Abstract
Neutral Hg2Cl4L (1), Hg2Br4L·dimethylformamide (2) and Hg2I4L (3) are synthesized where L is the 1:2 condensate of 1,2-diaminoethane and 1-methyl-2-imidazolecarboxaldehyde. X-ray crystal structures show that 1 and 3 are dinuclear with a distorted tetrahedral N2X2 (X=Cl or I) coordination sphere for Hg. Complex 2 is a one-dimensional polymer with bromide bridges. The metal has a square pyramidal (N2Br3) environment in all three complexes. Complexes 1–3 are reacted with R4NX (R=Me, Et or n-Butyl; X=Cl−, Br− or I−). While 1 and 3 show no reactions, 2 gives a crystalline complex (4) only when R=n-Bu and X=Br−. Complex 4 is ionic containing two independent n-Bu4N+ cations and two independent halves of centrosymmetric Hg2Br6L2− anions. The observed crystallisation of the anion Hg2Br6L2− only with the cation n-Bu4N+ and not with Me4N+ or Et4N+ is a consequence of Basolo’s principle of crystallisation of ionic salts which insists on the matching of the sizes of the counter ions. Though the size of the cation n-Bu4N+ matches with the hypothetical chloride and iodide analogues of 4, they are not formed. This is because while 2 has a tendency to increase the coordination number of Hg (as it polymerises), 1 and 3 do not show any such tendency.
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