Complexes monomeric/dimeric

The functional groups outlined in Fig. 10 are all bifunctional ligands that can, at least from a theoretical point of view, form monomeric, dimeric, or oligomeric complexes with metal ions or a diorganoboryl group. 

The unsolvated complexes Li[P(NR)(NR )] In may adopt monomeric, dimeric or tetrameric structures as indicated by the examples (4) [7], (5) [6] and (6) [7]. Variable temperature NMR studies reveal that the tetramer (6) dissociates into the corresponding dimer in solution [7]. The dimeric cubic structure is stabilized in the THF-solvated complex THF-Li [P(N Bu)2] 2 (7) [8]. 

The crystal structures of monomeric ligands such as GH and EPO in complex with their respective receptors show that these hormones are bivalent and one ligand binds simultaneously to two receptor molecules to form a 1 2 (ligand receptor) complex. Receptor dimerization is further stabilized by additional receptor-receptor interactions. 

Dialkyl zinc compounds form phosphine complexes of formula RZnP(SiMe3)2 on addition of one equivalent of bis(trimethylsilyl)phosphine. Solution and solid-state studies showed that the complexes are dimeric or trimeric in solution or the solid state. Bis(trimethylsilyl)phosphido-methylzinc crystallizes as a trimeric molecule with a Zn3P3 core in the twist-boat conformation. Bis(trimethylsilyl)phosphido- -butylzinc, shows a similar central Zn3P3 fragment. The sterically more demanding trimethylsilylmethyl substituent forms a dimeric species of bis(trimethylsilyl) phosphido-trimethylsilylmethylzinc. Solution studies of bis(trimethylsilyl)phosphido- .vo-propyl-zinc demonstrate a temperature-dependent equilibrium of the dimeric and trimeric species and the crystalline state contains a 1 1 mixture of these two oligomers. A monomeric bis(trimethyl-silyl)phosphido-tris(trimethylsilyl)methylzinc has also been synthesized.313... 

The products of electrochemical oxidation of conjugated dienes are considerably affected by the reaction conditions such as the material of the electrode, the supporting electrolyte and the solvent. The oxidation of butadiene with a graphite or carbon-cloth anode in 0.5 M methanolic solution of NaClCU mainly yields dimerized products along with small amounts of monomeric and trimeric compounds (equation 5)1. The use of platinum or glassy carbon mainly gives monomeric products. Other dienes such as isoprene, 1,3-cyclohexadiene, 2,4-hexadiene, 1,3-pentadiene and 2,3-dimethyl-l,3-butadiene yield complex mixtures of isomers of monomeric, dimeric and trimeric compounds, in which the dimeric products are the main products. 

Although there are many dyes which can photosensitise the production of singlet oxygen (see section 4.4.1), in PDT the first products of real interest came from haematoporphyrin. Subsequent, studies led to the haematoporphyrin derivatives HpD Stage 1 and Stage 11, which were found to be more active as PTD sensitisers as they localised preferentially in tumours. The first commercially available sensitiser, Photofrin, is based on processed material from HpD Stage 11, and is a complex mixture of monomeric, dimeric and oligomeric e.g. hexamer) porphyrins, in an... 

Green complexes [V0(SB)(H20)], where H2SB = 2-hydroxynaphthylidene amino acids, react with py or phen to form [VO(SB)(py)2] or [VO(SB)(phen)], which exhibit p g near the spin-only value.7 In methanol, these gave brown solutions from which the monomeric brown Vv complexes [VO(OMe)(SB)(MeOH)] were isolated. The treatment of these brown complexes with CH2C12 followed by n-hexane gave green precipitates of [VO(OH)(SB)]2 765 in CH2C12, the complexes are dimers. 

The Cu(PyrrolDtc)2 complex was found to be x-ray isomorphous to the square planar Ni(PyrrolDtc)2 complex (473). A structure determination of the former complex revealed a monomeric Cu(PyrrolDtc)2 unit with a square planar CuS4 chromophore (Table IX). This result is particularly interesting considering that the Cu(Et2Dtc)2 (53) and Cu(n-Pr2 Dtc)2 (507) complexes are dimeric species containing five-coordinate rectangular pyramidal Cu(II) ions. 

Ionophores X-573A (lasalocid A) and A23187 are usually regarded as carriers for Ca2+, but they will bind Na+. If formed from non-polar solvents the Na+/X-573A complex is dimeric, but if prepared in methanol it is monomeric, in which the Na+ is complexed by five oxygen donor atoms and the sixth position is filled by water. In the dimer, the water is absent and the coordination of the cation is completed by dimer formation.37 These results suggest that monomeric Na+-... 

In our studies of the open-framework zinc oxalates, we have recently isolated monomeric, dimeric, ID linear chain, 2D layer, and 3D structures by the reaction of amine oxalates with Zn2+ ions,21 suggesting thereby that the presence of a hierarchy of structures is not unique to the phosphates alone. We believe that the evidence provided by our studies for the existence of an Aufbau principle of open-framework complex structures is of considerable significance. Many other complex inorganic structures are also likely to be formed by similar building-up processes, involving basic building units and self-assembly. 

The reaction between either Cp2Mg or CpNa with [ScF3] leads to a complex mixture of three compounds an unidentified hexane-soluble species, a species characterised as [Cp3Sc] and a third toluene-soluble compound, identified as t ScF(Cp)2 3], which has been crystallographically characterised [Fig. 1] [5], The mixture was unaffected by variation of the ratio of the starting materials and, in solution, the fluoro complex exists as an equilibrium between the monomeric, dimeric and trimeric forms. 

Our contribution to this field was the synthesis, isolation, and full characterization a few new rhodium siloxide complexes, both dimeric [13] and monomeric (see Fig. 1) [14]. 

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