Erratum: μ-Oxalato-bis-[bis-(triphenyl-phosphine)copper(I)] dichloro-methane disolvate. Corrigendum.

An erroneous claim in the paper by Royappa et al. [Acta Cryst. (2013), E69, m126] is corrected and a reference added for a previously published report of a closely related structure.[This corrects the article DOI: 10.1107/S1600536813002080.]

Crystal structure of N,N,N-tris-[(1,3-benzo-thia-zol-2-yl)meth-yl]amine.

The title compound, C24H18N4S3, exhibits three near planar benzo-thia-zole systems in a pseudo-C 3 conformation. The dihedral angles between the planes of the benzo-thia-zole groups range from 112.56 (4) to 124.68 (4)° In the crystal, mol-ecules are connected to each other through three short C-H⋯N contacts, forming an infinite chain along [100]. The molecules are also linked by π-π interactions with each of the three five-membered thiazole rings. [inter-centroid distance range: 3.614 (1)-4.074 (1) Å, inter-planar distance range: 3.4806 (17)-3.6902 (15) Å, slippage range: 0.759 (3)-1.887 (3) Å]

Dimethyl 2,2'-di-nitro-biphenyl-4,4'-di-carboxyl-ate.

The title compound, C16H12N2O8, exhibits two near-planar aromatic ester groups with ar-yl-ester dihedral angles of 2.1 (2) and 4.2 (3)°. The dihedral angle between the aromatic rings is 58.0 (1)°. The two nitro groups are tilted slightly from the plane of the aromatic rings, making dihedral angles of 14.1 (1) and 8.2 (2)°. In the crystal, mol-ecules are connected by weak C-H⋯O inter-actions, forming a three-dimensional network

Crystal structure of dimethyl 9H-carbazole-2,7-di-carb-oxy-late.

In the title compound, C16H13NO4, the carbazole ring system is almost planar with non-H atoms possessing a mean deviation from planarity of 0.037 Å. The two ester groups are orientated trans to one another and tilted slightly from the mean plane of the carbazole ring system, making dihedral angles of 8.12 (6) and 8.21 (5)°. In the crystal, mol-ecules are linked by pairs of N-H⋯O hydrogen bonds forming inversion dimers. The dimers are linked by parallel slipped π-π inter-actions, forming slabs propagating along the b-axis direction [inter-centroid distance = 3.6042 (8) Å, inter-planar distance = 3.3437 (5) Å, slippage = 1.345 Å]

The concept of strong and weak virtual reality

We approach the virtual reality phenomenon by studying its relationship to set theory, and we investigate the case where this is done using the wellfoundedness property of sets. Our hypothesis is that non-wellfounded sets (hypersets) give rise to a different quality of virtual reality than do familiar wellfounded sets. We initially provide an alternative approach to virtual reality based on Sommerhoff's idea of first and second order self-awareness; both categories of self-awareness are considered as necessary conditions for consciousness in terms of higher cognitive functions. We then introduce a representation of first and second order self-awareness through sets, and assume that these sets, which we call events, originally form a collection of wellfounded sets. Strong virtual reality characterizes virtual reality environments which have the limited capacity to create only events associated with wellfounded sets. In contrast, the more general concept of weak virtual reality characterizes collections of virtual reality mediated events altogether forming an entirety larger than any collection of wellfounded sets. By giving reference to Aczel's hyperset theory we indicate that this definition is not empty, because hypersets encompass wellfounded sets already. Moreover, we argue that weak virtual reality could be realized in human history through continued progress in computer technology. Finally, we reformulate our characterization into a more general framework, and use Baltag's Structural Theory of Sets (STS) to show that within this general hyperset theory Sommerhoff's first and second order self-awareness as well as both concepts of virtual reality admit a consistent mathematical representation.Comment: 17 pages; several edits in v

1H and 19F spin-lattice relaxation and CH3 or CF3 reorientation in molecular solids containing both H and F atoms

