Symbiosis versus antisymbiosis: a study of the thiocynate bonding mode in trans-hydridothiocyanatotetrakispiperidineiridium(III) thiocyanate and tetraphenylborate
✍ Scribed by G.H. Weddle; J.L. Burmeister; E.R. Birnbaum
- Publisher
- Elsevier Science
- Year
- 1976
- Tongue
- English
- Weight
- 553 KB
- Volume
- 18
- Category
- Article
- ISSN
- 0020-1693
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✦ Synopsis
Examples of symbiotic and antisymbiotic behavior involving ambidentate ligands such as the NCS ion have thus far been restricted to, respectively, octahedral complexes of class 'a' metals and square planar complexes of class 'b' metals. In the latter case, only the strong trans-influence of n-acid ligands has heretofore been observed to cause antisymbiosis. The title complex was chosen for study because it involves an octahedral complex of an ambidentate l&and and a class 'b' metal (re: [Ir(SCN)6]3-) wherein the former is subjected to the strong trans-influence of a ligand which can only function as a o-base. In the solid state, antisymbiosis is demonstrated by the stability of the N-bound trans-[Ir(pip),H(NCS)]NCS, and counteranion control by the synthesis and stability of the S-bound isomer as the BPh, salt. When trans-[Ir(pip),(NCS)(H)]NCS or its BPh,-salt is put into solution, IR studies indicate that N-bonding initially prevails in solution, irrespective of solvent dielectric. The prolonged aging of methylene chloride solutions of either trans-]Ir(pip)4(NCS) (H)] NCS or of trans-[Ir(pip),(SCN)(H)]BPh, produces the soluble cation trans-[Ir(pip),(SCN),]+. The YCN frequency of the noncoordinated NCS is remarkably sensitive to the solvent dielectric, suggesting the existence of H-bonding to the amine proton of the piperidine ligands in the low dielectric solvents. NMR data support the existence of a mixture of six-and seven-coordinate species in all solvents for the NCS salt, as a consequence of the observation for each solution of a doublet hydride resonance. Solutions of the BPh, salt, on the other hand, exhibit only a single hydride resonance, indicating the presence of only a six-coordinate moiety.