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.
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.
Kimblin
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Department of Chemistry, Columbia University, New York, New York 10027, USA.
Bridgewater
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Churchill
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Hascall
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Parkin
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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*
D011720:Pyrazoles; D017967:Zinc Compounds; D002104:Cadmium; D005031:Ethylenethiourea; D003035:Cobalt; C077232:2-mercaptoimidazole