: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

The nature and characteristics of the CH/π interaction are discussed by comparison with other weak molecular forces such as the CH/O and OH/π interaction. The CH/π interaction is a kind of hydrogen bond operating between a soft acid CH and a soft base π-system (double and triple bonds, C6 and C5 aromatic rings, heteroaromatics, convex surfaces of fullerenes and nanotubes). The consequences of CH/π hydrogen bonds in supramolecular chemistry are reviewed on grounds of recent crystallographic findings and database analyses. The topics include intramolecular interactions, crystal packing (organic and organometallic compounds), host/guest complexes (cavity-type inclusion compounds of cyclodextrins and synthetic macrocyclic hosts such as calixarenes, catenanes, rotaxanes and pseudorotaxanes), lattice-inclusion type clathrates (including liquid crystals, porphyrin derivatives, cyclopentadienyl compounds and C60 fullerenes), enantioselective clathrate formation, catalytic enantioface discriminating reactions and solid-state photoreaction. The implications of the CH/π concept for crystal engineering and drug design are evident.

CH/π hydrogen bonds in crystals

The article deals with coordination compounds of iron(II) that may exhibit thermally induced spin transition, known as spin crossover, depending on the nature of the coordinating ligand sphere. Spin transition in such compounds also occurs under pressure and irradiation with light. The spin states involved have different magnetic and optical properties suitable for their detection and characterization. Spin crossover compounds, though known for more than eight decades, have become most attractive in recent years and are extensively studied by chemists and physicists. The switching properties make such materials potential candidates for practical applications in thermal and pressure sensors as well as optical devices. The article begins with a brief description of the principle of molecular spin state switching using simple concepts of ligand field theory. Conditions to be fulfilled in order to observe spin crossover will be explained and general remarks regarding the chemical nature that is important for the occurrence of spin crossover will be made. A subsequent section describes the molecular consequences of spin crossover and the variety of physical techniques usually applied for their characterization. The effects of light irradiation (LIESST) and application of pressure are subjects of two separate sections. The major part of this account concentrates on selected spin crossover compounds of iron(II), with particular emphasis on the chemical and physical influences on the spin crossover behavior. The vast variety of compounds exhibiting this fascinating switching phenomenon encompasses mono-, oligoand polynuclear iron(II) complexes and cages, polymeric 1D, 2D and 3D systems, nanomaterials, and polyfunctional materials that combine spin crossover with another physical or chemical property.

/pdf/spin-state-switching-in-iron-coordination-compounds-42yuqvvfsi.pdf

Spin state switching in iron coordination compounds

Carbohydrates as ligands: coordination equilibria and structure of the metal complexes

A study of the halogen···hal- ogen contacts in organic compounds using ab initio calculations and the re- sults of previously reported crystallo- graphic studies show that these interac- tions are controlled by electrostatics. These contacts can be represented by the geometric parameters of the C� X1···X2� C moieties (where q1 = C� X1···X2 and q2 = X1···X2 � C; ri = X1···X2 distance). The distributions of the con- tacts within the sum of van der Waals radii (rvdW) versus qi (q1 = q2) show a maximum at q � 1508 for X = Cl, Br, and I. This maximum is not seen in the distribution of F···F contacts. These re- sults are in good agreement with our ab initio calculations. The theoretical results show that the position of the maximum depends on three factors: 1) The type of halogen atom, 2) the hy- bridization of the ipso carbon atom, and 3) the nature of the other atoms that are bonded to the ipso carbon atom apart from the halogen atom. Calculations show that the strength of these contacts decreases in the follow- ing order: I···I > Br···Br > Cl···Cl. Their relative strengths decrease as a func- tion of the hybridization of the ipso carbon atom in the following order: sp 2 > sp > sp 3 . Attaching an electroneg- ative atom to the carbon atom strengthens the halogen···halogen con- tacts. An electrostatic model is pro- posed based on two assumptions: 1) The presence of a positive electrostatic end cap on the halogen atom (except for fluorine) and 2) the electronic charge is anisotropically distributed around the halogen atom.

http://tyr0.chem.wsu.edu/~kipeters/Pages/pdfs/CEJ12.8952.2006.pdf

The nature of halogen...halogen synthons: crystallographic and theoretical studies.

