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metal-organic compounds
The 100 K crystal structure of the title compound, [Cu(C3H4NO3)2(H2O)2], is composed of discrete [Cu(hipa)2(H2O)2] units (hipa = 2-hydroxyiminopropionate). The CuII atom lies on an inversion centre and exhibits a slightly distorted octahedral coordination geometry formed by two chelating bidentate hipa ligands occupying equatorial sites and two water molecules in axial positions. The hipa ligands are bound to the copper centre in a trans fashion, generating a planar {Cu(hipa)2} core with the six-membered chelate rings having Cu—O and Cu—N distances of 1.9421 (13) and 2.0488 (15) Å, respectively, and N—Cu—O bite angles of 80.70 (6)°. The bonding parameters agree with those of the 298 K crystal structure of the title compound, which has been deposited at the Cambridge Structural Database (refcode IGUZAL) [Holt (2002). Private communication to the Cambridge Structural Database. Cambridge Crystallographic Data Centre, Cambridge, England] but remained unpublished. In the title compound, each water molecule acts as both an intermolecular hydrogen-bond donor (to the carboxylate O atoms) or acceptor (of hydrogen from the hydroxyl oxygen), thus multiply linking neighbouring mononuclear units and forming polymeric hydrogen-bonded two-dimensional layers. They are further extended by means of weak intermolecular C—H
O hydrogen bonds between methyl groups and the hydroxyl O atoms of hipa. The shortest CuCu separations within these layers are equal to the unit-cell dimensions. The hipa ligands in the title compound are derived from a copper-promoted fragmentation of N-hydroxy-2,2′-iminodipropionic acid.
O hydrogen bonds between methyl groups and the hydroxyl O atoms of hipa. The shortest CuCu separations within these layers are equal to the unit-cell dimensions. The hipa ligands in the title compound are derived from a copper-promoted fragmentation of N-hydroxy-2,2′-iminodipropionic acid.
![[sigma]](http://journals.iucr.org/logos/entities/sigma_rmgif.gif){kind=small}
(C-C) = 0.003 Å
Alert level G
PLAT794_ALERT_5_G Check Predicted Bond Valency for Cu1 (2) 2.15
Alert level A
![[Figure 1]](http://journals.iucr.org/e/issues/2007/06/00/si2012/si2012fig1thm.gif)
![[Figure 2]](http://journals.iucr.org/e/issues/2007/06/00/si2012/si2012fig2thm.gif)
The N-hydroxy-2,2'-iminodipropionic acid (H3hidpa), HON(CH(CH3)COOH2, constitutes, in its basic form hidpa3-, the ligand in Amavadine (Berry et al., 1999), a natural bare vanadium(IV) complex [V(hidpa)2]2- which is present in some Amanita fungi and has been applied as an efficient catalyst in various alkane functionalization reactions (Reis et al., 2005). Hence, in pursuit of these and other studies, namely focusing on the self-assembly synthesis of copper(II) complexes with various N,O-ligands and their application in catalysis (Kirillov et al., 2006; Nesterov et al., 2006), we have attempted the preparation of the copper compound structurally related to Amavadine. However, the reaction of Cu(NO3)2×2.5H2O with H3hidpa in methanol and at room temperature resulted in the formation of the title compound, (I), due to the fragmentation of H3hidpa to give 2-hydroxyiminopropionate, HON=C(CH3)COO- (hipa). Such a type of fragmentation is unusual or even unknown, although other examples of H3hidpa fragmentations promoted by Re or Mo centres have already been described (Harben et al., 1997; Kirillov, Haukka et al., 2005). Herein we report the synthesis of compound (I) and its characterization by IR spectroscopy, elemental and low-temperature (100 K) single-crystal X-ray diffraction analyses.
The crystal structure of (I) (Fig. 1) is composed of discrete monomeric units, with a slightly distorted centrosymmetric octahedral geometry formed by two bidentate hipa ligands occupying equatorial sites and two water molecules in apical positions. Most of the bonding parameters in (I) (Table 1) agree with those of the related copper compounds (Malek et al., 2004; Dobosz et al., 1999) bearing hipa or derived moieties.
In (I), each water oxygen atom (O4) acts as both an intermolecular hydrogen-bond donor (to the carboxylate oxygen atoms O2 and O3) or acceptor (of hydrogen from the hydroxo oxygen O1) (Table 2), thus multiply linking the neighbouring mononuclear units and forming polymeric H-bonded chains (if seen along the a or b axis, Fig. 2a) or two-dimensional layers (if seen along the c axis, Fig. 2 b). These chains and layers are further extended by means of the weak intermolecular C2—H2C···O1 interactions resulting in a three-dimensional hydrogen bonded network.