Luminescent nitridoosmium(VI) complexes with aryl- and alkylacetylide ligands: Spectroscopic properties and crystal structures

Abstract

A series of air- and moisture-stable nitridoosmium(VI) complexes with arylacetylide ligands, [ nBu 4N][OsN(C≡CC 6H 4R-p) 4 ] (R = H (1), Et (2), OEt (3), Ph (4)), and the alkyl analogue [ nBu 4N] [OsN(C≡C tBu) 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(CH 2SiMe 3) 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 × 10 4 dm 3 mol -1 cm -1) that are attributed to overlapping of the [p π*(N 3-) → d π*(d xz, d yz)] and [π → π*(arylacetylides)] transitions. The moderately intense absorptions at λ max 403-418 nm (ε ≈ 10 3 dm 3 mol -1 cm -1) are assigned to admixture of [(d xy) 2 → (d xy) 1(d π*) 1] with intraligand charge-transfer transition of the arylacetylides. The broad structureless solid-state luminescence of 1-5 at 298 (λ max 600-632 nm) and 77 K (λ max 599-635 nm) are assigned to the triplet 3[(d xy) 1(d π*) 1] excited state. The 77 K glassy solutions of 1-5 also exhibit 3[(d xy) 1(d π*) 1] emissions at λ max 597-628 nm. Like [OsNX 4] - (X = Cl, Br), complexes 1-5 are nonemissive in dichloromethane at room temperature. Notably, 1 emits weakly at λ max 643 nm in benzene at room temperature, whereas 5 exhibits a more intense and long-lived luminescence at λ max 640 nm in diethyl ether. Correspondingly, a well-defined absorption at λ max 428 nm in the excitation spectrum of 5 (λ em 640 nm, concentration 8 × 10 -4 mol dm -3) is assigned to the 1[(d xy) 2] → 1[(d xy) 1(d π*) 1] transition.