Synthesis,structure and characterization of five new organically templated metal sulfates with 2‐aminopyridinium

The chemistry of organically templated metal sulfates has attracted interest from the materials science community and the development of synthetic strategies for the preparation of organic–inorganic hybrid materials with novel structures and special properties is of current interest. Sulfur–oxygen–metal linkages provide the possibility of using sulfate tetrahedra as building units to form new solid‐state materials. A series of novel organically templated metal sulfates of 2‐aminopyridinium (2ap) with aluminium(III), cobalt(II), magnesium(II), nickel(II) and zinc(II) were obtained from the respective aqueous solutions and studied by single‐crystal X‐ray diffraction. The compounds crystallize in centrosymmetric triclinic unit cells in three structure types: type 1 for 2‐aminopyridinium hexaaquaaluminium(III) bis(sulfate) tetrahydrate, (C₅H₇N₂)[Al(H₂O)₆](SO₄)₂·4H₂O, (I); type 2 for bis(2‐aminopyridinium) tris[hexaaquacobalt(II)] tetrakis(sulfate) dihydrate, (C₅H₇N₂)₂[Co(H₂O)₆]₃(SO₄)₄·2H₂O, (II), and bis(2‐aminopyridinium) tris[hexaaquamagnesium(II)] tetrakis(sulfate) dihydrate, (C₅H₇N₂)₂[Mg(H₂O)₆]₃(SO₄)₄·2H₂O, (III); and type 3 for bis(2‐aminopyridinium) hexaaquanickel(II) bis(sulfate), (C₅H₇N₂)₂[Ni(H₂O)₆](SO₄)₂, (IV), and bis(2‐aminopyridinium) hexaaquazinc(II) bis(sulfate), (C₅H₇N₂)₂[Zn(H₂O)₆](SO₄)₂, (V). The templating role of the 2ap cation in all of the reported crystalline substances is governed by the formation of characteristic charge‐assisted hydrogen‐bonded pairs with sulfate anions and the presence of π–π interactions between the cations. Additionally, both coordinated and uncoordinated water molecules are involved in hydrogen‐bond formation. As a consequence, extensive three‐dimensional hydrogen‐bonding patterns are formed in the reported crystal structures.     

Bis(1‐phenyl­ethyl­ammonium) hexa­chloridostannate(IV) and bis­(2‐phenyl­ethyl­ammonium) hexa­chloridostannate(IV)

The crystal structures of the two isomers bis­(1‐phenyl­ethyl­ammonium) hexa­chloridostannate(IV) and bis­(2‐phenyl­ethyl­ammonium) hexa­chloridostannate(IV), both (C₈H₁₂N)₂[SnCl₆], exhibit alternating organic and inorganic layers, which inter­act via N—H⋯Cl hydrogen bonding. The inorganic layer contains an extended two‐dimensional hydrogen‐bonded sheet. The Sn atom in the 1‐phenylethyl­ammonium salt lies on an inversion centre.     

Hydrogen‐bonded network structures in dipyridinium,bis(2‐methylpyridinium), bis(3‐methylpyridinium) and bis(4‐methylpyridinium) dioxidobis(oxydiacetato)uranate(VI)

Four complexes containing the [UO₂(oda)₂]²⁻ anion (oda is oxydiacetate) are reported, namely dipyridinium dioxidobis(oxydiacetato)uranate(VI), (C₅H₆N)₂[U(C₄H₄O₅)₂O₂], (I), bis(2‐methylpyridinium) dioxidobis(oxydiacetato)uranate(VI), (C₈H₈N)₂[U(C₄H₄O₅)₂O₂], (II), bis(3‐methylpyridinium) dioxidobis(oxydiacetato)uranate(VI), (C₈H₈N)₂[U(C₄H₄O₅)₂O₂], (III), and bis(4‐methylpyridinium) dioxidobis(oxydiacetato)uranate(VI), (C₈H₈N)₂[U(C₄H₄O₅)₂O₂], (IV). The anions are achiral and are located on a mirror plane in (I) and on inversion centres in (II)–(IV). The four complexes are assembled into three‐dimensional structures via N—H...O and C—H...O interactions. Compounds (III) and (IV) are isomorphous; the [UO₂(oda)₂]²⁻ anions form a porous matrix which is nearly identical in the two structures, and the cations are located in channels formed in this matrix. Compounds (I) and (II) are very different from (III) and (IV): (I) forms a layered structure, while (II) forms ribbons.     

