Electronic Structure of the Low-Lying States of the Triatomic MoS2 Molecule: The Building Block of 2D MoS2.

Molybdenum disulfide (MoS2 ) is the building component of 1D-monolayer, 2D-layered nanosheets and nanotubes having many applications in industry, and it is detected in various molecular systems observed in nature. Here, the electronic structure and the chemical bonding of sixteen low-lying states of the triatomic MoS2 molecule are investigated, while the connection of the chemical bonding of the isolated MoS2 molecule to the relevant 2D-MoS2 , is emphasized. The MoS2 molecule is studied via DFT and multireference methodologies, i. e., MRCISD(+Q)/aug-cc-pVQZ(-PP)Mo . The ground state, X ˜ ${\tilde{X}}$ 3 B1 , is bent (Mo-S=2.133 Šand ϕ(SMoS)=115.9°) with a dissociation energy to atomic products of 194.7 kcal/mol at MRCISD+Q. In the ground and in the first excited state a double bond is formed between Mo and each S atom, i. e., a 1 2 a 1 2 b 2 2 a 2 2 ${{{\rm a}}_{1}^{2}{{\rm a}}_{1}^{2}{{\rm b}}_{2}^{2}{{\rm a}}_{2}^{2}}$ . These two states differ in which d electrons of Mo are unpaired. The Mo-S bond distances of the calculated states range from 2.108 to 2.505 Å, the SMoS angles range from 104.1 to 180.0°, and the Mo-S bonds are single or double. Potential energy curves and surfaces have been plotted for the X ˜ ${\tilde{X}}$ 3 B1 , 5 A1 and 5 B1 states. Finally, the low-lying septet states of the triatomic molecule are involved in the material as a building block, explaining the variety of its morphologies.

Molybdenum-Sulfur Bond: Electronic Structure of Low-Lying States of MoS.

The molybdenum-sulfur bond plays an important role in many processes such as nitrogen-fixation, and it is found as a building block in layered materials such as MoS2, known for its various shapes and morphologies. Here, we present an accurate theoretical and experimental investigation of the chemical bonding and the electronic structure of 20 low-lying states of the MoS molecule. Multireference and coupled cluster methodologies, namely, MRCISD, MRCISD + Q, RCCSD(T), and RCCSD[T], were employed in conjunction with basis sets up to aug-cc-pwCV5Z-PP/aug-cc-pwCV5Z for the study of these states. We note the significance of including the inner 4s24p6 electrons of Mo and 2s22p6 of S in the correlated space to obtain accurate results. Experimentally, the predissociation threshold of MoS was measured using resonant two-photon ionization spectroscopy, allowing for a precise measurement of the bond dissociation energy. Our extrapolated computational D0 value for the ground state is 3.936 eV, in excellent agreement with our experimental measurement of 3.932 ± 0.004 eV. The largest calculated adiabatic D0 (5.74 eV) and the largest dipole moment (6.50 D) were found for the 5Σ+ state, where a triple bond is formed. Finally, the connection of the chemical bonding of the isolated MoS species to the relevant solid, MoS2, is emphasized. The low-lying septet states of the diatomic molecule are involved in the material as a building block, explaining the stability and the variety of the shapes and morphologies of the material.

Quadruple Bonding in the Ground and Low-Lying Excited States of the Diatomic Molecules TcN, RuC, RhB, and PdBe.

Multiple bonds between atoms are one of the most fundamental aspects of chemistry. Double and triple bonds are quite common, while quadruple bonds are a true oddity and very rare for the main group elements. Identifying molecules containing quadruple bonds is very important and, even more so, determining the necessary requirements for the existence of such bonds. Here we present high-level theoretical calculations on the isoelectronic MX molecules, i.e., TcN, RuC, RhB, and PdBe, showing that such a quadruple bond with main group elements is not that uncommon. We found that quadruple bonds are formed in their ground states X3Δ (TcN) and Χ1Σ+ (RuC, RhB, and PdBe) and in the two lowest excited states of TcN (1Σ+, 1Δ), RuC (1,3Δ), and RhB (1,3Δ). The quadruple bonds consist of two π and two σ bonds: (4dxz-2px)2, (4dyz-2py)2, (4dz2-2pz)2, and 5s0 ← 2s2 (1Σ+) or 5pz0←2s2 (1,3Δ). Bond lengths, dissociation energies, dipole moments, spectroscopic parameters, and relative energy ordering of the states were calculated via multireference and coupled cluster methodology using the aug-cc-pV5ZX(-PP)M basis sets. We study how the atomic states involved and how the gradual transition from covalent to dative bond, from TcN to PdBe, influence all of the calculated data, such as bond dissociation energies, bond lengths, and relative energy ordering of the states. Finally, we report the requirements for the occurrence of such bonds in molecular systems. All Be, B, C, and N atoms combining with the appropriate second-row transition metal can form quadruple bonds, while they cannot form such bonds with the first-row transition metals.

Prediction of 195 Pt NMR of photoactivable diazido- and azine-Pt(IV) anticancer agents by DFT computational protocols.

195 Pt NMR chemical shifts for a series of large-sized photoactivable anticancer diazido-Pt(IV), homopiperizine-Pt(IV) and multifunctional azine-Pt(IV) complexes hardly to be probed experimentally and by sophisticated four-component and two-component relativistic calculations are predicted with high accuracy by density functional theory computational protocols. The calculated 195 Pt NMR chemical shifts constitute a crucial descriptor for making highly predictive one-parameter quantitative structure activity relationships models that help in designing photoactivable Pt(IV)-based antitumor agents with high cytotoxicity and selectivity. Copyright © 2016 John Wiley & Sons, Ltd.

