trans-Bis(acetato-κO)bis(2-aminoethanol-κ2 N,O)nickel(II)

In the title compound, [Ni(CH3CO2)2(C2H7NO)2], the NiII cation, located on an inversion center, is N,O-chelated by two 2-aminoethanol molecules and further coordinated by two monodendate acetate anions in a slightly distorted octahedral geometry. The latter is stabilized by intramolecular O—H⋯O hydrogen bonds involving the non-coordinated O atom of the acetate and the H atom of the hydroxy group of the 2-aminoethanol ligand. In the crystal, N—H⋯O hydrogen bonds link the molecules into a three-dimensional supramolecular framework that involves (a) the coordinated acetate O atom and one of the H atoms of the amino group and (b) the non-coordinated acetate O atom and the other H atom of the amino group.

In the title compound, [Ni(CH 3 CO 2 ) 2 (C 2 H 7 NO) 2 ], the Ni II cation, located on an inversion center, is N,O-chelated by two 2-aminoethanol molecules and further coordinated by two monodendate acetate anions in a slightly distorted octahedral geometry. The latter is stabilized by intramolecular O-HÁ Á ÁO hydrogen bonds involving the non-coordinated O atom of the acetate and the H atom of the hydroxy group of the 2aminoethanol ligand. In the crystal, N-HÁ Á ÁO hydrogen bonds link the molecules into a three-dimensional supramolecular framework that involves (a) the coordinated acetate O atom and one of the H atoms of the amino group and (b) the non-coordinated acetate O atom and the other H atom of the amino group.

Comment
The synthesis of the title compound is performed at room temperature under ambient conditions by substituting H 2 O of [Ni(CH 3 CO 2 ) 2 (H 2 O) 4 ] with 2-aminoethanol. As the title compound is water-free, stable under ambient conditions and well soluble in lower alcohols, it represents a cost effective precursor for the sol-gel synthesis of NiO-based nanostrutures.
The latter are of interest for switchable automobile mirrors and smart windows (Ozer & Lampert, 1998). Another application of the title compound is the synthesis of nanocomposite materials; nickel-polysilazane materials with ultrasmall and well dispersed nickel nanoparticles were obtained at room temperature in the reaction between the title compound and a polysilazane (Bazarjani et al., 2011). The title compound possesses significantly higher stability and higher solubility in lower alcohols when compared with a similar Ni II complex coordinated by two N,N-dimethylaminoethanol molecules, [Ni(CH 3 CO 2 ) 2 (C 4 H 11 NO) 2 ], which is air-sensitive . These differences are due to the -NH 2 group of the 2-aminoethanol ligand which is in the solid state hydrogen bonded to neighbouring [Ni(CH 3 CO 2 ) 2 (C 2 H 7 NO) 2 ] units and in solution it can get involved in hydrogen bonding with lower alcohols. The former results in the increased stability of the title compound, the latter is responsible for higher solubility of the title compound in alcohols (e.g. for methanol, compare 0.18 mol l -1 for the title compund to 0.10 mol l -1 for [Ni(CH 3 CO 2 ) 2 (C 4 H 11 NO) 2 ] at 25 °C). Figure 1 shows a perspective view of the Ni II coordination in the title compound; the atom numbering scheme, the interatomic distances and angles are also indicated. The distortion from octahedral symmetry is due to the slight deviation of the internal bite angle of the 2-aminoethanol ligands from 90°, i.e. 83.16 (9)° for N1-Ni1-O1 i , which is similar to that observed in [Ni(CH 3 CO 2 ) 2 (C 4 H 11 NO) 2 ] . The title compound is stabilized through inter-and intramolecular O-H···O and N-H···O hydrogen bonds similar to those of other supramolecular crystals of transition metal complexes (Desiraju, 1995(Desiraju, , 2007 (Figure 2, Table 1).
The geometry and coordination of the monodentate acetate group in the title compound is comparable to those in [Ni(CH 3  , in [Ni(CH 3  , and in [Ni(CH 3 CO 2 ) 2 (C 4 H 11 NO) 2 ] . The acetate groups are close to be fully ionized (CH 3 CO 2 -); as in a fully ionized acetate, the C-C-O angles (B and C in Figure 3) are about 115.7° and the O-C-O angle is about 126° (A in Figure 3, Table 2) . The length of the Ni-O(acetate) (  , [Ni(CH 3 CO 2 ) 2 (H 2 O) 4 ]  and [Ni(CH 3 CO 2 ) 2 (C 6 H 7 N 3 O) 2 (EtOH) 2 ] .

Experimental
Synthesis of title compound. 5.76 g of nickel (II) acetate tetrahydrate (>=99.0%, Sigma Aldrich) was added to 150 cm 3 absolute ethanol (>=98, Sigma Aldrich) and mixed with 4.24 g of ethanolamine (>=99.0%, Sigma Aldrich) in a molar supplementary materials sup-2 Acta Cryst. (2012). E68, m567-m568 ratio of 1:3. The resultant bluish solution was stirred in air for 24 h, paper filtered to remove any insoluble compounds and used for the crystallization of single crystals based on the following procedure: one third of the latter bluish clear solution was removed via distillation under vacuum at room temperature. The solution was kept at 5 °C for two weeks to grow the single crystals.

Refinement
The H atoms of the NH group and OH group were located in a difference map and later restrained to the distance N-H = 0.86 (2) Å and O-H = 0.82 (2) Å. The other H atoms were positioned with idealized geometry using a riding model with C-H = 0.93-0.97 Å. All H atoms were refined with isotropic displacement parameters (set to 1.2 times of the U eq of the parent atom).    Geometry of the monodentate acetate group. For values of bond lengths a and b and bond angles A, B and C see Table 2.

Special details
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.