Conformational isomers of the [(5‐methyl‐2‐pyridinio)aminomethylene]diphosphonate dianion and [(5‐methyl‐2‐pyridyl)aminomethylene]diphosphonate trianion in salts with 4‐aminopyridine and ammonia

The crystal structures of two salts, products of the reactions between [(5‐methyl‐2‐pyridyl)aminomethylene]bis(phosphonic acid) and 4‐aminopyridine or ammonia, namely bis(4‐aminopyridinium) hydrogen [(5‐methyl‐2‐pyridinio)aminomethylene]diphosphonate 2.4‐hydrate, 2C₅H₇N₂⁺·C₇H₁₀N₂O₆P₂²⁻·2.4H₂O, (I), and triammonium hydrogen [(5‐methyl‐2‐pyridyl)aminomethylene]diphosphonate monohydrate, 3NH₄⁺·C₇H₉N₂O₆P₂³⁻·H₂O, (II), have been determined. In (I), the Z configuration of the ring N—C and amino N—H bonds of the bisphosphonate dianion with respect to the C_ring—N_amino bond is consistent with that of the parent zwitterion. Removing the H atom from the pyridyl N atom results in the opposite E configuration of the bisphosphonate trianion in (II). Compound (I) exhibits a three‐dimensional hydrogen‐bonded network, in which 4‐aminopyridinium cations and water molecules are joined to ribbons composed of anionic dimers linked by O—H...O and N—H...O hydrogen bonds. The supramolecular motif resulting from a combination of these three interactions is a common phenomenon in crystals of all of the Z‐isomeric zwitterions of 4‐ and 5‐substituted (2‐pyridylaminomethylene)bis(phosphonic acid)s studied to date. In (II), ammonium cations and water molecules are linked to chains of trianions, resulting in the formation of double layers.     

Dimeric copper(II) 3,3‐dimethyl­butyrate adducts with ethanol, 2‐methylpyridine, 3‐methylpyridine, 4‐methylpyridine and 3,3‐dimethylbutyric acid

In the crystals of the five title compounds, tetrakis‐(μ‐3,3‐dimethylbutyrato‐O:O′)bis(ethanol‐O)dicopper(II)–ethanol (1/2), [Cu₂(C₆H₁₁O₂)₄(C₂H₆O)₂]·2C₂H₆O, (I), tetrakis(μ‐3,3‐dimethylbutyrato‐O:O′)bis(2‐methylpyridine‐N)di­copper(II), [Cu₂(C₆H₁₁O₂)₄(C₆H₇N)₂], (II), tetrakis‐(μ‐3,3‐dimethylbutyrato‐O:O′)bis(3‐methylpyridine‐N)di‐copper(II), [Cu₂(C₆H₁₁O₂)₄(C₆H₇N)₂], (III), tetrakis‐(μ‐3,3‐dimethylbutyrato‐O:O′)bis(4‐methylpyridine‐N)di‐copper(II), [Cu₂(C₆H₁₁O₂)₄(C₆H₇N)₂], (IV), and tetrakis‐(μ‐3,3‐dimethylbutyrato‐O:O′)bis(3,3‐dimethylbutyric acid‐O)dicopper(II), [Cu₂(C₆H₁₁O₂)₄(C₆H₁₂O₂)₂], (V), the di­nuclear Cu^II complexes all have centrosymmetric cage structures and (IV) has two independent molecules. The Cu?Cu separations are: (I) 2.602 (3) Å, (II) 2.666 (3) Å, (III) 2.640 (2) Å, (IV) 2.638 (4) Å and (V) 2.599 (1) Å.     

