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The infrared spectra of several organic thiocyanates and isothiocyanates have been studied. The thiocyanates and the isothiocyanates can be distinguished by their characteristic vibration frequencies around 2140 cm−1 and between 2060–2105 cm−1, respectively. These respective frequencies serve as an analytical tool for distinguishing these isomers both singly and in mixtures.
A focus of frontline interdisciplinary research today is the development of the conceptual framework and the experimental background of the science of nanostructured materials and the perspectives of its technological applications. We consider some current directions in the preparation, characterization, manipulation, and interrogation of nanomaterials, in conjunction with the modeling of the unique structuredynamicsfunction relations of nanostructures and their assemblies. The implications of quantum size and shape effects on the energetics, nuclearelectronic level structure, electric-optical response and dynamics, reveal new unique physical phenomena that qualitatively differ from those of the bulk matter and provide avenues for the control of the function of nanostructures. Current applications in the realm of nanoelectronics, nanooptoelectronics, and information nanoprocessing are addressed, and other directions highlighted. Chemical sciences make a central contribution to this novel and exciting scientifictechnological area.
Magic-angle-spinning NMR has been used to study SiOSi bond-angle distributions associated with various structural elements, Q n , present in lithium silicate glasses of different compositions. It is shown that glasses contain a plurality of structural elements with a broad distribution of SiOSi bond angles, and that the width of the distribution is characteristic of a particular Q n species.
EELS studies provide definitive evidence for the hydroxylation of oxygen-covered Cu(110) and Zn(0001) surfaces on interaction with proton donor molecules such as H2O, CH3OH, HCOOH, NH3 and (CH3)2NH. The occurrence of surface hydroxylation is unambigouusly shown by a study of the interaction of H2S and HCl with an oxygen covered Cu(110) surface.
An unusual set of anomalous functional properties of rocksalt crystals of Group IV chalcogenides were recently linked to a kind of bonding termed as metavalent bonding (MVB) which involves violation of the 8-N rule. Precise mechanisms of MVB and the relevance of lone pair of Group IV cations are still debated. With restrictions of low dimensionality on the possible atomic coordination, 2D materials provide a rich platform for exploration of MVB. Here, we present first-principles theoretical analysis of the nature of bonding in five distinct 2D lattices of Group IV chalcogenides MX (M: Sn, Pb, Ge and X: S, Se, Te), in which the natural out-of-plane expression of the lone pair versus in-plane bonding can be systematically explored. While their honeycomb lattices respecting the 8-N rule are shown to exhibit covalent bonding, their square and orthorhombic structures exhibit MVB only in-plane, with cationic lone pair activating the out-of-plane structural puckering that controls their relative stability. Anomalies in Born-effective charges, dielectric constants, Grüneisen parameters occur only in their in-plane behaviour, confirming MVB is confined strictly to 2D and originates from p-p orbital interactions. Our work opens up directions for chemical design of MVB based 2D materials and their heterostructures.
Ammonolysis of rare earth niobates of the type LnNbO4 (Ln=Y, La, Pr, Nd, Gd, Dy) yields oxynitrides of different structures. When Ln=La, Nd and Pr, the structure is that of an orthorhombic perovskite of the general formula LnNbON2. As the size of the rare earth decreases, the oxynitride has a nitrogen-deficient defect fluorite (Ln=Pr, Nd, Gd), or pyrochlore (Ln=Y) structure. The IR spectra of the oxynitrides and the corresponding oxides are significantly different. Thermogravimetric analysis suggests the formation of an intermediate phase wherein the N2 molecule is attached to the oxide lattice above 400°C and decomposes to give the oxide on heating in an oxygen atmosphere. Raman spectra of the intermediate phases show evidence for the NN stretching vibration. Gadolinium niobium oxynitride is found to be paramagnetic.
