Pair-of-dimer complexes

The kinetics of this process is strongly affected by an association phenomenon. It has been known that the active center is the silanolate ion pair, which is in equUibrium with dormant ion pair complexes (99,100). The polymerization of cyclosiloxanes in the presence of potassium silanolate shows the kinetic order 0.5 with respect to the initiator, which suggests the principal role of dimer complexes (101). 

Ray, L., Shaikh, M.M. and Ghosh, P. (2008) Shorter Argentophilic Interaction than Aurophilic Interaction in a Pair of Dimeric (NHC)MC1 2 (M=Ag, Au) Complexes Supported over a N/O-Functionalized N-Heterocyclic Carbene (NHC) Ligand. Inorganic Chemistry, 47, 230-240. 

Pair-of-dimer effects, chromium, 43 287-289 Palladium alkoxides, 26 316 7t-allylic complexes of, 4 114-118 [9JaneS, complexes, 35 27-30 112-16]aneS4 complexes, 35 53-54 [l5]aneS, complexes, 35 59 (l8)aneS4 complexes, 35 66-68 associative ligand substitutions, 34 248 bimetallic tetrazadiene complexes, 30 57 binary carbide not reported, 11 209 bridging triazenide complex, structure, 30 10 carbonyl clusters, 30 133 carboxylates... 

Intermetallic distances around 2.80 A have been found in analogous complexes of formula trans- [A2Pt(l-MeCyH-,A(3),N(4))2Hg]X2 (X = Cl-, N03 ) [56], where 1-MeCyH binds Pt through N(3) and Hg through N(4) (II, Fig. 5). They will be indicated as 4 2 type complexes. The crystal structures reveal that pairs of dimers are held together by the counterions, Cl- or N03, in such a way as to form tetranuclear species. 

The crystal and molecular structure of [Ni2(PZl2)2(MeOH)4]Cl2 were determined (201), which confirms the previous assignment. More recently (204), the X-ray crystal structure of the Cuweakly associated pairs of dimers, with ir(rj5) interdinuclear interactions. 

Exchange Parameters for Planar-Parallelogram Pair-of-Dimer Cu(II) Complexes (J Values in cm" )... 

While the use of one terpyridine monomer results in only one dimeric complex, the use of more than one monomer leads to a mixture of complexes. Two monomers (X and Y) will lead to 25% dimeric X X, 25% dimeric Y Y, and 50% mixed complex X Y determined by high-pressure liquid chromatography (HPLC) of reaction products. Complexes (X Y) and (Y X) are degenerate and only one need be considered. Each bis(terpyridine) metal complex exists as a pair of stereoisomers due to the two possible arrangements around the metal center, and no attempt was made to distinguish or separate these stereogenic pairs. The total number of components of these combinatorial libraries must include both symmetric and asymmetric complexes. If n terpyridine monomers are combined, the same number of symmetric complexes (X X) are formed. The number of asymmetric complexes (X Y) formed is /[( -2) 2 ] or better represented as n(n-l)/2. Thus the total number of dimeric complexes is the sum of n and ( -l)/2, which is n(n+l)/2. For example, a library with 5 monomers will form 15 dimers, 10 monomers will produce 55 dimers, and 20 monomers will produce 210 dimers. 

Even if the peak behavior fits well for a given apparent desorption order, the real kinetic situation may be a different one. As a rate controlling step in a second-order desorption, random recombination of two particles is assumed most frequently. However, should the desorption proceed via a nonrandom recombination of neighboring particle pairs into an ordered structure, the resulting apparent first-order desorption kinetics is claimed to be possible (36). The term pseudo-first-order kinetics is used in this instance. Vice versa, second-order kinetics of desorption can appear for a nondissociative adsorption, if the existence of a dimer complex is necessary before the actual desorption step can take place (99). A possibility of switching between the apparent second-order and first-order kinetics by changing the surface coverage has also been claimed (60, 99, 100). 

A dimer made up of two zinc porphyrins bearing a 7-azabicy-clo[2.2.1]heptadiene fused at the C2-C3 /3-positions was reported by Knapp (61). The compound was designed to dimerize with a pyrrole-over-pyrrole geometry similar to that found in the photosynthetic special pair. Dimerization at KT3 M was confirmed by VPO and JH NMR spectroscopy. Dilution to 10-5 m or addition of DMAP caused disaggregation of the complex. In the solid state, this compound assembles as a cyclic hexamer with the vicinal porphyrin planes almost perpendicular. 

---