Bis­[4‐(di­methyl­amino)­pyridinium] hexa­chloro­stannate(IV)

In the title compound, 4‐(di­methyl­amino)­pyridine is proton­ated on the pyridine N atom. The N(CH₃)₂ moiety is twisted 4.4 (2)° from the pyridine‐ring plane. The octahedral [SnCl₆]^2? anion is hydrogen bonded via trans‐Cl atoms to pyridinium N atoms from two cations forming (C₇H₁₁N₂)₂[SnCl₆] structural units.     

A 4‐ethyl­pyridine complex of tetra­chloro­molybdenum(III) and its oxidation product

The Mo atoms in the title compounds, i.e. triethyl­ammonium cis‐tetra­chloro­bis(4‐ethyl­pyridine‐N)­molybdate(III), cis‐(C₆H₁₆N)­[MoCl₄(C₇H₉N)₂], and trans‐tetra­chloro­bis(4‐ethyl­pyridine‐N)molybdenum(IV), trans‐[MoCl₄(C₇H₉N)₂], are six‐coordinate with octahedral geometry. The Mo atom in the latter complex lies on a site with crystallographic 2/m symmetry.     

Nine compounds containing high‐nuclearity [CunX2n+2]2− (n = 4, 5 or 7; X = Cl or Br) quasi‐planar oligomers

The structures of seven A₂Cu₄X₁₀ compounds containing quasi‐planar oligomers are reported: bis(1,2,4‐trimethylpyridinium) hexa‐μ‐chlorido‐tetrachloridotetracuprate(II), (C₈H₁₂N)₂[Cu₄Cl₁₀], (I), and the hexa‐μ‐bromido‐tetrabromidotetracuprate(II) salts of 1,2,4‐trimethylpyridinium, (C₈H₁₂N)₂[Cu₄Br₁₀], (II), 3,4‐dimethylpyridinium, (C₇H₁₀N)₂[Cu₄Br₁₀], (III), 2,3‐dimethylpyridinium, (C₇H₁₀N)₂[Cu₄Br₁₀], (IV), 1‐methylpyridinium, (C₆H₈N)₂[Cu₄Br₁₀], (V), trimethylphenylammonium, (C₉H₁₄N)₂[Cu₄Br₁₀], (VI), and 2,4‐dimethylpyridinium, (C₇H₁₀N)₂[Cu₄Br₁₀], (VII). The first four are isomorphous and contain stacks of tetracopper oligomers aggregated through semicoordinate Cu...X bond formation in a 4(,) stacking pattern. The 1‐methylpyridinium salt also contains oligomers stacked in a 4(,) pattern, but is isomorphous with the known chloride analog instead. The trimethylphenylammonium salt contains stacks of oligomers arranged in a 4(,) stacking pattern similar to the tetramethylphosphonium analog. These six structures feature inversion‐related organic cation pairs and hybrid oligomer/organic cation layers derived from the parent CuX₂ structure. The 2,4‐dimethylpyridinium salt is isomorphous with the known (2‐amino‐4‐methylpyridinium)₂Cu₄Cl₁₀ structure, in which isolated stacks of organic cations and of oligomers in a 4(,) pattern are found. In bis(3‐chloro‐1‐methylpyridinium) octa‐μ‐bromido‐tetrabromidopentacuprate(II), (C₆H₇ClN)[Cu₅Br₁₂], (VIII), containing the first reported fully halogenated quasi‐planar pentacopper oligomer, the oligomers stack in a 5(,) stacking pattern as the highest nuclearity [Cu_nX_2n+2]²⁻ oligomer compound known with isolated stacking. Bis(2‐chloro‐1‐methylpyridinium) dodeca‐μ‐bromido‐tetrabromidoheptacuprate(II), (C₆H₇ClN)₂[Cu₇Br₁₆], (IX), contains the second heptacopper oligomer reported and consists of layers of interleaved oligomer stacks with a 7[(,)][(−,−)] pattern isomorphous with that of the known 1,2‐dimethylpyridinium analog. All the oligomers reported here are inversion symmetric.     

