Complex carboxylate

The carboxylates complexes of osmium have been studied less than the ruthenium analogues [173], 

Reaction of OsCl6 with acetic acid/acetic anhydride mixtures containing concentrated HC1 gives the diosmium compound Os2(OAc)4C12 (rather than mixed-valence species, see section 1.8.3) other carboxylates can be made by carboxylate exchange  

Copper Carboxylate Complexes. The structural literature on copper(n) carboxylate complexes prior to 1971 is extorsive a recent report on anti-ferromagnetism in dinuclear copper carboxylates makes reference to nearly forty relevant crystallographic papers a 1967 review of metal-peptide 

In a recent review metal-carboxylate interactions have been classified into five structural types unidentate (24), unsymmetrically bidentate (25), and bridging (26), (27), and (28) provided the metal atoms are nearly coplanar with the carboxylate group, the arrangements (26)—(28) are 

There is in addition a sixth structural type (29) in which a single carboxylate oxygen atom is simultaneously bonded to two copper atoms. An example of this rather unusual arrangement occurs in the structure of copper hippurate (36).  

Data on individual structures are presented in Table 5. Points of particular interest in these structures are discussed below. 

In the structure of copper hippurate tetrahydrate (36) both the bridging arrangement (see above) and the failure of the peptide nitrogen atom to co-ordinate the metal are unexpected. The Cu Cu distance is 3.30 A, and it is therefore unlikely that direct metal-metal bonding is involved.  

Ruthenium forms four significant families of carboxylate complexes. 

The complexes are 1 1 electrolytes in solution. Other such complexes can be made by a similar route or by halide (or carboxylate) exchange. The first monomeric system Ru2C1(02C.C4H4N)4 (thf), where the ruthenium at one end of the lantern is bound to a thf and the other to a chloride, has recently been made [97]. [Ru2Cl(02CBu )4(H20)] and [Ru2Cl(02CPr )4(thf )] are also monomeric [98]. 

These mixed-valence compounds have magnetic moments around 4 /xB, indicating an S = 3/2 (quartet) ground state, in keeping with their ESR spectra, which resemble those of Cr3+ compounds with a big zero-field splitting (gx = 4, g = 2) [99]. 

The analogous diruthenium(II, II) compounds can be made starting from the blue solution of reduced RuC13 in ethanol (section 1.3.5) on extended refluxing with sodium acetate, whereupon the solvate Ru2(OAc)4(MeOH)2 separates. This loses methanol readily on drying the resulting anhydrous acetate will form weak adducts Ru2(OAc)4L2 (L, e.g. H20, thf). These are all paramagnetic with two unpaired electrons [100]. 

Apart from carboxylates, other groups such as carbonate and triazenate (R-NNN-R R = Ph, p-tolyl, etc.) can fulfil the role of bridging ligands in the lantern [102], 

In Ru2(OAc)4C1, one ruthenium(II) supplies six electrons, the ruth-enium(III) five electrons, giving rise to a configuration 

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Oxygen-Gontaining Organics. Neutral and anionic oxygen-containing organic molecules form a wide variety of complexes with uranium. Much work has focused on alkoxides (222), aryloxides and carboxylates complexes with alcohols, ethers, esters, ketones, aldehydes, ketoenolates, and carbamates are also well known. 

The cationic species [IrX2(CO)(PMe2Ph)3]+ (XVI, Q = CO) undergoes nucleophilic attack by methoxide forming the carboxylate complex (XXI). In the presence of very strong base, a cyclometallation of a methyl group occurs forming (XXIV) [165],... 

Structure and metal-metal interactions in copper(II) carboxylate complexes. R. J. Doedens, Prog. Inorg. Chem., 1976, 21, 209-231 (70). 

The isolation, separation, and chemistry of dithio- and perthioaryl-carboxylate complexes of Ni(II), Pd(II), and Pt(II) were reported in two complementary reports (381, 415). The perthiocarboxylate complexes have also been obtained by oxidative addition of sulfur to the dithiocar-boxylic acid complexes. The abstraction of the sulfur atom adjacent to carbon by PPha was again observed, and rationalized as follows. 

