Bis(acetato-κO)bis(4,5-dimethylbenzene-1,2-diamine-κN)zinc

The structure of the title compound, [Zn(CH3COO)2(C8H12N2)2], has one half molecule in the asymmetric unit. The ZnII atom is situated on a twofold rotation axis and is tetrahedrally coordinated by two N and two O atoms. The crystal packing displays intermolecular N—H⋯O hydrogen bonds and intramolecular N—H⋯O and N—H⋯N hydrogen bonding.

The structure of the title compound, [Zn(CH 3 COO) 2 -(C 8 H 12 N 2 ) 2 ], has one half molecule in the asymmetric unit. The Zn II atom is situated on a twofold rotation axis and is tetrahedrally coordinated by two N and two O atoms. The crystal packing displays intermolecular N-HÁ Á ÁO hydrogen bonds and intramolecular N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonding.

Related literature
For the role of complexes in biochemical systems with zinc in tetrahedral coordination, see: Parkin (2004); Maret & Li (2009). For the structure of the corresponding 1,2-diaminobenzene complex, see: Mei et al. (2009). For an example of a structurally characterized tetramine complex with zinc in tetrahedral coordination, see: Xu et al. (1998). For an example carboxylate coordination in a similar complex, see: Harding (2001).

Comment
Tetrahedrally coordinated zinc complexes play important structural (e.g., zinc fingers) and catalytic (e.g., carbonic anydrase) roles in biochemical systems (Parkin 2004, Maret & Li 2009). Although coordination via three amino acid residues (Zn-N coordination) and a water or hydroxide ligand is the most common coordination motif, carboxylate

Refinement
The structure was originally solved in the non-centrosymmetric space group Cc because the mean |E*E-1| statistic was 0.745. The structure refined to R 1 = 0.051. However, many atoms displayed disc-shaped thermal ellipsoids and one of the nitrogen atoms coordinated to the zinc became nonpositive definite. Inverting the structure gave no improvement. Using TWIN resulted in a refined BASF of 0.49 with no significant improvement in the R 1 value (0.048) or thermal parameters (the nitrogen remained nonpositive definite). The structure was subsequently solved and successfully refined in the centrosymmetric space group C2/c, which resulted in a lower R 1 (0.0363)and much improved behavior of the thermal parameters. All H atoms atoms were found in difference fourier maps. Hydrogen atoms bonded to carbon atoms were refined using a riding model (AFIX 43 for aromatic C-H and AFIX 137 for methyl groups). The atomic coordinates and isotropic thermal parameters of all amine hydrogen atoms were refined.

Figure 1
Perspective view of the title compound with displacement ellipsoids of non-hydrogen atoms drawn at the 50% probability level.

Figure 2
Perspective view of the title compound displaying the intramolecular hydrogen bonding.  View of the unit cell of the title compound down the b axis displaying the intermolecular hydrogen bonding network. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq