Crystal structures of alkali metal (Group 1) citrate salts.

The crystal structures of 16 new alkali metal citrates were determined using powder and/or single crystal techniques. These structures and 12 previously determined citrate structures were optimized using density functional techniques. The central portion of a citrate ion is fairly rigid, while the conformations of the terminal carboxylate groups exhibit no preferences. The citrate-metal bonding is ionic. Trends in metal-citrate coordination are noted. The energy of an O-H...O hydrogen bond is proportional to the square root of the H...acceptor Mulliken overlap population, and a correlation between the hydrogen bond energy and the H...acceptor distance was developed: E (kJ mol-1) = 137.5 (5) - 45.7 (8) (H...A, Å). The hydrogen bond contribution to the crystal energy ranges from 62.815 to 627.6 kJ mol-1 citrate-1 and comprises ∼5 to 30% of the crystal energy. The general order of ionization of the three carboxylic acid groups of citric acid is: central, terminal, terminal, although there are a few exceptions. Comparisons of the refined and DFT-optimized structures indicate that crystal structures determined using powder diffraction data may not be as accurate as single-crystal structures.

Tricaesium citrate monohydrate, Cs3C6H5O7·H2O: crystal structure and DFT comparison.

The crystal structure of tricaesium citrate monohydrate, 3Cs+·C6H5O73-·H2O, has been solved and refined using laboratory X-ray single-crystal diffraction data, and optimized using density functional techniques. This compound is isostructural to the K+ and Rb+ compounds with the same formula. The three independent Cs cations are eight-, eight-, and seven-coordinate, with bond-valence sums of 0.91, 1.22, and 1.12 valence units. The coordination polyhedra link into a three-dimensional framework. The hy-droxy group forms the usual S(5) hydrogen bond with the central carboxyl-ate group, and the water mol-ecule acts as a donor in two strong hydrogen bonds.

Crystal structure of caesium di-hydrogen citrate from laboratory X-ray powder diffraction data and DFT comparison.

The crystal structure of caesium di-hydrogen citrate, Cs+·H2C6H5O7-, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The coordination polyhedra of the nine-coordinate Cs+ cations share edges to form chains along the a-axis. These chains are linked by corners along the c-axis. The un-ionized carb-oxy-lic acid groups form two different types of hydrogen bonds; one forms a helical chain along the c-axis, and the other is discrete. The hy-droxy group participates in both intra- and inter-molecular hydrogen bonds.

Crystal structure of trirubidium citrate monohydrate from laboratory X-ray powder diffraction data and DFT comparison.

The crystal structure of the title compound, 3Rb+·C6H5O73-·H2O, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The hy-droxy group participates in an intra-molecular hydrogen bond to the deprotonated central carboxyl-ate group with graph-set motif S(5). The water mol-ecule acts as a hydrogen-bond donor to both terminal and central carboxyl-ate O atoms. The three independent rubidium cations are seven-, six- and six-coordinate, with bond-valence sums of 0.84, 1.02, and 0.95, respectively. In the extended structure, their polyhedra share edges and corners to form a three-dimensional network. The hydro-phobic methyl-ene groups occupy channels along the b axis.

Crystal structure of dicesium hydrogen citrate from laboratory single-crystal and powder X-ray diffraction data and DFT comparison.

The crystal structure of dicesium hydrogen citrate, 2Cs+·C6H6O72-, has been solved using laboratory X-ray single-crystal diffraction data, refined using laboratory powder X-ray data, and optimized using density functional techniques. The Cs+ cation is nine-coordinate, with a bond-valence sum of 0.92 valence units. The CsO9 coordination polyhedra share edges and corners to form a three-dimensional framework. The citrate anion is located on a mirror plane. Its central hy-droxy/carboxyl-ate O-H⋯O hydrogen bond is short, and (unusually) inter-molecular. The centrosymmetric end-end carboxyl-ate hydrogen bond is exceptionally short (O⋯O = 2.416 Å) and strong. These hydrogen bonds contribute 16.5 and 21.7 kcal mol-1, respectively, to the crystal energy. The hydro-phobic methyl-ene groups occupy pockets in the framework.

Crystal structure of trirubidium citrate from laboratory X-ray powder diffraction data and DFT comparison.

The crystal structure of trirubidium citrate, 3Rb+·C6H5O73-, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The two independent Rb+ cations are seven- and eight-coordinate, with bond-valence sums of 0.99 and 0.92 valence units. The coordination polyhedra share edges and corners to form a three-dimensional framework. The only hydrogen bond is an intra-molecular one between the hy-droxy group and the central carboxyl-ate, with graph set S(5). The hydro-phobic methyl-ene groups lie in pockets in the framework.

Crystal structure of penta-sodium hydrogen dicitrate from synchrotron X-ray powder diffraction data and DFT comparison.

The crystal structure of penta-sodium hydrogen dicitrate, Na5H(C6H5O7)2, has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Each of the two independent citrate anions is joined into a dimer by very strong centrosymmetric O-H⋯O hydrogen bonds, with O⋯O distances of 2.419 and 2.409 Å. Four octa-hedrally coordinated Na+ ions share edges to form open layers parallel to the ab plane. A fifth Na+ ion in trigonal-bipyramidal coordination shares faces with NaO6 octahedra on both sides of these layers.

Crystal structure of dirubidium hydrogen citrate from laboratory X-ray powder diffraction data and DFT comparison.

