Paddlewheel Complexes

Figure 4.2 A number of secondary building units encountered in MOFs (a) the paddlewheel complex (b) the trioctahedral bipyramidal complex and (c) the infinite chain of octahedra. The squares and octahedra represent the metals within their...

The oxidation of a Cr24+ paddlewheel complex had previously been studied by X-band EPR but revealed only a single line near g = 2. However, at 95 GHz the analysis40 of the spectra of Cr2[(PhN)2CN(CH2)4]4PF6 and [Mo2(TiPB)4]PF6, where (TiPB) is the anion of 2,4,6-triisopropylbenzoic acid, provided the values for Cr of = 1.9701 and gt — 1.9767, and for Mo of = 1.9427, gyy = 1.9358 and g%% — 1.9310. The unpaired electrons were deduced to reside on the metal-based, rather than the ligand-based, orbitals. This proved that for both Cr and Mo the complex is of the form M25+ and correct the attribution for Cr based on the X-band spectra. This was the first confirmed report of the oxidation of a Cr24+ paddlewheel complex comparable to the Mo25+ compounds. 

Localized-to-delocahzed transition in mixed-valence chemistry Ditungsten paddlewheel complex, a powerful reductant... 

In the further investigation of divanadium paddlewheel complexes, 1,3,4,6,7,8-hexahydro-2H-pyrimido[l,2-a]pyrimidine (Hhpp) shown in Figure 12 coordinated as an anion to form... 

With the exception of [( 6-C5H3(But)2)Nb2(/i-ry6 6-P6)] (2.828(1) A),91 low oxidation state Nb—Nb triply bonded complexes fall primarily into two categories, anionic face-sharing bioctahedral or paddlewheel complexes. In 1997, NbCl3(DME), where DME is dimethoxyethane, was reacted with... 

Figure 22 ORTEP drawing of the paddlewheel complex Nb2(hpp)4 (reproduced by permission of the American Chemical Society from J. Am. Chem. Soc. 1997, 119, 7889-7890).

Dioxygen diiron complexes have been synthesized by mimicking the probable intermediate structures in methane monooxygenase oxygenations. Examples are summarized in the recent review. One is the Fc2(i7-0)2 diamond core type and the other is the Fe2(tJ-02) peroxo type. Recently, an unusual Fe"-X-Fe (tl -02) species has been suggested in the reaction of O2 with carboxylate-bridged diiron(II,II) paddlewheel complexes, but its role in the oxygenation has not been clarified. ... 

Table 5.3 Structural data for vanadium paddlewheel complexes.

Table 5.4 Structural matrices of niobium paddlewheel complexes.

Figure 5.14 ORTEP drawing of paddlewheel complex. (Reprinted with permission of American Chemical...

The first diruthenium paddlewheel complex, RUjfii-OjCMej Cl, was prepared in 1966 by Stephenson and Wilkinson [3]. The paddlewheel geometry was validated in 1969 when Cotton and coworkers reported the X-ray crystal structure of an analogous complex, Ru2(p-OjC"Pr) Cl [4j. In the crystal, RUjlii-OjC Prl Cl assembles in an infinite zig-zag chain, where each chloride atom bridges two diruthenium units. More significantly, a short Ru-Ru bond distance of 2.281(4) A was revealed. The FSR of this bond is 0.92, which is consistent with a multiple bond order. 

The RUj non-paddlewheel complexes can be classified by their geometry - tetragon2il versus trigonal - and further classified by their supporting ligands. Nearly all the unsupported Ruj complexes are tetragonal. 

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