Dinuclear carboxylates

Until recently, well-authenticated cases of the rhodium(II) oxidation state were rare, with the exception of the dinuclear carboxylates. They fall into two main classes, although there are other rhodium(II) complexes ... 

Dimeric carbonato-bridged complexes A4[Cr2(C03)4(H20)2] (A = NH4, Li, Na, K, Rb, Cs A2 = Mg) can be precipitated166 from aqueous suspensions of the acetate, and the ammonium salt (or CrC03)157 suspended in ether will react with the stronger acids CF3C02H164 and CF2HC02H167 to give dinuclear carboxylates (equation 17). 

There are a number of dinuclear carboxylate complexes of Co" which show interesting magnetic behavior and contain the [Co2(ft-OH2)(RC02)2]2+ or [Co2(/t-X)(/i-RC02)2]+ core (X = OH, Cl, Br), stabilized by chelating nitrogen ligands to complete the octahedral coordination. The latter can be oxidized to mixed-valence ConCom compounds in which the valences are localized.5... 

Table 52 Transition temperatures of some dinuclear carboxylates (93 and 95 to 97) with branched,...

Recently, further orthometallation reactions of phosphines in dinuclear carboxylate complexes were carried out to give compounds of the type [Os2(/x-OOCR)2 /i-P(C6H4)Ph2 2Cl2]/ " The complex [Ru(/x-PhCONH)4Cl] reacts with PPh3 to cause breaking of the phosphorus-phenyl bond with the formation of the phenyl compound [Ru2Ph2(PhCONH)2 Ph2POC(Ph)N 2]. " ... 

While most of the monocarboxylic acids can form quadruply-bridged dinuclear carboxylates with RE(III), with a bridging mode (ID) or (IV), only a few monocarboxylic... 

While most of the monocarboxylic acids can only form dinuclear carboxylates in bridging mode (III), i.e., (1x2-with tile help of auxiliary ligands such as phen, terp, bipy, DMSO, DMF, ethanol, methanol, NO, and even e carboxylate (L ) or the carboxylic acid (HL), trifluoroacetic acid is the only one so far, which can form dinuclear rare earth carboxylates in this mode without any auxiliary ligands. The structure of [GdL3(H20)3]2 (L = trifluoroacetate) is shown in Figure 5(a). This may be due to the unique geometry and the nucleoplulicity of tiie trifluoroacetate ligand. 

Almost all of tiie monocarboxylic acids can form dinuclear carboxylates in bridging mode (IV) with or without auxiliary ligands. The structures of [CeL3(phen)]2 (L = acetate) are shown in Figure 5(b). The two Ce ions are bridged in mode (IV), i.e., ((fi2-rj ri )2 + (M2- S )2). Each of the two Ce ions is then chelated by one simple chelating ( j ) carboxylate ligand and one phen, CN = 9. 

By comparing the structures of the four types of dinuclear carboxylates, we can see the following trends (i) large RE(III) ions prefer bridging modes (II) and (IV), while smaller RE(III) ions prefer modes (I) and (III) (ii) without auxiliary ligands, RE(in) ions tend to form double-bridged structures, i.e., type (I) and (A), whereas with auxiliary ligands, such as phen, bipy, and even other carboxylate anions. 

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