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Two cobalt oxyfluoride antiferromagnets CoMOF5(pyz)(H2O)2(M = Nb 1, Ta 2; pyz = pyrazine) have been synthesized via conventional hydrothermal methods and characterized by thermogravimetric (TGA) analysis, FTIR spectroscopy, electron spin resonance (ESR), magnetic susceptibility, and magnetization measurements at both static low field and pulsed high field. The single-crystal X-ray diffraction indicates both compounds 1and 2are isostructural and crystallize in the monoclinic space group C2/mwith a two-dimensional Co2+triangular lattice in the abplane, separated by the nonmagnetic MOF5(M = Nb 1, Ta 2) octahedra along the c-axis with large intertriangular-lattice Co···Co distance. Because of low dimensionality together with frustrated triangular lattice, compounds 1and 2exhibit no long-range antiferromagnetic order until ∼3.7 K. Moreover, a spin flop transition is observed in the magnetization curves at 2 K for both compounds, which is further confirmed by ESR spectra. In addition, the ESR spectra suggest the presence of a zero-field spin gap in both compounds. The high field magnetization measured at 2 K saturates at ∼7 T with Ms= 1.55 μBfor 1and 1.71 μBfor 2, respectively, after subtracting the Van Vleck paramagnetic contribution, which is usually observed for Co2+ions with pseudospin spin of 1/2 at low temperature. Powder-averaged magnetic anisotropy of g= 3.10 for 1(3.42 for 2) and magnetic superexchange interaction J/kB= −3.2 K for 1(−3.6 K for 2) are obtained.

RNase Z is a dinuclear zinc enzyme that catalyzes the removal of the tRNA 3′end trailer. Density functional theory is used to investigate the phosphodiester hydrolysis mechanism of this enzyme with a model of the active site constructed on the basis of the crystal structure. The calculations imply that the reaction proceeds through two steps. The first step is a nucleophilic attack by a bridging hydroxide coupled with protonation of the leaving group by a GluHis diad. Subsequently, a water molecule activated by the same GluHis diad makes a reverse attack, regenerating the bridging hydroxide. The second step is calculated to be the ratelimiting step with a barrier of 18 kcalmol, in good agreement with experimental kinetic studies. Both zinc ions participate in substrate binding and orientation, facilitating nucleophilic attack. In addition, they act as electrophilic catalysts to stabilize the pentacoordinate trigonalbipyramidal transition states.© WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009