Crystal structure of aqua[N-(2-oxidobenzyl-κO)-l-leucinato-κ2 N,O](1,10-phenanthroline-κ2 N,N′)nickel(II) pentahydrate

The NiII atom in the title compound is in a distorted octahedral coordination geometry with two N atoms of the phenanthroline ligand, two O and one N atom of the 2-[(2-hydroxybenzyl)amino]-4-methylpentanoic acid ligand and one water molecule. In the crystal, the complex molecules and solvate water molecules are associated via O—H⋯O hydrogen bonds into a three-dimensional network.

In the title compound, [Ni(C 13 H 17 NO 3 )(C 12 H 8 N 2 )(H 2 O)]Á5H 2 O, the Ni II atom is in a distorted octahedral coordination environment provided by the two N atoms of one bidentate phenanthroline ligand and two O atoms and one N atom from a tridentate 2-[(2-hydroxybenzyl)amino]-4-methylpentanoic acid (HAMA) ligand and one water molecule. The complex was prepared by the reaction of nickel(II) nitrate with HAMA in the presence of 1,10-phenanthroline in a 1:1:1 ratio. In the crystal, the complex molecules and solvate water molecules are associated via O-HÁ Á ÁO hydrogen bonds into a threedimensional network.

Chemical context
Metal complexes of 1,10-phenanthroline (phen) and its derivatives are of increasing interest because of their versatile roles in many fields such as analytical chemistry (Chalk & Tyson, 1994), catalysis (Samnani et al., 1996), electrochemical polymerization (Bachas et al., 1997), and biochemistry (Sammes & Yahioglu, 1994). 1,10-Phenanthroline is a chelating bidentate ligand with notable coordination ability for transition metal cations. It is widely used in coordination chemistry, in particular, for the preparation of mixed-ligand complexes (Fritsky et al., 2004;Kanderal et al., 2005), and in the synthesis of polynuclear complexes and coordination polymers in order to control nuclearity and dimensionality by blocking a certain number of vacant sites in the coordination sphere of a metal ion (Fritsky et al., 2006;Penkova et al., 2010). Over the last few decades, the complex formation of transition metal ions with amino acids has also been studied extensively (Auclair et al., 1984). Amino acid-metallic ion interactions are found to be responsible for enzymatic activity and the stability of protein structures (Dinelli et al., 2010). Nickel is also essential for the healthy life of animals. It is associated with several enzymes (Poellot et al., 1990) and plays a role in physiological processes as a co-factor in the absorption of iron from the intestine (Nielsen et al., 1980). Any change in its concentration leads to metabolic disorder (Kolodziej, 1994). With the discovery of the biological importance of nickel, it is essential to study its complex formation with amino acids in order to understand more about the functions of their complexes.

Structural commentary
The Ni II ion in the title compound is in a distorted octahedral coordination environment provided by the two N atoms of one ISSN 2056-9890 bidentate phen ligand and two O atoms and one N atom from a tridentate anion of HAMA and one water molecule (Fig. 1).
The equatorial plane consists of two nitrogen atoms of 1,10phenanthroline and two oxygen atoms of the HAMA ligand. The axial positions are occupied by the nitrogen atom from the HAMA ligand and a water O atom. The equatorial Ni-N and Ni-O bond lengths are in the range 2.0383 (11)-2.1058 (13) Å , the axial Ni-N and Ni-O bond lengths are 2.1429 (14) and 2.1110 (12) Å . The coordination Ni-N and Ni-O bond lengths are typical for distorted octahedral Ni II complexes with nitrogen and oxygen donors (Fritsky et al., 1998;Moroz et al., 2012). The N1-Ni1-N2 and O2-Ni1-N3 bite angles are decreased to 79.43 (5) and 80.50 (5) as a consequence of the formation of the five-membered chelate rings. The C-C and C-N bond lengths in the organic ligands are well within the limits expected for those in aromatic rings (Petrusenko et al., 1997;Strotmeyer et al., 2003;Penkova et al., 2009).

Figure 2
A view of the O-HÁ Á ÁO hydrogen-bond interactions between the donor atoms of the water molecules and acceptor oxygen atoms of the phenolic and carboxylic groups and solvate water molecules in the crystal of the title compound (hydrogen bonds are shown as dashed lines; see Table 1 for details).

Synthesis and crystallization
The ligand 2-[(2-hydroxybenzyl)amino]-4-methylpentanoic acid (HAMA) was prepared by following procedure: l-Leucine (1.00 g, 6.71 mmol) and LiOHÁH 2 O (0.284 g, 6.77 mmol) in dry methanol (30 ml) were stirred for 30 min to dissolve. A methanolic solution of salicylaldehyde (1.44 g, 6.72 mmol) was added dropwise to the above solution. The solution was stirred for 1 h and then treated with sodium borohydride (0.248 g, 6.71 mmol) with constant stirring. The solvent was evaporated and the resulting sticky mass was dissolved in water. A cloudy solution was obtained, which was then acidified with dilute HCl and the solution pH was maintained between 5-7. The ligand precipitated as a colourless solid. The solid was filtered off, thoroughly washed with water and finally dried inside a vacuum desiccator. Yield 2.08 g (85%).
The title compound was prepared as follows: HAMA (0.500 g, 1.43 mmol) was deprotonated with LiOHÁH 2 O (0.060 g, 1.44 mmol) in 25 ml MeOH, which resulted in a clear colourless solution after 30 min. A methanolic solution of Ni(NO 3 ) 2 Á6H 2 O (0.17 g, 0.71 mmol) was added dropwise to the ligand with stirring. The colour of the solution changed to green immediately. The solution was stirred for 2 h and evaporated to dryness on a rotary evaporator. The blue solid obtained by adding acetonitrile was recrystallized as green plates by slow diffusion of diethyl ether into a methanolic solution of the crude solid over 2-3 days. The crystals were filtered off and washed with diethyl ether. Yield 74%.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The N-H hydrogen atoms were located in a difference Fourier map and freely refined. The O-H hydrogen atoms were also located in a difference Fourier map but constrained to ride on their parent atoms with U iso (H) = 1.5U eq (O). The C-bound H atoms were included in calculated positions and treated as riding atoms: with C-H = 0.95 Å and U iso (H) = 1.2-1.5U eq (C).

sup-2
Acta Cryst. (2015). E71, 195-198 Δρ min = −0.24 e Å −3 Absolute structure: (Flack, 1983), 2291 Friedel pairs Absolute structure parameter: 0.008 (7) 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 > 2sigma(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.