Three anilides of 2,2′‐thiodibenzoic acid

The structures of N,N′‐bis(2‐methylphenyl)‐2,2′‐thiodibenzamide, C₂₈H₂₄N₂O₂S, (Ia), N,N′‐bis(2‐ethylphenyl)‐2,2′‐thiodibenzamide, C₃₀H₂₈N₂O₂S, (Ib), and N,N′‐bis(2‐bromophenyl)‐2,2′‐thiodibenzamide, C₂₆H₁₈Br₂N₂O₂S, (Ic), are compared with each other. For the 19 atoms of the consistent thiodibenzamide core, the r.m.s. deviations of the molecules in pairs are 0.29, 0.90 and 0.80 Å for (Ia)/(Ib), (Ia)/(Ic) and (Ib)/(Ic), respectively. The conformations of the central parts of molecules (Ia) and (Ib) are similar due to an intramolecular N—H...O hydrogen‐bonding interaction. The molecules of (Ia) are further linked into infinite chains along the c axis by intermolecular N—H...O interactions, whereas the molecules of (Ib) are linked into chains along b by an intermolecular N—H...π contact. The conformation of (Ic) is quite different from those of (Ia) and (Ib), since there is no intramolecular N—H...O hydrogen bond, but instead there is a possible intramolecular N—H...Br hydrogen bond. The molecules are linked into chains along c by intermolecular N—H...O hydrogen bonds.     

Structures of 1‐hydrophenanthroimidazoles: building blocks in the synthesis of expanded‐ring bis(imidazoles)

The structures of 1H‐phenanthro[9,10‐d]imidazole, C₁₅H₁₀N₂, (I), and 3,6‐dibromo‐1H‐phenanthro[9,10‐d]imidazole hemihydrate, C₁₅H₈Br₂N₂·0.5H₂O, (II), contain hydrogen‐bonded polymeric chains linked by columns of π–π stacked essentially planar phenanthroimidazole monomers. In the structure of (I), the asymmetric unit consists of two independent molecules, denoted (Ia) and (Ib), of 1H‐phenanthro[9,10‐d]imidazole. Alternating molecules of (Ia) and (Ib), canted by 79.07 (3)°, form hydrogen‐bonded zigzag polymer chains along the a‐cell direction. The chains are linked by π–π stacking of molecules of (Ia) and (Ib) along the b‐cell direction. In the structure of (II), the asymmetric unit consists of two independent molecules of 3,6‐dibromo‐1H‐phenanthro[9,10‐d]imidazole, denoted (IIa) and (IIb), along with a molecule of water. Alternating molecules of (IIa), (IIb) and water form hydrogen‐bonded polymer chains along the [110] direction. The donor–acceptor distances in these N(imine)...H—O(water)...H—N(amine) hydrogen bonds are the shortest thus far reported for imidazole amine and imine hydrogen‐bond interactions with water. Centrosymmetrically related molecules of (IIa) and (IIb) alternate in columns along the a‐cell direction and are canted by 48.27 (3)°. The present study provides the first examples of structurally characterized 1H‐phenanthroimidazoles.     

Dimorphism of ethyl 1,4‐dihydro‐2,4,6‐triphenylpyridine‐3‐carboxylate

The title compound, C₂₆H₂₃NO₂, (Ia) and (Ib), shows polymorphism with crystals obtained from different solvents displaying different crystal structures. However, it is not the geometry of the single mol­ecules nor the hydrogen‐bond pattern that is different in (Ia) and (Ib), but the way in which the hydrogen‐bonded chains, running along the a‐axis direction, are arranged with respect to each other.     

Competing intermolecular interactions in some `bridge‐flipped' isomeric phenylhydrazones