Salts of two pentahalo(N‐donor)­bismuthate(III) anions: [BiX5L]2− (X = Cl,Br; L = pyridine, 4‐picoline)

Two pentahalo(N‐donor)­bismuthate(III) salts, bis­[hydrogen bis(4‐picoline)(1+)] penta­bromo(4‐picoline‐N)bismuthate(III), (C₁₂H₁₅N₂)₂[BiBr₅(C₆H₇N)], (I), and bis­(pyridinium) penta­chloro­(pyridine‐N)­bismuthate(III), (C₅H₆N)₂[BiCl₅(C₅H₅N)], (II), are described which show modest deviations from octahedral geometry at bismuth. In (I), the cations comprise two 4‐picoline mol­ecules sharing a proton and in (II), pyridinium cations are present. The anion in (I) has twofold and that in (II) has mirror crystallographic symmetry. Both structures show a layered packing formed by the anions with the cations between the layers. Ring–ring interactions seem important in (I), whilst in (II), N/­C—H?Cl—Bi hydrogen bonding is abundant.     

4‐Aminopyridinium 4‐aminobenzoate dihydrate and 4‐aminopyridinium nicotinate

In the title compounds, 4‐aminopyridinium 4‐aminobenzoate dihydrate, C₇H₆NO₂⁻·C₅H₇N₂⁺·2H₂O, (I), and 4‐aminopyridinium nicotinate, C₅H₇N₂⁺·C₆H₄NO₂⁻, (II), the aromatic N atoms of the 4‐aminopyridinium cations are protonated. In (I), the asymmetric unit is composed of two 4‐aminopyridinium cations, two 4‐aminobenzoate anions and four water molecules, and the compound crystallizes in a noncentrosymmetric space group. The two sets of independent molecules of (I) are related by a centre of symmetry which is not part of the space group. In (I), the protonated pyridinium ring H atoms are involved in bifurcated hydrogen bonding with carboxylate O atoms to form an R₁²(4) ring motif. The water molecules link the ions to form a two‐dimensional network along the (10) plane. In (II), an intramolecular bifurcated hydrogen bond generates an R₁²(4) ring motif and inter‐ion hydrogen bonding generates an R₄²(16) ring motif. The packing of adduct (II) is consolidated via N—H...O and N—H...N hydrogen bonds to form a two‐dimensional network along the (10) plane.     

Cationic,neutral and anionic metal(II) complexes derived from 4‐oxo‐4H‐pyran‐2,6‐dicarboxylic acid (chelidonic acid)

The structures of five metal complexes containing the 4‐oxo‐4H‐pyran‐2,6‐dicarboxylate dianion illustrate the remarkable coordinating versatility of this ligand and the great structural diversity of its complexes. In tetraaquaberyllium 4‐oxo‐4H‐pyran‐2,6‐dicarboxylate, [Be(H₂O)₄](C₇H₂O₆), (I), the ions are linked by eight independent O—H...O hydrogen bonds to form a three‐dimensional hydrogen‐bonded framework structure. Each of the ions in hydrazinium(2+) diaqua(4‐oxo‐4H‐pyran‐2,6‐dicarboxylato)calcate, (N₂H₆)[Ca(C₇H₂O₆)₂(H₂O)₂], (II), lies on a twofold rotation axis in the space group P2/c; the anions form hydrogen‐bonded sheets which are linked into a three‐dimensional framework by the cations. In bis(μ‐4‐oxo‐4H‐pyran‐2,6‐dicarboxylato)bis[tetraaquamanganese(II)] tetrahydrate, [Mn₂(C₇H₂O₆)₂(H₂O)₈]·4H₂O, (III), the metal ions and the organic ligands form a cyclic centrosymmetric Mn₂(C₇H₂O₆)₂ unit, and these units are linked into a complex three‐dimensional framework structure containing 12 independent O—H...O hydrogen bonds. There are two independent Cu^II ions in tetraaqua(4‐oxo‐4H‐pyran‐2,6‐dicarboxylato)copper(II), [Cu(C₇H₂O₆)(H₂O)₄], (IV), and both lie on centres of inversion in the space group P; the metal ions and the organic ligands form a one‐dimensional coordination polymer, and the polymer chains are linked into a three‐dimensional framework containing eight independent O—H...O hydrogen bonds. Diaqua(4‐oxo‐4H‐pyran‐2,6‐dicarboxylato)cadmium monohydrate, [Cd(C₇H₂O₆)(H₂O)₂]·H₂O, (V), forms a three‐dimensional coordination polymer in which the organic ligand is coordinated to four different Cd sites, and this polymer is interwoven with a complex three‐dimensional framework built from O—H...O hydrogen bonds.     

