[N,N′-Bis(2,3,4-trimethoxybenzylidene)ethane-1,2-diamine-κ2 N,N′]dibromidomercury(II)

In the title compound, [HgBr2(C22H28N2O6)], the HgII ion is bonded to two Br− ions and two N atoms of the chelating Schiff base ligand in a distorted tetrahedral geometry. The Schiff base ligand adopts an E,E conformation. The dihedral angle between the planes of the two halves of the central N,N′-dimethylethylenediamine part of the ligand is 2.3 (11)°. The crystal studied was twinned by pseudomerohedry [twin law (0-10/-100/00-1)]; the contribution of the minor twin component refined to 0.208 (3).


Experimental
To a stirring solution of the (2,3,4-MeO-ba) 2 en ligand (0.2 mmol, in 5 ml of chloroform) was added HgBr 2 (0.2 mmol) in 10 ml of methanol and the mixture was stirred for 10 min in air at room temperature and was then left at 273 K for several days without disturbance yielding suitable crystals of (I) that subsequently were filtered off and washed with

Refinement
The hydrogen atoms were added geometrically, with a C-H distance of 0.96 Å, and refined as riding on their parent atoms. The methyl H atoms were allowed to rotate freely about the adjacent C-C bonds. The thermal displacement coefficients U iso (H) were set to 1.5U eq (C) for the methyl groups and to to 1.2U eq (C) for the CH-and CH 2 -groups. The structure of (I) can also be refined in space group C2/c with unit cell parameters of a = 10.332 Å, b =11.6601 Å, c = 21.1957 Å, β=95.017 ° to a relatively good R value of 0.055. In the monoclinic structure model two halves of the structure are symmetry-equivalent as found in the 1 H-NMR solution spectra. However, the true crystal symmetry is triclinic due to small rotations of aromatic rings as well as methyl groups.
The lowering of symmetry can be indicated by comparison of R int factors which are 0.035 for triclinic symmetry but almost 0.1 for monoclinic symmetry. In order to test that the triclinic structure model does not contain hidden monoclinic symmetry we used a simulated data set based on the refined triclinic structure, transformed to the twofold monoclinic unit cell and merged according to the monoclinic Laue group. The obtained R int of 0.1 was in agreement with the value found experimentally and confirmed the fact that tiny rotations of methyl groups and aromatic rings are responsible for lowering of symmetry from monoclinic to triclinic. Twofold rotation along b was used as the twinning operation, which became (0 1 0 / 1 0 0 / 0 0 1) after transformation to the final triclinic unit cell (the matrix acts to indices as columns).
The refined twin ratio of the second twin domain was 0.208 (3).
The highest residual electron density of 1.46 e Å -3 was located 1.814 (13) Å from C9; the deepest hole of -1.48 e Å -3 was located 2.187 (13) Å from C9.  Special details Refinement. The refinement was carried out against all reflections. The conventional R-factor is always based on F. The goodness of fit as well as the weighted R-factor are based on F and F 2 for refinement carried out on F and F 2 , respectively. The threshold expression is used only for calculating R-factors etc. and it is not relevant to the choice of reflections for refinement. The program used for refinement, Jana2006, uses the weighting scheme based on the experimental expectations, see _refine_ls_weighting_details, that does not force S to be one. Therefore the values of S are usually larger than the ones from the SHELX program.