Selective Crystallization of Linkage Isomers, [RhIII(NCS)(SCN)5]3- and [RhIII(SCN)6]3-, to Investigate Structural Trans Influence and Thermal Stability

Miki Mukai; Seiya Hagiwara; Rika Tanaka; Hiroyasu Tabe; Takashi Nakazono; Yusuke Yamada

doi:10.1021/acs.inorgchem.3c02292

Selective Crystallization of Linkage Isomers, [Rh^III(NCS)(SCN)₅]^3- and [Rh^III(SCN)₆]^3-, to Investigate Structural Trans Influence and Thermal Stability

Inorg Chem. 2023 Nov 6;62(44):18098-18107. doi: 10.1021/acs.inorgchem.3c02292. Epub 2023 Oct 20.

Authors

Miki Mukai¹, Seiya Hagiwara¹, Rika Tanaka^{1

2}, Hiroyasu Tabe³, Takashi Nakazono³, Yusuke Yamada^{1

3}

Affiliations

¹ Department of Chemistry and Bioengineering, Graduate School of Engineering, Osaka Metropolitan University, 3-3-138 Sugimoto, Sumiyoshi, Osaka 558-8585, Japan.
² Analytical Center of Osaka Metropolitan University, 3-3-138 Sugimoto, Sumiyoshi, Osaka 558-8585, Japan.
³ Research Center for Artificial Photosynthesis (ReCAP), Osaka Metropolitan University, 3-3-138 Sugimoto, Sumiyoshi, Osaka 558-8585, Japan.

PMID: 37862144
DOI: 10.1021/acs.inorgchem.3c02292

Abstract

Linkage isomers of homoleptic complexes, [Rh^III(SCN)₆]^3- and [Rh^III(NCS)(SCN)₅]^3-, formed in aqueous solution were successfully separated by employing methyltriphenylphosphonium (MePPh₃⁺) and 1-ethylquinolinium (EtQu⁺) ions as countercations, respectively. The single-crystal X-ray analysis of (MePPh₃)₃[Rh^III(SCN)₆] (1) indicated that all of the SCN^- ligands coordinate to the Rh^III ion by S atoms with an octahedral symmetry, where the average bond length of Rh-S is 2.374(7) Å. On the other hand, the Rh^III ion of (EtQu)₃[Rh^III(NCS)(SCN)₅]·H₂O (2) is coordinated by five S atoms and one N atom of the SCN^- ligands with a C_4v symmetry. Structural trans influence was observed in the shorter bond length of Rh-S at the trans position of Rh-N. The Rh-S bond length is 2.3398(13) Å significantly shorter than those of 1 by ca. 0.04 Å, although DFT calculations based on the crystal structures indicated that the effective bond order of Rh-N is higher than those of Rh-S. Thermal stability examination by thermogravimetric and differential thermal analyses (TG/DTA) and IR spectroscopy indicated that the linkage isomerization of [Rh^III(SCN)₆]^3- to [Rh^III(NCS)(SCN)₅]^3- proceeded after melting around 174 °C. These results clearly indicate that [Rh^III(NCS)(SCN)₅]^3- is thermodynamically more stable than [Rh^III(SCN)₆]^3- in solid states, although further linkage isomerization hardly occurs.