Tetranuclear compounds

The N,S-chelate 2-aminoethanethiolate (aet-) forms stable cobalt(III) complexes, including clusters where the S can take on a bridging role. Reaction of [Co(NH3)5C1]2+ with Ni(aet)2 in water for several hours affords the black tetranuclear compound Co4(aet)8, which features act in simple chelate and bridging roles (245).1083 The simple monomeric complex [Co(aet)2(en)]+ has been reported 1084 when heated in water at 50 °C, the trimer Co Co(aet)3 2 is one product, with the central Co surrounded by six bridging S atoms. 

CyNC)AuCl and MeONa in methanol yields a tetranuclear compound [(C6H4S2)Au(CNCy)]2Au2 and a mixed [(isocyanide)(carbene)Au]+Cl complex. Both products are associated into chains with alternating components through aurophilic contacts (Equation (45)).224... 

In the chromium triad, the only claimed tetranuclear compound is the anion [Mo4(CO)u ]2 which was mentioned together with [Mo3(CO)14]2, in a study of the reaction of sodium tetrahydroborate and hexacarbonyl-molybdenum in liquid ammonia14). Later work failed to confirm the existence of the trinuclear anions, [M3(CO)i4]2 (M = Cr, Mo, W)109 1S0,169 and, therefore, the real existence of the tetranuclear anion also seems dubious. 

Because of the large number of carbonyl groups required to satisfy the noble gas rule and the relatively small metallic radius, serious steric limitations are present for manganese tetranuclear closed clusters12). The only known tetranuclear compounds are some mixed clusters, MnOs3(CO)16H and MnOs3(CO)13H3 (see later), which have been prepared from Os3(CO)12 and [Mn(CO)s] 161). 

The increase of the potential, at which the oxidation of the metal ions coordinated to the 2,3-Medpp ligand takes place, is further evidenced by the different behavior of the tetranuclear compound 4A and (Scheme 1 and Thble 1). As clearly indicated by the differential pulse voltammetry, which exhibits a three-electron oxidation peak for the former and a one-electron oxidation peak for the latter (Figure 14), in 4A the oxidation involves the three peripheral Ru units (as mentioned before), whereas in 4J, only the central Ru unit can be oxidized in the accessible potential window (Table 2). 

In the case of tetranuclear compounds belonging to the polypyridine family, all four possible energy migration patterns, schematized in Figure 21, have been obtained. Pattern (i) is found for L = bpy, BL = 2,3-dpp, and M = Ru. In such a complex, the three peripheral units are equivalent and Aeir lowest excited state lies at lower energy than the lowest excited state of the central unit.The reverse... 

Figure 21. Energy-migration patterns in tetranuclear compounds. Empty and full labels indicate and Os, respectively. In the peripheral positions, circles and squares indicate M(bpy)j and M(biq)j components, respectively. For the bridging ligands -W- = 2,3-dpp — 2,5-dpp.

Bi- and tetranuclear, three-center two-electron gold(I) complexes have been prepared containing polyfluorophenyl groups (129). The binuclear complexes are of the type discussed previously, [Ar(AuL)2]X and [Ar Au2(dpe) ]BF4, whereas the diarylaurates reacted to give tetranuclear compounds [Eq. (35)] suggested to be of the same type as the mixed metal complexes discussed above. 

Molecular weight determinations by cryoscopy in benzene revealed that the MLi2BrAr2 stoichiometry found in the solid state is retained in solution. On the basis of NMR and cryoscopy, it can be concluded that the structural features of the bromoaurate are similar to those of the bromocuprate and -argentate. A multinuclear NMR study shows that the bonding between the [Li-Br-Li] and [Ar-M-Ar] is intermediate between ionic and covalent, with a more covalent Au-C,pjo bond than the Cu-C o or Ag-Cipso ones. A similar trend has also been reported previously by van Koten for tetranuclear compounds of the type [M2Li2 2-CH2NMe2C6H4 4] (M = Cu, Ag, Au).125... 

Another effect of aggregation is to allow the formation of core-substituted clusters. o-(Trifluoromethyl)phenylcopper exchanges with its silver analog to give copper-silver tetranuclear compounds of the type AgnCu4 (o-CFgCgH4)4, the parent ions of which have been detected by mass spectroscopy. The C—Ag bonds break preferentially on thermal decomposition, leaving the copper compound (37). A mixed cluster compound was also isolated by Seitz and Madl (258). Core substitution... 

Dodecacarbonyltetrarhodium(O), Rh4(CO)i2, is prepared from RhCfr and CO at 200 atm in the presence of a halogen acceptor, such as copper, silver, cadmium, or zinc. The nature of the products depends on the temperature at 50-80 °C the tetranuclear compound is mainly formed, whereas at... 

The tetranuclear compounds [V402(02CEt)7(bpy)2]-[CIO4] (bpy = 2,2-bipyridine), and the related complex [NEt4][V402(02CEt)7(pic)2] (pic = 2-picolinate) have a [ 402] + butterfly core (3) and a 5 = 3 ground state. ... 

The reaction of AcBu-f with NaHMDS gives the tetranuclear compound [Na /X3-0(=CH2)Bu-f (AcBu-f )]a, a type 9 structure like that of its thf lithium analogue. However, the potassium complex crystallizes with thf and its structure is hexameric type 10 [Kgf/zs-OC(Bu-r)=CH2 6(thf)6]. ... 

Treatment of [W(PMe3)3H6] with BunLi, NaH or KH gave [W(PMe3)3H5M] (M = Li, Na (15-crown-5) or K(18-crown-6)). The tetranuclear compound [W(PMe3)3H5Li ]4 (with bridging by... 

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