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The neutral diethyl 4,4'-(ferrocene-1,1'-diyl)dibenzoate, Fe[[eta]5-(C5H4)(4-C6H4CO2Et)]2 (I), yields (II) (following base hydrolysis) as the unusual complex salt poly[disodium bis[diethyl 4,4'-(ferrocene-1,1'-diyl)dibenzoate] 0.6-hydrate] or [Na+]2[Fe{[eta]5-(C5H4)-4-C6H4CO_2^-}2]·0.6H2O with Z' = 5. Compound (I) crystallizes in the triclinic system, space group P\bar 1, with two molecules having similar geometry in the asymmetric unit (Z' = 2). The salt complex (II) crystallizes in the orthorhombic system, space group Pbca, with the asymmetric unit comprising poly[decasodium pentakis[diethyl 4,4'-(ferrocene-1,1'-diyl)dibenzoate] trihydrate] or [Na+]10[Fe{[eta]5-(C5H4)-4-C6H4CO_2^-}2]5·3H2O. The five independent 1,1'-Fc[(4-C6H4CO2)-]2 dianions stack in an offset ladder (stepped) arrangement with the ten benzoates mutually oriented cisoid towards and bonded to a central layer comprising the ten Na+ ions and three water molecules [1,1'-Fc = [eta]5-(C5H4)2Fe]. The five dianions differ in the cisoid orientations of their pendant benzoate groups, with four having their -C6H4- groups mutually oriented at interplanar angles from 0.6 (3) to 3.2 (3)° (as [pi]...[pi] stacked C6 rings) and interacting principally with Na+ ions. The fifth dianion is distorted and opens up to an unprecedented -C6H4- interplanar angle of 18.6 (3)° through bending of the two 4-C6H4CO2 groups and with several ionic interactions involving the three water molecules (arranged as one-dimensional zigzag chains in the lattice). Overall packing comprises two-dimensional layers of Na+ cations coordinated mainly by the carboxylate O atoms, and one-dimensional water chains. The non-polar Fc(C6H4)2 groups are arranged perpendicular to the layers and mutually interlock through a series of efficient C-H...[pi] stacking contacts in a herringbone fashion to produce an overall segregation of polar and non-polar entities.

The isomers 2,3-, (I), 2,4-, (II), and 2,5-difluoro-N-(4-pyridyl)benzamide, (III), all with formula C₁₂H₈F₂N₂O, all exhibit intramolecular C-H...O=C and N-H...F contacts [both with S(6) motifs]. In (I), intermolecular N-H...O=C interactions form one-dimensional chains along [010] [N...O = 3.0181 (16) Å], with weaker C-H...N interactions linking the chains into sheets parallel to the [001] plane, further linked into pairs via C-H...F contacts about inversion centres; a three-dimensional herring-bone network forms via C-H...π(py) (py is pyridyl) interactions. In (II), weak aromatic C-H...N(py) interactions form one-dimensional zigzag chains along [001]; no other interactions with H...N/O/F < 2.50 Å are present, apart from long N/C-H...O=C and C-H...F contacts. In (III), N-H...N(py) interactions form one-dimensional zigzag chains [as C(6) chains] along [010] augmented by a myriad of weak C-H...π(arene) and O=C...O=C interactions and C-H...O/N/F contacts. Compound (III) is isomorphous with the parent N-(4-pyridyl)benzamide [Noveron, Lah, Del Sesto, Arif, Miller & Stang (2002). J. Am. Chem. Soc. 124, 6613-6625] and the three 2/3/4-fluoro-N-(4-pyridyl)benzamides [Donnelly, Gallagher & Lough (2008). Acta Cryst. C64, o335-o340]. The study expands our series of fluoro(pyridyl)benzamides and augments our understanding of the competition between strong hydrogen-bond formation and weaker influences on crystal packing.

In the title crystal structure, C20H18N2O10, there are two independent molecules, both of which lie on crystallographic inversion centres. In one molecule the 4-nitrophenyl dicarbonate groups are substituted in equatorial (Aeq) positions of the chair-form cyclohexane ring while in the other molecule the substitution is axial (Bax). The dihedral angles between the atoms of the symmetry-unique carbonate group (O=CO2—) and benzene ring for each molecule are 47.3 (1)° for Aeq and 11.7 (2)° for Bax. In Bax, this facilitates the formation of a weak intramolecular C—H...O hydrogen bond, while the packing is stabilized by weak intermolecular C—H...O interactions.