Mixed-valence Ru"-Ru" paddlewheel carboxylate complexes also have potential for oxidation reactions after incorporation in a microporous lattice with porphyrinic ligands. This MOF can be used for oxidation of alcohols and for hydrogenation of ethylene. Both the porosity of the lattice and the abihty of the diruthenium centers to chemisorb dioxygen are essential for the performance of the catalyst [62, 64]. 

Deacon, G. B. Phillips, R. (1982). Relationship between the carbon-oxygen stretching frequency of carboxylate complexes and the type of carboxylate coordination. Coordination Chemistry Reviews, 33, 227-50. 

Aluminium toxicity is a major stress factor in many acidic soils. At soil pH levels below 5.0, intense solubilization of mononuclear A1 species strongly limits root growth by multiple cytotoxic effects mainly on root meristems (240,241). There is increasing evidence that A1 complexation with carboxylates released in apical root zones in response to elevated external Al concentration is a widespread mechanism for Al exclusion in many plant species (Fig. 10). Formation of stable Al complexes occurs with citrate, oxalate, tartarate, and—to a lesser extent— also with malate (86,242,243). The Al carboxylate complexes are less toxic than free ionic Al species (244) and are not taken up by plant roots (240). This explains the well-documented alleviatory effects on root growth in many plant species by carboxylate applications (citric, oxalic, and tartaric acids) to the culture media in presence of toxic Al concentrations (8,244,245) Citrate, malate and oxalate are the carboxylate anions reported so far to be released from Al-stressed plant roots (Fig. 10), and Al resistance of species and cultivars seems to be related to the amount of exuded carboxylates (246,247) but also to the ability to maintain the release of carboxylates over extended periods (248). In contrast to P deficiency-induced carboxylate exudation, which usually increases after several days or weeks of the stress treatment (72,113), exudation of carboxylates in response to Al toxicity is a fast reaction occurring within minutes to several hours... 

Carboxylate Complexes with the Lantern -Type Structure... 

The electronic structure of carboxylate complexes with the lantern -type structure was studied [58] using EHT calculations (Fig. 10, Table 5). 

Mercuric o-carborane-l-carboxylate complexes decarboxylated when heated above their melting points or when refluxed in decane or benzene solution [Eq. (102), L = phen, bpy, or (py)2] (109,110). Asymmetric organomercury carboranes and their 1,10-phenanthroline complexes were also formed by thermal decarboxylation [e.g., Eq. (103), R = Me or Ph] (111). 

Polytopic macrocyclic receptors 1, 2 (Figure 10.1) are able to complex the zwitterionic form of the amino acids by a double non-covalent charge interaction [28,29]. The unsymmetrical benzocrown sulfonamide derivative, 2 which contains benzo-18-crown-6 and benzo-15-crown-5 moieties was used as a ditopic receptor for multiple molecular recognition of the amino acids, by combining two non-covalent interactions ammonium-crown hydrogen bonding and carboxylate- complexed Na+-benzo-15-crown-5 charge interactions [28,33]. 

As was stated above, no features that can be attributed to CO " were observed. However, peaks at 1690 cm-1 and 1720 cm" 1 were present in the spectra. The lower of these was attributed to the carboxylate complex. 

It has been several decades since oxo-centered triruthenium-carboxylate complexes with triangular cluster frameworks of Ru3(p3-0)(p-00CR)6 (R = alkyl or aryl) were first isolated [1,2]. In the early 1970s, the first oxo-centered triruthenium complex was structurally characterized by Cotton through X-ray crystal structural determination [3]. Since then, oxo-centered trinuclear ruthenium-carboxylate cluster complexes with general formula [Ru30(00CR)6(L)2L ]n+ (R = aryl or alkyl, L and... 

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