SHELXT - integrated space-group and crystal-structure determination

Crystal structure of (Z)-ethyl 2-{5-[(2-benzyl-idene-3-oxo-2,3-di-hydro-benzo[b][1,4]thia-zin-4-yl)meth-yl]-1H-1,2,3-triazol-1-yl}acetate

The title compound, C22H20N4O3S, features two fused six-membered rings linked to a 1,2,3-triazole ring which is attached to an ethyl acetate group. The heterocycle in the benzo-thia-zine residue has an envelope conformation with the S atom being the flap. The conformation of the ethyl acetate side chain, which is directed to the same side of the mol-ecule as the C6 ring of the fused-ring system, may be partially established by a pair of weak intra-molecular C-H⋯O(carbon-yl) inter-actions. The three-dimensional packing is aided by inter-molecular C-H⋯O and C-H⋯N inter-actions.

Crystal structure of tris-(N-methyl-salicyl-aldiminato-κ(2) N,O)chromium(III)

The crystal structure of the title compound, [Cr(C8H8NO)3], is isotypic with the vanadium(III) analogue. The asymmetric unit consists of one Cr(3+) cation and three N-methyl-salicylaldiminate anions. The metal cation is octa-hedrally coordinated by three N,O-chelating N-methyl-salicylaldiminate ligands, leading to discrete and neutral complexes. In the crystal, neighbouring complexes are linked via C-H⋯O hydrogen-bonding inter-actions into chains propagating parallel to the c axis.

Crystal structure of 5,5'-bis-(di-methyl-amino)-N,N'-(3-methyl-3-aza-pentane-1,5-di-yl)di(naphthalene-1-sulfonamide)

In the title compound, C29H37N5O4S2, two arms substituted with dansyl derivatives are connected to a central tertiary amine, where the dihedral angle between the planes of two dansyl units is 56.39 (4)°. Each arm contains a sulfonamide functional group and both N-H groups in the compound are pointed to the same side. The central part of the mol-ecule is disordered over three sets of sites with a refined occupancy ratio of 0.547 (4):0.328 (4):0.125 (3). No intra-molecular π-π or hydrogen-bonding inter-actions are observed. In the crystal, mol-ecules are linked via pairs of N-H⋯O inter-actions involving the same acceptor atom, forming inversion dimers. In addition, C-H⋯O inter-actions exist between molecules, providing further stabilization of dimers.

Crystal structure of ethyl 2-{2-[(1Z)-1-hy-droxy-3-(4-nitro-phen-yl)-3-oxoprop-1-en-1-yl]phen-oxy}acetate

The title compound, C19H17NO7, crystallized in a ratio of about 6:4 of the two possible keto-enol forms. This was observed as disorder over the central C3H2O2 unit. The dihedral angle between the rings is 8.2 (2)°.The mol-ecules pack by C-H⋯O interactions in a layered fashion parallel to (-104).

Crystal structure of (E)-(benzyl-idene)(pyridin-2-ylmeth-yl)amine

In the title mol-ecule, C13H12N2, all non-H atoms, except for those of the pyridine ring, are essentially coplanar, with an r.m.s. deviation of 0.025 Å. The mean plane of these atoms forms a dihedral angle of 80.98 (4)° with the pyridine ring. In the crystal, weak C-H⋯π inter-actions link the mol-ecules, forming a three-dimensional network.

Crystal structure of 2-oxo-N'-phenyl-2H-chromene-3-carbohydrazide

In the title compound, C16H12N2O3, the 2H-chromene moiety is essentially planar, with an r.m.s. deviation of the nine constituent atoms from the mean plane of 0.0093 Å, and makes a dihedral angle of 76.84 (3)° with the pendant phenyl ring. An intra-molecular N-H⋯O hydrogen bond helps to determine the conformation of the side chain. In the crystal, N-H⋯O and N-H⋯N hydrogen bonds link the mol-ecules, forming [100] chains.

