Crystal and molecular structure and infrared spectra of tetraethylammonium hydrogen phthalate and tetrabutylammonium hydrogen phthalate

Variation of counter quaternary ammonium cations of anionic cage germanoxanes as building blocks of nanoporous materials

Double-four ring (D4R)-type cage germanoxanes, having a fluoride anion in the cage, contain organic ammonium cations as counter cations outside the cage, and they are attractive as unique nano-building blocks of anionic porous materials. Although the variety of counter cations directly included in the cage germanoxane synthesis is limited, this study demonstrates that other tetraalkylammonium cations can be introduced by cation exchange in both discrete and cross-linked states. Tetraethylammonium (TEA) of a discrete cage germanoxane was replaced with tetrabutylammonium (TBA) in an organic solvent, which provides another starting material. TEA and TBA cations in cross-linked networks formed by hydrosilylation reactions of dimethylvinylsilylated cage germanoxanes with various oligosiloxanes as linkers were exchanged with tetramethylammonium (TMA) cations. The variation in the pore volume, which depends on the type of introduced counter cations and oligosiloxane linkers, is verified. In terms of bottom-up synthesis of nanoporous materials from cage-type germanoxanes, the selection of both the counter cation and cross-linker is important to vary the porosity.

Nuclear quadrupole resonance supported by periodic quantum calculations: a sensitive tool for precise structural characterization of short hydrogen bonds

Systems with short hydrogen bonds (H-bonds) are notoriously difficult to describe even using cutting edge experimental techniques supported by advanced computational protocols. One of the most challenging issues is the highly dislocated H-bonded proton, which is typically smeared over a large area, featuring complex dynamics governed by pronounced nuclear quantum effects. Thus, in combination with experimental results, these systems offer a rich platform for the benchmarking of various computational approaches and methods. Herein, we present a methodology combining experimental and computational assessment of H-bond observables probed by the nuclear quadrupole resonance technique. Focusing on the case of picolinic acid N-oxide featuring one of the shortest known hydrogen bonds (ROO ∼ 2.425 Å), we compare the predictions of nuclear quadrupole coupling constants (NQCCs) for a series of computational models differing in fine structural details of the H-bond. By comparing the computed 14N and 17O NQCCs with the measured ones and by analyzing the sensitivity of NQCCs to H-bond geometry variations, we demonstrate that NQCCs represent a very sensitive probe for H-bond geometry, particularly the proton location, thereby offering, in conjunction with computations, an accurate and reliable tool for the fine structural characterization of short H-bonds. Importantly, the present methodology is a good compromise between accuracy and computational cost.

2-Amino-5-bromopyridinium 2-carboxybenzoate

The asymmetric unit of the title compound, C₅H₆BrN₂⁺·C₈H₅O₄⁻, consists of two crystallographically independent 2-amino-5-bromo­pyridinium cations (A and B) and two 2-carb­oxy­benzoate anions (A and B). Each 2-amino-5-bromo­pyridinium cation is approximately planar, with a maximum deviation of 0.047 (1) Å in cation A and 0.027 (1) Å in cation B. The 2-amino-5-bromo­pyridinium unit in cation A is inclined at dihedral angles of 4.9 (3) and 2.2 (3)° with the phenyl rings of the A and B 2-carb­oxy­benzoate anions, respectively. The corresponding angles for cation B are 3.0 (3) and 5.6 (3)°. The mol­ecular structure is stabilized by an intra­molecular O—H⋯O hydrogen bond,which generates an S(7) ring motif. The cations and anions are linked via inter­molecular N—H⋯O and C—H⋯O hydrogen bonds, generating R₂²(8) ring motifs. In the crystal packing, mol­ecules are linked into wave-like chains along [001] via adjacent ring motifs. Short inter­molecular distances between the phenyl and pyridine rings [3.613 (4) and 3.641 (4) Å] indicate the existence of π–π inter­actions. The crystal structure is a non-merohedral twin with a contribution of 0.271 (3) of the minor component.

Geometric conditions for the formation of short intramolecular hydrogen bonds in dicarboxylic acids and their acid salts. Crystal structures of two cyclopropane derivatives containing such bonds: ammonium hydrogen caronate and potassium hydrogen caronate hydrate

(I) Ammonium hydrogen 3,3-dimethyl-cis-1,2-cyclopropanedicarboxylate (NH4H caronate), C7H13NO4, Mr = 175.2, orthorhombic Pbca, a = 6.530(1) Å, b = 18.366(5) Å, c = 14.956(2) Å, V = 1793.7(6) Å3, Z = 8, Dx = 1.290 g/cm3, μ = 0.10 mm−1, F(000) = 752, wR = 0.041, R = 0.062 for 723 observed reflections [I > 2σ(I)]. (II) Potassium hydrogen 3,3-dimethyl-cis-1,2-cyclopropanedicarboxylate (KH caronate) monohydrate, C7H9KO4 · H2O, Mr = 214.3, triclinic P[unk], a = 6.156(2) Å, b = 9.276(3) Å, c = 9.619(3) Å, α = 97.47(1)°, β = 107.94(2)°, γ = 107.29(1)°, V = 483.9(3) Å3, Z = 2, Dx = 1.469 g/cm3, μ = 0.53 mm−1, F(000) = 220, wR = 0.037, R = 0.044 for 1904 observed reflections [I > 2σ(I)].

