Search

The polymorphic phase transition of 1,2,4,5-tetrachlorobenzene (TCB) has been investigated using neutron powder diffraction and single-crystal X-ray diffraction. The diffraction experiments show a reversible phase change that occurs as a function of temperature with no apparent loss of sample quality on transition between the two phases. Neutron powder diffraction gives detailed information on the molecular structural changes and lattice parameters from 2 K to room temperature. The structure of the low-temperature form has been elucidated for the first time using single-crystal X-ray diffraction. Comparison of the α and β structures show that they are both based on the same sheet motif, with the differences between the two being very subtle, except in terms of crystal symmetry. Detailed analysis of the structures revealed the changes required for inter-conversion. A computational polymorph search showed that these two sheet structures are more thermodynamically stable than alternative herringbone-type structures.

The present work is aimed to investigate non-covalent bonding capabilities of uracil derivative bearing hydrophobic side chain in solid crystalline state. The synthesis and crystal structure of 5-(2-chloro-ethyl)-6-methyl-uracil 3 and 5-(2-chloro-ethyl)-6-methyl-2-thiouracil 4 are described, which revealed sulfur–π interaction including resonance-induced intermolecular H-bonding in 4 whereas compound 3 showed only strong H-bonding and formed a dimer. Thus the analysis of such moieties in solid state provides useful structural information on the binding characteristics of functional groups and has implications for the de novo design of drugs and enzyme's inhibitors.

Dianilines and diphenols form well-defined crystalline molecular complexes that arise from complementary O−H···N and N−H···O recognition. The crystal structures of four such 1:1 complexes 1, 2, 3 and 4 based on diphenylmethane frameworks are reported and discussed. Three supramolecular synthons are found, the N(H)O based square motif and infinite chain, already reported, and a new cyclohexane chair consisting of N(H)O, O−H···O and N−H···N hydrogen bridges. The replacement of a −CH2− group by an S-atom leads in two cases to little change in the crystal structure and in another to a complete change. It is possible that the dianiline component plays a more important role in molecular recognition in these complexes than does the diphenol component.

The compound trans-1,5-dichloro-9,10-diethynyl-9,10-dihydroanthracene-9,10-diol (DDDA) has an inversion center as the only molecular symmetry element and yet does not occupy an inversion center in the centrosymmetric space group that it adopts in the crystal structure. The reason for this very unusual occurrence is the crowded environment of the H-bond donors and acceptors that leads to less than optimal H-bonding. A centrosymmetric supramolecular synthon constituted with four Cl-atoms in a planar array occupies an i site in the crystal, and this appears to provide a satisfactory alternative packing. Based on the hypothesis that H-bonding is less than optimal in the crystal structure of DDDA, pseudopolymorphs were prepared with strongly H-bond-accepting solvents. The crystal structures of five of these solvates are described, wherein the DDDA molecule is able to occupy an i site and form strong and linear OH ⋅⋅⋅O H-bonds with the solvent molecules. Competition experiments show that a smaller solvent molecule with a greater H-bond-accepting ability is included more readily and that the H-bonds formed are correspondingly better.

Two related phosphonium aryloxides, [Ph3PCH3]+2[CH2(C6H2-3,5-tert-butyl-4-O)2]2-, 1a, and [Ph3PC2H5]+2[CH2(C6H2-3,5-tert-butyl-4-O)2]2-, 1b have been synthesized by protonation of nonstabilized phosphorus ylides with 4,4‘-methylenebis(2,6-di-tert-butylphenol) LH2. The crystal structures of 1a and 1b have been determined by single-crystal X-ray diffraction, and that of 1b has also been determined by low-temperature (20 K) neutron diffraction. Both crystallize as CH3CN solvates, and both exhibit polymeric supramolecular structures via extensive C−H···O hydrogen bonding. The predominant structural motif is chelation of the aryloxide oxygen atom of the anion by phosphonium alkyl and aryl C−H groups, such as has been previously observed for phosphonium monoaryloxide salts. The use of this motif as a supramolecular synthon in crystal engineering is explored. In the case of 1a, in addition to the expected intermolecular C−H···O hydrogen bonding pattern, C−H···π interactions between the anion and this solvent are...

