We have recently described a remarkable new way of exploring packing modes and intermolecular interactions in molecular crystals using a novel partitioning of crystal space. These molecular Hirshfeld surfaces reflect intermolecular interactions in a novel visual manner, offering a hitherto unseen picture of molecular shape in a crystalline environment. The surfaces encode information about all intermolecular interactions simultaneously, but sophisticated interactive graphics are required in order to extract the information most efficiently. To overcome this we have devised a two-dimensional mapping which summarizes quantitatively the nature and type of intermolecular interaction experienced by a molecule in the bulk, and presents it in a convenient graphical format. The mapping takes advantage of the triangulation of the Hirshfeld surfaces, and plots the fraction of points on the surface as a function of the closest distances from the point to nuclei inside and outside the surface.
In this manner all interaction types (for example, hydrogen bonding, close and distant van der Waals contacts, C–H⋯π interactions, π–π stacking) are readily identifiable, and it becomes a straightforward matter to classify molecular crystals by the nature of interactions, and to rapidly identify similarities and differences which can become obscured when examining crystal packing diagrams. These plots are a novel visual representation of all the intermolecular interactions simultaneously, and are unique for a given crystal structure and polymorph. Applications to a wide variety of molecular crystals and intermolecular interactions are presented, including polymorphic systems, as well as crystals where Z′ > 1.

Fingerprinting intermolecular interactions in molecular crystals

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

A self-consistent system of additive covalent radii, R(AB)=r(A) + r(B), is set up for the entire periodic table, Groups 1-18, Z=1-118. The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same fit. Both E-E, E-H, and E-CH 3 data are incorporated for most elements, E. Many E-E' data inside the same group are included. For the late main groups, the system is close to that of Pauling. For other elements it is close to the methyl-based one of Suresh and Koga [J. Phys. Chem. A 2001, 105, 5940] and its predecessors. For the diatomic alkalis MM' and halides XX', separate fits give a very high accuracy. These primary data are then absorbed with the rest. The most notable exclusion are the transition-metal halides and chalcogenides which are regarded as partial multiple bonds. Other anomalies include H 2 and F 2 . The standard deviation for the 410 included data points is 2.8 pm.

Molecular single-bond covalent radii for elements 1-118.

This review focuses on key aspects of the thermal decomposition of multinary or mixed hydride materials, with a particular emphasis on the rational control and chemical tuning of the strategically important thermal decomposition temperature of such hydrides, Tdec. An attempt is also made to predict the thermal stability of as-yet unknown, elusive or even unknown hydrides. The future of a particularly promising class of materials for hydrogen storage, namely the catalytically enhanced complex metal hydrides, is discussed. The predictions are supported by thermodynamics considerations, calculations derived from molecular orbital (MO) theory and backed up by simple chemical insights and intuition.

Thermal decomposition of the non-interstitial hydrides for the storage and production of hydrogen.

The use of liquid metals based on gallium for soft and stretchable electronics is discussed. This emerging class of electronics is motivated, in part, by the new opportunities that arise from devices that have mechanical properties similar to those encountered in the human experience, such as skin, tissue, textiles, and clothing. These types of electronics (e.g., wearable or implantable electronics, sensors for soft robotics, e-skin) must operate during deformation. Liquid metals are compelling materials for these applications because, in principle, they are infinitely deformable while retaining metallic conductivity. Liquid metals have been used for stretchable wires and interconnects, reconfigurable antennas, soft sensors, self-healing circuits, and conformal electrodes. In contrast to Hg, liquid metals based on gallium have low toxicity and essentially no vapor pressure and are therefore considered safe to handle. Whereas most liquids bead up to minimize surface energy, the presence of a surface oxide on these metals makes it possible to pattern them into useful shapes using a variety of techniques, including fluidic injection and 3D printing. In addition to forming excellent conductors, these metals can be used actively to form memory devices, sensors, and diodes that are completely built from soft materials. The properties of these materials, their applications within soft and stretchable electronics, and future opportunities and challenges are considered.

Stretchable and Soft Electronics using Liquid Metals.

Overview. The elements. Inorganic derivatives of the elements. Properties and uses of solid oxides. Properties and uses of other solids: metals, semi-metals, and semiconductors. Organometallic compounds. Organic transformations mediated by group 13 metal compounds. Coordination and solution chemistry. The elements in the environment. Analytical methods. References. Index.

