High-Spin Blatter's Triradicals.

Robust organic triradicals with high-spin quartet ground states provide promising applications in molecular magnets, spintronics, In this context, a triradical based on Blatter's radical has been synthesized recently, having two low-lying non-degenerate doublet states with a quartet ground state. The traditional broken-symmetry (BS)-DFT computed doublet-quartet energy gaps are reported to be somewhat overestimated in comparison to the experimentally observed values. In this work, we have employed different methods on this prototypical system to obtain more accurate doublet-quartet energy gaps for this triradical.

Toward an efficient implementation of internally contracted coupled-cluster methods.

A new implementation of the internally contracted multireference coupled-cluster with singles and doubles (icMRCCSD) method is presented. The new code employs an efficient tensor contraction kernel and can also avoid full four-external integral transformations, which significantly extends the scope of the applicability of icMRCCSD. The new implementation is currently restricted to the simple case of two active electrons in two orbitals and also supports the computation of spin-adapted doublet and triplet coupled-cluster wavefunctions.

Photochemistry of 3,6-Didehydropyridazine Biradical─An Untraceable Benzyne Analogue.

We report matrix isolation infrared spectroscopic studies to characterize 3,6-didehydropyridazine , a heterocyclic analogue of benzyne, combined with computations. In this regard, we have utilized 3,6-diiodopyridazine as a photolytic precursor. The experiments toward the generation of the biradical are carried out in argon and nitrogen matrices at 4 K.

Potential Energy Curves of Molecular Nitrogen for Singly and Doubly Ionized States with Core and Valence Holes.

Theoretical description of potential energy curves (PECs) of molecular ions is essential for interpretation and prediction of coupled electron-nuclear dynamics following ionization of parent molecule. However, an accurate representation of these PECs for core or inner valence ionized state is nontrivial, especially at stretched geometries for double- or triple-bonded systems. In this work, we report PECs of singly and doubly ionized states of molecular nitrogen using state-of-the-art quantum chemical methods.

Beyond Born-Oppenheimer constructed diabatic potential energy surfaces for F + H reaction.

First principles based beyond Born-Oppenheimer theory has been implemented on the F + H system for constructing multistate global diabatic Potential Energy Surfaces (PESs) through the incorporation of Nonadiabatic Coupling Terms (NACTs) explicitly. The spin-orbit (SO) coupling effect on the collision process of the F + H reaction has been included as a perturbation to the non-relativistic electronic Hamiltonian. Adiabatic PESs and NACTs for the lowest three electronic states (1A', 2A', and 1A″) are determined in hyperspherical coordinates as functions of hyperangles for a grid of fixed values of the hyperradius.

Aluminum containing molecular bowls and pyridinophanes: use of pyridine modules to access different molecular topologies.

Molecular topologies varying from simple complexes to pyridinophanes (neutral and cationic) and to bicyclic pyridinophane containing organoaluminum (Al-Me) species were synthesized by varying the relative stoichiometry of bis(trimethylsilyl)-N,N'-2,6-diaminopyridine (bap) and the reactive partner (AlMe). The ultimate goal of these reactions was to systematically design cyclic structures containing group 13 elements. To highlight the reaction potential of these shapes, the bowl-shaped pyridinophane was reacted with the Lewis acid, B(CF), to generate a stable cationic derivative.

Electronically Unsaturated Three-Coordinate Aluminum Hydride and Organoaluminum Cations.

New three-coordinate and electronically unsaturated aluminum hydride [LAlH] [HB(C F ) ] (LH=[{(2,6-iPr C H N)P(Ph )} N]H) and aluminum methyl [LAlMe] [MeB(C F ) ] cations have been prepared. The quantitative estimation of Lewis acidity by Gutmann-Beckett method revealed [LAlH] [HB(C F ) ] to be better Lewis acid than B(C F ) and AlCl making these compounds ideal catalysts for Lewis acid-mediated reactions. To highlight that the work is of fundamental importance, catalytic hydroboration of aliphatic and aromatic aldehydes and ketones have been demonstrated.

Two Different Pathways in the Reduction of [(S=)PCl(μ-NtBu)]2 with Na.

Reduction of the cyclodiphosphazane [(S=)ClP(μ-NtBu)]2 (1) with sodium metal in refluxing toluene proceeds via two different pathways. One is a Wurtz-type pathway involving elimination of NaCl from 1 followed by head-to-tail cyclization to give the hexameric macrocycle [(μ-S)P(μ-NtBu)2 P(=S)]6 (2). The other pathway involves reduction of the P=S bonds of 1 to generate colorless singlet biradicaloid dianion trans-[S-P(Cl)(μ-NtBu)]2 (2-) , which is observed in the polymeric structures of three-dimensional [{(S-)ClP(μ-NtBu)2 PCl(S)}Na(Na⋅THF2 )]n (3) and two dimensional [{(S-)ClP(μ-NtBu)2 PCl(S)} (Na⋅THF)2 ]n (4).

