Paddlewheels

Chromium, (ri6-benzene)tricarbonyl-stereochemistry nomenclature, 1,131 Chromium complexes, 3,699-948 acetylacetone complex formation, 2,386 exchange reactions, 2,380 amidines, 2,276 bridging ligands, 2,198 chelating ligands, 2,203 anionic oxo halides, 3,944 applications, 6,1014 azo dyes, 6,41 biological effects, 3,947 carbamic acid, 2,450 paddlewheel structure, 2, 451 carboxylic acids, 2,438 trinuclear, 2, 441 carcinogenicity, 3, 947 corroles, 2, 874 crystal structures, 3, 702 cyanides, 3, 703 1,4-diaza-1,3-butadiene, 2,209 1,3-diketones... 

E. Dinuclear lantern and paddlewheel -type amidinate and guanidinate 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...

Another MOF constructed from Cu paddlewheel SBUs and with 5-nitro-1,3-benzenedicarboxylate as the ligand can be used for the acetylation of methyl 4-hydroxybenzoate with acetic acid anhydride. The framework did not remain intact upon exposure to acetic acid, one of the reaction products [53]. 

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]. 

Figure 4.5 A MOF oxidation catalyst based on Cu paddlewheels connected by 1,4-trans-cyclohexane-dicarboxylate ligands (only carboxylate groups are explicitly shown). After oxidation by H2O2, paddlewheels are linked by peroxo bridges (Cu = blue O = red C = gray) [34], (Reproduced by permission of the Royal Society of Chemistry.)...

A MOF constructed from rhodium paddlewheel clusters linked to porphyrinic ligands already discussed in Section 4.3.1.1 shows an interesting synergetic behavior when the porphyrinic rings are loaded with metals like Cu , Ni , or Pd . In the hydrogenation of olefins, the hydride species at the rhodium center is transferred to the coordinated olefin adsorbed on a metal ion in the center of the porphyrin ring to form an alkyl species, and next this alkyl species reacts with a hydride species activated at the rhodium center to form the alkane [81]. 

Another example of rr-delocalized radical is cyclopentadienyl 43, which was reported by Sitzmann et al. to be rendered persistent and crystalline by derivatization with /io-propyl groups as in radical 44 (Fig. 7.19). ° "° An interesting feature in the X-ray structure of 44 is that the /io-propyl groups adopt a paddlewheel-like conformation, also showing disorder in the crystal. The bond distances show that the radical is not Dsh symmetric, but that it is slightly distorted (C1-C2 = 1.412 A, C2-C3 = 1.401 A). Radical 44 also packs in a columnar motif with rings eclipsing each other... 

We consider the work term to be composed of that pertaining to forces associated with turning paddlewheel shafts and shear stress (Ws), and work associated with normal pressure forces (Wp). For most applications in fire, Ws will not apply and therefore we will ignore it here. For the piston of face area, A, the work due to pressure (p) on the surroundings, moving at a distance (x2 x ), is... 

You can imagine the two atoms pressed onto a flat surface the bond axis is the imaginary line on this surface. The pi bonds connect the two atoms above the line and below the line. If you were to rotate the bonded atoms around the imaginary line, the pi bonds would rise up off the surface and sink below the surface as you rotated them, like the planks on a paddlewheel rise above the surface of the water and then sink below the surface of the water. 

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. 

The advanced integrated pond (AIP) system, shown in Figure 16.24, is a method of wastewater treatment that makes sense for many communities of 2000 to 10,000 people in both developed and developing nations. Wastewater is channeled into an extensive pond system where plants use nutrients from the sewage as fertilizer. A system of paddlewheels guarantees constant aeration of the effluent,... 

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