To examine the roles of competing intermolecular interactions in differentiating the molecular packing arrangements of some isomeric phenylhydrazones from each other, the crystal structures of five nitrile–halogen substituted phenylhydrazones and two nitro–halogen substituted phenylhydrazones have been determined and are described here: (E)‐4‐cyanobenzaldehyde 4‐chlorophenylhydrazone, C₁₄H₁₀ClN₃, (Ia); (E)‐4‐cyanobenzaldehyde 4‐bromophenylhydrazone, C₁₄H₁₀BrN₃, (Ib); (E)‐4‐cyanobenzaldehyde 4‐iodophenylhydrazone, C₁₄H₁₀IN₃, (Ic); (E)‐4‐bromobenzaldehyde 4‐cyanophenylhydrazone, C₁₄H₁₀BrN₃, (IIb); (E)‐4‐iodobenzaldehyde 4‐cyanophenylhydrazone, C₁₄H₁₀IN₃, (IIc); (E)‐4‐chlorobenzaldehyde 4‐nitrophenylhydrazone, C₁₃H₁₀ClN₃O₂, (III); and (E)‐4‐nitrobenzaldehyde 4‐chlorophenylhydrazone, C₁₃H₁₀ClN₃O₂, (IV). Both (Ia) and (Ib) are disordered (less than 7% of the molecules have the minor orientation in each structure). Pairs (Ia)/(Ib) and (IIb)/(IIc), related by a halogen exchange, are isomorphous, but none of the `bridge‐flipped' isomeric pairs, viz. (Ib)/(IIb), (Ic)/(IIc) or (III)/(IV), is isomorphous. In the nitrile–halogen structures (Ia)–(Ic) and (IIb)–(IIc), only the bridge N—H group and not the bridge C—H group acts as a hydrogen‐bond donor to the nitrile group, but in the nitro–halogen structures (III) (with Z′ = 2) and (IV), both the bridge N—H group and the bridge C—H group interact with the nitro group as hydrogen‐bond donors, albeit via different motifs. The occurrence here of the bridge C—H contact with a hydrogen‐bond acceptor suggests the possibility that other pairs of `bridge‐flipped' isomeric phenylhydrazones may prove to be isomorphous, regardless of the change from isomer to isomer in the position of the N—H group within the bridge.     

Polymorphism of 2,5‐[(diphenylphosphanyl)methyl]‐1,1,2,4,4,5‐hexaphenyl‐1,4‐diphospha‐2,5‐diboracyclohexane

2,5‐[(Diphenylphosphanyl)methyl]‐1,1,2,4,4,5‐hexaphenyl‐1,4‐diphospha‐2,5‐diboracyclohexane shows polymorphism as two tetrahydrofuran (THF) disolvates [C₆₄H₅₈B₂P₄·2C₄H₈O, (Ia) and (Ib)] and pseudo‐polymorphism as its toluene monosolvate [C₆₄H₅₈B₂P₄·C₇H₈, (Ic)]. In each of polymorphs (Ia) and (Ib), the diphosphadiboracyclohexane molecule is located on a centre of inversion. The THF molecule of (Ib) is disordered over two sites, with a site‐occupation factor of 0.612 (8) for the major‐occupied site. Both structures crystallize in the same space group (P2₁/n), but they display a different crystal packing. For pseudo‐polymorph (Ic), although the space group is P2₁/c, which is just a different setting of the P2₁/n space group of (Ia) and (Ib), the crystal packing is completely different. Although the crystal packing in these three structures is significantly different, their molecular conformations are surprisingly the same.     

Indole- and carbazole-substituted pyridinium iodide salts: a rare case of conformational isomerism in crystals

A series of indole- and carbazole-substituted pyridinium iodide salts has been synthesized and characterized. X-ray analysis revealed that the iodide salt of the indole-substituted cation (E)-4-(1H-indol-3-yl­vinyl)-N-methyl­pyridinium (IMPE⁺), C₁₆H₁₅N₂⁺·I⁻, (I), has two polymorphic modifications, (Ia) and (Ib), and a hemihydrate structure, C₁₆H₁₅N₂⁺·I⁻·0.5H₂O, (II). Until now, only one crystal modi­fication has been identified for the (E)-4-(9-ethyl-9H-carbazol-3-yl­vinyl)-N-methyl­pyridinium (ECMPE⁺) iodide salt, C₂₂H₂₁N₂⁺·I⁻, (III). Crystals of (Ia) and (Ib) comprise stacks of antiparallel cations with iodide anions located in the channels between the stacks. Due to the presence of the water mol­ecules, the packing in (II) is quite different to that found in (Ia) and (Ib), and positional disorder involving a statistical superposition of two rotamers of IMPE⁺, with different orientations of the indole fragment, was found. Crystals of (III) contain two independent ECMPE⁺ rotamers with different orientations of their carbazole substituents. The cations are packed in stacks, with the iodide anions located in the channels between the stacks. In (III), the iodide was found to be disordered over two sites, with occupancies of 0.83 and 0.17.     

