Structural disorder in alkaline earth metal doped Ba(x)Mn[Fe(CN)6](2(x+1)/3)·zH2O molecular magnets: a reverse Monte Carlo study.

We report a detailed structural disorder study of the Ba(x)Mn[Fe(CN)(6)](2(x+1)/3)·zH(2)O (x = 0 and 0.3) molecular magnets by carrying out Reverse Monte Carlo (RMC) simulations of neutron diffraction data. Both samples have also been investigated using X-ray diffraction, infrared spectroscopy and dc magnetization techniques. Rietveld refinement of X-ray and neutron diffraction patterns confirmed the single phase formation for both compounds in a face-centered cubic structure. IR spectral study establishes the presence of cyanide flipping in both compounds, thereby revealing inherent structural disorder in the compounds. A ferrimagnetic coupling of Mn(2+) (S = 5/2) spins and the Fe(3+) (S = 1/2) spins is found for both compounds. Results of RMC simulations of neutron diffraction data for both compounds show that: (i) around the coordinated oxygen atoms (located at the 24e crystallographic sites with [Fe(CN)(6)] vacancies), there are formations of small clusters of non-coordinated oxygen atoms; and (ii) Ba substitution leads to a reduction in this structural disorder. The role of reduced water content as well as vacancies of [Fe(CN)(6)] towards the observed reduction in the structural disorder is discussed.

DNA-templated assemblies of nickel hexacyanoferrate crystals.

We report here the synthesis of nickel hexacyanoferrate (NiHCF) crystals using calf thymus DNA (CT-DNA) as a template. The double-stranded CT-DNA has been used as a template to self-assemble NiHCF crystals and to produce aggregates having different morphologies at different temperatures. The guided self-assembly behavior of DNA was studied at different temperatures by scanning electron microscopy. The cube-shaped crystals of NiHCF with an average diameter of 400 nm are observed along the DNA framework at room temperature; however, at higher temperatures, the morphology of NiHCF changed from open tubular to dendrimer. The intermediate temperatures show long chains (up to many micrometers) and spherical structures of NiHCF crystals. The micrometer long DNA template plays a key role in the formation of extended arrays of NiHCF crystals, suggesting that the templating action is retained even at the higher temperatures.

SOM assembly of hydroxynaphthoquinone and its oxime: polymorphic X-ray structures and EPR studies.

Investigation on solvent-induced polymorphism in X-ray structures of 2-hydroxy-1,4-naphthoquinone (Lawsone) 1, is carried out. In protic methanol, 1 crystallizes in monoclinic space group P2(1)/c (1a) comprising of 2D hydrogen bonded network via cyclic dimers. In aprotic solvent such as acetone on the other hand, 1 exhibits orthorhombic space group Pna 2(1) (1b) and emerges with 1D catemeric chain. Solvent-induced topological isomerism of cyclic dimers and helical catemeric chains arising from (i) bifurcated intra- and inter molecular hydrogen bondings viz. O-H...O=C interactions between C(2) hydroxyl and C(1), C(4) carbonyls, (ii) C-H...O interactions viz. C(3)-H...O(1)C(1) have been discussed. A signal for radical in 1 at g = 2.0058 is signatured by EPR spectrum and it's oxime derivative viz. 2-hydroxy-4-naphthoquinone-1-oxime 2, in solid state shows biradical and monoradical formation with aggregation of dimer and monomer due to non-covalent hydrogen bonds. Zero field split parameters for 2 are estimated to be D = 215 G, Ex = 13 G, Ey = 47 G at 298 K. A half field signal at 77 K indicates triplet ground state. Frozen glass EPR of 2 resolves as regioregular dimeric-monomeric species showing hyperfine interactions with 1-oximino nitrogen in dimer A (14N) = 15.5 G].