In the present account, the real space fragment attributed molecular system energy change (FAMSEC) approach, interacting quantum atoms energy decomposition scheme as well as molecular orbitals based the extended transition state scheme coupled with natural orbitals for chemical valence (ETS-NOCV) have been, for the first time, successfully used to delineate factors of importance for stability of the 2-butene conformers (cis-eq, cis-TS, trans-eq, trans-TS). Our results demonstrate that atoms of the controversial H-H contact in cis-eq (i) are involved in attractive interaction dominated by the exchange-correlation term, (ii) are weekly stabilized, (iii) show trends in several descriptors found in other typical H-bonds, and (iv) are part of most stabilized CH-HC fragment (loc-FAMSEC = -3.6 kcal/mol) with most favourably changed intrafragment interactions on trans-eq→cis-eq. Moreover, lower stability of cis-eq vs. trans-eq is linked with the entire HCCH (ethylenic) fragment which destabilized cis-eq (mol-FAMSEC, +3.9 kcal/mol) the most. Although the H-H contact can be linked with smaller, relative to trans-, rotational energy barrier in cis-2-butene, we have proven that to rationalize this phenomenon one must account for changes in interactions between various fragments that constitute the entire molecule. Importantly, we discovered a number of comparable trends in fundamental properties of equivalent molecular fragments on a methyl group rotation; for example, interaction between BP-free H-atoms in trans-eq (involving CH bonds of the methyl and ethylenic units) and BP-linked H-atoms in cis-eq. Clearly, rotational energy barrier cannot be entirely (i) rationalized by the properties of or (ii) attributed to the H-H contact in cis-eq. © 2016 Wiley Periodicals, Inc.

We report the design as well as structural and spectroscopic characterizations of two new coordination compounds obtained from Cd(NO)·4HO and polydentate ligands, benzilbis(pyridin-2-yl)methylidenehydrazone (L) and benzilbis(acetylpyridin-2-yl)methylidenehydrazone (L), in a mixture with two equivalents of NHNCS in MeOH, namely [Cd(SCN)(NCS)(L)(MeOH)] (1) and [Cd(NCS)(L)(MeOH)] (2). Both L and L are bound via two pyridyl-imine units yielding a tetradentate coordination mode giving rise to the 12 π electron chelate ring. It has been determined for the first time (qualitatively and quantitatively), using the EDDB electron population-based method, the HOMA index, and the ETS-NOCV charge and energy decomposition scheme, that the chelate ring containing Cd can be classified as a quasi-aromatic Möbius motif. Notably, using the methyl-containing ligand L controls the exclusive presence of the NCS connected with the Cd atom (structure 2), while applying L allows us to simultaneously coordinate NCS and SCN ligands (structure 1). Both systems are stabilized mostly by hydrogen bonding, C-H···π interactions, aromatic π···π stacking, and dihydrogen C-H···H-C bonds. The optical properties have been investigated by diffused reflectance spectroscopy as well as molecular and periodic DFT/TD-DFT calculations. The DFT-based ETS-NOCV analysis as well as periodic calculations led us to conclude that the monomers which constitute the obtained chelates are extremely strongly bonded to each other, and the calculated interaction energies are found to be in the regime of strong covalent connections. Intramolecular van der Waals dispersion forces, due to the large size of L and L, appeared to significantly stabilize these systems as well as amplify the aromaticity phenomenon.

Anagostic C−H•••M (M = a metal center) intramolecular interactions, one of the most fundamental and elusive forces in organometallic chemistry, are intuitively considered as repulsive and purely electrostatic in nature because of significant metal−hydrogen distances (∼2.3−3.0 Å). Contrary to the current state of knowledge, it is shown herein by quantum chemical computations based on the case study of new square-planar Ni II isomers based on Nthiophosphorylated thiourea that despite significant metal− hydrogen anagostic distances, the covalent-type charge delocalization contribution [Ni(d z 2 ) → σ*(C−H) and σ(C− H) → Ni(d z 2)] exists and it covers, together with the London dispersion energy, up to ∼40% of the overall anagostic stabilization. This charge delocalization component is found to amplify the metalloaromaticity phenomenon although a lack of any stabilizing charge transfer is expected at such long metalhydrogen distances (>3 Å). Remarkably, for the relatively short regime (<3 Å) of anagostic distances, the electrostatic Coulomb forces are destabilizing, which leads to the repulsive anagostic interactions, whereas, surprisingly, an increase of anagostic distance above 3 Å makes anagostic interactions stabilizing mostly because of attractive Coulomb forces. It shows unprecedented agostic (attractive) ↔ anagostic (repulsive) transitions in ubiquitous d 8 square-planar Ni II complexes containing elongated metal−hydrogen distances.

