Neutron and X-ray diffraction study of a macrocyclic nickel(II) complex with NiII in a pseudoaromatic chelate ring

Amino-substituted O6-benzyl-5-nitrosopyrimidines: interplay of molecular, molecular-electronic and supramolecular structures

“…Secondly, bonds b and f are of similar length, while bond c is always much shorter than bond b. Finally, bonds j and k are similar in length, although in simple neutral compounds where there is no possibility of signi®cant electronic delocalization these distances normally differ by at least 0.20 A Ê (Talberg, 1977;Schlemper et al, 1986) and the NO distance rarely exceeds 1.25 A Ê (Davis et al, 1965;Bauer & Andreassen, 1972;Talberg, 1977;Schlemper et al, 1986). These observations taken together con®rm the polarized form (B) as the dominant contributor to the overall electronic structure, rather than the classical charge-localized form (A):…”

catena-Poly[[[aquachloridocopper(II)]-μ-N-(6-amino-3-methyl-5-nitroso-4-oxo-3,4-dihydropyrimidin-2-yl)glycinato] monohydrate] redetermined at 120 K: a highly polarized ligand within coordination polymer chains linked by hydrogen bonds

“…Displacement ellipsoids are shown at the 30% probability level. [Symmetry codes: Schlemper et al, 1986). Taken together, these observations indicate that the polarized, charge-separated form B (see scheme) is a more appropriate representation of the electronic structure than the classically localized form A.…”

4,6-Diamino-2-morpholino-5-nitrosopyrimidine: a polarized molecular structure within hydrogen-bonded sheets

“…is striking. The C5-N5 and N5-O5 distances in the nitroso group are rather similar, differing by less than 0.06 Å , whereas in simple unperturbed C-nitroso compounds, where no polarization of the structure can occur, the N-O distance is generally less than 1.25 Å (Davis et al, 1965;Bauer & Andreassen, 1972;Talberg, 1977;Schlemper et al, 1986), while the difference between the C-N and N-O distances is usually greater than 0.20 Å (Talberg, 1977;Schlemper et al, 1986). In sum, these observations point to the occurrence of significant contributions to the overall electronic structure from polarized forms (Ia) and (Ib), as well as from classical aromatic form (I) (see scheme).…”