Crystal structure, Hirshfeld surface analysis and electrostatic potential study of naturally occurring cassane-type diterpenoid Pulcherrimin C monohydrate at 100 K

The title cassane-type diterpenoid known as pulcherrimin C, C34H36O8·H2O, systematic name 5,6-bis-(benzo-yloxy)-4a-hy-droxy-4,7,11b-trimethyl-1,2,3,4,4a,5,6,6a,7,11,11a,11b-dodeca-hydro-phenanthro[3,2-b]furan-4-carb-oxy-lic acid monohydrate, was isolated as a monohydrate from the medicinally important plant Caesalpinia pulcherrima, found in the tropical regions of south and south-east Asia. The mol-ecule is composed of three trans-fused six-membered rings having chair, chair and half-chair conformations, and a five-membered planar furan ring. In the crystal, O-H⋯O hydrogen bonds link mol-ecules into chains parallel to the b axis. Weak C-H⋯π inter-actions are also observed. Hirshfeld surface analysis indicates that the contribution of O⋯H inter-actions towards the total generated Hirshfeld surface is 21.5%.

Rhodium(iii) complexes with isoquinoline derivatives as potential anticancer agents: in vitro and in vivo activity studies

Two rhodium complexes Rh1 and Rh2 with isoquinoline derivatives were synthesized and characterized.

Multi-spectroscopic and theoretical analyses on the diphenyl ether–tert-butyl alcohol complex in the electronic ground and electronically excited state

Multi-spectroscopic and theoretical investigations on the isolated diphenyl ether–tert-butyl alcohol complex – an ideal benchmark system for theory with strongly competing OH–O and OH–π binding motifs.

Improved description of the structure of molecular and layered crystals: ab initio DFT calculations with van der Waals corrections

The implementation of technique for full structural optimizations of complex periodic systems in the DFT-PAW package VASP, including the volume and shape of the unit cell and the internal coordinates of the atoms, together with a correction that allows an appropriate modeling of London dispersion forces, as given by the DFT-D2 approach of Grimme [Grimme, S. J. Comp. Chem. 2006, 27, 1787], is reported. Dispersion corrections are calculated not only for the forces acting on the atoms, but also for the stresses on the unit cell. This permits a simultaneous optimization of all degrees of freedom. Benchmark results on a series of prototype systems are presented and compared to results obtained by other methods and experimental data. It is demonstrated that the computationally inexpensive DFT-D2 scheme yields reasonable predictions for the structure, bulk moduli, and cohesive energies of weakly bonded materials.

Calculation of lattice energies of organic crystals: the PIXEL integration method in comparison with more traditional methods

The lattice energies of 47 crystal structures of organic compounds spanning a wide range of chemical functionalities are calculated using simple atom-atom potential energy functions, using coulombic terms with point-charge parameters, and using the PIXEL formulation, which is based on integral sums over the molecular electron density to obtain coulombic, polarization, dispersion and repulsion lattice energies. Comparisons among the different formulations, and the sensitivity and significance of the results against convenience, ease of application and number of parameters, are discussed. Improvements in the treatment of overlap repulsion in PIXEL are described, as well as a scheme for the minimization of the crystal lattice energy, based on the Symplex algorithm, which although computationally demanding, is shown to be feasible even with comparatively modest computing resources. The reproduction of experimental heats of sublimation is only marginally better with the PIXEL method, which however has great advantages in its being generally applicable in principle throughout the periodic table, at the expense of a minimal number of parameters, and in the fact that it sees the intermolecular interaction as the effect of the whole molecular electron density, in a physically more justifiable approach. This latter view in turn suggests a transition from a consideration of atom-atom bonds to a consideration of molecule-molecule bonding, opening a new view of packing factors in molecular crystals.

Structures, energetics, and dynamics of gas phase ions studied by FTICR and HPMS

Both Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and high-pressure mass spectrometry (HPMS) are very powerful tools in the field of gas phase ion chemistry. Many experimental method developments based on FTICR-MS and HPMS are summarized, including the coupling of a high-pressure external ion source to a FTICR mass spectrometer, blackbody infrared radiative dissociation (BIRD), coupling laser desorption ionization with HPMS, infrared multiple photon dissociation (IRMPD), radiative association and bimolecular routes to gas phase cluster ion formation. An abundance of thermochemical data, such as proton affinities, gas phase acidities, methyl cation affinities and metal cation affinities, have been obtained. Some of these data are the basis of the standard data listed in the NIST thermochemical databases. Ion-molecule interactions, energetics, reactivities, and structures of molecules have been extensively investigated using the methods developed based on HPMS and FTICR mass spectrometric techniques.

Geometry optimization of periodic systems using internal coordinates

An algorithm is proposed for the structural optimization of periodic systems in internal (chemical) coordinates. Internal coordinates may include in addition to the usual bond lengths, bond angles, out-of-plane and dihedral angles, various "lattice internal coordinates" such as cell edge lengths, cell angles, cell volume, etc. The coordinate transformations between Cartesian (or fractional) and internal coordinates are performed by a generalized Wilson B-matrix, which in contrast to the previous formulation by Kudin et al. [J. Chem. Phys. 114, 2919 (2001)] includes the explicit dependence of the lattice parameters on the positions of all unit cell atoms. The performance of the method, including constrained optimizations, is demonstrated on several examples, such as layered and microporous materials (gibbsite and chabazite) as well as the urea molecular crystal. The calculations used energies and forces from the ab initio density functional theory plane wave method in the projector-augmented wave formalism.