Counter anion dependent symmetry ofCuII–4-amino-1,2,4-triazole polymeric chains

New porous crystals of Cu(I) complexes with Schiff-base-containing triazole ligands

Three Schiff-base-containing triazole derivatives have been synthesized and investigated by X-ray crystallography. Structural motifs (zigzag or linear chains) formed in the solid state are stabilized by C−Br···N halogen bond interactions, while hydrogen bonds do not seem to play a significant role in the molecular self-organization of studied compounds. Quantum-chemical studies confirm that these interactions are sufficient to account for both the arrangement of structural motifs and very short Br···N distances observed experimentally. It is also shown that Br···N interactions can lead to generally shorter donor−acceptor distances than Cl···N contacts.

Dominant role of C-Br...N halogen bond in molecular self-organization. Crystallographic and quantum-chemical study of schiff-base-containing triazoles

The direct reaction between [VCl(3)(thf)3] or [VO(OEt)3] and 2,2'-thiobis{4-(1,1,3,3-tetramethyl-butyl)phenol (tbopH(2)) leads to the formation of [V(2)(micro-tbop-kappa(3)O,S,O)2Cl(2)(CH(3)CN)(2)] (1).4CH(3)CN or [V(2)(micro-OEt)2(O)2(tbop-kappa(3)O,S,O)2] (2), respectively, in high yield. Compounds 1 and 2 were characterized by chemical and physical techniques including X-ray crystallography and variable temperature magnetic susceptibility studies (J = -29.1 cm(-1)) for 1. Complexes 1 and 2 were supported on MgCl2 and when activated with aluminium alkyls, were found to effectively polymerize ethene to produce polyethylene with a narrow molecular weight distribution M(w)/M(n) approximately 3.

Synthesis, structural studies and reactivity of vanadium complexes with tridentate (OSO) ligand.

The new coordination compounds, [Fe(quin-2-c)2(EtOH)2] (1), [Co(quin-2-c)2(EtOH)2] (2), and [Fe(quin-2-c)2(PrOH)2] (3) (where quin-2-c = quinoline-2-carboxylate) have been synthesized and investigated by ligand field, IR, Raman, and Mossbauer spectroscopy and by magnetic measurements. The X-ray analysis of the structure of 3 has been performed and refined to an R factor of 0.0377. The compound crystallizes in the monoclinic space group P21/n with a = 6.104(1), b = 10.515(2), c = 19.339(4) A, β = 92.57(3)°. The trans N2O4 environment around the FeII ion has a distorted octahedral geometry and the quin-2-c ion coordinates to iron in the equatorial plane in a chelating mode. The axial positions are occupied by propan-1-ol molecules. The spectral studies indicate the same molecular structure for all three compounds. The magnetic susceptibility and the magnetization of 2 were calculated for Co2+ ions in an octahedral crystal field with a rhombic zero field distortion (|D| = 34 cm−1, E ≈ 0, giso = 2.35 and N = 6.9·10−4 emu·mol−1). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Synthesis, Spectroscopy, and Magnetic Properties of FeII and CoII Quinoline‐2‐carboxylates − Crystal Structure of trans‐Bis(quinoline‐2‐carboxylato)bis(propanol)iron(II)

Krzysztof Drabent

Papers

Counter anion dependent symmetry ofCuII–4-amino-1,2,4-triazole polymeric chains

New porous crystals of Cu(I) complexes with Schiff-base-containing triazole ligands

Dominant role of C-Br...N halogen bond in molecular self-organization. Crystallographic and quantum-chemical study of schiff-base-containing triazoles

Synthesis, structural studies and reactivity of vanadium complexes with tridentate (OSO) ligand.

Synthesis, Spectroscopy, and Magnetic Properties of FeII and CoII Quinoline‐2‐carboxylates − Crystal Structure of trans‐Bis(quinoline‐2‐carboxylato)bis(propanol)iron(II)