Synthesis and study of hydrogen hexamolybdonickelate and hydrogen hexamolybdozincate with the cobaltammine cation

[Co(NH₃)₆] · H₂[NiMo₆O₁₈(OH)₆] · 6H₂O (I) and [Co(NH₃)₆] · H₂[ZnMo₆O₁₈(OH)₆] · 6H₂O (II) have been synthesized and studied by mass spectroscopy, thermogravimetry, and X-ray powder diffraction. The crystals of compounds I and II are monoclinic, Z = 1; for compound I: a = 16.10 Å, b = 5.58 Å, c = 12.22 Å, β = 117.86°, V = 1045.14 ų, and ρ_calcd = 2.26 g/cm³; for compound II: a = 16.12 Å, b = 5.52 Å, c = 12.12 Å, β = 117.90°, V = 1043.21 ų, and ρ_calcd = 2.21 g/cm³.     

Tris(5-bromo-2-methoxyphenyl)bismuth bisbenzenesulfonate solvate with toluene: Synthesis and structure

Tris(5-bromo-2-methoxyphenyl)bismuth bisbenzenesulfonate, which crystallizes from toluene in the solvate form (5-Br-2-MeOC₆H₃)₃Bi(OSO₂Ph)₂ ? TolH (I), has been synthesized by the reaction between tris(5-bromo-2-methoxyphenyl)bismuth and benzenesulfonic acid in the presence of hydrogen peroxide (1: 2: 1 mol/mol/mol) in ether. A crystal contains two types of crystallographically independent molecules (a and b), in which bismuth atoms have a trigonal bipyramidal coordination to benzenesulfonate substituents in axial positions. The axial OBiO angle is 175.4(3)° (Ia) and 175.5(3)° (Ib), and the equatorial CBiC angles are 111.2(3)°, 122.0(4)°, 126.7(4)° (Ia) and 111.3(4)°, 123.3(3)°, 125.2(4)° (Ib). The Bi–C distances are 2.189(9), 2.198(9), 2.200(10) Å (Ia) and 2.198(9), 2.202(9), 2.209(9) Å (Ib). The Bi–O bond lengths are 2.274(8), 2.306(8) Å (Ia) and 2.248(8), 2.303(8) Å (Ib). Intramolecular contacts between the bismuth atom and the oxygen atoms of methoxy and sulfonate groups take place in molecules.     

Concomitant but disappearing: two polymorphs of 1,4‐bis(tribromomethyl)benzene

The title compound, C₈H₄Br₆, (I), initially crystallized from deuterochloroform as the comcomitant polymorphs (Ia) (prisms, space group P2₁/n, Z = 2) and (Ib) (hexagonal plates, space group C2/c, Z = 4). The molecules in both forms display crystallographic inversion symmetry. All further attempts to crystallize the compound led exclusively to (Ib), so that (Ia) may be regarded as a `disappearing polymorph'. Surprisingly, however, the density of (Ia) is greater than that of (Ib). The only significant difference between the molecular structures is the orientation of the CBr<sub>3</sub> groups. The molecular packing of both structures is largely determined by Br...Br interactions, although (Ia) also displays a C—H...Br hydrogen bond and both polymorphs display one Br...π contact. For (Ia), six of the eight contacts combine to form a tube‐like substructure parallel to the a axis. For (Ib), the two shortest Br...Br contacts link `half' molecules consisting of C—CBr₃ groups to form double layers parallel to (001) in the regions z≃, .     

Synthesis and structure of lithium and rubidium compounds with 2-(diphenylacetyl)-1,3-indanedione

Complexes RbL (I) and [Li₂(C₂H₅OH)L₂] (II) (L = C₂₃H₁₅O₃) have been synthesized and their crystal structures have been studied. Both compounds have monoclinic crystals with space group P2₁/c and Z = 4; I: a = 11.632(2) Å, b = 15.154(3) Å, c = 11.457(2) Å, β = 104.34(3)°; II: a = 12.982(3)Å, b = 12.083(2) Å, c = 25.317(5) Å β = 100.11(3)°. In the structure of I, dimeric groups [Rb₂O₆] with a shared edge are linked by the ligands to give infinite layers perpendicular to the x axis and cavities that form oblong channels. In the structure of II, Li₂O₇ dimers are formed by vertex sharing. The coordination of one of the lithium atoms (Li(1)) is completed to tetrahedral by the oxygen atom of the ethanol molecule. The structure of II, like that of I, is layered.     

