Electrides are ionic substances containing isolated electrons. These confined electrons are topologically characterised by a quasi-atom, that is, a non-nuclear attractor (NNA) of the electron density. The electronic structure of the octahedral A Li and A Be species shows that these species have a large number of NNAs. These NNAs have highly delocalised electron densities and, as a result, the chemical bonding pattern of these systems is reminiscent of that in solid metals, in which metal cations are surrounded by a "sea" of delocalised valence electrons. We propose the term metal cluster electrides to refer to this new class of compounds. In this study, we establish a computational protocol to identify, characterize, and design metal cluster electrides and we elucidate the intricate bonding patterns of this particular type of species.

We have developed and implemented a new ab initio code, Ceres (Computational Emulator of Rare Earth Systems), completely written in C++11, which is dedicated to the efficient calculation of the electronic structure and magnetic properties of the crystal field states arising from the splitting of the ground state spin-orbit multiplet in lanthanide complexes. The new code gains efficiency via an optimized implementation of a direct configurational averaged Hartree-Fock (CAHF) algorithm for the determination of 4f quasi-atomic active orbitals common to all multi-electron spin manifolds contributing to the ground spin-orbit multiplet of the lanthanide ion. The new CAHF implementation is based on quasi-Newton convergence acceleration techniques coupled to an efficient library for the direct evaluation of molecular integrals, and problem-specific density matrix guess strategies. After describing the main features of the new code, we compare its efficiency with the current state-of-the-art ab initio strategy to determine crystal field levels and properties, and show that our methodology, as implemented in Ceres, represents a more time-efficient computational strategy for the evaluation of the magnetic properties of lanthanide complexes, also allowing a full representation of non-perturbative spin-orbit coupling effects. © 2017 Wiley Periodicals, Inc.

A successful and commonly used ab initio method for the calculation of crystal field levels and magnetic anisotropy of lanthanide complexes consists of spin-adapted state-averaged CASSCF calculations followed by state interaction with spin-orbit coupling (SI-SO). Based on two observations valid for Ln(III) complexes, namely: (i) CASSCF 4f orbitals are expected to change very little when optimized for different states belonging to the 4f electronic configuration, (ii) due to strong spin-orbit coupling the total spin is not a good quantum number, we show here via a straightforward analysis and direct calculation that the CASSCF/SI-SO method can be simplified to a single configuration-averaged HF calculation and one complete active space CI diagonalization, including spin-orbit coupling, on determinant basis. Besides its conceptual simplicity, this approach has the advantage that all spin states of the 4f n configuration are automatically included in the SO coupling, thereby overcoming one of the computational limitations of the existing CASSCF/SI-SO approach.As an example, we consider three isostructural complexes [Ln(acac) 3 (H 2 O) 2 ], Ln = Dy 3+ , Ho 3+ , Er 3+ , and find that the proposed simplified method yields crystal field levels and magnetic g-tensors that are in very good agreement with those obtained with CASSCF/SI-SO.

