Metal-oxalate networks

Hauser A, von Arx ME, Langford VS, Oetliker U, Kairouani S, Pillonnet A (2004) Photophysical Properties of Three-Dimensional Transition Metal Tris-Oxalate Network Structures. 241 65-96... 

Photophysical Properties of Three-Dimensional Transition Metal Tris-Oxalate Network Structures... 

The two transition metal complexes, [Cr(ox)3]3" and [Cr(bpy)3]3+ (ox=ox-alate, bpy=2,2 -bipyridine) depicted in Fig. 3a are well known chromophores in transition metal photochemistry and photophysics. In the three-dimensional oxalate network structure of composition [Cr(bpy)3][NaCr(ox)3]C104, the two can be combined in an unique manner [16]. The sodium ions, in fact, serve as glue in such a way that each oxalate ligand serves as bridging... 

The corresponding curve in Fig. 9b yields an experimental value for n of 7. This also makes sense from a structural point of view. The nearest neighbour shell around a given donor chromophore in the three-dimensional oxalate network does indeed contain seven sites. However, as shown in Fig. 13, they are not all crystallographically equivalent. One of the seven, with a metal-metal distance RDA of only 6.1 A, sits on the same trigonal axis as the do-... 

A lot of research has also been devoted to the infiltration of macroporous templates by reactive components. Porous polymeric material was synthesized by either infiltration of a monomer-initiator mixture with subsequent polymerization [29], or by infiltration of a prepolymer solution, which can be UV-cured afterwards [27]. A quite common route to fabricate metal oxide networks is to infiltrate the precursor structure with its corresponding sol-gel solution, which eventually hydrolyzes and solidifies in the desired porous shape. This technique has been shown for a great variety of materials (compare Table 2 in [10], Table 1 in [37], and Table 1 in [38]), such as silica [52], titania [30,50], zirconia [30] or aliunina [30], just to mention a few. Another pathway to metal oxide structures was introduced by Park et al., who precipitated acetate salt solutions of the desired material in the free voids. After addition of oxalic acid the porous metal oxide was formed during the combustion of the latex template [73]. 

Chiral-at-metal cations can themselves serve as chirality inducers. For example, optically pure Ru[(bipy)3] proved to be an excellent chiral auxihary for the stereoselective preparation of optically active 3D anionic networks [M(II)Cr(III)(oxalate)3]- n (with M = Mn, Ni), which display interesting magnetic properties. In these networks all of the metalhc centers have the same configuration, z or yl, as the template cation, as shown by CD spectroscopy and X-ray crystallography [43]. 

Clarke BL (1992) Stoichiometric network analysis of the oxalate-persulfate-silver osdllator. J Chem Phys 97 2459-2472 Clarke BL (1995) What is stoichiometric network analysis Web site Alberta University at Edmonton (no longer online) Clemens S, Palmgren MG, Kramer U (2002) A long way ahead understanding and engineering plant metal accumulation. Trends Plant Sci 7 309-315... 

Instead of infiltration with neat metal nanoparticles, the interstitial voids of the template opal can also be filled wifh a mefal precursor. The impregnation of the preformed colloidal crystals with the metal precursor, followed by transformation of the precursor to the neat metal and removal of the template, results in metallic inverse opals. For example, nickel oxalate was precipitated in a PS opal and converted into a NiO macroporous network by calcination of the metal salt and combustion of the polymer. In a subsequent step, the nickel oxide was reduced to neat Ni in a hydrogen atmosphere to yield a macroporous metal network [82]. It was further suggested by the authors that by the same technique other metal networks (e.g.. Mg, Mn, Fe, Zn from their oxides and Ca, Sr, Ba etc. from their carbonates) should be accessible. 

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