Chemistry of Aluminium, Gallium, Indium and Thallium

The elusive binary hydride of gallium, [GaH 3 ] n , has at last been synthesized in rigorously conditioned all-glass apparatus by the reaction between monochlorogallane, [H 2 GaCl] 2 , and lithium tetrahydridogallate, LiGaH 4 , near −30°C. The compound, which decomposes to the elements at ambient temperatures, has been characterized by chemical analysis, by its vibrational and 1 H NMR spectra, and by chemical trapping with trimethylamine

Gallane: synthesis, physical and chemical properties, and structure of the gaseous molecule Ga2H6 as determined by electron diffraction

Matrix Infrared Spectroscopic and ab Initio Studies of ZnH2, CdH2, and Related Metal Hydride Species

boron gives little hint of the comparative wasteland making up much of the hydride estate of the heavier Group 13 elements., At a recent count2 about 100 binary boranes are now known, typically as discrete molecules remarkable for their stoicheiometries and structures which have done much to challenge and reshape our understanding of chemical bonding at large. By contrast, aluminium forms only one binary hydride stable under normal conditions as a polymeric solid, [AIH,],, the a-form of which is isostructural with AlF,, featuring 6-coordinate aluminium atom^.^^^ Attempts to prepare the analogous gallium compound have a chequered hist~ry,~ and it has taken nearly 50 years from the first reported sighting to establish the true credentials of gallane, [GaH,],,6 which now emerges as showing obvious affinities to diborane in the vapour state (i.e. n = 2) while being relatively short-lived under normal conditions. Despite some claims, however, it is unlikely that the hydrides [JnH,], and [TlH,], have yet materialized. In this account we review the current status of the hydrides formed by the Group 13 metals aluminium, gallium, indium, and thallium. Coordinatively saturated derivatives like MH, (M = Al, Ga, In, or T1) and Me,N. MH, (M = A1 or Ga) having been known for some year^,^?^ we are concerned primarily with the parent hydrides, [MH,], (m = 1, 2, or 3; n = 1, 2...), and related unsaturated derivatives. The last category includes species with more than one Group 13 element, for example tetrahydroborate derivatives like Al(BH,), and H,Ga(BH,),-, (m = 1 or 2) and tetraborane(l0) derivatives like 2-R2MB,H, (M = Al, R = Me; M = Ga, R = H or Me). It is appropriate first to consider the physical properties of the binary hydrides [MH,],. Hence it is possible to identify not only feasible methods of synthesizing compounds with M-H bonds, but also the origins of the thermal lability and reactivity besetting such compounds. 1.1 Theoretical Modelling Exploration of the Group 13 metal hydrides has been spurred by the greatly enhanced sophistication of modern computational methods which now admit the use of relatively elaborate basis sets, as well as making due allowance for factors like configuration interaction and relativistic correction^.^ Where comparisons can be made, such calculations typically yield dimensions and energetics which reproduce closely the experimental findings, and in some cases improve upon those findings. Such is the case, for example, with the monohydride molecules MH (M = B, Al, Ga, In, or Tl), which are short-lived under normal condition^.^,^ Accordingly we can place some trust in such results to anticipate the likely equilibrium molecular structures, vibrational properties, and binding energies of Group 13 hydrides, including numerous species whose existence has yet to be authenticated. Just what inferences are to be drawn will be discussed in Section 2.

The hydrides of aluminium, gallium, indium, and thallium: a re-evaluation

Ga2 reacts spontaneously with H2 in solid Ar matrixes at 12 K to form the cyclic molecule Ga(μ-H)2Ga. In2 does not react with H2 under similar conditions, but irradiation at wavelengths near 365 nm induces the formation of the corresponding indium hydride, In(μ-H)2In. The molecules have been identified and characterized by the IR spectra displayed by matrixes containing the metal and H2, D2, HD, or H2 + D2; they each have planar, dihydrido-bridged structures with D2h symmetry, as endorsed by comparison of the measured spectra (i) with the properties forecast by quantum chemical calculations and (ii) with the spectra of known gallium and indium hydrides. Both are photolabile under visible light (λ > 450 nm):  green light (λ = ca. 546 nm) causes Ga(μ-H)2Ga to isomerize to a mixture of HGaGaH and H2GaGa, whereas broad-band visible irradiation (λ > 450 nm) of In(μ-H)2In gives rise to the isomer HInInH, together with InH. The isomerization can be reversed by UV photolysis (λ = ca. 365 nm) of HGaGaH, H2GaGa, an...

Anthony J. Downs

Papers

Chemistry of Aluminium, Gallium, Indium and Thallium

Gallane: synthesis, physical and chemical properties, and structure of the gaseous molecule Ga2H6 as determined by electron diffraction

Matrix Infrared Spectroscopic and ab Initio Studies of ZnH2, CdH2, and Related Metal Hydride Species

The hydrides of aluminium, gallium, indium, and thallium: a re-evaluation

Formation and Characterization of the Gallium and Indium Subhydride Molecules Ga2H2 and In2H2: A Matrix Isolation Study