Andreas Lemmerer

Inorganic–organic hybrid materials incorporating primary cyclic ammonium cations: The lead iodide series

Six inorganic–organic hybrids have been synthesized and characterised by single-crystal X-ray diffraction experiments. The inorganic component is based on lead(II) iodide units and the organic component various cyclic hydrocarbons with only a primary ammonium group as a ring substituent. If the organic component is cyclopropylammonium, cyclobutylammonium, cyclopentylammonium and cyclohexylammonium, the inorganic motif observed is based on the cubic perovskite structure type and consists of 2-D layers of corner-sharing octahedra, in the ratio of 1∶2 inorganic–organic. lead(II) iodide and cycloheptylammonium combined to give 1-D chains of corner-sharing lead iodide octahedra and similarly, lead(II) iodide and cyclooctylammonium gave 1-D chains of face-sharing octahedra. A quantitative measure of the steric effects of the size of the cyclic rings on the tilting of the inorganic layers is proposed.

Inorganic–organic hybrid materials incorporating primary cyclic ammonium cations: The lead bromide and chloride series

Twelve inorganic–organic hybrids have been synthesized and characterised by single-crystal X-ray diffraction experiments. The inorganic component is based on lead(II) bromide and lead(II) chloride units and the organic component on various cyclic hydrocarbons, each with only a primary ammonium group as a ring substituent. When the organic component is cyclopropylammonium, cyclobutylammonium, cyclopentylammonium and cyclohexylammonium, the inorganic motif observed is based on the cubic perovskite structure type and consists of 2-D layers of corner-sharing octahedra, in the ratio of 1 : 2 inorganic–organic. Lead(II) bromide and cycloheptylammonium combined to give 1-D chains of corner-sharing PbBr6 octahedra and similarly, lead(II) bromide and cyclooctylammonium gave 1-D ribbons of corner-sharing PbBr6 octahedra. Lead(II) chloride and cycloheptylammonium have a ribbon motif, and lead(II) chloride and cyclooctylammonium have 2-D layers of corner-, edge- and face-sharing octahedra. These results are compared with a similar study involving lead(II) iodide units and the same set of six cations. General trends and conclusions are discussed.

Synthesis, characterization and phase transitions in the inorganic–organic layered perovskite-type hybrids [(CnH2n + 1NH3)2PbI4], n = 4, 5 and 6

Three inorganic-organic layered perovskite-type hybrids of the general formula [(C(n)H(2n+1)NH(3))(2)PbI(4)], n = 4, 5 and 6, display a number of reversible first-order phase transitions in the temperature range from 256 to 393 K. [(C(4)H(9)NH(3))(2)PbI(4)] has a single phase transition, [(C(5)H(11)NH(3))(2)PbI(4)] has two phase transitions and [(C(6)H(13)NH(3))(2)PbI(4)] has three phase transitions. In all three cases, the lowest-temperature phase transition is thermochromic and the crystals change colour from yellow in their lowest-temperature phase to orange in their higher-temperature phase for [(C(4)H(9)NH(3))(2)PbI(4)] and [(C(6)H(13)NH(3))(2)PbI(4)], and from orange to red for [(C(5)H(11)NH(3))(2)PbI(4)]. The structural details associated with this phase transition have been investigated via single-crystal X-ray diffraction, SC-XRD, for all three compounds.

Synthesis and crystal structures of inorganic–organic hybrids incorporating an aromatic amine with a chiral functional group

In this paper we report the synthesis and the crystal structure of inorganic–organic hybrids containing various lead halides as the inorganic motif and a primary amine as the organic constituent. The organic molecule investigated is (C6H5C*H(CH3)NH2) and both the R and S as well as the racemic (±) forms were used. Within the structures obtained, three different inorganic motifs are displayed by the lead halide octahedra: 1-D polymeric face-sharing chains of formula PbCl3((R)–C6H5CH(CH3)NH3), PbBr3((R)–C6H5CH(CH3)NH3), PbI3((R)–C6H5CH(CH3)NH3) and PbI3((S)–C6H5CH(CH3)NH3); 1-D polymeric corner-sharing chains of formula PbCl5((±)–C6H5CH(CH3)NH3)3 and PbBr5((±)–C6H5CH(CH3)NH3)3; and 2-D corner-sharing layers of formula PbI4((S)–C6H5CH(CH3)NH3)2 and PbI4((R)–C6H5CH(CH3)NH3)2. The changes in geometry and intermolecular interactions such as hydrogen bonding and pi stacking are discussed and compared between the eight structures.

Synthesis, characterization and phase transitions of the inorganic–organic layered perovskite-type hybrids [(CnH2n+1NH3)2PbI4] (n = 12, 14, 16 and 18)

The room temperature single-crystal structures of the inorganic–organic layered perovskite-type hybrids of general formula [(CnH2n+1NH3)2PbI4] (n = 12, 14, 16 and 18) have been determined. The four compounds each display two reversible phase transitions above room temperature, with phases labelled III, II and I. The single-crystal structures of phase II have also been determined. The phase transition from phase III to phase II is a first-order transition and corresponds to a change in the conformation of the alkylammonium chains and a shift of the inorganic layers relative to each other. The phase change from III to II is thermochromic for all compounds, going from a yellow to an orange colour.