Crystal structure of bis-(acetonyltri-phenyl-phospho-nium) tetra-chlorido-cobaltate(II)

The complex title salt, (C21H20OP)2[CoCl4], is the reaction product of CoCl2 with acetonyltri-phenyl-phospho-nium chloride in aceto-nitrile. In the anion, the Co(II) atom exhibits a typical tetra-hedral environment, with Co-Cl distances ranging from 2.2721 (6) to 2.2901 (6) Å, and with Cl-Co-Cl angles ranging from 106.12 (2) to 112.24 (2)°. The two phospho-nium cations likewise show the expected tetra-hedral configuration, with P-C distances ranging from 1.785 (2) to 1.8059 (18) Å and C-P-C angles ranging from 106.98 (8) to 112.85 (15)°. The mol-ecules inter-act in the lattice mainly through Coulombic and van der Waals forces because there is no particular polarity to the charges carried by the cations or anion. In the crystal, the cations and anions are arranged in sheets parallel to (001).

Crystal structure of 1-(cyclo-pentyl-idene-amino)-3-(prop-2-en-1-yl)thio-urea

In the title compound, C9H15N3S, the cyclo-pentyl ring adopts an envelope conformation with one of the methyl-ene C atoms as the flap. The thio-semicarbazide fragment is almost planar (r.m.s. deviation = 0.038 Å) and a short intra-molecular N-H⋯N contact occurs. In the crystal, mol-ecules are linked into helical (41 symmetry) chains propagating in [001] by N-H⋯N and N-H⋯S hydrogen bonds. A very weak C-H⋯S inter-action is also observed.

Crystal structure of 5-(5,6-di-hydro-benzo[4,5]imidazo[1,2-c]quinazolin-6-yl)-2-meth-oxy-phenol

In the mol-ecule of the title compound, C21H17N3O2, the 5,6-di-hydro-benzimidazo[1,2-c]quinazoline moiety is disordered over two orientations about a pseudo-mirror plane, with a refined occupancy ratio of 0.863 (2):0.137 (2). The dihedral angles formed by the benzimidazole ring system and the benzene ring of the quinazoline group are 14.28 (5) and 4.7 (3)° for the major and minor disorder components, respectively. An intra-molecular O-H⋯O hydrogen bond is present. In the crystal, mol-ecules are linked by O-H⋯N hydrogen bonds, forming chains running parallel to [10-1].

Crystal structure of 4-(4-meth-oxy-phen-yl)-4',4'-dimethyl-3-p-tolyl-3',4'-di-hydro-1'H,3H-spiro-[isoxazole-5,2'-naphthalen]-1'-one

In the title compound, C28H27NO3, the cyclo-hexa-none and isoxazole rings have envelope conformations, with the methyl-ene and spiro C atoms as the flaps, respectively. The mean plane of the isoxazole ring is inclined slightly to the p-tolyl ring, making a dihedral angle of 14.20 (9)°, and is nearly perpendicular to the mean plane through the tetra-lone moiety and to the meth-oxy-phenyl ring [dihedral angles = 83.41 (8) and 72.12 (9)°, respectively]. The crystal packing is stabilized mainly by van der Waals forces.

Crystal structure of di-aqua-bis-(2,6-di-methyl-pyrazine-κN (4))bis-(thio-cyanato-κN)cobalt(II) 2,5-di-methyl-pyrazine monosolvate

In the crystal structure of the title compound, [Co(NCS)2(C6H8N2)2(H2O)2]·C6H8N2, the Co(II) cation is coordinated by the N atoms of two terminal thio-cyanate anions, the O atoms of two water mol-ecules and two N atoms of two 2,6-di-methyl-pyrazine ligands. The coordination sphere of the resulting discrete complex is that of a slightly distorted octa-hedron. The asymmetric unit comprises a Co(II) cation and half of a 2,5-di-methyl-pyrazine ligand, both of which are located on centres of inversion, and a water ligand, a 2,6-di--methyl-pyrazine ligand and one thio-cyanate anion in general positions. In the crystal, the discrete complexes are arranged in such a way that cavities are formed in which the 2,5-di-methyl-pyrazine solvent mol-ecules are located. The coordination of the 2,5-di-methyl-pyrazine mol-ecules to the metal is apparently hindered due to the bulky methyl groups in vicinal positions to the N atoms, leading to a preferential coordination of the 2,6-di-methyl-pyrazine ligands. The discrete complexes are linked by O-H⋯N hydrogen bonds between one water H atom and the non-coordinating N atom of the 2,6-di-methyl-pyrazine ligands. The remaining water H atom is hydrogen bonded to one N atom of the 2,5-di-methyl-pyrazine solvent mol-ecule. This arrangement leads to the formation of a two-dimensional network extending parallel to (010).