Isostructural crystal packing and hydrogen bonding in alkyl­ammonium tin(IV) chloride compounds

The three isostructural compounds butyl­ammonium hexa­chlorido­tin(IV), pentyl­ammonium hexa­chlorido­tin(IV) and hexyl­ammonium hexa­chlorido­tin(IV), (C_nH_2n+1NH₃)₂[SnCl₆], with n = 4, 5 and 6, respectively, crystallize as inorganic–organic hybrids. As such, the structures consist of layers of [SnCl₆]²⁻ octa­hedra, separated by hydro­carbon layers of inter­digitated butyl­ammonium, pentyl­ammonium or hexyl­ammonium cations. Corrugated layers of cations alternate with tin(IV) chloride layers. The asymmetric unit in each compound consists of an anionic component comprising one Sn and two Cl atoms on a mirror plane, and two Cl atoms in general positions; the two cations lie on another mirror plane. Application of the mirror symmetry generates octa­hedral coordination around the Sn atom. All compounds exhibit bifurcated and simple hydrogen‐bonding inter­actions between the ammonium groups and the Cl atoms, with little variation in the hydrogen‐bonding geometries.     

Oxidation of a dinuclear manganese(II) complex to an oxide‐bridged dimanganese(IV) complex

Bis{μ‐2‐[bis(pyridin‐2‐ylmethyl)amino]acetato}bis[diaquamanganese(II)] bis(trifluoromethanesulfonate) monohydrate, [Mn₂(C₁₄H₁₄N₃O₂)₂(H₂O)₄](CF₃O₃S)₂·H₂O, (I), and bis{μ‐3‐[bis(pyridin‐2‐ylmethyl)amino]propionato}bis[aquamanganese(II)] bis(trifluoromethanesulfonate) dihydrate, [Mn₂(C₁₅H₁₆N₃O₂)₂(H₂O)₂](CF₃O₃S)₂·2H₂O, (II), form binuclear seven‐coordinate complexes. Oxidation of (II) with ammonium hexanitratocerate(IV), (NH₄)₂[Ce(NO₃)₆], gave the oxide‐bridged dimanganese(IV) complex di‐μ‐oxido‐bis(bis{3‐[bis(pyridin‐2‐ylmethyl)amino]propionato}manganese(IV)) bis[triaquatetranitratocerate(IV)], [Mn₂O₂(C₁₅H₁₆N₃O₂)₂][Ce(NO₃)₄(H₂O)₃]₂, (III). The manganese complexes in (II) and (III) sit on a site of symmetry.     

