title: Structure and isomerization comparison of Zn(II), Cd(II) and Hg(II) perchlorate complexes of 2,6-bis([(2-pyridyl-methyl)amino]methyl)pyridine.
abstract: The divalent zinc triad perchlorate coordination chemistry of 2,6-bis([(2-pyridyl-methyl)amino]methyl)pyridine (L) was investigated by X-ray crystallography and solution state (1)H NMR. New complexes [HgL(ClO4)2] (1) and [CdL(ClO4)2] (2) were isolated as bicapped distorted square pyramidal racemates, contrasting with the approximate trigonal bipyramidal structure of [ZnL](ClO4)2 (3). Although rapid inter- and intramolecular exchange is common for simple complexes of zinc triad metal ions, conditions for slow intramolecular isomerization on both the δ and J(HH) time scales were established for 1, 2 and 3. Trends in geminal (1)H coupling suggested that an asymmetric structure was favored for all three metal ions at or below 40 °C. Contributions of a symmetric structure to solution equilibria were both temperature- and metal ion-dependent. Spectral trends were consistent with interconversion of a pair of enantiomeric square pyramidal ligand conformers through a symmetric trigonal bipyramidal ligand conformer by M-N bond cleavage and nitrogen inversion. Racemization was slower than the coupling constant time scale up to 40 °C for all complexes. Differential stabilization of specific small ligand conformations in solution has potential toxicological significance.
authors: Department of Chemistry, The College of William & Mary, Williamsburg, VA, USA. dcbebo@wm.edu.
authors: Bradley J
authors: BJ
authors: Carra
authors: Steven M
authors: SM
authors: Berry
authors: Robert D
authors: RD
authors: Pike
authors: Deborah C
authors: DC
authors: Bebout
mesh_terms: D002104:Cadmium / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D013237:Stereoisomerism; D015032:Zinc / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D009942:Organometallic Compounds; D011725:Pyridines; D002104:Cadmium; D008628:Mercury; D015032:Zinc