Both compounds show short intramolecular hydrogen bonds with O…O distances of 2.477(5) Å in (I) and 2.425(3) Å in (II). The present structures complement a series of comparable chelate systems. The different geometries in these chelates influence the hydrogen bond lengths (O…O) and produce distortions of the anions to different extents. These considerations, which make the tendency to form intramolecular hydrogen bonds (instead of intermolecular ones) plausible, are in accordance with predictions of the formation of intramolecular hydrogen bonds in aqueous solution by interpretation of the ratio between first and second dissociation constants of the respective dibasic acids.

Molecular structure and vibrational assignment of melaminium phthalate by density functional theory (DFT) and ab initio Hartree-Fock (HF) calculations

The molecular geometry, the normal mode frequencies and corresponding vibrational assignment of melaminium phthalate (C3H7N6+.C8H5O4(-)) in the ground state were performed by HF and B3LYP levels of theory using the 6-31G(d) basis set. The optimized bond length numbers with bond angles are in good agreement with the X-ray data. The vibrational spectra of melaminium phthalate which is calculated by HF and B3LYP methods, reproduces vibrational wave numbers with an accuracy which allows reliable vibrational assignments. The title compound has been studied in the 4000-100 cm(-1) region where the theoretical evaluation and assignment of all observed bands were made.

Construction of hydrogen-bonded and coordination-bonded networks of cobalt(II) with pyromellitate: synthesis, structures, and magnetic properties

Synthesis (hydrothermal and metathesis), characterization (UV-vis, IR, TG/DTA), single-crystal X-ray structures, and magnetic properties of three cobalt(II)-pyromellitate complexes, purple [Co(2)(pm)](n) (1), red [Co(2)(pm)(H(2)O)(4)](n) x 2nH(2)O (2), and pink [Co(H(2)O)(6)](H(2)pm) (3) (H(4)pm = pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid)), are described. 1 consists of one-dimensional chains of edge-sharing CoO(6) octahedra that are connected into layers via O-C-O bridges. The layers are held together by the pyromellitate (pm(4-)) backbone to give a three-dimensional structure, each ligand participating in an unprecedented 12 coordination bonds (Co-O) to 10 cobalt atoms. 2 consists of a three-dimensional coordination network possessing cavities in which unbound water molecules reside. This highly symmetric network comprises eight coordinate bonds (Co-O) between oxygen atoms of pm(4-) to six trans-Co(H(2)O)(2). 3 possesses a hydrogen-bonded sandwich structure associating layers of [Co(H(2)O)(6)](2+) and planar H(2)pm(2-). The IR spectra, reflecting the different coordination modes and charges of the pyromellitate, are presented and discussed. The magnetic properties of 1 indicate complex behavior with three ground states (collinear and canted antiferromagnetism and field-induced ferromagnetism). Above the Néel temperature (T(N)) of 16 K it displays paramagnetism with short-range ferromagnetic interactions (Theta = +16.4 K, mu(eff) = 4.90 mu(B) per Co). Below T(N) a weak spontaneous magnetization is observed at 12.8 K in low applied fields (H < 100 Oe). At higher fields (H > 1000 Oe) metamagnetic behavior is observed. Two types of hysteresis loops are observed; one centered about zero field and the second about the metamagnetic critical field. The critical field and the hysteresis width increase as the temperature is lowered. The heat capacity data suggest that 1 has a 2D or 3D magnetic lattice, and the derived magnetic entropy data confirm an anisotropic s(eff) = 1/2 for the cobalt(II) ion. Magnetic susceptibility data indicate that 2 and 3 are paramagnets.

A theoretical study of the effect of a tetraalkylammonium counterion on the hydrogen bond strength in Z-hydrogen maleate

High-level ab initio calculations (B3LYP/6-31+G and QCISD(T)/6-311+G**) were carried out to resolve the disagreement between recent experimental and computational estimates of the relative strength of the intramolecular hydrogen bond in Z-hydrogen maleate anion with respect to the normal hydrogen bond in maleic acid. The computational estimates for the strength of the intramolecular hydrogen bond in the gas-phase maleate anion are in a range of 14-28 kcal/mol depending on the choice of the reference structure. Computational data suggest that the electrostatic influence of a counterion such as a tetraalkylammonium cation can considerably weaken the hydrogen bonding interaction (by 1.5-2 times) in the complexed hydrogen maleate anion relative to that in the naked anion. The estimated internal H-bonding energies for a series of Z-maleate/R4N+ salts (R = CH3, C2H5, CH3CH2CH2CH2) range from 8 to 13 kcal/mol. The calculated energy differences between the E- and Z-hydrogen maleates complexed to Me4N+, Et4N+, and Bu4N+ cation are 4.9 (B3LYP/6-31+G(d,p)) and 5.7 and 5.8 kcal/mol (B3LYP/6-31G(d)). It is also demonstrated that the sodium cation exerts a similar electrostatic influence on the hydrogen bond strength in bifluoride anion (FHF-). The present study shows that while low-barrier short hydrogen bonds can exist in the gas phase (the barrier for the hydrogen transfer in maleate anion is only 0.2 kcal/mol at the QCISD(T)/6-311+G//QCISD/6-31+G level), whether they can also be strong in condensed media or not depends on how their interactions with their immediate environment affect their strength.