Osmium(II) complexes bearing C,N,C-pincer ligand 2,6-bis(alkylimidazolin-2-ylidene)pyridine (CNC-Me and CNC-Bu for alkyl = methyl and n-butyl, respectively) or 2,6-bis(3-butylbenzimidazolin-2-ylidene)pyridine (CNC 0 -Bu) and aromatic diimine (2,2 0 -bipyridine (bpy)/1,10-phenanthroline (phen)) have been prepared. The X-ray crystal structure of [Os(CNC-Me)(bpy)Cl](PF 6 ) shows that the Os-C bonds are essentially single (Os-C distances = 2.042(4) and 2.059(4) A ˚). Spectroscopic comparisons of [Os(C,N,C)(diimine)Cl] þ and [Os(tpy)(bpy)Cl] þ (tpy = 2,2 0 ;6 0 ,2 00terpyridine) suggest that the lowest-energy absorption bands for [Os(C,N,C)(diimine)Cl] þ originate from a d π (Os II ) f π*(diimine) metal-to-ligand charge-transfer (MLCT) transition. Density functional theory calculations reveal that the π*(diimine) levels in [Os(C,N,C)(diimine)Cl] þ are lower lying than the π*(C,N,C). The Os(II/III) oxidation waves for [Os(C,N,C)(diimine)Cl] þ are reversible, with E 1/2 = -0.03 to 0.16 V vs Cp 2 Fe þ/0 . The absorption spectra for the Os(III) species have been obtained by spectroelectrochemical methods.

Ruthenium-methoxycarbene and -allenylidene complexes bearing 1,4,7-trimethyl-1,4,7-triazacyclononane (Me 3 Tacn) and 1,10-phenanthroline (phen), [(Me 3 Tacn)(phen)RudC(OMe)R] 2+ (R ) CH 2 Ph (1), CHdCPh 2 (2), CHdC(C 6 H 4 Cl-4) 2 (3), CHdC(C 6 H 4 Me-4) 2 ( 4)), and [(Me 3 Tacn)(phen)Rud CdCdCR 2 ] 2+ (R ) Ph (5), C 6 H 4 OMe-4 (6)) have been prepared. The molecular structures of 1(PF 6 ) 2 and 2(PF 6 ) 2 reveal Ru-C distances of 1.917(3) and 1.906(4) Å, respectively. The lowest-energy dipoleallowed absorptions for complexes 1-4 (λ max ≈ 435 nm) are assigned as d π (Ru II ) f π*(phen) metalto-ligand charge transfer (MLCT) transitions, while those for complexes 5 and 6 (λ max ) 530 and 585 nm, respectively) are assigned as metal-perturbed π-π* [RudCdCdCR 2 ] intraligand transitions. Complexes 1-4 are emissive in glassy MeOH/EtOH at 77 K: excitation at λ ) 430 nm produces emission at λ max ) 570-620 nm, which are tentatively assigned as d π (Ru II ) f π*(phen) 3 MLCT in nature. Density functional theory (DFT) calculations, charge decomposition analysis (CDA), and natural bond orbital (NBO) analysis on complexes 1, 2, 5, and 6 suggest that allenylidene ligands are better electron donors and poorer acceptors compared with methoxycarbene ligands, and the Ru-C interactions in ruthenium-allenylidene and -methoxycarbene complexes can be depicted by the polarized formulation Ru δ+ dC δand nonpolarized formulation RudC, respectively. The methoxycarbene/allenylidene rotational barriers on 1, 2, and 5 are calculated to be 8.3, 6.3, and 1.5 kcal mol -1 , respectively.

Ruthenium(II)−isocyanide complexes bearing cyclic tridentate amine/thioether (1,4,7-trimethyl-1,4,7-triazacyclononane, Me3Tacn/1,4,7-trithiacyclononane, [9]aneS3) and aromatic diimine (1,10-phenanthroline, phen/2,2′-bipyridine, bpy) have been prepared. The molecular structures of [(Me3Tacn)(bpy)Ru(t-BuNC)]2+, [([9]aneS3)(phen)Ru(t-BuNC)]2+, and the nitrile-ligated congener [(Me3Tacn)(phen)Ru(CH3CN)]2+ show that the Ru−C distances in the isocyanide complexes are sensitive to the electron richness of the metal center, and isocyanide has a stronger trans influence than nitrile. The lowest-energy dipole-allowed absorptions for the isocyanide and nitrile complexes (λmax = 330−405 and 417−458 nm, respectively, εmax = (3−6) × 103 dm3 mol−1 cm−1) are assigned as dπ(RuII) → π*(diimine) metal-to-ligand charge transfer (MLCT) transitions. These complexes are emissive in glassy MeOH/EtOH at 77 K upon photoexcitation and give emission at λmax = 477−601 nm. Density functional theory (DFT) calculations and charge decomposition analysis (CDA) have been used to compare the σ-donating and π-accepting abilities of nitrile and different organometallic ligands including isocyanide, methoxycarbene, and allenylidene. The molecular structure of the cofacial bioctahedral complex [(Me3Tacn)Ru(μ-Cl)3Ru(Me3Tacn)]+ has also been determined, and the Ru···Ru distance has been found to be 3.1842(6) Å.

Novel phosphorescent conjugated oligo(phenylene-ethynylene)s featuring a central tunable platinum(II) Schiff base signalling unit with promising photophysical properties have been investigated to pave their development towards polymeric congeners for sensing applications.

Ruthenium(II)-acetylide complexes bearing 1,4,7-trithiacyclononane ([9]aneS3) and 1,10-phenanthroline (phen) have been prepared. The molecular structure of [([9]aneS3)(phen)Ru-CtCPh] þ shows that the trans influence of the acetylide ligand is only slightly weaker than that of isocyanide and is stronger than that of chloride. The Ru(II/III) oxidation waves for the complexes are irreversible, with E pa = 0.30-0.39 V vs Cp 2 Fe þ/0 . The lowest-energy dipole-allowed absorptions for the complexes (λ max = 441-466 nm, ε max = (4-5) Â 10 3 dm 3 mol -1 cm -1 ) are assigned as d π (Ru II ) f π*(phen) metal-to-ligand charge transfer (MLCT) transitions. The complexes are emissive in glassy MeOH/EtOH at 77 K upon photoexcitation and give emission at λ max = 606-623 nm. Density functional theory (DFT) calculations and charge decomposition analysis (CDA) have been used to probe the Ru-C bonding interaction in these complexes, and the results are compared with their isocyanide congeners. The rotational barrier for the phenyl ring in [([9]aneS3)(phen)Ru-CtCPh] þ is calculated to be 0.53 kcal mol -1 , suggesting that the Ru-C π-interaction in these complexes is weak and cannot lock the rotational motion of the acetylide ligand effectively.