger interaction than the N···O distance of 2.813 (3) Å and the angle of 150°. Two intermolecular N-H···O hydrogen bonds together with two intramolecular N-H···O interactions form another R 4 4 (4) ring.
The methanol molecules also link the dimers through O-H···O and C-H···O hydrogen bonds, generating two R 3 3 (9) rings.
Thus five hydrogen-bonded rings, namely two R 3 3 (9), two R 1 2 (6) and one R 4 4 (4), form a complicated hydrogen-bonding network (Fig. 2). In this network, O3 acts as an acceptor of three hydrogen atoms and forms a trifurcated hydrogen bond (Jeffrey et al., 1985), which is not observed very often. Meanwhile, O3 and one of its equivalents by symmetry share H1A, forming a bifurcated hydrogen bond. Neighbouring dimers are linked to each other via O-H···O hydrogen bonds. Four such dimers constitute a repeat unit with a thirty-four-membered R 6 6 (34) ring, generating two-dimensional sheets parallel to (102). A C-H···π weak interaction involving ethyl and hydroxyphenyl groups also helps to stabilize the crystal structure

Refinement
The C13-C14 bond length was restrained to 1.50 (1) Å, because free refinement gave an unacceptably short bond, possibly due to unresolved disorder. H atoms attached to C atoms of (I) were placed in geometrically idealized positions with Csp 2 -H = 0.93, Csp 3 (methyl)-H = 0.96, and Csp 3 (methylene)-H = 0.97 Å and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C) (1.5U eq for methyl H). H atoms attached to N and O atoms were located in a difference Fourier map and refined as riding, with U iso = 1.2U eq (N,O). Fig. 1. The molecular structure of (I) with displacement ellipsoids drawn at the 30% probability level. Dotted lines indicate intramolecular hydrogen bonds. Fig. 2. The dimer formed via R 4 4 (4), R 1 2 (6) and R 3 3 (9) rings, and the two-dimensional sheet formed through R 6 6 (34) rings. Dotted lines indicate hydrogen bonds and C-H···π interactions.  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.