The crystal structure of dirubidium hydrogen citrate, 2Rb+·HC6H5O72-, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The un-ionized carb-oxy-lic acid group forms helical chains of very strong hydrogen bonds (O⋯O ∼ 2.42 Å) along the b axis. The hy-droxy group participates in a chain of intra- and inter-molecular hydrogen bonds along the c axis. These hydrogen bonds result in corrugated hydrogen-bonded layers in the bc plane. The Rb+ cations are six-coordinate, and share edges and corners to form layers in the ab plane. The inter-layer contacts are composed of the hydro-phobic methyl-ene groups.

Disodium hydrogen citrate sesquihydrate, Na2HC6H5O7(H2O)1.5.

The crystal structure of disodium hydrogen citrate sesquihydrate, 2Na2 (+)·C6H6O7 (2-)·1.5H2O, has been solved and refined using laboratory X-ray single-crystal diffraction data, and optimized using density functional techniques. The asymmetric unit contains two independent hydrogen citrate anions, four sodium cations and three water molecules. The coordination polyhedra of the cations (three with a coordination number of six, one with seven) share edges to form isolated 8-rings. The un-ionized terminal carb-oxy-lic acid groups form very strong hydrogen bonds to non-coordinating O atoms, with O⋯O distances of 2.46 Å.

Crystal structure of anhydrous tripotassium citrate from laboratory X-ray powder diffraction data and DFT comparison.

The crystal structure of anhydrous tripotassium citrate, [K3(C6H5O7)] n , has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The three unique potassium cations are 6-, 8-, and 6-coordinate (all irregular). The [KO n ] coordination polyhedra share edges and corners to form a three-dimensional framework, with channels running parallel to the c axis. The only hydrogen bond is an intra-molecular one involving the hy-droxy group and the central carboxyl-ate group, with graph-set motif S(5).

Trisodium citrate, Na3(C6H5O7).

The crystal structure of anhydrous tris-odium citrate, Na3(C6H5O7), has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory (DFT). There are two independent five-coordinate Na(+) and one six-coordinate Na(+) cations in the asymmetric unit. The [NaO5] and [NaO6] polyhedra share edges and corners to form a three-dimensional framework. There are channels parallel to the a and b axes in which the remainder of the citrate anions reside. The only hydrogen bonds are an intra-molecular one between the hy-droxy group and one of the terminal carboxyl-ate O atoms and an intermolecular one between a methylene group and the hydroxyl O atom.

A second polymorph of sodium di-hydrogen citrate, NaH2C6H5O7: structure solution from powder diffraction data and DFT comparison.

The crystal structure of a second polymorph of sodium di-hydrogen citrate, Na(+)·H2C6H5O7 (-), has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The powder pattern of the commercial sample used in this study did not match that corresponding to the known crystal structure [Glusker et al. (1965). Acta Cryst. 19, 561-572; refcode NAHCIT]. In this polymorph, the [NaO7] coordination polyhedra form edge-sharing chains propagating along the a axis, while in NAHCIT the octa-hedral [NaO6] groups form edge-sharing pairs bridged by two hy-droxy groups. The most notable difference is that in this polymorph one of the terminal carboxyl groups is deprotonated, while in NAHCIT the central carboxyl-ate group is deprotonated, as is more typical.

Sodium potassium hydrogen citrate, NaKHC6H5O7.

The crystal structure of sodium potassium hydrogen citrate has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional theory techniques. The Na(+) cation is six-coordinate, with a bond-valence sum of 1.17. The K(+) cation is also six-coordinate, with a bond-valence sum of 1.08. The distorted [NaO6] octahedra share edges, forming chains along the a axis. The likewise distorted [KO6] octahedra share edges with the [NaO6] octahedra on either side of the chain, and share corners with other [KO6] octahedra, resulting in triple chains along the a axis. The most prominent feature of the structure is the chain along [111] of very short, very strong hydrogen bonds; the O⋯O distances are 2.414 and 2.400 Å. The Mulliken overlap populations in these hydrogen bonds are 0.138 and 0.142 e, which correspond to hydrogen-bond energies of 20.3 and 20.6 kcal mol(-1).

Sodium dipotassium citrate, NaK2C6H5O7.

The crystal structure of sodium dipotassium citrate, Na(+)·2K(+)·C6H5O7 (3-), has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The Na(+) and one of the K(+) cations are six-coordinate, with bond-valence sums of 1.13 and 0.92 valence units, respectively, while another crystallographically independent K(+) cation is seven-coordinate with a bond-valence sum of 1.20. The [KO6] and [KO7] polyhedra share edges and corners to form layers perpendicular to the b axis. The distorted [NaO6] octa-hedra share edges to form chains along the a axis. The result is a three-dimensional network. The only O-H⋯O hydrogen bond is an intra-molecular one between the hy-droxy group and a terminal carboxyl-ate group.

(3-Phenyl-sulfanyl-1-phenyl-sulfonyl-1H-indol-2-yl)methyl acetate.

In the title compound, C(23)H(19)NO(4)S(2), the indole ring system makes dihedral angles of 89.6 (1) and 84.5 (8)° with the phenyl-sulfonyl and phenyl-sulfanyl rings, respectively. In the crystal, the mol-ecules are linked into C(10) chains running along the c axis by an inter-molecular C-H⋯O hydrogen bond. In addition, the crystal packing is stabilized by C-H⋯π inter-actions.