We report design and structural characterization of six new coordination polymers fabricated from PbCl and a series of closely related bis-pyridyl ligands L and HL-HL, namely, [Pb(L)Cl], [Pb(HL)Cl]·nMeOH, [Pb(HL)Cl]·0.5 nMeOH, [Pb(L)Cl], [Pb(HL)Cl], and [Pb(L)Cl]·nMeOH. The topology of the obtained networks is dictated by the geometry of the organic ligand. The structure of [Pb(L)Cl] is constructed from the [PbCl] two-dimensional (2D) sheets, linked through organic linkers into a three-dimensional framework, which exhibits a unique binodal 4,7-connected three-periodic topology named by us as sda1. Topological analysis of the 2D metal-organic sheet in [Pb(HL)Cl]·nMeOH discloses a binodal 3,4-connected layer topology, regardless of the presence of tetrel bonds. A one-dimensional (1D) coordination polymer [Pb(HL)Cl]·0.5 nMeOH is considered as a uninodal 2-connected chain. The overall structure of [Pb(L)Cl] is constructed from dimeric tetranuclear [Pb(μ-L-κN:N':N″:μ-O)(μ-Cl)(μ-Cl)] cationic blocks linked in a zigzag manner through bridging μ-Cl ligands, yielding a 1D polymeric chain. Topological analysis of this chain reveals a unique pentanodal 3,4,4,5,6-connected chain topology named by us as sda2. The structure of [Pb(HL)Cl] exhibits a 1D zigzaglike polymeric chain. Two chains are further linked into a 1D gridlike ribbon through the dimeric [Pb(μ-Cl)Cl] blocks as bridging nodes. With the bulkiest ligand HL, a 2D layered coordination polymer [Pb(L)Cl]·nMeOH is formed, which network, considering all tetrel bonds, reveals a unique heptanodal 3,3,3,3,4,5,5-connected layer topology named by us as sda3. Compounds [Pb(L)Cl], [Pb(L)Cl], and [Pb(HL)Cl] were found to be emissive in the solid state at ambient temperature. While blue emission of [Pb(L)Cl] is due to the ligand-centered transitions, bluish-green and white luminescence of [Pb(L)Cl] and [Pb(HL)Cl], respectively, was assigned to ligand-to-metal charge transfer mixed with metal-centered excited states. Molecular as well as periodic calculations were additionally applied to characterize the obtained polymers.

Abstract:In the present work, an in-depth, qualitative and quantitative description of non-covalent interactions in the hydrogen storage materials LiN(CH 3 ) 2 BH 3 and KN(CH 3 ) 2 BH 3 was performed by means of the charge and energy decomposition method (ETS-NOCV) as well as the Interacting Quantum Atoms (IQA) approach. It was determined that both crystals are stabilized by electrostatically dominated intra-and intermolecular M¨¨¨H-B interactions (M = Li, K). For LiN(CH 3 ) 2 BH 3 the intramolecular charge transfer appeared (B-HÑLi) to be more pronounced compared with the corresponding intermolecular contribution. We clarified for the first time, based on the ETS-NOCV and IQA methods, that homopolar BH¨¨¨HB interactions in LiN(CH 3 ) 2 BH 3 can be considered as destabilizing (due to the dominance of repulsion caused by negatively charged borane units), despite the fact that some charge delocalization within BH¨¨¨HB contacts is enforced (which explains H¨¨¨H bond critical points found from the QTAIM method). Interestingly, quite similar (to BH¨¨¨HB) intermolecular homopolar dihydrogen bonds CH¨¨¨HC appared to significantly stabilize both crystals-the ETS-NOCV scheme allowed us to conclude that CH¨¨¨HC interactions are dispersion dominated, however, the electrostatic and σ/σ*(C-H) charge transfer contributions are also important. These interactions appeared to be more pronounced in KN(CH 3 ) 2 BH 3 compared with LiN(CH 3 ) 2 BH 3 .