Diruthenium and triruthenium compounds of the potential redox active non-chelated η1-N,η1-N-benzothiadiazole bridge

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 51; no. 22; pp. 8657 - 8670
• Main Authors: Dey, Sanchaita, Arijit Singha Hazari, Mobin, Shaikh M, Lahiri, Goutam Kumar
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 07.06.2022
• Subjects: Charge transfer; Coordination compounds; Crystal structure; Electron paramagnetic resonance; Electrons; Free radicals; Infrared analysis; Refluxing; Single crystals
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d2dt00533f

In the present study, a series of non-chelated BTD (2,1,3-benzothiadiazole)-bridged diruthenium(ii) ([{(CH3CN)(acac)2RuII}2(μ-BTD)] 1, [{CH3CN(acac)2RuII}(μ-BTD){RuII(acac)2(η1-N-BTD)}] 2, [{(η1-N-BTD)(acac)2RuII}2(μ-BTD)] 3), and triruthenium ([{(acac)2RuII}3(μ-BTD)2(η1-N-BTD)2] 4) complexes with varying ratios of η1-N and μ-bis-η1-N,η1-N modes of BTD were studied. Complexes 1–4 (S = 0) were obtained via the one-pot reaction of electron-rich Ru(acac)2(CH3CN)2 and electron-deficient BTD in refluxing acetone. The relatively low Ru(ii)/Ru(iii) potential of 1–4 (0.08–0.44 V versus SCE) further facilitated the isolation of the corresponding mixed valent RuIIRuIII (S = 1/2) and RuIIRuIIRuIII (S = 1/2)/RuIIRuIIIRuIII (S = 1) forms [1]ClO4–[3]ClO4 and [4]ClO4/[4](ClO4)2, respectively. The single-crystal X-ray structures of the representative mixed valent [1]ClO4 and [3]ClO4 established (i) Ru⋯Ru distances of 6.227 Å and 6.256 Å (molecule A)/6.184 Å (molecule B), respectively, (ii) a significant variation of the N–S distance of BTD in [3]ClO4 as a function of its binding mode μ versus η1 and (iii) similar Ru–N (μ-BTD) distances in each case corresponding to a valence delocalised situation. The mixed valent diruthenium (1+–3+) and triruthenium (4+/42+) complexes exhibited metal-based anisotropic electron paramagnetic resonance (EPR) and moderately intense low-energy intervalence charge-transfer (IVCT) transitions in the near-infrared region of 1730–1890 nm. Analysis of the IVCT band using the Hush treatment revealed a valence delocalised class III mixed valent state with the electronic coupling Vab of ≈2640–2890 cm−1, as also corroborated by the Kc values of 105–108, solvent independency of the IVCT band and uniform spin distribution between the metal ions in the singly occupied state(s). Furthermore, the involvement of the BTD (η1 and μ)-based orbitals in the reduction processes was evident by its free radical EPR feature.