Theoretical Studies of [Os3(CO)10(α-Diimine)]: Structures, Frontier Orbitals and Bonding

Abstract

DFT calculations were performed on Os 3 (CO) 10 (α-diimine) clusters, for α-diimine = DAB (1,4-diaza-1,3-butadiene), PYCA (σ-N,σ-NЈ-pyridine-2-carbaldehyde-imine), and BIPY (2,2Ј-bipyridine). Geometry optimizations were performed for several models of the possible isomers under different conditions. Axial isomers were always found to be the most stable, in agreement with the available X-ray determined structures. A full optimization of the geometry was required in order to improve the quality of the results, but the dis-

Bonding and Redox Properties of [Os3(CO)9(tmbp)(L)] (tmbp=4,4′,5,5′-tetramethyl-2,2′-biphosphinine; L=CO, PPh3) Clusters with an Unprecedented Electron-Deficient Metallic Core and Doubly Bridging Biphosphinine Dianion

“…The four OsÀP bonds (2.477, 2.536, 2.426 and 2.485 ä) are also longer than the corresponding experimental distances of 2.395, 2.441, 2.351, and 2.376 ä, respectively, but the same trends are observed. This difference appears to be a general result of DFT calculations and was also observed for the related complexes [Os 3 (CO) 12 ], [25] [Os 3 (CO) 10 (a-diimine)], [26] and [W(tmbp) 3 ] [11] . In the optimized geometry of [Os 3 -(CO) 10 (bp)], however, the alternation of the CÀC and CC bonds in the biphosphinine rings is well reproduced.…”

Syntheses, Structures and Photophysical Properties of Metal Carbonyl Clusters with Dansyl and Acridone Luminophores

“…The energy gap was calculated to be 33,792 cm Ϫ1 , which is much greater than that of 1. Contrary to what we have observed here, previous calculations on other [Os 3 (CO) 10 (α-diimine)] clusters [34,35] showed that the HOMOs are mainly metal orbital-based (OsϪOs bonding) while the LUMOs are more localized on the α-diimine ligand. Clearly, the bridging acetylene ligands in the currently studied clusters, significantly affect the orbital structures in the HOMOϪLUMO region.…”

Heterosite Effects in Novel Heteronuclear Clusters [Os2Ru(CO)11(PPh3)] and [Os2Ru(CO)10(2‐acetylpyridine‐N‐isopropylimine)]

“…Based on the contribution of the atomic wavefunctions to the frontier orbitals, the HOMO-LUMO transition has predominant σ(Ru-Os2)-to-π*(α-diimine) character. A comparison of the frontier orbitals with those of [Os 3 (CO) 10 (H-PyCa)] [18] shows that the HOMOs of both clusters are very similar, with only one specific metalmetal(α-diimine) bond involved in the bonding interactions. Notably, the ruthenium centre in 3Ј contributes slightly more (25 %) to the HOMO than the corresponding osmium centre in [Os 3 (CO) 10 (H-PyCa)] (18 %).…”

“…In both model systems, H-PyCa is coordinated with the pyridine ring in the axial position. A recent DFT study of the related cluster [Os 3 (CO) 10 (HPyCa)] [18] has shown that this geometric isomer is more stable than those with the pyridine ring equatorially bound or with both nitrogen atoms coordinated in the equatorial plane.…”

“…[3,11] 12 ] are of particular interest for our investigations, as the bonding properties, photochemistry and redox behaviour of the homonuclear dodecacarbonyl analogues and, in particular, their α-diimine-substituted derivatives [M 3 (CO) 10 (α-diimine)] (M = Ru, Os), have been studied thoroughly in our groups. [12][13][14][15][16][17][18][19][20][21] A continued systematic study of their heterometallic Ru/Os derivatives is desired in order to reveal the influence of the cluster core variation on the photochemistry and redox reactivity. However, one of the underlying reasons for the lacking studies of [Os 2 Ru(CO) 12 ] and [Ru 2 Os(CO) 12 ] is the serious difficulty to obtain these clusters in the pure form.…”