A series of dizinc(II) complexes based on the pyrazolate ligands 3-[(1E)-N-hydroxyethanimidoyl]-4-methyl-1H-pyrazole-5-carboxylic acid (H(3)L(1)), (1E,1'E)-1,1'-(4-methyl-1H-pyrazole-3,5-diyl)diethanone dihydrazone (HL(2)), (E,E)-(4-methyl-1H-pyrazole-3,5-diyl)bis(methylmethanone) dioxime (H(3)L(3)), (E,E)-(4-phenyl-1H-pyrazole-3,5-diyl)bis(phenylmethanone) dioxime (H(3)L(4)), and 1H-pyrazole-3,5-dicarboxylic acid (H(3)L(5)) have been synthesized and investigated as functional models of phosphoesterases, focusing on correlations between the hydrolytic activity and molecular parameters of the bimetallic core. Speciation of the various dizinc complexes in solution has been determined potentiometrically, and the structures in the solid state have been established by X-ray crystallography. The hydrolysis of two phosphoesters, an RNA model 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) and the pesticide paraoxon-ethyl (POE), promoted by the dinuclear phosphoesterase model complexes has been investigated in DMSO/buffered water (1:1) at 50 degrees C as a function of complex concentration, substrate concentration, and pH. Drastic differences in the hydrolytic activities of [Zn(2)(HL(1))(2)](0), [Zn(2)(L(2))(2)](2+), [Zn(2)(H(2)L(3))(2)](2+), and [Zn(2)(HL(5))(2)](2-) are observed and can be attributed to molecular peculiarities. Pyrazolate-bridged dinuclear zinc(II) complexes seem to provide a sufficient number of coordination sites for both activating the substrate and generating the nucleophile, where the phosphate esters are preferentially bound in a bidentate bridging fashion (in the case of HPNP) and in a monodentate fashion (in the case of POE).

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In the crystal, strong O—H⋯N hydrogen bonds link the mol­ecules into supra­mol­ecular chains propagating along the c-axis direction.

The title structure, C9H11N3O2, is a racemate. The chiral centre is situated at the N—C—N C atom of the imidazolidine ring. The inter­planar angle between the mean planes of the pyridine and imidazolidine rings is 89.41 (5)°. The methyl group is in a trans position with respect to the pyridine N atom. In the crystal, the mol­ecules are arranged in zigzag layers parallel to the b axis. The mol­ecules within the layers are inter­connected by strong O—H⋯N and weak N—H⋯O hydrogen bonds; the former take place between OH groups and amine N atoms and the latter between the amine N atom and the carbonyl O atom. In addition, C—H⋯O inter­actions are also present.

Oximes, PhenanthrolineThe new mixed metal assembly [Ni (phen)3][Cu(H.ipap)]2(N0 3 ) * 8 H2O (2) (Ehpap = CH 3-C(=N0 H)-C(0 )-NH-(CH2)3-NH-C(0 )-C(=N0 H )-CH 3) was obtained by co-crystallisation of [Li(H20)4][Cu(H.ipap)] • 2 H20 (1) and tris(l,10-phenanthroline)nickel(II) nitrate and studied by means of X-ray crystallography (triclinic, space group P i, a = 13.471(3), b = 13.641(3), c = 15.401(3) A, a = 108.21(3), ß = 97.73(3),7 = 107.74(3)°, V = 2476.6(9) A , Z = 2 ,R \ = 0.0677 for 4672 unique reflections with I > 2a(I)). The assembly indicates a network structure and consists of isolated cationic and anionic modules (octahedral [Ni(phen)3]2+ and square-planar [Cu(H.lPaP)]), non-coordinated nitrate anions and solvating water molecules. The elements of the crystal structure are linked by interactions of different types: by an extended system of H bonds, stacking interactions between aromatic rings, long apical Cu-N contacts and specific 7r-7r interaction between a deprotonated oxime group of the complex anion and a phenanthroline ligand.