Direct Observation of the Luminescence from the ³δδ* Excited State of Re₂Cl₂(p-OCH₃form)₄

Abstract

There are only a few reports on the measurement of the energy of the low-lying (3)deltadelta state of quadruply bonded bimetallic complexes, and the direct observation of the (1)deltadelta excited electronic state was only recently reported. In the quadruply bonded bimetallic complexes reported to date, luminescence arises from their (1)deltadelta excited state, and the (3)deltadelta state is nonemissive. Here we report the luminescence of Re(2)Cl(2)(p-OCH(3)form)(4) [p-OCH(3)form = (p-CH(3)OC(6)H(4))NCHN(p-CH(3)OC(6)H(4))(-)] observed upon 400-460 nm excitation with maxima at 820 nm (CH(2)Cl(2), tau = 1.4 micros) and 825 nm (CH(3)CN, tau = 1.3 micros) at 298 K. From the large Stokes shift, the vibronic progression at 77 K, the quenching by O(2), the long lifetime, and the calculated energy of the (3)deltadelta state, the luminescence of Re(2)Cl(2)(p-OCH(3)form)(4) and the corresponding transient absorption signal are assigned as arising from the (3)deltadelta ((3)A(2u)) excited state of the complex.

Tunable Rh2(II,II) Light Absorbers as Excited-State Electron Donors and Acceptors Accessible with Red/Near-Infrared Irradiation

“…It should be noted that the formamidinate ligands also impact the metal orbitals that make up the HOMO. − While archetypal d 7 d 7 metal paddlewheels, considering only d orbitals, have a (σ) 2 (π) 4 (δ) 2 (δ*) 2 (π*) 4 (σ*) 0 electronic configuration, , formamidinate ligands L­(π*) orbitals have the correct symmetry to interact with Rh 2 (δ*) MO, thus raising its energy above the Rh 2 (π*) orbitals in some cases. This switch is observed in tetraformamidinate complexes of rhodium, as well as those of other metals, − where the formamidinate π* orbitals of b 1 u symmetry interact with the δ* orbitals of the same symmetry to impart mixed DTolF­(π*)/Rh 2 (δ*) HOMO character.…”

Physical, Spectroscopic and Theoretical Results

“…Only recently 279 has emission from the 3 A 2u state been shown to occur, namely in Re 2 (DAniF) 4 Cl 2 .…”

Photophysical Studies of trans-Bis(phenylethynyldiisopropylamidinato)bis(acetato)dimetal Complexes Involving MM Quadruple Bonds Where M = Mo or W

“…Emission from the 3 δδ* state of quadruply bonded complexes was first observed in Re 2 Cl 2 (L) 4 (where L ) N,N′-p-anisoleformamidinate). 29 In this complex, emission occurs due to a larger energy gap between the 1 δ 2 and 3 δδ* states relative to that for complexes of the type [M 2 Cl 8 ] n-(where M ) Mo 2+ , Re 3+ ) or [Mo 2 Cl 4 (P t Bu 3 ) 4 ], which have emissive 1 δδ* states and nonradiative 3 δδ* states. 30,31 For π-conjugated…”

“…While 3 δδ* emission from the Mo 2 −carboxylates occurs at ∼1100 nm, complex I emits at significantly higher energy, with λ max ∼ 860 nm. Emission from the 3 δδ* state of quadruply bonded complexes was first observed in Re 2 Cl 2 (L) 4 (where L = N , N ′- p- anisoleformamidinate) . In this complex, emission occurs due to a larger energy gap between the 1 δ 2 and 3 δδ* states relative to that for complexes of the type [M 2 Cl 8 ] n − (where M = Mo 2+ , Re 3+ ) or [Mo 2 Cl 4 (P t Bu 3 ) 4 ], which have emissive 1 δδ* states and nonradiative 3 δδ* states. , For π-conjugated bridging ligands such as formamidinates or carboxylates, there exists an occupied, nonbonding p orbital combination that has appropriate symmetry to interact with the metal δ* orbital, resulting in higher energy 1 δδ* and 3 δδ* excited states and allowing radiative decay to occur from the latter.…”