The crystal structure of mercury tetrathiocyanate–copper diethylenediamine, [Hg(SCN)4][Cu(en)2]

Crystals of [Hg(SCN)4 ] [Cu(en)2 ] are monoclinic with: a ~-7.51, b ---18.03,c = 14.20 A,/3 ----96 ° 32'.The space group is P21/c with four molecules per unit cell containing four units of [Hg(SCN)4] [Cu(en)9.].The structure was determined by two-and three-dimensional Fourier methods, using the heavyatom technique.The two-dimensional analyses established the positions of the tIg, Cu and the four S atoms, and then from three-dimensional Fourier syntheses more accurate co-ordinates for all the atoms were obtained.The results are as follows: The four S atoms were found to be tetrahcdrally situated about the Hg atom but the thioeyanate groups themselves, which are placed at an angle to the Hg-S bonds, do not follow the tetrahedral arrangement of the S atoms.The (SCN) groups appear to be kinked at the C atom.Mean values of bond lengths and bond angles in the Hg(SCN)4 unit are:Hg-S -~ 2.55/~, S-C ----1-57 A, C-N = 1.34 ~.S-Hg-S = 109 ° 16', Hg-S-C ~-102 ° 5', S-C-N =-163 ° 12'.The Cu(en)~ grbups form two five-membered non-planar rings symmetrically placed about each copper atom, but with different orientation for the two crystallographically different copper atoms.Mean dimensions of the Cu(en) rings are: Cu-N----2-07 /~, N-C ----1-41 /~, C--C = 1.53 A, with N-Cu-N angle of about 80 °.Two N atoms of the (SCN) groups are co-ordinated to each Cu atom, thus giving it a total of sixfold co-ordination.This co-ordination direction is approximately at right angles to the plane containing the Cu and the amino N atoms.