Coordination selectivity

The mechanisms of photoreactivity of coordination compounds limiting cases of decay on a specific nuclear coordinate (dosenco) or via random coordinate selection (dercos). B. R. Hollebone, C. H. Langford and N. Serpone, Coord. Chem. Rev., 1981, 39,181-224 (95). 

The NCO", NCS- and NCSe- ions can coordinate through N and O, S or Se atoms.1078,1079 In the nickel(II) complexes terminal NCX- ligands are invariably N-coordinated. Selected examples of nickel(II) complexes with NCO, NCS and NCSe are reported in Table 57. 

There is a possibility that an FC state will react before complete thermal equilibration. In the case of diatomic molecules, the process is usually known as predissociation — a dissociative state crosses the excited state potential surface. The situation is more complicated in the case of a coordination compound, but one can imagine an FC state relaxing along some nuclear coordinate leading to bond breaking. A state capable of such a process has been called a DOSENCO state, an acronym for Decay On SElected Nuclear Coordinates .21 The same authors use the term DERCOS (DEcay via Random Coordinate Selection) for a thexi state. 

Chromium coordinates selectively with the 1,2-diol, forming a stable cyclic chromate ester that evolves producing the formation of a tetrahydrofuran. Observe that no formation of tetrahydrofuran from the alcohol on the left occurs, for this would involve the intermediacy of a less stable simple chromate ester (vide infra). The experimental conditions are so mild that no direct oxidation of the secondary alcohol to ketone is observed, either on the starting compound or in the product. 

The data reported in the literature relative to the IR spectra of metallocorrolates have been used mainly to characterized their axial coordination. Selected data are reported in Table 5. 

The most common strategy in the synthesis of heteronuclear complexes is the use of bidentate donor ligands bearing different donor centers. In that way both donor atoms can be coordinated selectively to two different metal centers in a consecutive way. If the space between the donor atoms of the ligands is short, interactions between both metals usually appear, normally intramolecular. Sometimes, albeit not very often, the bidentate units bind to one another, leading to extended structures through metallophilic interactions. As we have commented, in the case of gold-silver derivatives the number of luminescent studies of these derivatives is very scarce. 

Generally, a homoorganocopper reagent has two different metals in the cluster. Their chiral modification needs a chiral ligand whose heteroatoms coordinate selectively to copper and other metals. The first approach along this line was reported by Kretchmer, who used chiral natural diamine 7 as a ligand for methyl-copper in the reaction with cyclohexenone to afford the adduct in only 6% ee [49]. 

The ionophore should coordinate selectively, but reversibly, with the analyte. 

Reaction schemes for hydrogenation of dienes using dihydride catalysts usually follow the basic hydride or unsaturated pathways of Scheme 1 species 2 will be, however, a hydrido cr-alkenyl or a 7r-allyl intermediate [see equation (f) below]. Transfer of the second hydrogen yields a monoene product if diene coordination is preferred over monoene coordination, selective reduction of diene to monoene can occur. Some Rh (and Ir ) dihydride catalysts that effect such catalysis are listed in Table 2, although systems based on the Cr and Fe carbonyl have been studied most (see also 14.3.3.5) . 

Each trajectory is launched at chosen initial values of Jb and ipb and at fra = 0. Since any point on the 3-dimensional energy shell may be specified by three linearly independent coordinates, selection of initial values J , ip%, and ip°, implies a definite value of J°. Thus trajectories are launched at various [Jfi, ip%, ip° = 0, J°(J , ipl, ip°,) ] initial values until all of the qualitatively distinct regions of phase space are represented on the surface of section by either a family of closed curves (quasiperiodic trajectories) that surround a fixed point (a periodic trajectory that defines the qualitative topological nature of the neighboring quasiperiodic trajectories) or an apparently random group of points (chaos). Often, color is used to distinguish points on the surface of section that belong to different trajectories. 

Protection of C—C double bonds. The olefinic ligand of this cationic complex can be exchanged when heated above 20° with an excess of certain other olefins. Nicholas has used this property for protection of C—C double bonds, since the olefins can be regenerated by treatment of the complex with sodium iodide in acetone. The method is particularly useful for selective protection of dienes and polyenes. For example, the complex of norbomadiene undergoes electrophilic additions without isomerization to nortricyclane derivatives (equation I). The complex coordinates selectively with the less substituted and/or... 

The preceding Cartesian coordinates selected for the diatomic are then randomly rotated through Euler s angles [45] to give a random orientation ... 

Koemer, Younathan, and Wander have provided additional evidence for the j8 configuration of 2,3 4,5-di-0-benzylidene-)8-D-fi ictopyranose (93). The p.m.r. spectrum of 9.3 in carbon tetrachloride solution was measured at 100 MHz and 35 before and after serial additions of a saturated solution of tris [2,2,6,6-tetramethyl-3,5-heptanedionato] europium (III) in carbon tetrachloride. Apparently, this reagent coordinates selectively with 0-1, because a two-proton... 

The structures determined by X-ray analysis of the complexes [Ni(Me3[12]eneN3)2](NCS)2 (Me3[12]eneN3 = 2,4,4-trimethyl-l,5,9-triazacyclododec-l-ene) and [Ni(TRI)(H20)N03]N03 (TRI = tribenzo[6,/,)][l,5,9]triazacydododecane) show that the two triaza macrocycles coordinate facially in both square pyramidal and octahedral complexes. Other complexes with triaza macr cles have been prepared and are assumed to be either five- or six-coordinate.Selected examples of nickel(II) complexes with unsaturated macrocycles are reported in Table 106. 

The internal coordinates were selected so as to make it physically meaningful to compare force constants of different molecules. For the free and the coordinated benzene ring, the internal coordinates selected were based on suggestions by Pulay et al. [10b, 13c]. The C-Cr-C bending coordinates of Cr(CO)g were chosen in a way that allowed analogous definitions in the case of... 

While the detailed structures of most catalyst sites are still unknown, it was established that stereoselectivity does not come from the chirality of the growing chain end. Rather, it is built into the catalyst site itself. Normal preparations of the catalysts give equal numbers of (/ ) and (5) chiral catalyst sites. These coordinate selectively with (R) and (5) monomers, respectively, in the process of catalytic-site control. ... 

Fig. 8.26 Cylindrical coordinates selected for a stack of smectic layers that becomes unstable in the infinitely thick sample...

Boundary conditions of the type (2.7.12) are important in crystallization where secondary nucleation, as pointed out by Randolph and Larson (1988), may be governed by the growth rate of existing particles. For example, consider a well-mixed crystallizer where the number density is only a function of the sole internal coordinate selected as particle size x as represented by a characteristic length, which should satisfy a population balance equation of the type (2.7.6). Randolph and Larson discuss a variety of nucleation mechanisms and conclude that contact nucleation is the most significant form of nucleation. Thus, the mechanical aspects of the crystallizer equipment which provide contact surfaces contribute to increased nucleation rate. When growing crystals, containing adsorbed solute on their surfaces, come into contact with other solid surfaces, nucleation is induced. The boundary condition for the formation of new nuclei in a real crystallizer is therefore considerably more complicated than that implied by (2.7.7). Instead, the boundary condition must read as... 

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