Lantern structures

Figure 1.32 The lantern structure adopted by Ru2(OAc)4C1 and other similar compounds.

They have binuclear tetracarboxylate-bridged lantern structures in the butyrate Os-Os is 2.301 A and Os-Cl 2.417 A. Most reactions involve cleavage of the Os-Os bond (Figure 1.66). 

These compounds all have the lantern structure shown in Figure 2.35. 

Figure 2.35 The lantern structure adopted by dimeric rhodium(II) carboxylates.

The lantern structure is quite stable, unlike certain other Rh2 dimers. Protonation was formerly claimed to give Rh2+ aqua ions, but they are believed now to be [Rh2(OCOMe)3]+ (aq.) and [Rh2(OCOMe)2]2+ (aq.) [73],... 

Other compounds with the lantern structure include the acetamidates Rh2(MeCONH)4L2 and the mixed-valence anilinopyridinate Rh2(ap)4Cl (Figure 2.39), which has an unusual ESR spectrum in that the electron is localized on one rhodium [79]. 

Figure 2.39 The lantern structure of the dimeric rhodium antipyrine complex Rh2(ap)4Cl. (Reprinted with permission from Inorg. Chem., 1988, 27, 3783. Copyright (1988) American...

The iridium(II) complexes are rarer that those of rhodium(II). Iridium does not seem to form carboxylates Ir2(02CR)4 with the lantern structure complexes analogous to trans-RhX2 (PR3 )2 are not formed with bulky tertiary phosphines, probably because the greater strength of Ir-H bonds leads to IrHX2(PR3)2. 

Platinum(III) complexes are remarkably rare and most examples date from less than 30 years ago. The great majority are dimeric species with only a few authenticated stable monomers reported. Most of the dimers are bridged by bidentate ligands and are almost exclusively doubly or quadruply bridged, the latter giving rise to the classic lantern structure. 

Unsolvated [Rh2(OCOR)4]2 can be obtained by sublimation. The lantern structure is retained with the axial position occupied by oxygens from neighbouring dimer units. The presence of axial ligands has little effect on the Rh-Rh bond therefore, in [Rh2(OCOCF3)4] Rh-Rh is 2.382 A compared with 2.394 A in [Rh2(OCOCF3)4(H202)] and 2.418 A in Rh2(OCOCF3)4 (MeCN)2 [74],... 

Rhodium(II) forms a dimeric complex with a lantern structure composed of four bridging hgands and two axial binding sites. Traditionally rhodium catalysts faU into three main categories the carboxylates, the perfluorinated carboxylates, and the carboxamides. Of these, the two main bridging frameworks are the carboxylate 10 and carboxamide 11 structures. Despite the similarity in the bridging moiety, the reactivity of the perfluorinated carboxylates is demonstrably different from that of the alkyl or even aryl carboxylates. Sohd-phase crystal structures usually have the axial positions of the catalyst occupied by an electron donor, such as an alcohol, ether, amine, or sulfoxide. By far the most widely used rhodium] 11) catalyst is rhodium(II) acetate [Rh2(OAc)4], but almost every variety of rhodium] 11) catalyst is commercially available. 

Lantern structure, in bridging triazenide transition metal complexes, 30 10, 32 Lantern-type complexes, see Dinuclear complexes, quadruply bridged Lanthanides, see also Metals, ions specific elements... 

Figure 9.42 Secondary Building Units (SBU) using carboxylates with rigid coordination geometries that replace metal ions as vertices in MOFs. (a) Paddlewheel or lantern structure as in 9.17, (b) octahedral basic zinc acetate SBU used in MOF-5 and (c) a trigonal prismatic oxo-centred trimer. The poly-hedra use carboxylate carbon atoms as their vertices and the MOFs propagate via the linkers attached to these carbon atoms. The metal atoms are bound to only terminal ligands in addition to those shown.

The benzamidato complex Os2Cl2(NHCOPh)4 is made from Os2(OAc)4Cl2 and molten benza-mide, and Os2Br2(NHCOPh)4 from the chloro species and Br . The X-ray crystal structures show these to have lantern structures with four bridging benzamido ligands and the halide ligands axial. Each has two closely related molecules in the unit cell with slightly different structures. For the chloro complex the mean distances are Os—Os = 2.367, Os—Cl = 2.491, Os—O = 1.99 and Os—N = 2.02 A for the bromo species the mean values are Os—Os = 2.384, Os—Br = 2.610, Os—O = 2.02 and Os—N = 1.93 A.870 871... 

Despite the vast number of cobalt(IT) complexes known, the dipositive oxidation state is rare for rhodium. The bulk of the rhodium(ri) complexes known are dimeric, the classic examples being the diamagnetic carboxylato complexes that adopt the classic lantern structure (26). However, even the aqua complex is dimeric so the bridging carboxylato ligands are not essential for the formation of the rhodium-rhodium bond. 

There seem to be very few complexes in which there are two rhodium ions in different oxidation states. The best-authenticated examples are the [RhH2(PR3)2]2 complexes (R = NMe2, PfOPr1 ]. The dimethylamino complex has been shown to have the structure (129) and contains both rhodium(I) and rhodium(III).1287 The other example is provided by the [Rh(02CMe)2]+ ion in [Rh(02CMe)2]2C104. This ion retains the classic lantern structure of the rhodium(II) carboxylato complexes, but the salt contains both rhodium(II) and rhodium(III).1288... 

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