Oxalate-Bridged Complexes of Dimolybdenum and Ditungsten Supported by Pivalate Ligands: (tBuCO2)3M2(mg src="http://pubs.acs.org/images/entities/mgr.gif" b

详细信息    查看全文

• 作者：Bruce E. Bursten ; Malcolm H. Chisholm ; Robin J. H. Clark ; Steven Firth ; Christopher M. Hadad ; Ann M. MacIntosh ; Paul J. Wilson ; Patrick M. Woodward ; and Jeffrey M. Zaleski
• 刊名：Journal of the American Chemical Society
• 出版年：2002
• 出版时间：March 27, 2002
• 年：2002
• 卷：124
• 期：12
• 页码：3050 - 3063
• 全文大小：525K
• 年卷期：v.124,no.12(March 27, 2002)
• ISSN：1520-5126

文摘

The compounds (^tBuCO₂)₃M₂(mages/entities/mgr.gif">-O₂CCO₂)M₂(O₂C^tBu)₃ (M₄OXA), where M = Mo or W, are shownby analysis of powder X-ray diffraction data to have extended lattice structures wherein oxygen atomsfrom the oxalate and pivalate ligands of one M₄OXA molecule are linked to metal atoms of neighboringmolecules. Raman, resonance Raman, electronic absorption (2-325 K in 2-MeTHF), and emission spectraare reported, together with corresponding spectra of the mages/entities/mgr.gif">-O₂¹³C¹³CO₂ isotopomers. To aid in the assignment,the Raman spectra of K₂C₂O₄·H₂O and K₂¹³C₂O₄·H₂O have also been recorded. The visible region of theelectronic spectra is dominated by intense, fully allowed MLCT transitions, M₂ mages/gifchars/delta.gif" BORDER=0 > to oxalate mages/gifchars/pi.gif" BORDER=0 >*, which showpronounced thermochromism and extensive vibronic progressions associated with the oxalate ligand atlow temperatures. With excitation into these charge-transfer bands, strong resonance enhancement is seenfor Raman bands assigned to the oxalate mages/gifchars/nu.gif" BORDER=0 >₁(a_g) and, to a lesser extent, mages/gifchars/nu.gif" BORDER=0 >₂(a_g) modes. Electronic structurecalculations for the model compounds (HCO₂)₃M₂(mages/entities/mgr.gif">-O₂CCO₂)M₂(O₂CH)₃, employing density functional theory(gradient corrected and time-dependent) with the Gaussian 98 and ADF 2000 packages, predict the planaroxalate D_2h configuration to be favored, which maximizes M₂ mages/gifchars/delta.gif" BORDER=0 > to oxalate mages/gifchars/pi.gif" BORDER=0 >* back-bonding, and indicatelow barriers (<8 kcal mol^-1) to rotation about the oxalate C-C bonds.