A new polymorph of 1,4‐dibromo‐2,5‐dimethylbenzene: H...Br and Br...πversus Br...Br interactions

A new polymorph, (Ib), of the title compound, C₈H₈Br₂, crystallizes in the space group P2₁/n, the same as the known polymorph (Ia) but with Z = 2 (imposed inversion symmetry) rather than Z = 4. The molecular structures are closely similar because the molecule has no degrees of torsional freedom except for methyl groups, but the packing arrangements are completely different. Polymorph (Ia) is characterized by linked trapezia of Br...Br interactions, whereas polymorph (Ib) features H...Br and Br...π interactions.     

Syntheses, structures, and vibrational spectroscopy of the two-dimensional iodates Ln(IO3)3 and Ln(IO3)3(H2O) (LnYb, Lu)

The reaction of Lu³⁺ or Yb³⁺ and H₅IO₆ in aqueous media at 180 °C leads to the formation of Yb(IO₃)₃(H₂O) or Lu(IO₃)₃(H₂O), respectively, while the reaction of Yb metal with H₅IO₆ under similar reaction conditions gives rise to the anhydrous iodate, Yb(IO₃)₃. Under supercritical conditions Lu³⁺ reacts with HIO₃ and KIO₄ to yield the isostructural Lu(IO₃)₃. The structures have been determined by single-crystal X-ray diffraction. Crystallographic data are (MoKα, λ=0.71073 Å): Yb(IO₃)₃, monoclinic, space group P2₁/n, a=8.6664(9) Å, b=5.9904(6) Å, c=14.8826(15) Å, β=96.931(2)°, V=766.99(13), Z=4, R(F)=4.23% for 114 parameters with 1880 reflections with I>2σ(I); Lu(IO₃)₃, monoclinic, space group P2₁/n, a=8.6410(9), b=5.9961(6), c=14.8782(16) Å, β=97.028(2)°, V=765.08(14), Z=4, R(F)=2.65% for 119 parameters with 1756 reflections with I>2σ(I); Yb(IO₃)₃(H₂O), monoclinic, space group C2/c, a=27.2476(15), b=5.6296(3), c=12.0157(7) Å, β=98.636(1)°, V=1822.2(2), Z=8, R(F)=1.51% for 128 parameters with 2250 reflections with I>2σ(I); Lu(IO₃)₃(H₂O), monoclinic, space group C2/c, a=27.258(4), b=5.6251(7), c=12.0006(16) Å, β=98.704(2)°, V=1818.8(4), Z=8, R(F)=1.98% for 128 parameters with 2242 reflections with I>2σ(I). The f elements in all of the compounds are found in seven-coordinate environments and bridged with monodentate, bidentate, or tridentate iodate anions. Both Lu(IO₃)₃(H₂O) and Yb(IO₃)₃(H₂O) display distinctively different vibrational profiles from their respective anhydrous analogs. Hence, the Raman profile can be used as a complementary diagnostic tool to discern the different structural motifs of the compounds.     

Isomorphous crystal structures of 4,7,13,16,21,24-hexaoxo-1,10-diaziniabicyclo[8.8.8]·hexacosane bis(tribromide) and bis(bromoiodide)

Two compounds, 7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane bis(tribromide) and bis(bromodiiodide) — [H₂(Crypt-222)]²⁺·2Br ₃ ^? (I) and [H₂(Crypt-222)]²⁺·1.45(BrI₂)^?·0.4(Br₂I)^?·0.15 I ₃ ^? (II) — are prepared and characterized by single crystal XRD; the refinement of the second compound was more accurate. Isomorphous monoclinic structures (I, space group C2/c, Z = 4, a = 12.090, b = 15.833 Å, c = 15.732 Å, β = 95.83°; II, a = 12.548 Å, b = 16.417 Å, c = 15.748 Å, β = 94.53°) are solved by a direct method and refined in the anisotropic full-matrix approximation to R = 0.057 (I) and 0.044 (II) using all 2635 (I) and 2852 (II) measured independent reflections (automated CAD-4 diffractometer, λMoK _α). In the structures of I and II one of the trihalide anions sits at the inversion center i(000), and the second trihalide anion and the dication [H₂(Crypt-222)]²⁺ are situated at crystallographic axis 2. In the structure of II iodine is located in the center of trihalide anions, while the terminal atoms are disordered and are represented by a statistical combination of iodine and bromine atoms.     

