Bis(mercaptoimidazolyl)(pyrazolyl)hydroborato complexes of zinc, cadmium, and cobalt: Structural evidence for the enhanced tendency of zinc in biological systems to adopt tetrahedral M[S-4] coordination
C. Kimblin et al., Bis(mercaptoimidazolyl)(pyrazolyl)hydroborato complexes of zinc, cadmium, and cobalt: Structural evidence for the enhanced tendency of zinc in biological systems to adopt tetrahedral M[S-4] coordination, INORG CHEM, 39(19), 2000, pp. 4240-4243
The bis(2-mercapto-1-methylimidazolyl)(pyrazolyl)hydroborato derivatives [p
zBm(Me)](2)Zn, [pzBm(Me)](2)Co, and [pzBm(Me)](2)Cd have been isolated and
structurally characterized by X-ray diffraction. Despite their common [pzBm
(Me)](2)M composition, each of these complexes adopts a different structure
. Thus, (i) the zinc complex exhibits a tetrahedral Zn[S-4] structure in wh
ich only the sulfur donors coordinate to zinc, (ii) the cobalt complex exhi
bits a trigonal-bipyramidal Co[S3NH] structure in which one of the pyrazoly
l groups and one of the B-H groups coordinate to cobalt, and (iii) the cadm
ium complex exhibits a six-coordinate Cd[S4H2] structure in which both B-H
groups interact with the cadmium center. These comparisons emphasize that z
inc has a greater preference For tetrahedral M[S-4] coordination than does
either cobalt or cadmium, an observation that is in accord with the prevale
nt role of zinc in the structural sites of enzymes.