Metal-oxalato

This thinking applies, in particular, when planning the design of a chiral three-dimensional supramolecular host-guest system, since the mutual interaction of the two distinct complementary molecular units or coordination entities is necessary. Examples of this methodology include the above-described anionic, tris-chelated transition metal oxalato complexes [Mzl(ox)3/6 which form the host system together with the cationic, tris-chelated transition metal diimino complexes, e.g. [M(bpy)3]21/31, bpy = 2,2 -bipyridine, which play the role of the guest compounds. 

The Raman spectra of metal oxalato complexes have also been examined to investigate the solution equilibria and the nature of the M-O bond. Vibrational assignments have been made on metal oxamido complexes of V , symmetry ... 

Figure 29 Sketch of the building blocks of metal-oxalato derivatives.

The actual structure of the polymers will depend also on the nature of the cations which are needed to counterbalance the negative charges on the metal-oxalato framework. " The most investigated systems are the 2D ones, where an ordered array of M and M ions is observed as shown in Figure 31. An interesting example is provided " by A[Fe"Fe" (ox)3],... 

Table 57 hRf Values of Metal Oxalato and Thiocyanate Complexes... 

Molecular Recognition Processes between Nucleobases and Metal-Oxalato Frameworks... 

IV. HYBRID SYSTEMS BASED ON METAL-OXALATO AND PROTONATED NUCLEOBASES... 

It should be pointed out that the parallel orientation of the purine ligands with respect to the metal-oxalato framework locates the nonprotonated minor groove N3 atom over the carbon-carbon bond of one centrosymetric oxalato ligand with a mean N3 C distance of 3.0 A and a dihedral angle between the pyrimidinic ring and the oxalato plane of 90° (Fig. 8). This fact precludes the involvement of the potential hydrogen-bonding N3 atom in any other interaction. 

The different coordination sites of the adenine nucleobase generate a markedly different topology of the polymerie ehains, relative to the purine complexes. The coordinated adenine molecules are almost perpendicular to the metal-oxalato framework instead of being arranged along the growing axis of the polymeric chain like in the purine complexes. This feature results in the presence of bulkier chains, which leads to a less effective packing with crystallization water molecules and noncoordinated adenine molecules inserted between the chains. 

Hybrid Systems Based on Metal-Oxalato and Protonated Nucleobases 433... 

Cytosinium compounds display the desired layered supramolecular structure in which homomeric cationic ribbon-like ID supramolecular aggregates are inserted between 2D hydrogen-bonded sheets of metal-oxalato complexes. Nevertheless, the projected fork-like interactions are absent owing to the distinctive features of the self-assembling pattern of the nucleobase ribbons. 

To verify the feasible stabilization of noncanonical forms of the protonated adenine nucleobase, we extended our B3LYP/6-31G(d) calculations to the study of the tautomeric forms of isolated cations on a water-simulated dielectric medium and including different metal-oxalato surroundings simulating those experimentally found in the eompoimds. 

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