The tantalum complex [closo-3,1,2-Ta(NMe2)3(C2B9H11)] underwent insertion into the NC bond of acetonitrile and p-fluorobenzonitrile to give the N,N-dimethylacetamidinate complex [closo-3,1,2-Ta{NC(Me)NMe2}3(C2B9H11)], and p-fluoro-N,N-dimethylbenzamidinate, [closo-3,1,2-Ta{NC(C6H4F)NMe2}3(C2B9H11)], respectively. Attempted re-crystallisation of the latter from chlorinated solvents led to [closo-3,1,2-Ta{NC(C6H4F)NMe2}2Cl(C2B9H11)], in which one amidinate ligand has been replaced by a chloride. [closo-3,1,2-Ta(NMe2)3(C2B9H11)] reacts with cyclohexylisocyanide to give [Ta(NMe2)2{η2-N(Cy)CNMe2}(C2B9H11)]. The structures of the novel N,N-dialkylamidinate complexes have been determined by single crystal X-ray diffraction, and reveal the extensive delocalisation and strong π-donor character of the amidinate ligands. The M–N bonds of [closo-3,1,2-Ta(NMe2)3(C2B9H11)] are cleaved by protic reagents, and it reacts with 2,6-dimethylphenol to give [closo-3,1,2-Ta(OC6H3Me2-2,6)3(C2B9H11)] and with benzenethiol to give the charge-compensated complex [closo-3-Ta(SC6H5)4(9-NHMe2-1,2-C2B9H10)] where the β-boron of the C2B3 face bears a NHMe2+ substituent. The structures of the last two compounds have also been determined.

Proton NMR analysis on newly synthesized 1,2-bis(4,6-diethylthio-1H-pyrazolo[3,4-d]pyrimidin-1-yl)ethane, 2c , and 1,2-bis(4,6-diethylthio-1H-pyrazolo[3,4-d]pyrimidin-1-yl)propane, 2d , showed intramolecular stacking in solution. X-Ray crystallography on 2c and 2d , however, confirmed the presence of such intramolecular stacking only in case of the ‘propylene linker’ compound, 2d , while the ‘ethylene linker’ compound, 2c , was devoid of it.

The asymmetric unit of the title compound, C11H9NO2, contains two mol­ecules which are related by a pseudo-inversion centre and form an N—H⋯O hydrogen-bonded dimer. The least-squares planes through the non-H atoms of the mol­ecules illustrate the overall molecular planarity. The mol­ecules assume Z configurations about the exocyclic C=C bond. In the crystal, intermolecular hydrogen bonds link the mol­ecules into infinite chains.

The crystal structures and packing features of a family of 13 aminophenols, or supraminols, are analyzed and correlated. These compounds are divided into three groups: (a) compounds 1-5 with methylene spacers of the general type HO-C6H4-(CH2)n-C6H4-NH2 (n = 1 to 5) and both OH and NH2 in a para position; (b) compounds 1a, 2a, 2b, 2c, and 3a in which one or more of the methylene linkers in 1 to 3 are exchanged with an S-atom; and (c) compounds 2d, 1b, and 6a prepared with considerations of crystal engineering and where the crystal structures may be anticipated on the basis of structures 1-5,1a, 2a, 2b, 2c, and 3a. These 13 aminols can be described in terms of three major supramolecular synthons based on hydrogen bonding between OH and NH2 groups: the tetrameric loop or square motif, the infinite N(H)O chain, and the beta-As sheet. These three synthons are not completely independent of each other but interrelate, with the structures tending toward the more stable beta-As sheet in some cases. Compounds 1-5 show an alternation in melting points, and compounds with n = even exhibit systematically higher melting points compared to those with n = odd. The alternating melting points are reflected in, and explained by, the alternation in the crystal structures. The n = odd structures tend toward the beta-As sheet as n increases and can be considered as a variable series whereas for n = even, the beta-As sheet is invariably formed constituting a fixed series. Substitution of a methylene group by an isosteric S-atom may causes a change in the crystal structure. These observations are rationalized in terms of geometrical and chemical effects of the functional groups. This study shows that even for compounds with complex crystal structures the packing may be reasonably anticipated provided a sufficient number of examples are available.

