N.W. Alcock

Bio: N.W. Alcock is an academic researcher from University of Warwick. The author has contributed to research in topics: Folding (chemistry) & Van der Waals strain. The author has an hindex of 1, co-authored 1 publications receiving 460 citations.

Secondary Bonding to Nonmetallic Elements

Abstract: Publisher Summary A number of recent crystal structure determinations on compounds of the nonmetals have discovered intramolecular distances that are much longer than normal bonds, and intermolecular distances that are much shorter than van der Waals distances. In this chapter, these interactions are examined and a qualitative explanation is attempted. It will become clear that in most of them an approximately linear arrangement is found, Y-A—X where Y-A is a normal bond and A—X is a short intermolecular distance. It is with these approximately linear interactions that we are particularly concerned, and it will be our contention that they are the result of directed forces and that their behavior is sufficiently regular and understandable for the name secondary bond to be appropriate. The only conclusive method of establishing the presence of secondary interactions is by crystal structure determinations. An intermolecular interaction can be recognized as being significant by being shorter than the expected intermolecular (van der Waals) distance, but if it is the result of directed forces— that is, bonds rather than electrostatic or nondirectional van der Waals forces.

From crystal statics to chemical dynamics

Abstract: The three-dimensional structure of senkirkine, ClsHnN06, was determined by X-ray crystallography. The substance crystallizes in the orthorhombic space group P212121 with four molecules in a unit cell with dimensions a = 24.601 k 0.002, b = 9.133 f 0.001, and c = 8.708 f 0.001 A. Intensity data were collected with a diffractometer and the structure was solved by statistical methods. Refinement by least squares, which included hydrogen atoms, tonverged at R 0.045 for 2275 observed reflections. The transannular N . . .C distance was found to be 2.292 (4) A. The extent of the partial bond in this and in several other structures is assessed. A correlation is established between the bond number and the frequency of the carbonyl peak in the infrared spectrum. uring the past years the crystal structures of three D alkaloids in which there exists an intramolecular N . . . C=O interaction were determined in these laboratories, viz., protopine, cryptopine, and clivorine. More recently it was suggested4 that such an interaction may be pertinent to the physiological activity of methadone. It seemed desirable, therefore, to obtain additional geometrical information and, if possible, to correlate it to the extensive chemical and spectroscopic (1) S. R. Hall and F. R. Ahmed, Acta Crystallogr., Sect. B, 24, (2) S. R. Hall and F. R. Ahmed, Acta Crystallogr., Sect. B , 24, 346 (3) K . B. Birnbaum, Acta Crystallogr., Secf. B, 28,2825 (1972). (4) H. B. Burgi, J. D. Dunitz, and E. Shefter, Nature (London), New 337(1968).

Organoselenium chemistry: role of intramolecular interactions.

Abstract: In 1836 the first organoselenium compound, diethyl selenide, was prepared by Löwig,1 and it was isolated in the pure form in 1869.2 Early selenium chemistry involved the synthesis of simple aliphatic compounds such as selenols (RSeH), selenides (RSeR), and diselenides (RSeSeR); however, because of their malodorous nature, these compounds were difficult to handle. This, combined with the instability of certain derivatives and difficulties in purification, meant that selenium chemistry was slow to develop. By the 1950s, the number of known selenium compounds had increased significantly, but it was not until the 1970s, when several new reactions leading to novel compounds with unusual properties were discovered, that selenium chemistry began to attract more general interest.3-9 Aryl-substituted compounds were synthesized that were found to be less volatile and more pleasant to handle than the earlier aliphatic compounds. Compounds containing selenium in high oxidation states are relatively easy to manipulate using modern techniques.4c Organoselenium chemistry has now become a well-established field of research, and recent advances have been brought about by the potential technical applications of selenium compounds. Today selenium compounds find application in many areas including organic synthesis,4 biochemistry,5 xerography,6 the synthesis of conducting materials7 and semiconductors,8 and ligand chemistry.4c,9 Many of these aspects of selenium chemistry are wellcovered elsewhere in the literature; however, the subject of hypervalency has not attracted much attention and is the focus of this review.10

Conducting metal dithiolene complexes: structural and electronic properties.

