Divalent zinc triad metal ion complexes of type M(L)2(ClO4)2 (L = N-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine) with N4S2 metal coordination spheres were isolated and characterized by X-ray crystallography and variable temperature proton NMR. Although bis-tridentate chelates have nine geometric isomers, the crystallographically characterized complexes of all three metal ions had trans facial octahedral coordination geometry with Ci symmetry. Despite the low coordination number and geometric preferences of d10 metal ions, which facilitate inter- and intramolecular exchange processes, dilute solutions of these bis-tridentate chelates exhibited slow geometric isomerization. Symmetry, sterics and shielding arguments supported specific isomeric assignments for the major and minor chemical shift environments observed at low temperature. At elevated temperature, rapid intramolecular exchange occurred for all three complexes but slow intermolecular exchange on the coupling constant time scale was evidenced through detection of JHgH interactions for Hg (L)22 +. These unusual observations are discussed in the context of the zinc triad metal ion coordination chemistry of related bis-tridentate chelates.
Bibliographical noteFunding Information:
This work was supported in part by the Petroleum Research Fund under Grant 40151-B3, the US National Science Foundation Division of Chemistry under Grant 0315934, the National Institutes of Health Academic Research Enhancement Aware 1 R15 GM59043-01 and the Jeffress Memorial Trust under J-627. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. We also thank the Camille and Henry Dreyfus Foundation for a Scholar/Fellow award to D.C.B. for support of S.M.B. and the research, as well as a Jean Boissevain Dreyfus Undergraduate Scholarship for S.MS. R.J.B. acknowledges the DoD-ONR instrumentation program for funds to upgrade the diffractometer and the NIH-MBRS program for funds to maintain the diffractometer. The authors are also thankful for the help of Louise Menges in preparing Fig. 6 and for many helpful discussions with Christopher Abelt.
- Bis-tridentate chelate
- Group 12
- Single crystal X-ray structure