Alberding, Brian G., Barybin, Mikhail V., Chisholm, Malcolm H., Gustafson, Terry L., Reed, Carly R., Robinson, Randall E., Patmore, Nathan J., Singh, Namrata and Turro, Claudia (2010) Molecular, electronic structure and spectroscopic properties of MM quadruply bonded units supported by trans-6-carboethoxy-2-carboxylatoazulene ligands. Dalton Transactions, 39 (8). p. 1979. ISSN 1477-9226

The reaction between M2(TiPB)4 (M = Mo, W) where TiPB = 2,4,6-triisopropylbenzoate and 6-carboethoxy-2-azulenecarboxylic acid (2 equiv.) in toluene leads to the formation of complexes M2(TiPB)2(6-carboethoxy-2-azulenecarboxylate)2. Compound I (M = Mo) is blue and compound II (M = W) is green. Both are air sensitive, hydrocarbon soluble species that gave the corresponding molecular ions in their mass spectra (MALDI-TOF). They show metal based oxidations and ligand based reductions. Electronic structure calculations (DFT and time dependent DFT) indicate that the two azulene carboxylate π systems are coupled by their interactions with the M2δ orbitals. Their intense colors arise from M2δ to azulene π* electronic transitions. While compound I exhibits weak emission at [similar] 900 nm, no emission has been detected for II. Both I and II have been studied by fs and ns transient absorption spectroscopy. The X-ray analysis of the molecular structure of II in the solid state confirmed the paddlewheel nature of its W2(O2C)4 core and the trans orientation of the ligands.

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