Crystal structure of 1-(2,4-di-nitro-phen-yl)-3,5-diphenyl-1H-pyrazole

In the title mol-ecule, C21H14N4O4, the phenyl rings make dihedral angles of 39.61 (8) and 9.4 (1)°, respectively, with the central pyrazole ring. The dihedral angle between the pyrazole and di-nitro-phenyl rings is 46.95 (5)°. In the crystal, mol-ecules pack in helical stacks parallel to the a axis aided by weak C-H⋯O inter-actions.

Crystal structure of 2-amino-3-cyano-4-(4-meth-oxy-phen-yl)-4H-1-benzo-thieno[3,2-b]pyran

The three fused five- and six-membered rings in the title compound, C19H14N2O2S, are virtually coplanar, with the maximum deviation from the mean plane being 0.060 (1) Å. This benzothieno[3,2-b]pyran ring system is nearly perpendic-ular to the plane of the 4-meth-oxy-phenyl ring, forming a dihedral angle of 83.65 (5)°. In the crystal, mol-ecules are linked by pairs of N-H⋯N hydrogen bonds into inversion dimers. The dimeric units are further connected by an N-H⋯O hydrogen bond into a tape running along the b axis. The tapes are linked together by C-H⋯N and π-π inter-actions [centroid-centroid distance = 3.7743 (8) Å], forming a three-dimensional network.

Synthesis and properties of mono- and dimetal Fischer multicarbene complexes derived from thiophene and thieno[2,3-b]thiophene

Access to multicarbene complexes of a fused thienothiophene substrate was obtained by the use of the tetrabrominated thieno[2,3-b]thiophene precursor in a lithium-bromide exchange reaction, followed by nucleophilic attack on metal hexacarbonyls (M = Cr, W). Subsequent alkylation afforded unique triscarbene complexes [M(CO)4{{C(OEt)}2C6H1S2C(OEt)}M(CO)5] (M = Cr 12, W 13) featuring three non-equivalent carbene ligands on a single thiophene linker, as well as the bischelated tetracarbene complexes [M(CO)4{{C(OEt)}2C6S2{C(OEt)}2}M(CO)4] (M = Cr 14, W 15). The triscarbene complexes 12 and 13 are the first examples of multi-alkoxycarbene complexes featuring three non-equivalent carbene ligands. The reaction also afforded the chelated mononuclear biscarbene complexes [M(CO)4{C(OEt)}2C6H2S2] (M = Cr 10, W 11) in low yields. Similarly, employing tetrabromothiophene as precursor yielded the mononuclear chelate biscarbene complexes [M(CO)4{C(OEt)}2C4H2S] (M = Cr 6, W 7) and the dinuclear tetracarbene complexes [M(CO)4{{C(OEt)}2C4S{C(OEt)}2}M(CO)4] (M = Cr 8, W 9). Modification of the classic Fischer carbene synthetic methodology to a process of stepwise additions of lithiating agent and metal carbonyls to thieno[2,3-b]thiophene, facilitates the formation of the mixed metal biscarbene complex [W(CO)5C(OEt){C6H2S2}C(OEt)Cr(CO)5] 5, as analogue of the homonuclear biscarbene complexes [M(CO)5C(OEt){C6H2S2}C(OEt)M(CO)5], (M = Cr 3, W 4). The monocarbene complexes [M(CO)5{C(OEt)C6H3S2}], (M = Cr 1, W 2) were also obtained in high yields, and the molecular structures of the tungsten complexes, with the exception of 9 and 11, were confirmed by single crystal X-ray diffraction studies.