Reactivity of a dihydroboron species: synthesis of a hydroborenium complex and an expedient entry into stable thioxo- and selenoxo-boranes.

The reaction of a recently synthesized dihydroboron species complexed with bis(phosphinimino)amide, LBH2 (), (L = [N(Ph2PN(2,4,6-Me3C6H2))2](-)) with 3 equivalents of BH2Cl·SMe2 or one equivalent of BCl3 affords the first stable monohydridoborenium ion, [LBH](+)[HBCl3](-) () that is stable without a weakly coordinating bulky anion. Compound can also be prepared directly by refluxing LH with 3 equivalents of BH2Cl·SMe2. Interestingly, reaction of LBH2 () with elemental sulfur and selenium involves oxidative addition of S and Se into B-H bonds and subsequent release of H2S (or H2Se) from the intermediate LB(SH)2 (or LB(SeH)2) species forming stable compounds with terminal boron-chalcogen double bonds LB[double bond, length as m-dash]S () and LB[double bond, length as m-dash]Se ().

Charge symmetric dissociation of doubly ionized N2 and CO molecules.

We report a comparative study of the features in dissociative double ionization by high energy electron impact of N2 and CO molecules. The ratio of cross-section of charge symmetric dissociative ionization to non-dissociative ionization (CSD-to-ND ratio) and the kinetic energy release (KER) spectra of dissociation are experimentally measured and carefully corrected for various ion transmission losses and detector inefficiencies. Given that the double ionization cross sections of these iso-electronic diatomics are very similar, the large difference in the CSD-to-ND ratios must be attributable to the differences in the evolution dynamics of the dications.

Communication: multireference equation of motion coupled cluster: a transform and diagonalize approach to electronic structure.

The novel multireference equation-of-motion coupled-cluster (MREOM-CC) approaches provide versatile and accurate access to a large number of electronic states. The methods proceed by a sequence of many-body similarity transformations and a subsequent diagonalization of the transformed Hamiltonian over a compact subspace. The transformed Hamiltonian is a connected entity and preserves spin- and spatial symmetry properties of the original Hamiltonian, but is no longer Hermitean.

A new internally contracted multi-reference configuration interaction method.

We present a new internally contracted multi-reference configuration interaction (MRCI) method which, at the same time, efficiently handles large active orbital spaces, long configuration expansions, and many closed-shell orbitals in the reference function. This is achieved by treating the closed-shell orbitals explicitly, so that all required coupling coefficients and density matrices only depend on active orbital labels. As a result, closed-shell orbitals are handled as efficiently as in a closed-shell single-reference program, and this opens up the possibility to perform high-accuracy MRCI calculations for much larger molecules than before.

Cumulant decomposition of reduced density matrices, multireference normal ordering, and Wicks theorem: A spin-free approach.

We propose a spin-free approach to the cumulant decomposition of reduced density matrices of singlet and spin-rotation or SU(2) invariant ensemble of nonsinglet states as in [W. Kutzelnigg and D. Mukherjee, J.

State specific equation of motion coupled cluster method in general active space.

The state specific equation of motion coupled cluster (SS-EOMCC) method is an internally contracted multireference approach, applicable to both ground and excited states. Attractive features of the method are as follows: (1) the SS-EOMCC wave function is qualitatively correct and rigorously spin adapted, (2) both orbitals and dynamical correlation are optimized for the target state, (3) nondynamical correlation and differential orbital relaxation effects are taken care of by a diagonalization of the transformed Hamiltonian in the multireference configuration-interaction singles space, (4) only one- and two-particle density matrices of a complete-active-space self-consistent-field reference state are needed to define equations for the cluster amplitudes, and (5) the method is invariant with respect to orbital rotations in core, active, and virtual subspaces. Prior applications focused on biradical-like systems, in which only one extra orbital is needed to construct the active space, and similarly, single bond breaking processes.

Application of double ionization state-specific equation of motion coupled cluster method to organic diradicals.

The state-specific equation of motion coupled cluster method is applied to three systems of diradical character: automerization of cyclobutadiene, singlet-triplet gaps of trimethylmethylene, and Bergman reaction. The aim of the paper is to assess the performance of the method and test numerically the importance of orbital optimization, three-body terms in transformed Hamiltonian, and the choice of cluster equations.

A constrained variational approach for energy derivatives in Fock-space multireference coupled-cluster theory.

In this paper, we present a formulation based on constrained variational approach to enable efficient computation of energy derivatives using Fock-space multireference coupled-cluster theory. Adopting conventional normal ordered exponential with Bloch projection approach, we present a method of deriving equations when general incomplete model spaces are used. Essential simplifications arise when effective Hamiltonian definition becomes explicit as in the case of complete model spaces or some special quasicomplete model spaces.