Hybrid organic-inorganic compounds are an intriguing class of materials that have been experimentally studied over the past few years because of a potential broad range of applications. The electronic and magnetic properties of three organic-inorganic hybrid compounds with compositions (NH4)2CuCl4, (CH3NH3)2CuCl4 and (C2H5NH3)2CuCl4 are investigated for the first time with density functional theory plus on-site Coulomb interaction. A strong Coulomb interaction on the copper causes a relatively weak exchange coupling within the layers of the octahedral network, in good agreement with experiment. The character of the exchange interaction (responsible for magnetic behavior) is analyzed. The calculations reveal that (C2H5NH3)2CuCl4 has the strongest Jahn-Teller (JT) distortion in comparison with the two other compounds. The easy axis of magnetization is investigated, showing a weak anisotropic interaction between inter-layer Cu(2+) ions in the (C2H5NH3)2CuCl4 structure. Orbital ordering is concluded from our partial density of states calculations: a cooperation of the JT distortion with an antiferro-distortive pattern.
Aramid fibers are of practical interest due to their high tensile strength, high elastic modulus, low elongation at breakage, and thermomechanical stability. Here we combine high-resolution solid-state NMR and density functional theory (DFT) calculations to gain insight into the details of the molecular packing of p-phenylene terephthalamides (PPTA). On the basis of the four models discussed thus far in the literature, we create a family of 16 possible structures. Calculations relate 1 H and 13 C chemical shifts obtained from experiments to structural aspects. Nucleus independent chemical shift (NICS) calculations show that ring currents and σ−π interactions as well as hydrogen bonding influence the chemical shifts on the rings. We obtain an unambiguous assignment, which differs from the literature data for carbon, for all resonances relating to the repeating unit of PPTA and obtain new insights into the possible packings of the PPTA units within the unit cell. Article pubs.acs.org/Macromolecules
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