Ni(bipy)2Ni(CN)4, a new type of one‐dimensional square tetra­cyano complex

The one‐dimensional structure of catena‐poly­[[bis(2,2′‐bi­pyri­dyl‐1κ²N,N′)‐μ‐cyano‐1:2κ²N:C‐di­cyano‐2κ²C‐di­nickel(II)]‐μ‐cyano‐C:N], [Ni₂(CN)₄(C₁₀H₈N₂)₂]_n, consists of infinite zigzag chains running parallel to the c axis. The chains are composed of paramagnetic [Ni(bipy)₂]²⁺ cations (bricks; nickel on a twofold axis) linked by diamagnetic [Ni(CN)₄]^2? anions (mortar; nickel on an inversion center) via bridging cyano groups. The bridging cyano groups occupy cis positions in the cation and trans positions in the anion, giving rise to a new previously unknown CT‐type chain (i.e. cis–trans‐type) among square tetra­cyano complexes. The coordination polyhedron of the paramagnetic Ni atom (twofold symmetry) is a slightly deformed octahedron with the two Ni—N(bipy) bonds in cis positions being somewhat longer [2.112 (3) Å] than the remaining four Ni—N bonds with a mean value of 2.065 (6) Å. The bond distances and angles in the anion have typical values.     

Largest mixed transition metal/actinide cluster: a bimetallic Mn/Th complex with a [Mn10Th6O22(OH)2]18+ core

A high-nuclearity mixed transition metal/actinide complex has been prepared from the reaction of a Mn(III)4 complex with Th(NO3)4 in MeCN/MeOH. The complex [Th6Mn10O22(OH)2(O2CPh)16(NO3)2-(H2O)8] is the largest such complex to date and the first Th/Mn species. It is rich in oxide groups, which stabilize all of the metals in the high Th(IV) and Mn(IV) oxidation levels. Magnetic characterization establishes that the complex has an S = 3 ground-state spin value.     

Ab initio and experimental thermodynamic and kinetic study of proton-assisted bond activation in gaseous hydrocarbons: deconvolution of reaction efficiencies in the case of adamantane

1) Protonation at all possible sites of adamantane (C(10)H(16)) was studied at the MP2/6-311++G(3df,2p)//MP2/6-311++G(d,p) level. This provided values of the changes in the thermodynamic state functions for these processes. Whenever direct comparison was possible, the agreement with experimental data was very good. 2) By the same means, the reaction paths linking the various species obtained in these reactions were analyzed. 3) Fourier transform ion cyclotron resonance (FT-ICR) spectroscopy was used to determine the rate constants for proton transfer from 16 protonated reference bases to adamantane in the gas phase. Also, the rate constants for the formation of ionic products in these reactions were determined. 4) The experimental reaction rates were successfully predicted and refined on the basis of a simple mechanistic model based on the reaction profiles indicated above. 5) Our results hint at the potential usefulness of this approach for mechanistic studies.     

Self-complementary purines by quadruple hydrogen bonding

The first discrete, self-complementary, quadruply hydrogen-bonded complexes based on the 2,6-diaminopurine (DAP) scaffold have been prepared; regioselective urea formation at the C2 amino group of the heterocycle allows intermolecular dimerization (K(dim) approximately 1-1.6 x 10(3) M(-1) in CDCl3) through a DADA hydrogen bonding motif.     

Particle-swarm optimization of axially superresolving binary-phase diffractive optical elements

A particle-swarm optimization (PSO) algorithm was developed for designing binary-phase-only diffractive optical elements (DOEs) that superresolve the axially focused point-spread function. The method is based on vector diffraction theory to ensure solutions are valid under high-NA conditions. A DOE is identified that superresolves the focal spot by 34% and maintains the sidelobes below 50% of the peak intensity. The algorithm was used to obtain the Pareto front of the fitness-value space, which describes the achievable superresolution versus an allowed upper bound in sidelobe intensity. The results suggest that the algorithm yields solutions that are global in terms of the co-optimized fitness values G and M.     

Mixed-valence MnIIIMnIV clusters [Mn7O8(O2SePh)8(O2CMe)(H2O)] and [Mn7O8(O2SePh)9(H2O)]: single-chain magnets exhibiting quantum tunneling of magnetization

The syntheses, structures, and magnetic properties of two new Mn7 complexes containing phenylseleninate ligands are reported. [Mn7O8(O2SePh)8(O2CMe)(H2O)] (1) and [Mn7O8(O2SePh)9(H2O)] (2) were both prepared by the reaction of 18 equiv of benzeneseleninic acid (PhSeO2H) with [Mn12O12(O2CMe)16(H2O)4] in MeCN. Complex 1 x 6MeCN crystallizes in the triclinic space group P, and complex 2 x 2CH2Cl2 crystallizes in the monoclinic space group P2(1)/m. Both compounds possess an unprecedented [Mn7O8]9+ core comprising a central [MnIII3(micro3-O)4]+ unit attached to [MnIV2(micro-O)2]4+ and [MnIV2(micro-O)(micro3-O)]4+ units on either side. In each cluster, the PhSeO2- groups function as bridging ligands between adjacent Mn centers. The structure reveals strong Se.O intermolecular contacts between Mn7 units to give a one-dimensional chain structure, with weak interchain interactions. Solid-state DC magnetic susceptibility measurements of complexes 1 and 2 reveal that they have very similar properties, and detailed studies on 1 by AC susceptibility measurements confirm an S = 2 ground-state spin value. In addition, out-of-phase AC signals are observed, suggesting slow magnetization relaxation. Magnetization versus DC field sweeps down to 0.04 K reveals hysteresis loops, but the temperature dependence of the coercivity is not what is expected of a single-molecule magnet. Instead, the behavior is due to single-chain magnetism, albeit with weak antiferromagnetic interactions between the chains, with the barrier to relaxation arising from a combination of molecular anisotropy and ferromagnetic intermolecular exchange interactions mediated by the Se...O contacts. An Arrhenius plot was constructed from the magnetization versus time decay data. The thermally activated region at > 0.5 K gave an effective relaxation barrier (Ueff) of 14.2 K. Below approximately 0.1 K, the relaxation is independent of temperature, which is characteristic of magnetization quantum tunneling through the anisotropy barrier. These Mn7 compounds are thus the first single-chain magnets to comprise polynuclear metal clusters and also the first for which the temperature-independent relaxation characteristic of tunneling has been identified. The work also emphasizes that out-of-phase AC signals for ostensibly molecular compounds are not sufficient proof by themselves of a single-molecule magnet.     

High-nuclearity homometallic iron and nickel clusters: Fe22 and Ni24 complexes from the use of N-methyldiethanolamine

The use of N-methyldiethanolamine (mdaH2) in reactions with Fe(III) and Ni(II) sources has led to Fe22 and Ni24 products; the clusters are the highest and second-highest, respectively, homometallic clusters for these metals to date, and possess S = 0 and S = 6 ground states, respectively.