The dynamics of methyl (CH3) and fluoromethyl (CF3) groups in organic molecular (van der Waals) solids can be exploited to survey their local environments. We report solid state 1H and 19F spin-lattice relaxationexperiments in polycrystalline 3-trifluoromethoxycinnamic acid, along with an X-ray diffraction determination of the molecular and crystal structure, to investigate the intramolecular and intermolecular interactions that determine the properties that characterize the CF3 reorientation. The molecule is of no particular interest; it simply provides a motionless backbone (on the nuclear magnetic resonance (NMR) time scale) to investigate CF3reorientation occurring on the NMR time scale. The effects of 19F–19F and 19F–1H spin-spin dipolar interactions on the complicated nonexponential NMRrelaxation provide independent inputs into determining a model for CF3 reorientation. As such, these experiments provide much more information than when only one spin species (usually 1H) is present. In Sec. IV, which can be read immediately after the Introduction without reading the rest of the paper, we compare the barrier to CH3 and CF3 reorientation in seven organic solids and separate this barrier into intramolecular and intermolecular components

1H and 19F spin-lattice relaxation and CH3 or CF3 reorientation in molecular solids containing both H and F atoms

The dynamics of methyl (CH3) and fluoromethyl (CF3) groups in organic molecular (van der Waals) solids can be exploited to survey their local environments. We report solid state 1H and 19F spin-lattice relaxationexperiments in polycrystalline 3-trifluoromethoxycinnamic acid, along with an X-ray diffraction determination of the molecular and crystal structure, to investigate the intramolecular and intermolecular interactions that determine the properties that characterize the CF3 reorientation. The molecule is of no particular interest; it simply provides a motionless backbone (on the nuclear magnetic resonance (NMR) time scale) to investigate CF3reorientation occurring on the NMR time scale. The effects of 19F–19F and 19F–1H spin-spin dipolar interactions on the complicated nonexponential NMRrelaxation provide independent inputs into determining a model for CF3 reorientation. As such, these experiments provide much more information than when only one spin species (usually 1H) is present. In Sec. IV, which can be read immediately after the Introduction without reading the rest of the paper, we compare the barrier to CH3 and CF3 reorientation in seven organic solids and separate this barrier into intramolecular and intermolecular components

A proton spin-lattice relaxation rate study of methyl and t-butyl group reorientation in the solid state

We have measured the solid state nuclear magnetic resonance (NMR) 1H spin-lattice relaxation rate from 93 to 340 K at NMR frequencies of 8.5 and 53 MHz in 5-t-butyl-4-hydroxy-2-methylphenyl sulfide. We have also determined the molecular and crystal structures from X-ray diffraction experiments. The relaxation is caused by methyl and t-butyl group rotation modulating the spin–spin interactions and we relate the NMR dynamical parameters to the structure. A successful fit of the data requires that the 2-methyl groups are rotating fast (on the NMR time scale) even at the lowest temperatures employed. The rotational barrier for the two out-of-plane methyl groups in the t-butyl groups is 14.3±2.7 kJ mol−1 and the rotational barrier for the t-butyl groups and their in-plane methyl groups is 24.0±4.6 kJ mol−1. The uncertainties account for the uncertainties associated with the relationship between the observed NMR activation energy and a model-independent barrier, as well as the experimental uncertainties

Methyl and t-butyl group rotation in a molecular solid: 1H NMR spin-lattice relaxation and X-ray diffraction

We report solid state 1H nuclear magnetic resonance spin-lattice relaxation experiments and X-ray diffractometry in 2-t-butyldimethylsilyloxy-6-bromonaphthalene. This compound offers an opportunity to simultaneously investigate, and differentiate between, the rotations of a t-butyl group [C(CH3)3] and its three constituent methyl groups (CH3) and, simultaneously, a pair of \u27lone\u27 methyl groups (attached to the Si atom). The solid state 1H relaxation experiments determine activation energies for these rotations. We review the models for the dynamics of both \u27lone\u27 methyl groups (ones whose rotation axes do not move on the NMR time scale) and models for the dynamics of the t-butyl group and its constituent methyl groups (whose rotation axes reorient on the NMR time scale as the t-butyl group rotates)