Carboxylate paddlewheel

A final TCPP MOF of interest is found in a report that described the synthesis of M + (TCPP) (M +=Cu +, Ni +, and Pd + ) MOFs with dirhodium(II) carboxylate paddlewheel SBUs (110). The compounds were prepared via solvothermal reaction of rhodium acetate and M (TCPP) in methanol. The materials were poly cry stalline, and so structural information was deduced from powder X-ray deffraction (PXRD), elemental analysis, infrared (IR) spectroscopy, and other... 

More recently. Hupp and Nguyen used salen-based chiral Mn-complex as a chiral linker to generate chiral MOPM through pillaring with Zn-carboxylate paddlewheel [54], Bu et al. also employed the same sbategy to consbuct several homochiral open-framework materials using homochiral camphoric acid as a rigid linker [55]. 

Another noticeable example of an MOF constructed from a polytopic carboxylic acid and the binuclear metal-carboxylate paddlewheel-like cluster MBB, equivalent to a square planar SBU, is the one commonly referred to as HKUST-1 MOF, with the general formula [Cu3(TMA)2 (H20)3] where TMA denotes trimesic acid (1,3,5-benzene-tricarboxylic acid) (Figure 13, ). The MBB is defined by four carboxylate ions coordinating two Cu(II) ions in a paddlewheel-like structure with four points of extension defining a square-planar SBU. The authors reported the capability of exchanging the axial water molecules coordinated to the Cu(II) paddlewheel, postsynthetically, with pyridine molecules, opening the door for further investigations toward the viability of preferential sorption of small molecules and/or catalysis on coordinatively unsaturated metal centers. 

Figure 29 (From left to right) Combination of 5-(l//-tetrazol-5-yl)-isophthalic acid and Cn(II)-carboxylate paddlewheel (MBBs) generate the rhombihexahedron, SBB. Association of the SBBs throngh tetrazolate-Cu(II) trinnclear clnsters, MBBs, generate the rht-MOF. Cu (green), N (blue), C (gray), O (red), hydrogen atoms and disordwed guest molecules are omitted for clarity. Yellow and purple spheres represent the largest, gnest-accessible, voids within the rht-MOF.

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... 

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.)...

Many carboxylic acids exist in the free state as hydrogen-bonded dimers with an oxygen-oxygen separation (between oxygens linked to the same carbon atom) close to 220 pm. Replacement of these hydrogens by two metal atoms results in the close approach of the two metal atoms.28 Much of the interest in these dinuclear paddlewheel systems has been generated by a need to understand the nature of these metal-metal interactions. The natural desire of chemists is to use formal bond orders as an index of this interaction and much has been published to this end. However, there are growing indications that such a formal concept is not entirely appropriate for such systems.29... 

Chromium complexes acetylacetone complex formation, 386 exchange reactions, 380 amidines, 276 bridging ligands, 198 chelating ligands, 203 carbamic add, 450 paddlewheel structure, 451 carboxylic adds, 438 trinuclear, 441 oorroles, 874... 

An elegant and efficient approach for the synthesis of structural models of carboxylate-rich non-heme dinuclear iron proteins involves the use of bulky ligands of the terphenyl carboxylate family [47, 48]. The resulting dinuclear iron(II) complexes can adopt two conformations, called the windmill and the paddlewheel motif (Scheme 2.9). 

Scheme 2.9 Equilibrium between windmill (left) and paddlewheel (right) structures of dinuclear iron(ll) complexes comprising ligands from the terphenyl carboxylate family (Scheme 2.8b).

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.

Carbamate (R2NC02 ) complexes are similar electronically and structurally to monocarboxylate complexes, although they are not as accessible synthetically and are generally less stable. Unidentate, chelate, and bridging coordination modes have been observed, although the number of bridging modes found to date is less than that known for carboxylates. Syn-syn bridging is the most common, and bimetallic paddlewheel type structures (53) are known. 

Dioxygen binding rates to diiron-carboxylate cores can be retarded and oxygenated intermediate can be trapped by embedding the metal complex into dendrimers.96 A third-generation dendrimer assembled around a paddlewheel diiron complex with 02CArTo1 reacts with 02 300 times slower than its nondendritic counterpart. 

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