Hydrogen-bonded chains formed by 5,5-diethylbarbituric acid and bipyridyl tectons

Triphenylbismuth(v) di[(iso)nicotinates] - transmetallation agents or divergent organometalloligands? First organobismuth(v)-based silver(i) coordination polymers

The reaction of Ph₃BiCl₂ with alkali salts of isonicotinic and nicotinic acids afforded Ph₃Bi[O(O)CC₅H₄N-4]₂ (1) and Ph₃Bi[O(O)CC₅H₄N-3]₂ (2), respectively, which were characterized by multinuclear NMR spectroscopy in solution, mass spectrometry and IR spectroscopy in the solid state. Their molecular structures were established by single-crystal X-ray diffraction. For both 1 and 2 the molecules contain a trigonal bipyramidal C₃BiO₂ core, with the phenyl groups in equatorial positions. The potential use of 1 and 2 as ditopic organometalloligands was investigated. The reaction of 1 or 2 with Me₃SnCl (1 : 2 molar ratio) resulted in carboxylato ligand exchange and the formation of Me₃Sn[O(O)CC₅H₄N-4] (3) and Me₃Sn[O(O)CC₅H₄N-3] (4) besides Ph₃BiCl₂. The crystals of both 3 and 4 contain 1-D coordination polymers built through intermolecular N → Sn interactions. The treatment of Ni[S₂P(OⁱPr)₂]₂ with 1 and 2, respectively, resulted, in addition to di(carboxylato)nickel(ii) derivatives, in isolation of Ph₃Bi and the disulphane [(ⁱPrO)₂P(S)S]₂. New coordination polymers were obtained by reacting 1 and 2 with various silver(i) salts: [Ag{Ph₃Bi[O(O)CC₅H₄N-4]₂}(OTf)] (5), [Ag{Ph₃Bi[O(O)CC₅H₄N-3]₂}(OTf)]·CH₂Cl₂ (6·CH₂Cl₂), [Ag{Ph₃Bi[O(O)CC₅H₄N-4]₂}](SbF₆)·2THF (7·2THF), [Ag{Ph₃Bi[O(O)CC₅H₄N-3]₂}](SbF₆)·CH₂Cl₂ (8·CH₂Cl₂) and [Ag{Ph₃Bi[O(O)CC₅H₄N-3]₂}(NO₃)]·CH₂Cl₂ (9·CH₂Cl₂). The crystal structures of 5 and 6 can be described as 1-D chains linked by triflate bridges in pairs of chains and 2-D networks, respectively. Compound 7 features a 2-D grid-like topology of the network, with tecton 1 acting as a tridentate ligand through both nitrogen and one oxygen atoms. The linker 2 molecules adopt either cis (compound 6) or trans (compounds 8 and 9) conformation. Complexes 8 and 9 are 1-D chain polymers exhibiting zig-zag and wavy motifs, respectively. The dimensionality of the structures is extended by the presence of supramolecular interactions (ππ, AgAg, AgO).

Crystal polymorphs of barbital: news about a classic polymorphic system

Barbital is a hypnotic agent that has been intensely studied for many decades. The aim of this work was to establish a clear and comprehensible picture of its polymorphic system. Four of the six known solid forms of barbital (denoted I(0), III, IV, and V) were characterized by various analytical techniques, and the thermodynamic relationships between the polymorph phases were established. The obtained data permitted the construction of the first semischematic energy/temperature diagram for the barbital system. The modifications I(0), III, and V are enantiotropically related to one another. Polymorph IV is enantiotropically related to V and monotropically related to the other two forms. The transition points for the pairs I(0)/III, I(0)/V, and III/IV lie below 20 °C, and the transition point for IV/V is above 20 °C. At room temperature, the order of thermodynamic stability is I(0) > III > V > IV. The metastable modification III is present in commercial samples and has a high kinetic stability. The solid-state NMR spectra provide information on aspects of crystallography (viz., the asymmetric units and the nature of hydrogen bonding). The known correlation between specific N-H···O═C hydrogen bonding motifs of barbiturates and certain IR characteristics was used to predict the H-bonded pattern of polymorph IV.