Electronic structure, phase stability and chemical bonding in Th2_2Al and Th2_2AlH4_4

We present the results of theoretical investigation on the electronic structure, bonding nature and ground state properties of Th$_2$Al and Th$_2$AlH$_4$ using generalized-gradient-corrected first-principles full-potential density-functional calculations. Th$_2$AlH$_4$ has been reported to violate the "2 \AA rule" of H-H separation in hydrides. From our total energy as well as force-minimization calculations, we found a shortest H-H separation of 1.95 {\AA} in accordance with recent high resolution powder neutron diffraction experiments. When the Th$_2$Al matrix is hydrogenated, the volume expansion is highly anisotropic, which is quite opposite to other hydrides having the same crystal structure. The bonding nature of these materials are analyzed from the density of states, crystal-orbital Hamiltonian population and valence-charge-density analyses. Our calculation predicts different nature of bonding for the H atoms along $a$ and $c$. The strongest bonding in Th$_2$AlH$_4$ is between Th and H along $c$ which form dumb-bell shaped H-Th-H subunits. Due to this strong covalent interaction there is very small amount of electrons present between H atoms along $c$ which makes repulsive interaction between the H atoms smaller and this is the precise reason why the 2 {\AA} rule is violated. The large difference in the interatomic distances between the interstitial region where one can accommodate H in the $ac$ and $ab$ planes along with the strong covalent interaction between Th and H are the main reasons for highly anisotropic volume expansion on hydrogenation of Th$_2$Al.Comment: 14 pages, 9 figure

Computationally synthesised inorganic and organometallic complexes : a thesis presented in partial fulfilment of the requirements of the degree of Doctor of Philosophy in Chemistry at Massey University, Albany, New Zealand

Catalytic aromatic ring C–H bond functionalisations by transition metal cyclometallation reactions are important for organic transformation reactions. The cyclometallated product, which contains a new metal–carbon bond is formed as a consequence of different types of carbon–hydrogen····metal (C–H····M) interactions. These C–H···M interactions have been known as anagostic, preagostic and agostic interactions. By nature, the anagostic interaction has mainly electrostatic components, the preagostic interaction has electrostatic components with some back-bonding from metal to C–H antibonding orbital involved and the agostic interaction has mainly covalent components when the C–H bond donates electron density to the partially occupied metal centre. Prior to the current thesis work, an in-depth study that addresses the influence of steric and electronic factors on the anagostic, preagostic and agostic carbon–hydrogen····metal interaction was missing. In this thesis, the influence of both the steric and electronic factors on the anagostic, preagostic and agostic C–H···M interactions has been studied. It is seen that the electronic and steric influences play differently for different ligand systems as with the flexible tetralone ligand, a maximum of steric and electronic influence results into another type of anagostic interaction named as the 'C-anagostic' interaction. It is also seen that a stronger steric and electronic effect can trigger agostic covalency at the anagostic stage of the reaction. The inflexible ligand ensures the short anagostic approach, which has some back-bonding character and the nature of the interaction lies into the preagostic category. Finally, the aromatic ring agostic interactions have more complexity as new donations named as 'syndetic' from C–C pi bond to metal antibonding orbitals were recognised which shares the same antibonding acceptor orbitals as the agostic donation does. The recognition of new bonding situations in C–H····M interactions can have significant implications for C–H bond functionalisation reactions

Intermolecular interactions in N-(ferrocenylmethyl)anthracene-9-carboxamide

The title compound, [Fe(C₅H₅)(C₂₁H₁₆NO)], was synthesized from the coupling reaction of anthracene-9-carboxylic acid and ferrocenylmethylamine. The ferrocenyl (Fc) group and the anthracene ring system both lie approximately orthogonal to the amide moiety. An amide-amide interaction (along the a axis) is the principal interaction [N...O = 2.910 (2) Å]. A C-H...π(arene) interaction [C...centroid = 3.573 (2) Å] and a C-H...O interaction [C...O = 3.275 (3) Å] complete the hydrogen bonding; two short (Fc)C...C(anthracene) contacts are also present

Anion–arene adducts: C–H hydrogen bonding, anion– interaction, and carbon bonding motifs

This article summarizes experimental and theoretical evidence for the existence of four distinct binding modes for complexes of anions with charge-neutral arenes. These include C–H hydrogen bonding and three motifs involving the arene– system—the noncovalent anion– interaction, weakly covalent interaction, and strongly covalent interaction

Large potential steps at weakly interacting metal-insulator interfaces

Potential steps exceeding 1 eV are regularly formed at metal|insulator interfaces, even when the interaction between the materials at the interface is weak physisorption. From first-principles calculations on metal|h-BN interfaces we show that these potential steps are only indirectly sensitive to the interface bonding through the dependence of the binding energy curves on the van der Waals interaction. Exchange repulsion forms the main contribution to the interface potential step in the weakly interacting regime, which we show with a simple model based upon a symmetrized product of metal and h-BN wave functions. In the strongly interacting regime, the interface potential step is reduced by chemical bonding

Exploiting hydrogen bonding to direct supramolecular polymerization at the air/water interface

Fluid interfaces provide an advanced platform for directed self-assembly of organic composites and formation of supramolecular polymers (SPs). Intermolecular interactions govern the supramolecular polymerization processes, with hydrogen bonding (H-bonding) as a key interaction in supramolecular chemistry and biology. Two purposefully designed supra-amphiphiles for assessing the role of H-bonding were designed and their supramolecular polymerization (SP) at the air/water interface was compared. H-bonding was confirmed by in situ experimental and computational techniques as the required intermolecular interaction for attaining SPs with well-defined molecular arrangement. Control of H-bonding as opposite to traditionally considered interactions, e.g., π-π stacking is proposed as a successful strategy for SP at fluid interfaces