Abstract: Since the first report of superconductivity in synthetic organic conductors in 1980, chemistry and physics of molecular-based conductors have achieved remarkable progress and a number of exotic phenomena have been reported. From the viewpoint of the electronic structure, this progress has been driven along the following two major trends: (1) from “onedimensional” to “higher dimensional” and (2) from “single-component” to “multicomponent”.1 Since planar π-conjugated molecules tend to stack to form the column structure, molecular metals developed in the early stage had the one-dimensional (1D) electronic structure. The 1D metallic electron system characterized by a pair of planar Fermi surface is inherently unstable and undergoes a metal-insulator transition accompanied by the density wave formation at low temperatures.2 Much effort to increase the dimensionality of the electronic structure has been made by means of chemical modification and/or application of pressure. The first organic superconducting system, (TMTSF)2X (TMTSF ) tetramethyltetraselenafulvalene), forms a quasi1D system.3 The organic donor BEDT-TTF (ET, bis(ethylenedithio)tetrathiafulvalene) has provided various types of two-dimensional (2D) metallic systems.4 And, the DCNQI-Cu (DCNQI ) N,N′-dicyanoquinonediimine) salt is the first molecular conductor where the existence of a three-dimensional (3D) Fermi surface is confirmed.5 On the other hand, for many years, molecular conductors were assumed to be electronically single-component systems which exhibit only one electron type. Although the first organic metal TTF-TCNQ (TTF ) tetrathiafulvalene; TCNQ ) tetracyanoquinodimethane) is well-known to consist of two conducting components, the electronic structure of this system has an only 1D pπ electron character.1 Over the past decade, however, an increasing number of multicomponent systems, where there exist “two” energy bands with different characters (for example, orbital character and dimensionality) near the Fermi level or where a strong interaction between itinerant pπ electrons and localized d electron spins operates, have been reported. Reizo Kato was born in 1955 in Yamaguchi, Japan. He received his B.Sc. in 1979, M.Sc. in 1981, and D.Sc. in 1984 from the University of Tokyo. He was appointed research associate of Department of Chemistry at Toho University in 1984, and he was promoted to lecturer in 1988. He joined the Institute for Solid State Physics in The University of Tokyo as an associate professor in 1990. Since 1999 he has been a chief scientist and a director of the Condensed Molecular Materials laboratory in RIKEN (The Institute of Physical and Chemical Research). He received the Chemical Society of Japan Award for Young Chemists in 1990 and the IBM Japan Science Prize in 1995 for his works on molecular conductors. His research has been focused on development of new molecular materials, especially molecular metals and superconductors. 5319 Chem. Rev. 2004, 104, 5319−5346

Utilizing Hirshfeld surface calculations, non-covalent inter­action (NCI) plots and the calculation of inter­action energies in the analysis of mol­ecular packing

Abstract: The analysis of atom-to-atom and/or residue-to-residue contacts remains a favoured mode of analysing the mol­ecular packing in crystals. In this contribution, additional tools are highlighted as methods for analysis in order to complement the `crystallographer's tool', PLATON [Spek (2009). Acta Cryst. D65, 148–155]. Thus, a brief outline of the procedures and what can be learned by using Crystal Explorer [Spackman & Jayatilaka (2009). CrystEngComm 11, 19–23] is presented. Attention is then directed towards evaluating the nature, i.e. attractive/weakly attractive/repulsive, of specific contacts employing NCIPLOT [Johnson et al. (2010). J. Am. Chem. Soc. 132, 6498–6506]. This is complemented by a discussion of the calculation of energy frameworks utilizing the latest version of Crystal Explorer. All the mentioned programs are free of charge and straightforward to use. More importantly, they complement each other to give a more complete picture of how mol­ecules assemble in mol­ecular crystals.