A recently proposed theory of chiral discrimination in NMR spectroscopy based on the detection of a molecular electric polarization P rotating in a plane perpendicular to the NMR magnetic field [A. D. Buckingham, J. Chem. Phys. 140, 011103 (2014)], is here generalized to paramagnetic systems. Our theory predicts new contributions to P , varying as the square of the inverse temperature. Ab initio calculations for ten Dy 3+ complexes, at 293K, show that in strongly anisotropic paramagnetic molecules P can be more than 1000 times larger than in diamagnetic molecules, making paramagnetic NMR chiral discrimination amenable to room temperature detection.Despite its central role in biological processes and in a wide range of chemical reactions, chirality, the property of molecules lacking improper symmetry elements to be distinguishable from their mirror image (or enantiomer), remains a challenging property to detect and quantify [1], making the development of new spectroscopic techniques to achieve this goal a strategic research field [2-9].Magnetic resonance spectroscopies, despite being among the most useful characterization techniques due to their high sensitivity to tiny details of the geometrical and electronic structure of molecules, are blind to chirality. However, it has been recently proposed by Buckingham [3,9] and Fischer [5] that NMR could be used to achieve chiral discrimination for closed-shell chiral molecules via a minor modification of the experimental set up, so to make it fit for the detection of a rotating average electric polarization P induced by the combined effect of the NMR magnetic field B, and the nuclear magnetic dipole moment m I associated to a nucleus I of the chiral molecule, rotating in the plane perpendicular to B following a resonant π/2 radiofrequency pulse. In particular, the induced P is always oriented along B × m I (thus rotating with m I ), points in opposite directions for the two enantiomers (hence its chirality-sensitivity), and is proportional to the pseudoscalar σ (1) , isotropic average of a third-rank tensor σ ijk (i, j, k = x, y, z) known as shielding polarizability [3, 5,10]. However, computational estimates of σ (1) in diamagnetic molecules suggest that it is generally too small to be detected [9,11,12].In this Letter we propose a theory of paramagnetic NMR chiral discrimination which is valid for molecules with a ground state of arbitrary degeneracy. We describe the response of the degenerate system in terms of a generalized shielding polarizability tensor Φ ijk defined by analytical third-derivatives of the free energy, reducing to σ ijk in the limit of a non-degenerate ground state. The proposed free-energy response theory features previously unexplored terms proportional to the square of the inverse temperature β = 1/k B T , so that σ (1) becomes σ (1) + β 2 σ (1p) . Finally, we present ab initio calculations showing that β 2 σ (1p) yields a contribution to P at 293K that is orders of magnitude larger than in closed-shell molecules, potentially observable at room...

Recent advances in single-molecule magnet (SMM) research have placed great value on interpretation of inelastic neutron scattering (INS) data for rare earth (RE)-containing SMMs. Here, we present the synthesis of several rare earth complexes where combined magnetic and INS studies have been performed, supported by ab initio calculations. The reaction of rare earth nitrate salts with 2,2′-bipyridine (2,2′-bpy) and tetrahalocatecholate (X 4 Cat 2− , X = Br, Cl) ligands in methanol (MeOH) afforded two new families of compounds [RE(2,2′-bpy) 2 (X 4 Cat)(X 4 CatH)-(MeOH)] (X = Br and RE = Y, Eu, Gd, Tb, Dy, Ho, Yb for 1-RE; X = Cl and RE = Y, Tb, Dy, Ho, and Yb for 2-RE). Addition of triethylamine (Et 3 N) to the reaction mixture delivered Et 3 NH[RE-(2,2′-bpy) 2 (Br 4 Cat) 2 ] (3-RE, RE = Er and Yb).Interestingly, cerium behaves differently to the rest of the series, generating (2,2'-bpyH) 2 [Ce(Br 4 Cat) 3 (2,2′-bpy)] (4-Ce) with tetravalent Ce(IV) in contrast to the trivalent metal ions in 1−3. The static magnetic properties of 1-RE (RE = Gd, Tb, Dy and Ho) were investigated in conjunction with INS measurements on 1-Y, 1-Tb, and 1-Ho to probe their ground state properties and any crystal field excitations. To facilitate interpretation of the INS spectra and provide insight into the magnetic behavior, ab initio calculations were performed using the single-crystal X-ray diffraction structural data of 1-RE (RE = Tb, Dy and Ho). The ab initio calculations indicate ground doublets dominated by the maximal angular momentum projection states of Kramers type for 1-Dy and Ising type for 1-Tb and 1-Ho. Dynamic magnetic susceptibility measurements indicate that 1-Dy exhibits slow magnetic relaxation in the presence of a small applied magnetic field mainly through Raman pathways. Inelastic neutron scattering spectra exhibit distinct transitions corresponding to crystal field-induced tunneling gaps between the pseudo-doublet ground state components for 1-Tb and 1-Ho, which is one of the first direct experimental measurements with INS of such tunneling transitions in a molecular nanomagnet. The power of high-resolution INS is demonstrated with evidence of two distinct tunneling gaps measurable for the two crystallographically unique Tb coordination environments observed in the single crystal X-ray structure.

Single-molecule magnets are promising candidates for data storage and quantum computing applications. A major barrier to their use is rapid magnetic relaxation and quantum decoherence due to thermal vibrations. Here...

We have studied the effect of thermally populated crystal field states on room temperature chiral discrimination in NMR spectroscopy.

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