A novel triruthenium nitrosyl bearing a quinolinic ligand: a comparison of its spectroscopic behavior with its pyridine analogues

• Published in: New journal of chemistry 2022-03, Vol.46 (10), p.4819-4826
• Main Authors: Santos, Nicolle Azevedo Portela dos, Silva, Amanda Batista, Silva, Camila Fontes Neves da, Alexiou, Anamaria Dia Pereira, Nikolaou, Sofia
• Format: Article
• Language: English
• Subjects: Acetonitrile; Anisotropy; Aromatic compounds; Carbonyl compounds; Carbonyls; Charge transfer; Infrared spectroscopy; Ligands; NMR; Nuclear magnetic resonance; Perturbation; Pyridines; Spectrum analysis; Ultraviolet radiation
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/D1NJ05849E

We present the novel compound [Ru 3 O(CH 3 COO) 6 (iq) 2 NO]PF 6 , iq = isoquinoline. Its electronic spectrum displays three charge-transfer bands between 350 and 550 nm and a band due to intra-cluster transitions centered at metallic levels at 701 nm (842 L mol −1 cm −1 ). This compound releases NO (g) under UV irradiation ( λ irrad = 365 nm), with ϕ = 0.23 in acetonitrile solution. Its 1 H NMR spectrum shows attenuated paramagnetic anisotropy of the [Ru 3 O] unit. As for IR spectroscopy, the ν (NO) stretching band (1904 cm −1 ) arises at a relatively high frequency, suggesting that the NO ligand has important NO + character. To understand the nature of the [Ru 3 O]–NO metallic core, we have compared the spectroscopic data of [Ru 3 O(CH 3 COO) 6 (iq) 2 NO]PF 6 with the data of pyridinic analogues bearing 4-acetylpyridine, 3-methylpyridine, pyridine, 4-methylpyridine, or 4- tert -butylpyridine as ancillary ligands. Except for the value of ν (NO), the introduction of a ligand (iq) bearing a second aromatic ring does not impact the other spectroscopic properties of the metallic core. The nitrosyl compounds with the general formula [Ru 3 O(CH 3 COO) 6 (L) 2 NO]PF 6 share similarities with both symmetric compounds ([Ru III Ru III Ru III O(CH 3 COO) 6 (L) 3 ]PF 6 ) and with the isoelectronic carbonyl compounds ([Ru III Ru III Ru II O(CH 3 COO) 6 (L) 2 CO]) and there is no clear evidence for the role of π-backbonding in their spectroscopic characteristics. These findings point to the presence of two metallic subunits: a {RuNO} 6 portion with high covalence and electron pairing, and thus less sensitivity to variations in L; and a second subunit, Ru 2 III,III , which is susceptible to perturbations to its electronic density by σ-donation from L. This analysis finally suggests that the triruthenium nitrosyl compounds constitute multiconfigurational systems with relevant contributions from both Ru III Ru III Ru III –NO 0 and Ru III Ru III Ru II –NO + configurations.