The title complex has been studied using low-temperature X-ray (150 K) and neutron (100 K) diffraction. Molecules of the triazine host form a two-dimensional hexagonal network mediated by trigonally symmetric Cl3 synthons having Cl...Cl interactions of 3.441 (3) Å, a C—Cl...Cl angle of 165° and a Cl...Cl—C angle of 105°, close to the ideal values of 180 and 90°, respectively. The guest molecules are of an appropriate size to fit the hexagonal networks and interact with the host via C—H...π (phenyl) and C—Br...π (phenyl) interactions which stabilize the overall structure. Both C-donor bond vectors are directed more closely towards the mid-point (X) of an individual aromatic bond, rather than the ring centroid, with H...X 2.817 (9) Å and C—H...X 174.0 (9)°, and Br...X 3.353 (4) Å and C—Br...X 158.1 (2)°.

The title compound, 1-(5,8-dihydro-1,4-dihydroxy-5,8-dioxo-2-naphthyl)-4-methylpent-3-en-1-yl cinnamate, C(25)H(22)O(6), crystallizes in space group P2(1). The phenyl ring of the cinnamate is anti to the carbonyl group of the same moiety [C-C-C-C = -175.6 (2) degrees] and is nearly parallel to the naphthyl ring system. Two six-membered rings formed by intramolecular hydrogen bonds, with O-H...O distances of 2.587 (2) and 2.589 (2) A, occur on either side of the fused ring system, creating a tetracyclic pyrene-shaped system. The phenyl ring forms an intermolecular stack with the benzoquinone ring, as a result of aromatic pi-pi interactions.

The title compound, C16H12N2O, consists of planar quinoxaline and tolyl moieties linked by a carbonyl group. The carbonyl group is nearly coplanar with the tolyl ring but is inclined at an angle of 34.9 (1)° to the quinoxaline ring. Intermolecular hydrogen bonds stabilize the packing of the mol­ecules in the unit cell.

The crystal structure of [2-(4-bromophenyl)-4-cyano-5-ferrocenylpyrazolo[2,3-a]pyridin-7-yl]acetonitrile, C(26)H(17)N(4)FeBr or [Fe(C(5)H(5))(C(21)H(12)BrN(4))], shows that the pyrazolopyridine ring system (PP), the bromophenyl ring (BP) and the cyclopentadiene ring (Cp) are nearly planar. The PP ring system is twisted out of the plane of the BP and Cp rings by about 20 degrees.

Treating Li[tBuMe2Si-1,2-C2B10H10] with excess α,α′-dihalo-o-xylenes, 1,2-C6H4(CH2X)2 (X = Br, Cl), generates only 1-(α-C,α′-halo-o-xylyl)-2-(tert-butyldimethylsilyl)-1,2-dicarba-closo-dodecaboranes, 1-{o-(XCH2C6H4CH2)}-2-tBuMe2Si-1,2-C2B10H10 (X = Cl 1a, Br 1b). The structures of both 1a and 1b were determined by single crystal X-ray diffraction. Reaction of either 1a or 1b with nBuLi or MeLi affords the substituted ethane, (2-tBuMe2Si-1,2-C2B10H10-1-o-CH2C6H4)2C2H42 whereas reaction with tBuHNLi affords the substituted ethene (2-tBuMe2Si-1,2-C2B10H10-1-o-CH2C6H4)2C2H23; both structures were confirmed by X-ray diffraction. Cleavage of the carborane–silicon bond in 1a or 1b by Bu4NF gives dihydronaphthocarborane, 4, which has been structurally characterised.