Tris(imidazolyl) cadmium and zinc complexes: structural and spectroscopic characterization of M–OH2 motifs
Monomeric aqua complexes of Cd and Zn coordinated by a tris(imidazolyl) ligand are reported. The molecular structures are characterized by trigonal pyramidal metal ion coordination and hydrogen-bonding between the bound water molecule and the noncoordinating counter ions.
Introduction
The tris(pyrazolyl)hydroborato ligand, [TpR,R′], developed by Jerry Trofimenko more than 35 years ago [1], [2] has found great utility as a scaffold for modeling a number of important metallobiochemistry motifs [2], [3], [4]. The tripodal [N3] donor environment of the ligand mimics the nitrogen-rich ligation sphere found at the active site of numerous non-heme proteins. Leading examples include Kitajima’s dicopper peroxo complex [5], [(Tp2iPr)Cu]2(O2) and Parkin’s and Vahenkamp’s [TpR,R′]Zn(OH) species [6]. The former was prepared and authenticated as a structural and spectroscopic precedent of the oxygenated form of the O2-binding protein hemocyanin in advance of evidence of such μ-η2:η2-O2 coordination at the protein active site [7]. The mononuclear zinc hydroxide species provided the opportunity to assess the inherent nucleophilicity, and more recently, basicity [8] of a [N3]Zn(OH) species. Inherent in each of these examples is the utility of systematic variation of the pyrazole substituents in controlling structure and reactivity at the attendant metal complexes, clearly one of the strengths of the [Tp] ligand family.
Recently, we have prepared a new tris(imidazolyl)-based cavitand ligand and reported aspects of its coordination chemistry with copper(I) [9]. The ligand, TriMIm,1 is preorganized to ligate a single metal ion in a trigonal planar array of imidazoles. The enforced geometry is distinct from the [Tp] ligands where more acute N–M–N angles are observed. Herein, we report the synthesis and structural characterization of cadmium- and zinc-aqua complexes, [(TriMIm)M(OH2)]2+.
Section snippets
Materials
2-Mercapto-1-methylimidazole, NaH, MgSO4, Cd(BF4)2 · 6H2O, Cd(NO3)2 · 4H2O, Zn(BF4)2 · xH2O, and Zn(NO3)2 · 6H2O were used as supplied by commercial vendors. [Cu(MeCN)4]BF4 [10], and TriMIm [9] were prepared according to literature procedures. Pentanes, tetrahydrofuran, and diethyl ether were freshly distilled from sodium/benzophenone. Methylene chloride was freshly distilled from calcium hydride. Acetone was freshly distilled over MgSO4. Acetonitrile (UV Grade) was purchased from Burdick and Jackson
Synthesis of Cd and Zn aqua complexes
Reaction of equimolar mixtures of TriMIm and a hydrated metal salt in the appropriate solvent yielded the corresponding monomeric metal aqua complex, [(TriMIm)M(OH2)]X2 (M=Cd, X=BF4 (1); M=Zn, X=BF4 (4) and M=Zn, X=NO3 (5)), in moderate to good yields as a white, microcrystalline solid. The materials possess good solubility in acetone, acetonitrile, and methanol but, are only sparingly soluble in hydrocarbons and chlorinated solvents. Spectroscopic (1H, 13C NMR, FT-IR) and combustion analytical
Acknowledgements
We thank the National Institutes of Health (GM-59191) for support of this work.
References (27)
- et al.
Inorg. Chim. Acta
(1995) - et al.
J. Mol. Biol.
(1992) - et al.
J. Mol. Biol.
(1994) - et al.
J. Inorg. Biochem.
(1993) - et al.
Polyhedron
(1998) J. Am. Chem. Soc.
(1966)Scorpionates – The Coordination Chemistry of Polypyrazolylborate Ligands
(1999)- et al.
Prog. Inorg. Chem.
(1995) Chem. Commun.
(2000)- et al.
J. Am. Chem. Soc.
(1992)
Inorg. Chem.
Proteins
J. Am. Chem. Soc.
Cited by (13)
Zinc in Biology
2013, Comprehensive Inorganic Chemistry II (Second Edition): From Elements to ApplicationsSynthesis, crystal structure and photoluminescence of a new Cd(II) coordination polymer with unusual geometry
2010, Inorganic Chemistry CommunicationsAlcohol dehydrogenase and its simple inorganic models
2010, Coordination Chemistry ReviewsVibrational and electronic circular dichroism study of bile pigments: Complexes of bilirubin and biliverdin with metals
2009, Analytical BiochemistryCitation Excerpt :Highly chelating BV binds strongly to Zn in aqueous solution, preventing precipitation of Zn(OH)2 at high pH and allowing characterization of the species [Zn(BV)OH]. Zn forms five-coordinate complexes, with the BV ligand occupying four coordination sites [37–39] and the fifth site being occupied by water or a hydroxo group. An excess of Zn does not cause further variation in the absorption or ECD signals.
Metallosupramolecular zinc and cadmium complexes of Bis[4-(2-pyridyl)pyrimidinylthiomethyl]benzenes
2008, Journal of Molecular Structure