Synthesis and study of tetraamminecobalt hydrogen hexamolybdometalates(III)

Tetraamminecobalt hydrogen hexamolybdoferrate [Co(NH₃)₄] · H[FeMo₆O₁₈(OH)₆] · 6H₂O (I) and tetraamminecobalt hydrogen hexamolybdogallate(III) [Co(NH₃)₄] · H[GaMo₆O₁₈(OH)₆] · 6H₂O (II) were synthesized and studied by mass spectrometry, thermogravimetry, IR spectroscopy, and X-ray diffraction. Crystals of I and II are monoclinic; a = 16.21 Å, b = 5.43 Å, c = 12.32 Å, β = 119.63°, V = 1092.11 ų, ρ_calcd = 2.21 g/cm³, and Z = 1 for I; a = 16.24 Å, b = 5.59 Å, c = 12.29 Å, β = 119.79°, V = 1064.05 ų, ρ_calcd = 2.15 g/cm³, and Z = 1 for II. Compounds I and II were used as catalysts for soft oxidation of natural gas.     

Synthesis of tricyclic isoindoles and thiazolo[3,2-c][1,3]benzoxazines

The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac₂O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from l-cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The thermolysis of (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazine-3-carboxylic acid in Ac₂O gave 5-acetyl-2-phenyl-2,3-dihydrothiazole. The structures of methyl (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylate 1a and methyl (2R,4R)-N-chlorocarbonyl-2-(2-hydroxyphenyl)thiazolidine-4-carboxylate 9 were determined by X-ray crystallography.     

Synthesis, structure of [H3dien]·(MF6)·H2O (M=Cr, Fe) and Fe Mössbauer study of [H3dien]·(FeF6)·H2O

Single crystals of [H₃dien]·(FeF₆)·H₂O (I) and [H₃dien]·(CrF₆)·H₂O (II) are obtained by solvothermal synthesis under microwave heating. I is orthorhombic (Pna2₁) with a=11.530(2) Å, b=6.6446(8) Å, c=13.787(3) Å, V=1056.3(2) Å³ and Z=4. II is monoclinic (P2₁/c) with a=13.706(1) Å, b=6.7606(6) Å, c=11.3181(9) Å, β=99.38(1)°, V=1034.7(1) Å³ and Z=4. The structure determinations, performed from single crystal X-ray diffraction data, lead to the R₁/wR₂ reliability factors 0.028/0.066 for I and 0.035/0.102 for II. The structures of I and II are built up from isolated FeF₆ or CrF₆ octahedra, water molecules and triprotonated amines. In both structures, each octahedron is connected by hydrogen bonds to six organic cations and two water molecules. The iron-based compound is also characterized by ⁵⁷Fe Mössbauer spectrometry: the hyperfine structure confirms the presence of Fe³⁺ in octahedral coordination and reveals the existence of paramagnetic spin fluctuations.     

Pseudopolymorphs of chelidamic acid and its dimethyl ester

Different tautomeric and zwitterionic forms of chelidamic acid (4‐hydroxypyridine‐2,6‐dicarboxylic acid) are present in the crystal structures of chelidamic acid methanol monosolvate, C₇H₅NO₅·CH₄O, (Ia), dimethylammonium chelidamate (dimethylammonium 6‐carboxy‐4‐hydroxypyridine‐2‐carboxylate), C₂H₈N⁺·C₇H₄NO₅⁻, (Ib), and chelidamic acid dimethyl sulfoxide monosolvate, C₇H₅NO₅·C₂H₆OS, (Ic). While the zwitterionic pyridinium carboxylate in (Ia) can be explained from the pK_a values, a (partially) deprotonated hydroxy group in the presence of a neutral carboxy group, as observed in (Ib) and (Ic), is unexpected. In (Ib), there are two formula units in the asymmetric unit with the chelidamic acid entities connected by a symmetric O—H...O hydrogen bond. Also, crystals of chelidamic acid dimethyl ester (dimethyl 4‐hydroxypyridine‐2,6‐dicarboxylate) were obtained as a monohydrate, C₉H₉NO₅·H₂O, (IIa), and as a solvent‐free modification, in which both ester molecules adopt the hydroxypyridine form. In (IIa), the solvent water molecule stabilizes the synperiplanar conformation of both carbonyl O atoms with respect to the pyridine N atom by two O—H...O hydrogen bonds, whereas an antiperiplanar arrangement is observed in the water‐free structure. A database study and ab initio energy calculations help to compare the stabilities of the various ester conformations.     