Organically templated metal sulfates are relatively new. Six amine‐templated transition‐metal sulfates with different types of chain structures, including a novel iron sulfate with a chain structure corresponding to one half of the kagome structure, were synthesized by hydro/solvothermal methods. Amongst the one‐dimensional metal sulfates, [C 10 N 2 H 10 ][Zn(SO 4 )Cl 2 ] ( 1 ) is the simplest, being formed by corner‐linked ZnO 2 Cl 2 and SO 4 tetrahedra. [C 6 N 2 H 18 ][Mn(SO 4 ) 2 (H 2 O) 2 ] ( 2 ) and [C 2 N 2 H 10 ][Ni(SO 4 ) 2 (H 2 O) 2 ] ( 3 ) have ladder structures comprising four‐membered rings formed by SO 4 tetrahedra and metal–oxygen octahedra, just as in the mineral kröhnkite. [C 4 N 2 H 12 ][V III (OH)(SO 4 ) 2 ]⋅H 2 O ( 4 ) and [C 4 N 2 H 12 ][VF 3 (SO 4 )] ( 5 ) exhibit chain topologies of the minerals tancoite and butlerite, respectively. The structure of [C 4 N 2 H 12 ][H 3 O][Fe III Fe II F 6 (SO 4 )] ( 6 ) is noteworthy in that it corresponds to half of the hexagonal kagome structure. It exhibits ferrimagnetic properties at low temperatures and the absence of frustration, unlike the mixed‐valent iron sulfate with the full kagome structure.
LaMnO3+δ samples with Mn4+ content up to 50% have been prepared by different methods. The structure of LaMnO3+δ changes from orthorhombic to cubic (via rhombohedral) with increase in the Mn4+ content. LaMnO3+δ samples containing greater than 20% Mn4+ are ferromagnetic and show resistivity maxima at a temperature T t which is close to the ferromagnetic Curie temperature. The resistivity maximum is due to the occurrence of a metal-insulator transition. In samples heated to the same temperature, the value of T t increases with % Mn4+. For a given sample, T t increases with the temperature of heat treatment due to the increase in particle size. The onset of ferromagnetism in LaMnO3+δ accompanied by an insulator-metal transition is similar to that found in La1-x Ca x MnO3 and La1-x Sr x CoO3.
Three new framework cobalt (II) phosphates have been synthesized hydrothermally in the presence of piperazine as a structure-directing agent. Crystal data: compound I, [C4N2H12][Co(HPO4)2], monoclinic space group=P21/n 001(no. 14), a=8.5521(10) Å, b=13.5791(15) Å, c=10.0405(11) Å, β=96.855(2)°, V=1157.7(2) Å3, Z=4, M=339.04, D c= 1.945 g m−3, MoKα, λ=0.71073 Å, R 1(F 0)=0.053; compound II, [C4N2H11][Co2(PO4)(H2PO4)2], monoclinic space group=C2/c (no. 15), a=13.444(5) Å, b=12.874(5) Å, c=8.224(2) Å, β=94.64(2)°, V=1418.8 (2)A 3, Z=8, M=494.96, D c=2.317 g cm−3, MoKα, λ=0.71073 Å ,R 1(F0)=0.047; compound III, [C4N2H12]2[Co4(HPO4)6], monoclinic space group=P2 1/c (no. 14) a=12.8780(13) Å, b=26.671(3) Å, c=8.2592(8) Å, β=96.931(2)°, V=2816.0(5) Å3, Z=4, M=987.90, D c =2.330gcm–3, MoKα, λ=0.71073 Å, R 1(F 0)=0.048. The structure of I consists of one-dimensional chains built up of corner-shared four rings (Co2P2) which are key structural units that form the sodalite cage. Compounds II and III have interrupted sodalite-type structures resulting from the removal of Co2+ atoms from sites related by two-fold axes passing through the four rings of the normal sodalite cage structure. The modes of the interruptions in II and III differ in relation to the structure of a regular sodalite cage.
Energy loss spectra of superconducting YBa2Cu3O6.9' Bi1.5Pb0.5Ca2.5Sr1.5Cu3O10+δ and Tl2CaBa2Cu3O8 obtained at primary electron energies in the 170–310 eV range show features reflecting the commonalities in their electronic structures. The relative intensity of the plasmon peak shows a marked drop across the transition temperature. Secondary electron emission spectra of the cuprates also reveal some features of the electronic structure.
