title: 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[S4] coordination.
abstract: The bis(2-mercapto-1-methylimidazolyl)(pyrazolyl)hydroborato derivatives [pzBmMe]2Zn, [pzBmMe]2Co, and [pzBmMe]2Cd have been isolated and structurally characterized by X-ray diffraction. Despite their common [pzBmMe]2M composition, each of these complexes adopts a different structure. Thus, (i) the zinc complex exhibits a tetrahedral Zn[S4] structure in which only the sulfur donors coordinate to zinc, (ii) the cobalt complex exhibits a trigonal-bipyramidal Co[S3NH] structure in which one of the pyrazolyl groups and one of the B-H groups coordinate to cobalt, and (iii) the cadmium complex exhibits a six-coordinate Cd[S4H2] structure in which both B-H groups interact with the cadmium center. These comparisons emphasize that zinc has a greater preference for tetrahedral M[S4] coordination than does either cobalt or cadmium, an observation that is in accord with the prevalent role of zinc in the structural sites of enzymes.
authors.affiliation: Department of Chemistry, Columbia University, New York, New York 10027, USA.
authors.forename: C
authors.initials: C
authors.lastname: Kimblin
authors.forename: B M
authors.initials: BM
authors.lastname: Bridgewater
authors.forename: D G
authors.initials: DG
authors.lastname: Churchill
authors.forename: T
authors.initials: T
authors.lastname: Hascall
authors.forename: G
authors.initials: G
authors.lastname: Parkin
mesh_terms: D002104:Cadmium / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D005031:Ethylenethiourea / Q000031:analogs & derivatives* / Q000737:chemistry*; D015394:Molecular Structure; D011720:Pyrazoles / Q000737:chemistry; D017967:Zinc Compounds / Q000737:chemistry*
chemical_list: D011720:Pyrazoles; D017967:Zinc Compounds; D002104:Cadmium; D005031:Ethylenethiourea; D003035:Cobalt; C077232:2-mercaptoimidazole