Hydrogen‐bonded networks in 5‐chloropyridin‐2‐amine–fumaric acid (2/1) and 2‐aminopyridinium dl‐malate

Crystals of 5‐chloropyridin‐2‐amine–(2E)‐but‐2‐enedioate (2/1), 2C₅H₅ClN₂·C₄H₄O₄, (I), and 2‐aminopyridinium dl ‐3‐carboxy‐2‐hydroxypropanoate, C₅H₇N₂⁺·C₄H₅O₅⁻, (II), are built from the neutral 5‐chloropyridin‐2‐amine molecule and fumaric acid in the case of (I) and from ring‐N‐protonated 2‐aminopyridinium cations and malate anions in (II). The fumaric acid molecule lies on an inversion centre. In (I), the neutral 5‐chloropyridin‐2‐amine and fumaric acid molecules interact via hydrogen bonds, forming two‐dimensional layers parallel to the (100) plane, whereas in (II), oppositely charged units interact via ionic and hydrogen bonds, forming a three‐dimensional network.     

Bis­(benzyl­ammonium) hexa­chloro­tin(IV)

The crystal structure of bis­(benzyl­ammonium) hexa­chloro­tin(IV), (C₇H₇NH₃)₂[SnCl₆], exhibits ionic layers separated by hydro­carbon layers. The hydro­carbon layer contains two crystallographically inequivalent benzyl groups and aromatic π–π stacking interactions are observed in this layer. In the inorganic layer, the ammonium groups interact with isolated tilted [SnCl₆]²⁻ octahedra through normal, bifurcated and trifurcated N—H⋯Cl hydrogen bonds.     

Dimeric copper(II) trimethylsilyl­acetate adducts with pyridine, 2‐­methylpyridine, 3‐methylpyridine and quinoline,and a polymeric copper(II) trimethylsilylacetate

In the crystals of bis(pyridine‐N)tetrakis(μ‐trimethylsilylacetato‐O:O′)dicopper(II), [Cu₂(C₅H₁₁O₂Si)₄(C₅H₅N)₂], (I), the dinuclear Cu^II complexes have cage structures with Cu?Cu distances of 2.632 (1) and 2.635 (1) Å. In the crystals of bis(2‐­methylpyridine‐N)tetrakis(μ‐trimethylsilylacetato‐O:O′)dicopper(II), [Cu₂(C₅H₁₁O₂Si)₄(C₆H₇N)₂], (II), bis­(3‐methylpyridine‐N)tetrakis(μ‐trimethylsilylacetato‐O:O′)dicopper(II), [Cu₂(C₅H₁₁O₂Si)₄(C₆H₇N)₂], (III), and bis(quinoline‐N)­tetrakis(μ‐­trimethylsilylacetato‐O:O′)dicopper(II), [Cu₂(C₅H₁₁O₂Si)₄(C₉H₇N)₂], (IV), the centrosymmetric dinuclear Cu^II complexes have a cage structure with Cu?Cu distances of 2.664 (1), 2.638 (3) and 2.665 (1) Å, respectively. In the crystals of catena‐poly­[tetrakis(μ‐trimethylsilylacetato‐O:O′)dicopper(II)], [Cu₂(C₅H₁₁O₂Si)₄]_n, (V), the dinuclear Cu^II units of a cage structure are linked by the cyclic Cu—O bonds at the apical positions to form a linear chain by use of a glide translation.     

Polymeric [dihydrobis(pyrazol‐1‐yl)borato]potassium(I) and three dihydrobis(pyrazol‐1‐yl)borate–magnesium(I) compounds obtained by disproportionation of the Grignard reagent

