Journal
RUSSIAN CHEMICAL BULLETIN
Volume 60, Issue 11, Pages 2180-2187Publisher
SPRINGER
DOI: 10.1007/s11172-011-0336-z
Keywords
carbenes; matrix isolation; ESR spectroscopy; zero-field splitting tensor; electronic spin-spin interactions; quantum chemical calculations; density functional theory
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Funding
- Russian Foundation for Basic Research [10-03-00065]
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The ESR spectrum of the first representative of highly conjugated triplet ethynylvinylcarbenes, 5-methylhexa-1,2,4-triene-1,3-diyl (1), was recorded in solid argon matrix. The zero-field splitting (ZFS) parameters of carbene 1 (D = 0.5054 +/- 0.0006 cm(-1) and E = 0.0045 +/- 0.0002 cm(-1)) determined from the experimental ESR spectrum are in between the corresponding parameters of ethynylcarbene C3H2 (2) and vinylcarbene C3H4 (3): D(3) < D(1) < D(2) and E(2) < E(1) < E(3). Quantum chemical calculations of the ZFS parameters of 1, 2, and 3 have been carried out for the first time using two DFT-based approaches, RODFT and UDFT. An analysis of the experimental and theoretical ZFS parameters shows that carbene 1 is characterized by a greater extent of delocalization of the spin density of unpaired electrons than carbenes 2 and 3. The characteristic structural fragments of carbene 1 possess the principal features of the electronic structure of both ethynylcarbene (2) and vinylcarbene (3), respectively. Magnetic spin-spin interactions are identical in carbenes 1 and 2. The dominant contribution to D in 1 and 2 results from the one-center spin-spin interactions on carbon atoms in the propynylidene group, which are subjected to strong spin polarization.
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