Trinuclear chromium structures

A very recent and exciting example of a 3-D coordination polymers can found in the work of Ferey et al,25 on the use of trinuclear chromium clusters in combination with benzene-1,4-dicarboxylic acid. This reaction yields porous structures with unit cells volumes of up to 700 000 A3, i.e. similar to that of a small protein In the absence of single crystals for structure determination, the structures were solved by the ingenious use of Monte Carlo simulations with simulated annealing. 

An intercalation process under reflux conditions for 4 days has been performed by Ma et al. to prepare chromium oxide-pillared manganese oxides [38]. In this reaction chromium hydroxyl acetate clusters, Cr3(OAc)7(OH)2, are used as the pillaring species. Cr + self-polymerizes under reflux to form polynuclear clusters between the manganese oxide layers. Intercalation of this trinuclear chromium complex constitutes a challenge because redox reactions may occur between manganese oxide and the transition metal oxide during the process, which could destroy the layer structure. 

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... 

Further condensation of the dinuclear species may occur either by continuing the edge-to-edge condensation, which leads to linear trinuclear structures such as 4a and 4b, or by condensation of a third chromium ion to each of the two chromium(III) centers in structure 2, yielding the cyclic structure 5. The (NH3)4Co(OH)2Co(CN)2(OH)2-Co(NH3)43+ cation (49) possesses structure 4a, and there is good evidence that the trinuclear amine complex Cr3(en)5(OH)45+ has the same structure (42). The linear trinuclear structure 4b has not been observed in crystal structures. The cyclic, trinuclear structure 5 has been observed in crystal structures of chromium(III) complexes with ammonia, tacn, and bispicam (40, 50, 51). 

The trinuclear cation Cr,(NH,) 0(OH)45 and the tetranuclear cation Crj(OH),Cr(NH have been prepared similarly by the Cr(II) charcoal catalytic method and were separated by cation-exchange chromatography (40). The trinuclear species was isolated as a bromide salt and has structure 5 in Fig. 1. The tetranuclear species Cr[(0H),Cr(NH,)4[/f has been shown to be a chromium ammonia analog of the so-called Werner s brown salt, Co[(OH)2Co(en),J 3f,f (structure 6 in Fig. 1) (41). 

Fig. 10. A possible structure of the trinuclear aqua chromium(III) species Cr, (OH)45, . The metal ions and hydroxo bridges are indicated by O and , respectively. Another very plausible structure is 4a in Fig. 1.

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... 

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