Luminescent Nitridoosmium(VI) Complexes with Aryl- and Alkylacetylide Ligands:  Spectroscopic Properties and Crystal Structures

A series of air- and moisture-stable nitridoosmium(VI) complexes with arylacetylide ligands, [nBu4N][OsN(C⋮CC6H4R-p)4] (R = H (1), Et (2), OEt (3), Ph (4)), and the alkyl analogue [nBu4N][OsN(C⋮CtBu)4] (5) were synthesized. The structures of 1, 2, and 4 were determined by X-ray crystal analyses. The Os⋮N (1.65(1) Å in 1, 1.620(8) Å in 2, and 1.619(6) Å in 4) and Os−C (mean 2.03 Å) distances are similar to that observed for [OsN(CH2SiMe3)4]-, whereas the C⋮C distances (mean 1.20 Å) correspond to terminal arylacetylide groups. The UV−vis absorption spectra of 1−4 display intense absorptions at 248−324 nm (ε ≈ 5 × 104 dm3 mol-1 cm-1) that are attributed to overlapping of the [pπ *(N3-) → dπ *(d xz , d yz )] and [π → π*(arylacetylides)] transitions. The moderately intense absorptions at λmax 403−418 nm (ε ≈ 103 dm3 mol-1 cm-1) are assigned to admixture of [(d xy )2 → (d xy )1(dπ *)1] with intraligand charge-transfer transition of the arylacetylides. The broad structureless solid-state luminescence of 1−5 at 298 (λmax 600−632 nm) and 77 K (λmax 599−635 nm) are assigned to the triplet 3[(d xy )1(dπ *)1] excited state. The 77 K glassy solutions of 1−5 also exhibit 3[(d xy )1(dπ *)1] emissions at λmax 597−628 nm. Like [OsNX4]- (X = Cl, Br), complexes 1−5 are nonemissive in dichloromethane at room temperature. Notably, 1 emits weakly at λmax 643 nm in benzene at room temperature, whereas 5 exhibits a more intense and long-lived luminescence at λmax 640 nm in diethyl ether. Correspondingly, a well-defined absorption at λmax 428 nm in the excitation spectrum of 5 (λem 640 nm, concentration 8 × 10-4 mol dm-3) is assigned to the 1[(d xy )2] → 1[(d xy )1(dπ *)1] transition.