195 Pt NMR parameters as strong descriptors in one-parameter QSAR models for platinum-based antitumor compounds.

Highly predictive one-parameter quantitative structure-activity relationship models have been developed for platinum-based anticancer drugs using the 195 Pt NMR parameters as strong descriptors. The developed quantitative structure-activity relationship models were applied in diverse homogeneous sets of antiproliferative Pt(II) and Pt(IV) compounds. These observations form the basis for making predictions of cytotoxicity for a broad range of platinum-based antitumor compounds just from inspection of calculated or experimentally determined 195 Pt NMR parameters. Copyright © 2016 John Wiley & Sons, Ltd.

Prediction of (195) Pt NMR chemical shifts of dissolution products of H2 [Pt(OH)6 ] in nitric acid solutions by DFT methods: how important are the counter-ion effects?

(195) Pt NMR chemical shifts of octahedral Pt(IV) complexes with general formula [Pt(NO3 )n (OH)6 - n ](2-) , [Pt(NO3 )n (OH2 )6 - n ](4 - n) (n = 1-6), and [Pt(NO3 )6 - n - m (OH)m (OH2 )n ](-2 + n - m) formed by dissolution of platinic acid, H2 [Pt(OH)6 ], in aqueous nitric acid solutions are calculated employing density functional theory methods. Particularly, the gauge-including atomic orbitals (GIAO)-PBE0/segmented all-electron relativistically contracted-zeroth-order regular approximation (SARC-ZORA)(Pt) ∪ 6-31G(d,p)(E)/Polarizable Continuum Model computational protocol performs the best. Excellent second-order polynomial plots of δcalcd ((195) Pt) versus δexptl ((195) Pt) chemical shifts and δcalcd ((195) Pt) versus the natural atomic charge QPt are obtained. Despite of neglecting relativistic and spin orbit effects the good agreement of the calculated δ (195) Pt chemical shifts with experimental values is probably because of the fact that the contribution of relativistic and spin orbit effects to computed σ(iso) (195) Pt magnetic shielding of Pt(IV) coordination compounds is effectively cancelled in the computed δ (195) Pt chemical shifts, because the relativistic corrections are expected to be similar in the complexes and the proper reference standard used. To probe the counter-ion effects on the (195) Pt NMR chemical shifts of the anionic [Pt(NO3 )n (OH)6 - n ](2-) and cationic [Pt(NO3 )n (OH2 )6 - n ](4 - n) (n = 0-3) complexes we calculated the (195) Pt NMR chemical shifts of the neutral (PyH)2 [Pt(NO3 )n (OH)6 - n ] (n = 1-6; PyH = pyridinium cation, C5 H5 NH(+) ) and [Pt(NO3 )n (H2 O)6 - n ](NO3 )4 - n (n = 0-3) complexes. Counter-anion effects are very important for the accurate prediction of the (195) Pt NMR chemical shifts of the cationic [Pt(NO3 )n (OH2 )6 - n ](4 - n) complexes, while counter-cation effects are less important for the anionic [Pt(NO3 )n (OH)6 - n ](2-) complexes. The simple computational protocol is easily implemented even by synthetic chemists in platinum coordination chemistry that dispose limited software availability, or locally existing routines and knowhow. Copyright © 2016 John Wiley & Sons, Ltd.

Accurate prediction of 195Pt NMR chemical shifts for a series of Pt(II) and Pt(IV) antitumor agents by a non-relativistic DFT computational protocol.

The GIAO-PBE0/SARC-ZORA(Pt)∪6-31+G(d)(E) (E = main group element) computational protocol without including relativistic and spin-orbit effects is offered here for the accurate prediction of the (195)Pt NMR chemical shifts of a series of cis-(amine)2PtX2 (X = Cl, Br, I) anticancer agents (in total 42 complexes) and cis-diacetylbis(amine)platinum(II) complexes (in total 12) in solutions employing the Polarizable Continuum Model (PCM) solvation model, thus contributing to the difficult task of computation of (195)Pt NMR. Calculations of the torsional energy curves along the diabatic (unrelaxed) rotation around the Pt-N bond of the cis-(amine)2PtX2 (X = Cl, Br, I) anticancer agents revealed the high sensitivity of the (195)Pt NMR chemical shifts to conformational changes. The crucial effect of the conformational preferences on the electron density of the Pt central atom and consequently on the calculated δ(195)Pt chemical shifts was also corroborated by the excellent linear plots of δ(calcd)((195)Pt) chemical shifts vs. the natural atomic charge Q(Pt). Furthermore, for the accurate prediction of the (195)Pt NMR chemical shifts of the cis-bis(amine)Pt(II) anticancer agents bearing carboxylato- as the leaving ligands (in total 8) and a series of octahedral Pt(IV) antitumor agents (in total 20 complexes) the non-relativistic GIAO-PBE0/SARC-ZORA(Pt)∪6-31+G(d)(E) computational protocol performs best in combination with the universal continuum solvation model based on solute electron density called SMD for aqueous solutions. Despite neglecting relativistic and spin orbit effects the agreement of the calculated δ(195)Pt chemical shifts with experimental values is surprising probably due to effective error compensation. Moreover, the observed solvent effects on the structural parameters of the complexes probably overcome the relativistic effects, and therefore the successful applicability of the non-relativistic GIAO-PBE0/SARC-ZORA(Pt)∪6-31+G(d)(E) computational protocol in producing reliable δ(calcd)((195)Pt) chemical shifts could be understood. In a few cases (e.g. the dihydroxo Pt(IV) complexes) the higher deviations of the calculated from the experimental values of δ(195)Pt chemical shifts are probably due to the fact that the experimental assignments refer to a different composition of the complexes in solutions than that used in the calculations, and different hydrogen bonding and formation of dimeric species.