In each of N-(6-amino-3, 4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)valine, C(10)H(15)N(5)O(4) (3) (orthorhombic, P2(1)2(1)2(1)), N-(6-amino-3, 4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)serine monohydrate, C(8)H(11)N(5)O(5).H(2)O (4) (orthorhombic, P2(1)2(1)2(1)), and N-(6-amino-3, 4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)threonine, C(9)H(13)N(5)O(5)(5) (monoclinic, P2(1)), the C-nitroso fragments exhibit almost equal C-N and N-O bond lengths: the C-N range is 1. 315 (3)-1.329 (3) A and the N-O range is 1.293 (3)-1.326 (3) A. In each compound there are also very short intermolecular O-H.O hydrogen bonds, in which carboxyl groups act as hydrogen-bond donors to the nitrosyl O atoms: the O.O distances range from 2.440 (2) to 2. 504 (4) A and the O-H.O angles lie between 161 and 163 degrees. An interpretation of the relationship between the unusual intramolecular bond lengths and the very short intermolecular hydrogen bonds has been developed based on database analysis and computational modelling. In each of (3)-(5) there is an extensive network of intermolecular hydrogen bonds, generating three-dimensional frameworks in (3) and (5), and two-dimensional sheets in (4).

The title anion, (C(7)H(8)N(5)O(4))(-), L(-), forms hydrated metal complexes with a range of metal ions M(+) and M(2+). Lithium and manganese(II) form finite molecular aggregates [Li(L)(H(2)O)(3)] (1) and [Mn(L)(2)(H(2)O)(4)].6H(2)O (4) in which the molecular aggregates are linked into three-dimensional frameworks by extensive hydrogen bonding. The sodium and potassium derivatives, [Na(2)(L)(2)(H(2)O)(3)] (2) and [K(L)(H(2)O)] (3) both form organic-inorganic hybrid sheets in which metal-oxygen ribbons are linked by strips containing only organic ligands: these sheets are linked by hydrogen bonds into three-dimensional frameworks. In (2) the metal-oxygen ribbon is built from pairs of edge-shared trigonal bipyramids linked by water molecules, while in (3) it consists of a continuous chain of vertex-sharing octahedra. The nitroso group in the anion acts as an eta(1) ligand towards Na(+) and as an eta(2) ligand towards K(+). In all cases the anion L(-) shows the same unusual pattern of interatomic distances as the neutral parent LH.

The synergistic action of the different binding groups of the polyfunctional HL receptor leads to the recognition of ADP over ATP in water, with a selectivity coefficient of up to 116, a phenomenon which is unprecedented in the context of synthetic receptors in water. The recognition is mostly due to the good matching between H(3)L(2+) and the protonated forms of ADP.

No abstract

Nine hydrated complexes of Group 2 (alkaline earth) cations with organic ligands which are N-substituted amino acids containing the 6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl group have been structurally characterized. The octahydrated calcium glycinate complex, where the six-coordinate Ca cation lies on an inversion centre in the space group P\bar 1, forms a finite (zero-dimensional) complex. The hexahydrated barium glycinate complex contains eight-coordinate Ba and it is isostructural with the known Sr analogue, and its one-dimensional coordination polymer takes the form of a simple chain. The octahydrated calcium and strontium threonine complexes are isostructural, with eight-coordinate cations lying on twofold rotation axes in the space group C2: the one-dimensional coordination polymers take the form of a chain of spiro-fused rings and a similar chain of spiro-fused rings is found in the heptahydrated barium serine complex, although here the ten-coordinate cation lies in a general position. In the tetrahydrated strontium and barium glycylglycinate complexes, the eight-coordinate cations lie on twofold rotation axes in the space group C2/c, but in the Sr complex the coordination polymer is a chain of spiro-fused rings, while in the Ba complex the coordination polymer forms deeply puckered sheets. There are two types of Ca site in the hexahydrated calcium valine complex: one is eight coordinate and gives rise to a two-dimensional coordination polymer, while the other is seven coordinate forming a finite, zero-dimensional coordination complex. In the heptahydrated barium methionine complex, the coordination polymer is three dimensional. In all of the complexes, the coordination aggregates are further linked by an extensive series of hydrogen bonds.