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The title compound, Li⁺·C₂BF₂O₄^-·2C₄H₈O₂S, is a dimeric species, which resides across a crystallographic inversion center. The dimers form eight-membered rings containing two Li⁺ cations, which are joined by O₂S sulfone linkages. The Li⁺ cations are ligated by four O atoms from the anions and solvent mol­ecules, forming a pseudo-tetra­hedral geometry. The exocyclic coordination sites are occupied by O atoms from the oxalate group of the difluoro­(oxalato)borate anion and an additional tetra­methyl­ene sulfone ligand.

The title compound {systematic name: poly[[aqua­lithium]--3,3,8,8-tetra­methyl-1,4,6,9-tetra­oxa-5⁴-borataspiro­[4.4]nonane-2,7-dione]}, [Li(C₈H₁₂BO₆)(H₂O)]_n (LiBMLB), forms a 12-membered macrocycle, which lies across a crystallographic inversion center. The lithium cations are pseudo-tetra­hedrally coordinated by three methyl­lactate ligands and a water mol­ecule. The asymmetric units couple across crystallographic inversion centers, forming the 12-membered macrocycles. These macrocycles, in turn, cross-link through the Li⁺ cations, forming an infinite polymeric structure in two dimensions parallel to (101).

The title compound, [Na(C₂BF₂O₄)(CH₃CN)₂]_n, forms infinite two-dimensional layers running parallel to (010). The layers lie across crystallographic mirror planes at y = 1/4 and 3/4. The Na, B and two F atoms reside on these mirror planes. The Na⁺ cations are six-coordinate. Two equatorial coordination positions are occupied by acetonitrile mol­ecules. The other two equatorial coordination sites are occupied by the chelating O atoms from the difluoro­(oxalato)borate anion (DFOB^-). The axial coordination sites are occupied by two F atoms from two different DFOB^- anions.

The structure of the title compound, C₂₁H₁₉O₂P, has been redetermined to provide a more precise molecular geometry. Close C-HO contacts, not remarked upon in the original paper, are discussed briefly.

Clear crystals of anhydrous theophylline (3,7-dihydro-1,3-dimethyl-1H-purine-2,6-dione), C₇H₈N₄O₂, were grown by sublimation and the X-ray structure determined. The planar molecules are stacked in columns along [010] and are inclined at an angle of 26.05 (10)° relative to (010). The melting point has been determined to be 548.8 (5) K.

Crystals of the title compound, C₁₈H₂₄N₂O₂, were grown from ethanol by slow evaporation and the structure has been determined. The mol­ecule resides on a crystallographic inversion center and the bi­phenyl moiety is essentially planar. The structure forms an infinite two-dimensional array of N-H(arene) interactions parallel to the (101) direction.

The title compounds, C₁₈H₂₂Cl₂N₂O₂ and C₂₀H₂₈N₂O₂, respectively, are isomorphous. The mol­ecules lie at general positions in the unit cell. In each structure, chemically equivalent but crystallographically inequivalent amine N atoms exhibit different degrees of pyramidalization. The structures exhibit weak N-HN hydrogen bonding, which is influenced by the differences in hybridization around the amine N atoms. The torsion angles across the bi­phenyl linkage for the two compounds are 67.2 (2) and 68.3 (3)°.

Clear crystals of anhydrous theobromine (3,7-dihydro-3,7-dimethyl-1H-purine-2,6-dione, C₇H₈N₄O₂) were grown by vacuum sublimation and the X-ray structure determined. The melting point of anhydrous theobromine has been determined as 620 (1) K. Two molecules in the asymmetric unit form a pseudo- centrosymmetric dimer and pack to form a layered structure of two-dimensional hydrogen-bonded networks.

In the title compound, C₁₈H₂₃N₅O₄·CH₂Cl₂, the di­chloro­methane solvent mol­ecule is disordered over two sets of sites in a 0.630 (13):0.370 (13) ratio. The dihedral angle between the uracil and phenyl rings is 30.2 (1)°. In the crystal, the principal inter­actions are N-HO hydrogen bonds, which link uracil units across centres of symmetry, forming eight-membered rings with an R²₂(8) graph-set motif. The structure also displays C-HO and C-HCl hydrogen bonds. Intra­molecular C-HO short contacts are also observed.

The title compound, poly[-aqua-aqua-₆-(1,1-dioxo-1⁶,2,5-thia­diazo­lidine-3,4-diolato)-dilithium], [Li₂(C₂N₂O₄S)(H₂O)₂]_n or (H₂O)₂:Li₂TDD, forms an infinite three-dimensional structure containing five-coordinate (Li/5) and six-coordinate (Li/6) Li⁺ cations. Li/5 is coordinated by three water mol­ecules, one carbonyl O atom and one sulfuryl O atom while Li/6 is coordinated by one water mol­ecule, three carbonyl O atoms, and two sulfuryl O atoms. Each water mol­ecule bridges two Li⁺ cations, while also hydrogen bonding to either one endocyclic N atom and one sulfuryl O atom or two endocyclic N atoms. While the endocyclic N atoms in the anion do not coordinate the Li⁺ cations, the carbonyl and sulfuryl groups each coordinate three Li⁺ cations, which gives rise to the infinite three-dimensional structure.

The absolute configuration of the title mol­ecular salt, C₁₅H₁₈N⁺·C₈H₆ClO₃^-, has been confirmed by resonant scattering. In the (R)-N-benzyl-1-phenyl-ethyl­ammonium cation, the phenyl rings are inclined to one another by 44.65 (7)°. In the crystal, the (R)-4-chloro­mandelate anions are linked via O-HO hydrogen bonds and bridged by N-HO hydrogen bonds involving the cations, forming chains along [010]. There are C-HO hydrogen bonds present within the chains, which are linked via C-H inter­actions and a short ClCl inter­action [3.193 (1) Å] forming a three-dimensional framework. The structure was refined as a two-component inversion twin giving a Flack parameter of 0.05 (4).

In the title compound, [Li₂(CF₃SO₂NSO₂CF₃)₂(CH₃CN)₂]_n, two Li⁺ cations reside on crystallographic inversion centers, each coordinated by six O atoms from bis(trifluoromethanesulfonyl)imide (TFSI^-) anions. The third Li⁺ cation on a general position is four-coordinated by two anion O atoms and two N atoms from acetonitrile mol­ecules in a tetra­hedral geometry.

The structure of the title compound, [Li(BF₄)(CH₃CN)]_n, consists of a layered arrangement parallel to (100) in which the Li⁺ cations are coordinated by three F atoms from three tetra­fluoridoborate (BF₄^-) anions and an N atom from an acetonitrile mol­ecule. The BF₄^- anion is coordinated to three different Li⁺ cations though three F atoms. The structure can be described as being built from vertex-shared BF₄ and LiF₃(NCCH₃) tetra­hedra. These tetra­hedra reside around a crystallographic inversion center and form 8-membered rings.

In the title compound, [Li(CH₃CN)₄]PF₆·CH₃CN, the asymmetric unit consists of three independent tetra­hedral [Li(CH₃CN)₄]⁺ cations, three uncoordinated PF₆^- anions and three uncoordinated CH₃CN solvent mol­ecules. The three anions are disordered over two sites through a rotation along one of the F-P-F axes. The relative occupancies of the two sites for the F atoms are 0.643 (16):0.357 (16), 0.677 (10):0.323 (10) and 0.723 (13):0.277 (13). The crystal used was a racemic twin, with approximately equal twin components.