Covalent assistance to supramolecular synthesis: modifying the drug functionality of the antituberculosis API isoniazid in situ during co-crystallization with GRAS and API compounds

The anti-tuberculosis molecule isonicotinic acid hydrazide (isoniazid) is a promising molecule in the supramolecular synthesis of multi-component molecular complexes and also allows for its biological activity to be improved and modified by a simple covalent reaction. The low temperature crystal structures of both isoniazid (1) and the related N′-(propan-2-ylidene)isonicotinohydrazide molecule (2), the latter known to be a more effective agent against Mycobacterium tuberculosis, are reported. In addition, these two molecules were then co-crystallized with the same three Generally Regarded As Safe (GRAS) molecules, succinic acid, 4-hydroxybenzoic acid and 2-hydroxybenzoic acid, to produce the following pharmaceutical co-crystals: (isonicotinic acid hydrazide)2·(succinic acid) 3, (N′-(propan-2-ylidene)isonicotinohydrazide)2·(succinic acid) 4, (isonicotinic acid hydrazide)·(4-hydroxybenzoic acid) 6, (N′-(propan-2-ylidene)isonicotinohydrazide)·(4-hydroxybenzoic acid) 7, (isonicotinic acid hydrazide)·(2-hydroxybenzoic acid) 8, and (N′-(propan-2-ylidene)isonicotinohydrazide)·(2-hydroxybenzoic acid) 9. In addition, a co-crystal using 2-butanone as a modifier is also reported, (N′-(butan-2-ylidene)isonicotinohydrazide)2·(succinic acid) 5. Drug–drug co-crystals were also made with the anti-HIV compound 2-chloro-4-nitrobenzoic acid: (isonicotinic acid hydrazide)·(2-chloro-4-nitrobenzoic acid) 10, and (N′-(propan-2-ylidene)isonicotinohydrazide)·(2-chloro-4-nitrobenzoic acid) 11. All the co-crystals use the carboxylic acid⋯pyridine hydrogen bond to connect the GRAS or drug molecule to the pyridine ring. In general, the co-crystals with the modified isoniazid feature the C(4) homosynthon, and those with the original isoniazid a variety of homo- and heterosynthons. By comparing the melting points of the co-crystals that use isoniazid and those that use the modified isoniazid, a reduction in melting point is observed.

Lead halide inorganic–organic hybrids incorporating diammonium cations

Diammonium cations of general formula (H3N–R–NH3) have been used as templating moieties on lead(II) halide motifs, forming a variety of inorganic–organic nanocomposites. The R group can have simple, straight alkyl chains, which if even-membered and greater than ethane, form 2-D layers based on the RbAlF4 structure type, as found in [(H3N(CH2)4NH3)PbBr4] (1), [(H3N(CH2)4NH3)PbI4] (2), [(H3N(CH2)8NH3)PbI4] (4), [(H3N(CH2)10NH3)PbBr4] (5), and [(H3N(CH2)12NH3)PbI4] (6). If the R group has fused aromatic rings like naphthalene, the 2-D layered perovskite-type motif is still adopted, as in [(H3NC10H6NH3)PbI4] (7). If the chain is odd-membered, a 0-D inorganic motif, consisting of isolated blocks of face-sharing PbI6 octahedra and isolated iodide anions is seen, as in [(H3N(CH2)7NH3)4Pb3I12·2I−] (3). 1-D motifs, which have edge-sharing twin-anionic chains of corner-sharing ribbons are also observed in the compounds [(H3NC2H4NH3)4PbBr4] (8) and [(H3NC6H4CH2C6H4NH3)PbI6] (9) respectively.

Co-crystals and molecular salts of carboxylic acid/pyridine complexes: can calculated pKa's predict proton transfer? A case study of nine complexes

A series of nine complexes and 109 literature examples containing a carboxylic acid functional group and a pyridine functional group on separate molecules follow the ΔpKa rule such that proton transfer occurs at values above 3 to form a molecular salt and none at values below 0 to form a co-crystal. In the intermediate range, there is a predominance of molecular salt over co-crystal formation. The complexes discussed show that calculated pKas are good predictors of the outcome.

Effect of heteroatoms in the inorganic–organic layered perovskite-type hybrids [(ZCnH2nNH3)2PbI4], n = 2, 3, 4, 5, 6; Z = OH, Br and I; and [(H3NC2H4S2C2H4NH3)PbI4]

Ten inorganic–organic hybrids have been synthesized and characterized by single crystal X-ray diffraction experiments. The inorganic component is based on lead(II) iodide units and four different types of alkylammonium cations. The structural motif adopted by the inorganic component has 2-D layers of corner-sharing PbI6 octahedra, which are closely related to the K2NiF4 and RbAlF4 structure types. This motif is observed in hybrids containing alkylammonium cations (ZCnH2nNH3) that contain three different heteroatoms: [(HOC2H4NH3)2PbI4] and [(HOC3H6NH3)2PbI4], [(BrC2H4NH3)2PbI4] and [(ICnH2nNH3)2PbI4] (n = 2–6). Additionally the hybrids [(H3NC2H4S2C2H4NH3)PbI4] and [(NH3C2H4S2C2H4NH3)2PbI5·I] crystallized from a single solution and have two distinct inorganic motifs, the former has 2-D layers of corner-sharing octahedra and the latter has 1-D chains of corner-sharing octahedra. The identity of the heteroatom and the chain length have an effect on the overall packing exhibited by the hybrid structures.

Covalent assistance to supramolecular synthesis: directing the supramolecular assembly of co-crystals by in situ modification of hydrogen bonding functionality

Nicotinic acid hydrazide (niazid) readily co-crystallizes with carboxylic acids in methanol to form a 2-D sheet structure that utilizes all three H bond donors on the carbohydrazide functional group. In acetone solution niazid undergoes a condensation reaction with the solvent, which replaces the amine group with a hydrocarbon group leaving only one hydrogen bond donor on the modified niazid molecule, now containing a N-acylhydrazone functional group. The resulting reduced hydrogen bonding functionality leads to a new supramolecular assembly when co-crystallized with the same dicarboxylic acids.