Two-Center Complexes

In 2008, Robinson and coworkers reported on the serendipitous synthesis of the disilicon compound Si2(NHCi PP)2 (Dipp = diisopropylphenyl), which was obtained when SiCl4 was reacted with NHCI PP [44]. The authors also presented the results of quantum ciemical calculations which suggested that the bonding situation in the molecule can be understood in terms of (NHC PP)- SiSi-(-(NHC PP) donor-acceptor interactions. In the following years, numerous analogues of the 

The geometries of group 14 complexes E2(NHC )2 possess a trans arrangement of the ligands at the E2 moieties with rather acute bending angles N-E-E 

1) The orbitals of the complex are a mixture of several fragment MOs. Columns 3 and 4 show the most important pairs of orbitals which lead to the associated MO of the comply. 

E2(NHC )2 (E=Si-Pb) and associated interaction energies AE. Shape of the most important interacting occupied and vacant orbitals of E2 and (NHC )2 which yield relevant occupied orbitals of E2 (NHC )2- 

Two-Center Croup 13 and Croup 15 Complexes BjLj and NjLj 

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Electron Transport Between Photosystem I and Photosystem II Inhibitors. The interaction between PSI and PSII reaction centers (Fig. 1) depends on the thermodynamically favored transfer of electrons from low redox potential carriers to carriers of higher redox potential. This process serves to communicate reducing equivalents between the two photosystem complexes. Photosynthetic and respiratory membranes of both eukaryotes and prokaryotes contain stmctures that serve to oxidize low potential quinols while reducing high potential metaHoproteins (40). In plant thylakoid membranes, this complex is usually referred to as the cytochrome b /f complex, or plastoquinolplastocyanin oxidoreductase, which oxidizes plastoquinol reduced in PSII and reduces plastocyanin oxidized in PSI (25,41). Some diphenyl ethers, eg, 2,4-dinitrophenyl 2 -iodo-3 -methyl-4 -nitro-6 -isopropylphenyl ether [69311-70-2] (DNP-INT), and the quinone analogues,... 

No region of the cytochrome penetrates the membrane nevertheless, the cytochrome subunit is an integral part of this reaction center complex, held through protein-protein interactions similar to those in soluble globular multisubunit proteins. The protein-protein interactions that bind cytochrome in the reaction center of Rhodopseudomonas viridis are strong enough to survive the purification procedure. However, when the reaction center of Rhodohacter sphaeroides is isolated, the cytochrome is lost, even though the structures of the L, M, and H subunits are very similar in the two species. 

Oxidative addition of XY substrates to [IrL2(/x-pz)]2 [La = (CO)2, cod] and [Ir(CD)(PPh3)(/i,-pz)]2 occurs via a two-center, two-electron route toward the iridium-iridium bond-containing species 131 (960M3785 980M2743). Complex 132, which is prepared by the ligand-substitution reaction from [Ir(CO)2 (/x-pz)]2, adds methyl iodide to give 133. 

The crystal and molecular structure of (PPh3)2(CO)(H)Ir(/u3-B3H7) have been reported.5 The structure is interpreted as a capped octahedral, 7-orbital, 18-electron d4, Irv complex in which the metal-borane bonding occurs predominantly via three two-electron, two-center Ir—B bonds. 

Two dinuclear complexes, with five-coordinate zinc centers, derived from tris((2-pyridyl)-methyl) amine were synthesized and bridging phosphate or phosphate ester groups. The X-ray structure of the phosphate monoester complex shows a syn-anti bridging mode in contrast to alkaline phosphatase in which it is syn-syn 448 Fenton and co-workers have also studied other related dizinc species of compartmental ligands 449... 

The criterion for association in the classical trajectory calculations is the presence of multiple inner turning points between Cl and the CH3Clb center of mass. Two types of Cl -CH3Clb complexes, short-range and long-range, were observed in the trajectories. The two different complexes were identified by the Cl -C distance... 

There may, however, be specific reasons to study a signal over an extended temperature range. For one, a linear increase in EPR amplitude with the inverse of the temperature (Curie s law) is proof that a spin system is a two-level system, i.e., an S = 1/2 or an effective S = 1/2 system. More importantly, in complex multicenter metalloproteins, overlapping spectra may be deconvoluted by virtue of their Tu value being different if two centers, a and b, have rMa < TMb then at TMb the spectrum of center a is broadened and that of center b is not. It is once more emphasized that these types of studies require determination of (anisotropic) saturation behavior at all relevant temperatures. 

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