Tetrameric species

Hydrolysis constants for Zr3(OH)/ were first proposed by [53ZIE] and [56ZIE/CON]. Based on the data of [56ZIE/CON], a reference value of log,o Pl ((V.12), 298.15 K) = 

This value is considerably lower than the value of-4010.2 kJ-moP proposed by the review of [92SLO/KRI]. 

The presence of Zr (OH),/ was first suggested by [99VEY]. Subsequently, however, the author determined that a better fit to her solubility and potentiometric data was achieved using the stoichiometry of (OH). This review accepts the initial suggestion of [99VEY] due to structural [64CLE] and solubility evidence (see Appendix D) of the formation of a unit charged tetramer. For Reaction (V.13)  

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LCo(H20)6] ion, and bidentate /V-donor ligands such as cn, bipy and phen form octahedral cationic complexes [Co(L-L)3] , which are much more stable to oxidation than is the hexaammine [Co(NH3)6l . Acac yields the orange [Co(acac)2(H20)2] which has the tram octahedral structure and can be dehydrated to [Co(acac)2l which attains octahedral coordination by forming the tetrameric species shown in Fig. 26.3. This is comparable with the trimeric [Ni(acac>2]3 (p. 1157), like which it shows evidence of weak ferromagnetic interactions at very low temperatures. fCo(edta)(H20)] is ostensibly analogous to the 7-coordinate Mn and complexes with the same stoichiometry, but in fact the cobalt is only 6-coordinate, 1 of the oxygen atoms of the cdta being too far away from the cobalt (272 compared to 223 pm for the other edta donor atoms) to be considered as coordinated. 

Tilley and co-workers reported the isolation of coordinatively unsaturated complexes Cp Ru(L)Cl (Cp =/j -C-sMes, L = PCy3 and P Pr ) by a simple reaction with the tetrameric species fCp RuCI]4. This synthetic pathway has allowed us... 

E. and Randaccio, L. (1992) Gold(III) glycyl-L-histidine dipeptide complexes. Preparation and x-ray structures of monomeric and cyclic tetrameric species. Inorganic Chemistry, 31, 1983 (b) Carotti, S., Marcon, G., Marussich, M., Mazzei, T., Messori, L., Mini, E. and Orioli, P. (2000) Cytotoxicity and DNA binding properties... 

A polymeric chain structure is frequently observed for zinc carboxylates. Basic zinc carboxylates form a common tetrameric species, and altering conditions can result in an interconversion between the basic and regular carboxylates.369 Mass spectrometry studies have been carried out... 

The 31P NMR spectra of 28-30 showed signals characteristic of their structural features. Dimeric species 28 with l,l,l-tri(diphenylphosphinomethyl)ethane affords two singlets at 23.0 and —28.6 ppm due to the coordinated and nonco-ordinated P donors, respectively. For trimeric species 29, two singlets occur at 24.3 and 14.4 ppm, ascribed to two classes of P donors in bis[2-(diphenylphos-phino)ethyl]phenylphosphine. Because of two types of P donors in tri[2-(diphenylphosphino)ethyl]phosphine, tetrameric species 30 exhibits two singlets at 16.4 and 24.0 ppm. 

Insertion of a third methylene bridge into M leads to hypho P with 20 SE. The tetrameric species [Li(thp)2Li87]4 and Li([12]cr-4)2 4(Li87)4 suggest that one Li+ has to be assigned to each [(MeCH)3BMe]32 arachno cluster. The former is coordinated by two C-B bonds of the neighboring cluster [103]. This increases the total... 

The cavitands are essentially synthesized from their resorc[4]arene precursors which are readily obtained by resorcinol condensation with aldehydes. The main feature comes from the different configurations that are expected for this tetrameric species and the relative thermodynamical stability of each isomer, which has been widely investigated by several authors. In addition, the conformational mobility of the resorc[4]arene molecules will depend on substitution at the upper and lower rims [28, 36, 40, 41]. The first attempt to synthesize a phosphorus bridged cavitand was to treat resorc[4]arene la (1, R=CH3) with phenylphosphonic dichloride or phenylphosphonothioic dichloride. Only inseparable isomer mixtures were obtained and isolation of the desired cavitands was not possible [42]. The first isolated phosphorylated resorcinol-based cavitand was described in 1992 by Markovsky et al., who prepared compound D from la and four equivalents of o-phenylenechlorophos-phate in the presence of triethylamine [43, 44]. For this compound, a tautomeric temperature and solvent dependent equilibrium exists between the spirophosphorane structure and the cyclic phosphate form (Scheme 4). 

Geurink and Klumpp measured the protodelithiation enthalpies of 3-lithiopropyl methyl ether, 3-lithiobutyl methyl ether, 5-lithiopentyl methyl ether and 7-5yn-methoxy-2-exo-lithionorbornane in the same study that was discussed in an earlier section for the non-oxygenated compounds n-propyl lithium, n-butyl lithium, 5ec-butyl lithium and 2-norbornyl lithium. The reaction enthalpies for the oxygen-containing lithium species with 5ec-butyl alcohol in benzene were —190 2, —199 4, —190 3 and —199 2 kJmoU, respectively, where all of the lithiated ethers purportedly exist as tetrameric species. 

Oligomers of perfluorohexyl-ethene fulfilled these expectations in all preclinical studies, in vitro tests as well in animal tests. A radical polymerisation, followed by ultra-purification steps, created a crystal clear gel-like substance. The behaviours of the mixture of dimeric, trimeric and tetrameric star-shaped species with an inner core of hydrocarbon bonds and an outer layer of perfluoro-alkyl chains could be adjusted by the ratio of the dimeric, trimeric and tetrameric species, using a thin layer distillation. In dependence on this ratio, the viscosity could be adjusted in the range between 90 mPas and 1700 mPas, the specific density between 1.60 g/ml and 1.66 g/ml and the interfacial tension against water between... 

The reaction of 5-methylpyrazole with cadmium tetrafluoroborate gives a complex which is formulated as the tetrameric species [Cd4F4Li2] [BF. 447 It is thought that the fluoride ion is generated by the (possibly metal-assisted) hydrolysis of tetrafluoroborate, and that a heterocubane Cd4F4 cluster core (63) is formed. 

The alkylmetal alkoxides and phenoxides of the alkaline earth metals and zinc are much more soluble and volatile and have been extensively studied. Cryoscopic molecular weight measurements on compounds RZn(OR ) and RZn(OAr) in benzene indicate tetrameric species in splution.95"98 H NMR studies of a number of such compounds have been carried out.98... 

Honda and Tokushige reinvestigated the effect of temperature and monovalent cations on the quaternary structure of tryptophanase using the HPLC gel-filtration analysis.28 In contrast to the above-mentioned data, they found that in the absence of K+ or NH4+ ions the tetrameric holoenzyme undergoes dissociation into dimers and inactivation at 5°C. Their results also indicate that formation of the active holoenzyme from the apoenzyme and PLP proceeds in two steps the inactive tetrameric species are first formed then converted to the active species only the second step requires the presence of K+ or NH4+ ions (Fig. 9.3)... 

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