Piotr Kubisiak

A sodium atom in a large water cluster: Electron delocalization and infrared spectra

Ab initio molecular dynamics simulations modeling low-energy collisions of a sodium atom with a cluster with more than 30 water molecules are presented. We follow the dynamics of the atom-cluster interaction and the delocalization of the valence electron of sodium together with the changes in the electron binding energy. This electron tends to be shared by the nascent sodium cation and the water cluster. IR spectra of the sodium-water cluster are both computationally and experimentally obtained, with a good agreement between the two approaches.

Relative Complexation Energies for Li+ Ion in Solution: Molecular Level Solvation Versus Polarizable Continuum Model Study

Relative complexation energies for the lithium cation in acetonitrile and diethyl ether have been studied. Quantum-chemical calculations explicitly describing the solvation of Li(+) have been performed based on structures obtained from molecular dynamics simulations. The effect of an increasing number of solvent molecules beyond the first solvation shell has been found to consist in reduction of the differences in complexation energies for different coordination numbers. Explicit-solvation data have served as a benchmark to the results of polarizable continuum model (PCM) calculations. It has been demonstrated that the PCM approach can yield relative complexation energies comparable to the predictions based on molecular-level solvation, but at significantly lower computational cost. The best agreement between the explicit-solvation and the PCM results has been obtained when the van der Waals surface was adopted to build the molecular cavity.

Solvent-induced 1,3-N,S- vs. 1,5-S,S′-coordination in the NiII complex [Ni{p-Me2NC6H4NHC(S)NP(S)(OiPr)2}2]

Reaction of the deprotonated N-thiophosphorylated thiourea p-Me2NC6H4NHC(S)NHP(S)(OiPr)2 (HL) with NiCl2 leads to violet [Ni(L-1,3-N,S)2] or dark violet [Ni(L-1,5-S,S′)2]·(CH3)2CO crystals that were isolated by recrystallization from a mixture of CH2Cl2 or acetone, respectively, and n-hexane.

Steric and electronic effects in the host-guest hydrogen bonding in clathrate hydrates.

Clathrate hydrates with polar guest molecules (dimethyl ether, ethylene oxide, trimethylene oxide, tetrahydrofuran, and tetrahydropyran) were studied by means of the density functional theory. A model of a large cage of structure-I clathrate was employed. Optimal configurations of encaged guests were investigated with a focus on the host-guest hydrogen bond formation. Weak hydrogen bonds were found to be formed by each guest, while for THP a strong hydrogen bond and formation of L-defect was also observed. This is in accord with previous computational and experimental studies. Steric factors were shown to play a key role for the strength of the hydrogen bond formed. Interestingly, the host-guest binding is influenced not only by the size of a guest molecule but also by its shape. This work demonstrates that both electronic and steric properties of a polar guest should be considered for a full description of clathrate systems.

Molecular dynamics study on the effect of Lewis acid centers in poly(ethylene oxide)/LiClO4 polymer electrolyte.

Molecular dynamics simulations employing a polarizable force field have been performed for the model poly(ethylene oxide)/LiClO(4) electrolytes with boron or aluminum centers. Influence of Lewis acid centers on radial distribution functions, coordination numbers, percentage of free cations, diffusion coefficients and conductivity has been investigated. Results confirm the effect of acid centers on ion complexation and show that the properties of the electrolyte result from interplay of different interactions.

Quantum-chemical and molecular dynamics study of M+ [TOTO]- (M = Li, Na, K) ionic liquids.

Quantum-chemical calculations and classical molecular dynamics simulations with the Optimized Potentials for Liquid Simulations-All Atom (OPLS-AA) force field are presented for ionic liquids based on 2,5,8,11-tetraoxatridecan-13-oate anion (TOTO) and alkali cations (Li, Na, K). Complexation energies decrease with increasing cation radius from Li to K. Cation interactions with carboxylate oxygen atoms are preferred over complexation to ether oxygens. Cross-linking occurs in the structure of the liquid because of interactions of multiple metal ions with carboxylate oxygen atoms from multiple TOTO anions. Anticorrelated motion of ions of the same charge is an important factor decreasing conductivity of the liquid. Results of modeling agree with available experimental data for Na-TOTO.

Polarizable continuum model study on the solvent effect of polymer matrix in poly(ethylene oxide)-based solid electrolyte.

The Polarizable Continuum Model has been used to study the effect of polymer matrix on Li (+) and Mg (2+) complexation in poly(ethylene oxide)-based solid electrolyte. Structures of complexes, stabilization energies, and vibrational frequencies are compared with corresponding vacuum values. The solvent effect of the polymer decreases with increasing cation coordination number. Optimized complex geometries do not differ significantly compared to vacuum calculations. Calculated shifts in vibrational frequencies depend on the complex structure; for hexacoordinated ion most frequencies are slightly red-shifted. The most important effect is the decrease of differences between relative stabilities of different structures in the solvent.

Influence of CH2Cl2 for the structure stabilization of the NiII complex [Ni{6-MeO(O)CC6H4NHC(S)NP(S)(OiPr)2-1,5-S,S′}2]·CH2Cl2

The reaction of the deprotonated N-thiophosphorylated thiourea 6-MeO(O)CC6H4NHC(S)NHP(S)(OiPr)2 (HL) with NiCl2 leads to violet [NiL22]·CH22Cl22 crystals, which were isolated by recrystallization from a mixture of CH2Cl2 and n-hexane. It was established that the deprotonated ligands, L, are 1,5-S,S′-coordinated. The influence of CH2Cl2 for the complex stabilization was studied.

Stability of ion triplets in ionic liquid/lithium salt solutions: Insights from implicit and explicit solvent models and molecular dynamics simulations

Binding energies of ion triplets formed in ionic liquids by Li+ with two anions have been studied using quantum‐chemical calculations with implicit and explicit solvent supplemented by molecular dynamics (MD) simulations. Explicit solvent approach confirms variation of solute‐ionic liquid interactions at distances up to 2 nm, resulting from structure of solvation shells induced by electric field of the solute. Binding energies computed in explicit solvent and from the polarizable continuum model approach differ largely, even in sign, but relative values generally agree between these two models. Stabilities of ion triplets obtained in quantum‐chemical calculations for some systems disagree with MD results; the discrepancy is attributed to the difference between static optimized geometries used in quantum chemical modeling and dynamic structures of triplets in MD simulations.

Experimental and theoretical investigations of the NiII complex with N-phosphorylated thiourea iPrNHC(S)NHP(O)(OPh)2

The N-phosphorylated thiourea iPrNHC(S)NHP(O)(OPh)2 (HL) has been synthesized by the reaction of iPrNH2 and (PhO) 2P(O)NCS. Recrystallization of HL from aqueous acetone leads to [iPrNH3]+[P(O)2(OPh)2]- in a quantitative yield. Reaction of the deprotonated HL with NiCl2 leads to violet [NiL2] crystals with a 1,3-N,S-coordination mode of the ligands. Static DFT and ab initio molecular dynamics studies indicated that [NiL2] is stabilized predominantly by intramolecular N-H⋯OP hydrogen bonding and dynamically by secondary CPh-H⋯S interactions. All compounds have been characterized by IR, diffuse reflectance, UV-vis and NMR spectroscopy, single crystal X-ray diffraction analysis and elemental analysis. Thermal properties investigated in an air atmosphere by means of TGA revealed a residue corresponding to NiPS3.