Reaction of the Grignard reagent with polydentate nitrogen‐donor ligands yields new species with rare magnesium coordination and possible catalytic activity. In the first of the title compounds, poly[[μ₄‐dihydrobis(pyrazol‐1‐yl)borato‐κ²N,N′]potassium(I)], [K(C₆H₈BN₄)]_n, (I), polymeric chains form a two‐dimensional network in the [100] plane. Each potassium ion is coordinated by four N atoms of pyrazolyl ligands, while weak (μ‐BH)...K⁺ interactions additionally stabilize the structure. The K and B atoms both lie on a mirror plane. In three new structures obtained by disproportionation of the Grignard reagent, each Mg atom is bound to a κ²N,N′‐type ligand, forming the basal plane, and tetrahydrofuran molecules occupy the axial positions. Di‐μ‐chlorido‐bis[dihydridobis(pyrazol‐1‐yl)borato]tris(tetrahydrofuran)dimagnesium(II), [Mg₂(C₆H₈BN₄)₂Cl₂(C₄H₈O)₃], (II), adopts a dimeric structure with μ‐Cl—Mg interactions. One of the Mg atoms has an octahedral coordination, while the other has a distorted square‐pyramidal environment. However, in the bis‐chelate compounds bis[dihydridobis(pyrazol‐1‐yl)borato‐κ²N,N′](tetrahydrofuran‐κO)magnesium(II), [Mg(C₆H₈BN₄)₂(C₄H₈O)], (III), and bis[dihydridobis(pyrazol‐1‐yl)borato‐κ²N,N′]bis(tetrahydrofuran‐κO)magnesium(II), [Mg(C₆H₈BN₄)₂(C₄H₈O)₂], (IV), the Mg atoms have square‐pyramidal and octahedral environments, respectively. The Mg atom in (IV) lies on an inversion centre.     

A new polymorph of bis(2‐aminopyridinium) fumarate–fumaric acid (1/1) from powder X‐ray diffraction

A new polymorph of bis(2‐aminopyridinium) fumarate–fumaric acid (1/1), 2C₅H₇N₂⁺·C₄H₂O₄²⁻·C₄H₄O₄, was obtained and its crystal structure determined by powder X‐ray diffraction. The new polymorph (form II) crystallizes in the triclinic system (space group P), while the previous reported polymorph [form I; Ballabh, Trivedi, Dastidar & Suresh (2002). CrystEngComm, 4 , 135–142; Büyükgüngör, Odabaşoğlu, Albayrak & Lönnecke (2004). Acta Cryst. C 60 , o470–o472] is monoclinic (space group P2₁/c). In both forms I and II, the asymmetric unit consists of one 2‐aminopyridinium cation, half a fumaric acid molecule and half a fumarate dianion. The fumarate dianion is involved in hydrogen bonding with two neighbouring 2‐aminopyridinium cations to form a hydrogen‐bonded trimer in both forms. In form II, the hydrogen‐bonded trimers are interlinked across centres of inversion via pairs of N—H...O hydrogen bonds, whereas such trimers are joined via single N—H...O hydrogen bonds in form I, leading to different packing modes for forms I and II. The results demonstrate the relevance and application of the powder diffraction method in the study of polymorphism of organic molecular materials.     

Tetraethylammonium Hexafluoro Uranate(IV), Hafnate(IV), and Cerate(IV) Salts: Preparation and Solid‐state Structure

The {N(C₂H₅)₄}₂[UF₆] · 2H₂O ( 1 ), {N(C₂H₅)₄}₂[HfF₆] · 2H₂O ( 2 ), and {N(C₂H₅)₄}₂[CeF₆] · 6H₂O ( 3 ) salts were prepared in high yield (ca. 80 %) from the reaction of MF₄ with tetraethylammonium fluoride in propylene carbonate and for the first time their solid‐state structures characterized by single‐crystal X‐ray diffraction. The compounds 1 , 2 and 3 crystallize in the space groups Pcca, P2₁/n₁ and Pca2₁, respectively. In 1 , 2 , and 3 the MF₆^2– anions are almost octahedral with average M–F distances of 2.16, 1.999, and 2.148 Å.     

Tetrabromo(2‐methylpyridine‐N)titanate(IV)

The reaction of 2‐methyl­pyridine with TiBr₄ affords tetra­bromo(2‐methyl­pyridine‐N)­titanate(IV), C₆H₇Br₄NTi. The environment around the Ti atom can be described as a slightly distorted trigonal bipyramid, with the nitro­gen base occupying an equatorial position. The crystal structure of the title compound is isomorphous with tetra­chloro(2‐methyl­pyridine‐N)­titanate(IV).