Department of Chemistry, The Ohio State University, 100 West 18th Avemue, Columbus, Ohio 43210-1185, USA.
Inorg Chem. 2012 Jan 2;51(1):491-8. doi: 10.1021/ic201957a. Epub 2011 Nov 30.
The compounds M(2)(O(2)C(t)Bu)(4) and M(2)(O(2)CC(6)H(5))(4), where M = Mo or W, have been examined by femtosecond time-resolved IR (fs-TRIR) spectroscopy in tetrahydrofuran with excitation into the singlet metal-to-ligand charge-transfer ((1)MLCT) band. In the region from 1500 to 1600 cm(-1), a long-lived excited state (>2 ns) has been detected for the compounds M(2)(O(2)C(t)Bu)(4) and Mo(2)(O(2)C-C(6)H(5))(4) with an IR absorption at ~1540 cm(-1) assignable to the asymmetric CO(2) stretch, ν(as)(CO(2)), of the triplet metal-metal δ-δ star ((3)MM δδ*) state. The fs-TRIR spectra of W(2)(O(2)C-C(6)H(5))(4) are notably different and are assigned to decay of the MLCT states. In (3)MM δδ*, the removal of an electron from the δ orbital reduces MM δ to CO(2) π* back-bonding and causes a shift of ν(as)(CO(2)) to higher energy by ~30-60 cm(-1), depending on the metal. TRIR spectroscopy also provides evidence for M(2)(O(2)C(t)Bu)(4), where M = Mo or W, having MM δδ* S(1) states with ν(as)(CO(2)) distinct from those of the (3)MM δδ* states.
二茂基金属配合物 M(2)(O(2)C(t)Bu)(4) 和 M(2)(O(2)CC(6)H(5))(4)（M = Mo 或 W）的飞秒时间分辨红外（fs-TRIR）光谱研究
本文采用飞秒时间分辨红外（fs-TRIR）光谱技术，在四氢呋喃溶液中，对激发到单重态金属-配体电荷转移（(1)MLCT）带的二茂基金属配合物 M(2)(O(2)C(t)Bu)(4) 和 M(2)(O(2)CC(6)H(5))(4)（M = Mo 或 W）进行了研究。在 1500 至 1600cm(-1) 范围内，检测到化合物 M(2)(O(2)C(t)Bu)(4) 和 Mo(2)(O(2)C-C(6)H(5))(4)存在长寿命激发态（>2ns），其红外吸收位于~1540cm(-1)，可归属于三重态金属-金属 δ-δ态((3)MM δδ)的不对称 CO(2)伸缩振动 ν(as)(CO(2))。W(2)(O(2)C-C(6)H(5))(4)的 fs-TRIR 光谱明显不同，可归因于 MLCT 态的衰减。在(3)MM δδ中，从 δ 轨道上除去一个电子使 MM δ降低到 CO(2)π反键，导致 ν(as)(CO(2))向高能移动约 30-60cm(-1)，具体取决于金属。TRIR 光谱还为 M(2)(O(2)C(t)Bu)(4)（M = Mo 或 W）中存在 MM δδS(1)态提供了证据，其 ν(as)(CO(2))与(3)MM δδ态的 ν(as)(CO(2))不同。
