Diaqua[N-(5-nitro-2-oxidobenzylidene)glycinato]copper(II) dihydrate

In the title complex, [Cu(C9H6N2O5)(H2O)2]·2H2O, the CuII atom has a square-pyramidal coordination environment with a tridentate N-(5-nitro-2-oxidobenzylidene)glycinate Schiff base ligand and a water molecule in the basal plane. The apical site is occupied by an O atom from another coordinated water molecule. The crystal structure is stabilized by O—H⋯O hydrogen bonds, building a two-dimensional network parallel to (100).

In the title complex, [Cu(C 9 H 6 N 2 O 5 )(H 2 O) 2 ]Á2H 2 O, the Cu II atom has a square-pyramidal coordination environment with a tridentate N-(5-nitro-2-oxidobenzylidene)glycinate Schiff base ligand and a water molecule in the basal plane. The apical site is occupied by an O atom from another coordinated water molecule. The crystal structure is stabilized by O-HÁ Á ÁO hydrogen bonds, building a two-dimensional network parallel to (100).

Comment
Metal Schiff-base complexes derived from amino acids (or peptides) play an important role as key compounds for modeling more complicated PLP-amino acid Schiff bases (PLP = pyridoxal-5'-phosphate), as these are key intermediates in a variety of metabolic reactions involving amino acids, such as decarboxylation, transamination, racemization and C-C bond cleavage, which are catalyzed by enzymes that require PLP as a cofactor (Bkouche-Waksman et al., 1988;Wetmore et al., 2001;Zabinski & Toney, 2001). Considerable effort has been devoted to the preparation, structural characterization, appropriate spectroscopy and magnetic studies of Schiff-base complexes derived from salicylaldehyde and amino acids and reduced salicylidene amino acid (Ganguly et al., 2008), but little attention has been given to Schiff bases derived from nitro-substituted salicylaldehyde, and few structurally characterized complexes have been reported (Jammi et al., 2008).
Herein, we report the synthesis and structural study of a copper(II) complex with the Schiff base derived from glycine and 5-nitrosalicylaldehyde.
The title complex is characterized by a square-pyramidal Cu II coordination with a deprotonated tridentate Schiff base, 5-nitrosalicylideneglycinate, and a water molecule in the basal plane (Fig. 1). The Cu-N bond distance is 1.897 (4) Å. The two Cu-O bonds are 1.916 (3) and 1.930 (3) Å. The apical Cu1-O8 bond length is 2.447 (4) Å, which is little longer than that in the parent compound of this structure type, aqua(N-salicylideneglycinato)copper(II) hemihydrate [2.334 (6) Å] (Ueki et al., 1967). The phenyl ring (C1-C6) and the C1, C6, C7, N1, O1, Cu1 chelating ring are almost coplanar, with a small dihedral angle of 4.3 (4)°. Hydrogen bonds between the coordinated water molecules and the phenol O atoms of symmetry-related complex molecules lead to the formation of zigzag chains along the c axis (Table 1). Hydrogen bonds between the uncoordinated water molecules and carbonylate O atoms link the chains into a two-dimensional layer (Fig. 2).

Experimental
The title compound was prepared as follows: Glycine (10 mmol), 5-nitrosalicylaldehyde (10 mmol) and LiOH (20 mmol) were dissolved and refluxed in MeOH/H 2 O (v/v 1:1). CuCl 2 .2H 2 O (10 mmol) was then added to the solution and the resulting solution was adjusted to pH = 9-11. The mixture was stirred at room temperature for 24 h. Violet-blue precipitate that formed was filtered. The filtrate was allowed to evaporate slowly at room temperature. After several days, blue crystals suitable for X-ray diffraction were obtained.

Refinement
H atoms of water molecules were located in a difference Fourier map and refined with distance restraints of O-H = 0.85 (1) Å, and with U iso (H) = 1.2U eq (O). Other H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 (CH) and 0.97 (CH 2 ) Å and with U iso (H) = 1.2U eq (C).