Preparation and study of hydrogen hexamolybdometallates(III) with the hexamminecadmium cation

Hydrogen hexamolybdogallate and hexamolybdoaluminate with the hexamminecadmium cation [Cd(NH₃)₆] · H[GaMo₆O₁₈(OH)₆] · 6H₂O (I) and [Cd(NH₃)₆] · H[AlMo₆O₁₈(OH)₆] · 6H₂O (II) were synthesized and studied by mass spectrometry, thermogravimetric analysis, powder X-ray diffraction, and IR spectroscopy. The crystals are monoclinic; I: a = 10.82 Å, b = 3.69 Å, c = 11.99 Å, β = 91.06°, V= 469.72 ų, ρ_calcd = 2.34 g/cm³, Z = 2; II: a = 10.81 Å, b = 3.67 Å, c =11.98 Å, β = 91.08°, V = 469.78 ų, ρ_calcd = 2.38 g/cm³, Z = 2.     

Crystal and molecular structure of complex compound (C5H5)2Re(H)Cu(μ-I)2CuRe(H)(C5H5)2: A first direct proof of the formation of the Cu(I)Cu(I) bond

The structure of the bimetallic dimer complex [(η⁵-C₅H₅)₂Re(H)CuI]₂ has been investigated. The crystals are monoclinic: a = 16.070(4) Å, b = 7.788(2)Å, c = 17.439(5) Å; b = 96.62(2)°; the space group I2/a; z = 4. The bond between rhenium and copper atoms (2.60 Å) is of the donor-acceptor type; dimerization occurs by the way of formation of the double bridge CuI₂Cu and the direct inter-metal bond CuCu(2.55 Å). The hydride hydrogen atom is the terminal one. The cyclopentadienyl rings form a bent sandwich with the angle between the ring centres and rhenium atom being equal to 158°. It is suggested that the CuCu inter-metal bonding takes place on account of the transition of the non-bonding d-electrons of copper atoms to a high-spin state.     

Two polymorphs and the diethylammonium salt of the barbiturate eldoral

Polymorph (Ia) of eldoral [5‐ethyl‐5‐(piperidin‐1‐yl)barbituric acid or 5‐ethyl‐5‐(piperidin‐1‐yl)‐1,3‐diazinane‐2,4,6‐trione], C₁₁H₁₇N₃O₃, displays a hydrogen‐bonded layer structure parallel to (100). The piperidine N atom and the barbiturate carbonyl group in the 2‐position are utilized in N—H...N and N—H...O=C hydrogen bonds, respectively. The structure of polymorph (Ib) contains pseudosymmetry elements. The two independent molecules of (Ib) are connected via N—H...O=C(4/6‐position) and N—H...N(piperidine) hydrogen bonds to give a chain structure in the [100] direction. The hydrogen‐bonded layers, parallel to (010), formed in the salt diethylammonium 5‐ethyl‐5‐(piperidin‐1‐yl)barbiturate [or diethylammonium 5‐ethyl‐2,4,6‐trioxo‐5‐(piperidin‐1‐yl)‐1,3‐diazinan‐1‐ide], C₄H₁₂N⁺·C₁₁H₁₆N₃O₃⁻, (II), closely resemble the corresponding hydrogen‐bonded structure in polymorph (Ia). Like many other 5,5‐disubstituted derivatives of barbituric acid, polymorphs (Ia) and (Ib) contain the R₂²(8) N—H...O=C hydrogen‐bond motif. However, the overall hydrogen‐bonded chain and layer structures of (Ia) and (Ib) are unique because of the involvement of the hydrogen‐bond acceptor function in the piperidine group.