Nickel(II) N2X2 Schiff-base complexes incorporating pyrazole (X = NH, O or S): syntheses and characterization †
| Autor: | Agnete la Cour, Carl Erik Olsen, Rita G. Hazell, Susie M. Miller, Bibhutosh Adhikhari, Oren P. Anderson, Hans Toftlund |
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| Rok vydání: | 1997 |
| Předmět: | |
| Zdroj: | Journal of the Chemical Society, Dalton Transactions. :4539-4548 |
| ISSN: | 1364-5447 0300-9246 |
| DOI: | 10.1039/a703258g |
| Popis: | A series of four-co-ordinate nickel(II) N2X2 complexes (X = NH, O or S) with tetradentate Schiff-base ligands incorporating pyrazole has been prepared in order to compare the influence on the nickel(II) centre of the donor atoms in N2(NH)2 and N2S2 complexes versus N2O2 complexes. In each case, two identical parts of the ligand are linked by a two- or three-carbon aliphatic chain (n = 2 or 3). Crystal structures have been determined for a n = 3 N2(NH)2 complex, for two n = 3 N2S2 complexes and for a n = 2 N2O2 complex. All of the complexes have been investigated in solution by spectroscopic methods (UV/VIS/NIR, 1H NMR). The n = 2 and 3 N2(NH)2 complexes and the n = 2 N2S2 complexes are fully diamagnetic. An extension of the chain linking the two halves of the ligand from two to three carbon atoms induces a spin-equilibrium process (S = 0 ⇄ S = 1) for the resulting N2S2 complex (ΔG = 19–26 kJ mol–1 at 50 °C). Ligand-field parameters have been derived from the electronic spectra and the electrochemical properties of the N2S2 complexes have been investigated by cyclic voltammetry. From these results it is clear that low-spin character is emphasized in N2(NH)2 and N2S2 complexes of nickel(II) when compared with the corresponding N2O2 complexes. |
| Databáze: | OpenAIRE |
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