Quadruply Bonded Dimetal Units Supported by 2,4,6-Triisopropylbenzoates MM(TiPB)₄ (MM = Mo₂, MoW, and W₂): Preparation and Photophysical Properties

Abstract

The preparation and characterization (elemental analysis, (1)H NMR, and cyclic voltammetry) of the new compounds MM(TiPB)(4), where MM = MoW and W(2) and TiPB = 2,4,6-triisopropylbenzoate, are reported. Together with Mo(2)(TiPB)(4), previously reported by Cotton et al. (Inorg. Chem. 2002, 41, 1639), the new compounds have been studied by electronic absorption, steady-state emission, and transient absorption spectroscopy (femtosecond and nanosecond). The compounds show strong absorptions in the visible region of the spectrum that are assigned to MMdelta to arylcarboxylate pi* transitions, (1)MLCT. Each compound also shows luminescence from two excited states, assigned as the (1)MLCT and (3)MMdeltadelta* states. The energy of the emission from the (1)MLCT state follows the energy ordering MM = Mo(2) > MoW > W(2), but the emission from the (3)MMdeltadelta* state follows the inverse order: MM = W(2) > MoW > Mo(2). Evidence is presented to support the view that the lower energy emission in each case arises from the (3)MMdeltadelta* state. Lifetimes of the (1)MLCT states in these systems are approximately 0.4-6 ps, whereas phosphorescence is dependent on the MM center: Mo(2) approximately 40 micros, MoW approximately 30 micros, and W(2) approximately 1 micros.

Assessing Metal–Metal Multiple Bonds in CrCr, MoMo, and WW Compounds and a Hypothetical UU Compound: A Quantum Chemical Study Comparing DFT and Multireference Methods

“…Alberding et al [3] prepared the [MM'A C H T U N G T R E N N U N G (TiPB) 4 ] compounds, in which M = Mo or W and M' = W and characterized them with various techniques. Electronic absorption, steady-state emission and transient absorption spectroscopy indicate that these compounds have strong absorptions in the visible region that are assigned to MM' d to arylcarboxylate p* transitions, 1 MLCT.…”

“…Electron-rich metal-metal units are of general interest because of their unique electronic and optical properties. [3] Several new examples of metal-metal multiply bonded compounds incorporating the Group 6 metals have recently been of interest. For example, various groups have shown interest in oligothiophene compounds incorporating metal-metal multiple bonds because of their potential applications in optoelectronic and magnetic devices.…”

Tuning the electronic structure of Mo–Mo quadruple bonds by N for O for S substitution

“…16,17 Investigations by Chisholm and coworkers on the photoexcited states of trans-[M 2 (TiPB) 2 (O 2 CR) 2 ] (R = 2-thiophene 18,19 or C 6 H 4 -4-CN; TiPB = 2,4,6-triisopropylbenzoate) 20 show emission from T 1 states that are about the dimetal core also makes MM multiply bonded paddlewheel compounds good candidates for incorporation into materials with potentially interesting optoelectronic properties. [21][22][23][24][25][26][27] This was highlighted in a detailed study by Zhou and co-workers which demonstrated that the shape and size of molecular architectures formed using dicarboxylate ligands to bridge Mo 2 4+ units can be controlled by tuning the bridging angle and size of the bridging dicarboxylate ligand.…”

MM quadruply bonded complexes supported by vinylbenzoate ligands: synthesis, characterization, photophysical properties and application as synthons

“…Mo 2 T i PB 4 and W 2 T i PB 4 were synthesized from known procedures. 16,23 Iodobenzene and palladium (II) acetate were purchased from Sigma Aldrich. Iodobenzene was degassed by freeze-pump-thaw and stored over 4Å molecular sieves in a Kontes top flask under argon.…”