The title compound, [Ni(C₅H₅)(C₁₂H₇)(C₁₈H₁₅P)], does not contain strong hydrogen-bond donors or acceptors and the primary interactions are limited to those of the weak C-H...π(arene) type and mainly involving the arene rings.

Ferrocenyl derivatives are currently under investigation by our group and several series containing both amidothienyl and amidothiazolyl systems have been synthesised and characterised. The incorporation of thienyl/thiazolyl groups into a ferrocenyl- or ferrocenylphenyl system greatly enhances the number of potential donor atoms for coordination with metal fragments e.g. PtII, PdII with a view to platinum anti-cancer studies and/or interaction with guest molecules through suitable hydrogen bonding interactions. In nature, thiazole has been found to be vital in certain natural products: examples include the antibiotic bacitracin and the siderophore yersiniabactin. In therapeutic studies the antitumour compound epothilone A and myxothiazole (inhibitor) have been extensively studied.

The conformations and hydrogen bonding in the thiophene and thiazole title compounds, [Fe(C₅H₅)(C₂₀H₁₄NO₃S)], (I), and [Fe(C₅H₅)(C₁₉H₁₇N₂O₃S)], (II), are discussed. The sequence (C₅H₄)-(C₆H₄)-(CONH)-(C₄H₂S)-(CO₂Me) of rings and moieties in (I) is close to being planar; all consecutive interplanar angles are less than 10°. An intramolecular N-H...O=Cester hydrogen bond [graph set S(6), N...O = 2.768 (2) Å and N-H...O = 134 (2)°] effects the molecular planarity, and aggregation occurs via hydrogen-bonded chains formed from intermolecular Car-H...O=Cester/amide interactions along [010], with C...O distances ranging from 3.401 (3) to 3.577 (2) Å. The thiazole system in (II) crystallizes with two molecules in the asymmetric unit; these differ in the conformation along their long molecular axes; for example, the interplanar angle between the phenylene (C₆H₄) and thiazole (C₃NS) rings is 8.1 (2)° in one molecule and 27.66 (14)° in the other. Intermolecular N-H...O=Cester hydrogen bonds [N...O = 2.972 (4) and 2.971 (3) Å], each augmented by a Cphenylene-H...O=Cester interaction [3.184 (5) and 3.395 (4) Å], form motifs with graph set R¹₂(7) and generate chains along [100]. The amide C=O groups do not participate in hydrogen bonding. Compound (II) is the first reported ferrocenyl-containing thiazole structure.

The structure of fampridine (EL-970) or 4-aminopyridine, C₅H₆N₂, has been redetermined at 150 K. The room-temperature structure has been reported previously [Chao & Schempp (1977). Acta Cryst. B33, 1557-1564]. Pyramidalization at the amine N atom occurs in fampridine, with the N atom 0.133 (11) Å from the plane of the three C/H/H atoms to which it is bonded; the interplanar angle between the pyridyl ring and NH2 group is 21 (2)°. Aggregation in the solid state occurs by N-H...N and N-H...[pi](pyridine) interactions with N...N and N...[pi](centroid) distances of 2.9829 (18) and 3.3954 (15) Å, respectively; a C-H...[pi](pyridine) contact completes the intermolecular interactions [C...[pi](centroid) = 3.6360 (16) Å].

The title compound, C₂₀H₂₅NO₂, a condensation product of l-ephedrine and 4-propoxyaldehyde, is of interest in studies on weak interactions. It crystallizes with C-H...O and C-H...π(arene) intermolecular interactions as a one-dimensional chain [C...O = 3.3745 (19) Å, C-H...O = 139°; C-H...Cg1 = 3.6987 (16) Å, C-H...Cg1 = 161°, where Cg1 is the centroid of the symmetry-related 4-propoxy-substituted aromatic ring].

The title compound, [Fe(C₅H₅)(C₂₁H₁₆NO)], was synthesized from the coupling reaction of anthracene-9-carboxylic acid and ferrocenylmethylamine. The ferrocenyl (Fc) group and the anthracene ring system both lie approximately orthogonal to the amide moiety. An amide-amide interaction (along the a axis) is the principal interaction [N...O = 2.910 (2) Å]. A C-H...π(arene) interaction [C...centroid = 3.573 (2) Å] and a C-H...O interaction [C...O = 3.275 (3) Å] complete the hydrogen bonding; two short (Fc)C...C(anthracene) contacts are also present.