A zwitterion produced by a strong intramolecular N→B interaction in 1-hydroxy-2-(pyridin-2-ylcarbonyl)benzo[d][1,2,3]diazaborinine

2-Acylated 2,3,1-benzodiazaborines can display unusual structures and reactivities. The crystal structure analysis of the boron heterocycle obtained by condensing 2-formylphenylboronic acid and picolinohydrazide reveals it to be an N→B-chelated zwitterionic tetracycle (systematic name: 1-hydroxy-11-oxo-9,10,17λ5-triaza-1λ4-boratetracyclo[8.7.0.02,7.012,17]heptadeca-3,5,7,12,14,16-hexaen-17-ylium-1-uide), C13H10BN3O2, produced by the intramolecular addition of the Lewis basic picolinoyl N atom of 1-hydroxy-2-(pyridin-2-ylcarbonyl)benzo[d][1,2,3]diazaborinine to the boron heterocycle B atom acting as a Lewis acid. Neither of the other two pyridinylcarbonyl isomers (viz. nicotinoyl and isonicotinoyl) are able to adopt such a structure for geometric reasons. A favored yet reversible chelation equilibrium provides an explanation for the slow D2O exchange observed for the OH resonance in the1H NMR spectrum, as well as for its unusual upfield chemical shift. Deuterium exchange may take place solely in the minor open (unchelated) species present in solution.

Stereochemical Assignment of Strigolactone Analogues Confirms Their Selective Biological Activity

Strigolactones (SLs) are new plant hormones with various developmental functions. They are also soil signaling chemicals that are required for establishing beneficial mycorrhizal plant/fungus symbiosis. In addition, SLs play an essential role in inducing seed germination in root-parasitic weeds, which are one of the seven most serious biological threats to food security. There are around 20 natural SLs that are produced by plants in very low quantities. Therefore, most of the knowledge on SL signal transduction and associated molecular events is based on the application of synthetic analogues. Stereochemistry plays a crucial role in the structure-activity relationship of SLs, as compounds with an unnatural D-ring configuration may induce biological effects that are unrelated to SLs. We have synthesized a series of strigolactone analogues, whose absolute configuration has been elucidated and related with their biological activity, thus confirming the high specificity of the response. Analogues bearing the R-configured butenolide moiety showed enhanced biological activity, which highlights the importance of this stereochemical motif.

Quinolone-Hydroxyquinoline Tautomerism in Quinolone 3-Esters. Preserving the 4-Oxoquinoline Structure To Retain Antimalarial Activity

Recent publications report in vitro activity of quinolone 3-esters against the bc1 protein complex of Plasmodium falciparum and the parasite. Docking studies performed in silico at the yeast Qo site established a key role for the 4-oxo and N-H groups in drug-target interactions. Thus, the possibility of 4-oxoquinoline/4-hydroxyquinoline tautomerism may impact in pharmacologic profiles and should be investigated. We describe the synthesis, structure, photochemistry, and activity against multidrug-resistant P. falciparum strain Dd2 of ethyl 4-oxo-7-methylquinoline-3-carboxylate (7Me-OQE) and ethyl 4-hydroxy-5-methylquinoline-3-carboxylate (5Me-HQE), obtained from diethyl 2-[((3-methylphenyl)amino)methylene]malonate. Theoretically (B3LYP/6-311++G(d,p)), 5Me-HQE and 7Me-OQE show clear preference for the hydroxyquinoline form. The difference between the lowest energy hydroxyquinoline and quinolone forms is 27 and 38 kJ mol(-1), for 5Me-HQE and 7Me-OQE, respectively. Calculations of aromaticity indexes show that in 5Me-HQE both rings are aromatic, while in the corresponding oxo tautomers the nitrogen-containing ring is essentially non-aromatic. The structure of monomeric 5Me-HQE was studied using matrix isolation coupled to FTIR spectroscopy. No traces of 4-oxoquinoline tautomers were found in the experimental IR spectra, revealing that the species present in the crystal, 5Me-HQE·HCl, was lost HCl upon sublimation but did not tautomerize. Continuous broadband irradiation (λ > 220 nm; 130 min) of the matrix led to only partial photodecomposition of 5Me-HQE (ca. 1/3).

Taming Tin(IV) Polyazides

The first charge-neutral Lewis base adducts of tin(IV) tetraazide, [Sn(N3)4(bpy)], [Sn(N3)4(phen)] and [Sn(N3)4(py)2], and the salt bis{bis(triphenylphosphine)iminium} hexa(azido)stannate [(PPN)2Sn(N3)6] (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline; py = pyridine; PPN = N(PPh3)2) have been prepared using covalent or ionic azide-transfer reagents and ligand-exchange reactions. The azides were isolated on the 0.3 to 1 g scale and characterized by IR and NMR spectroscopies, microanalytical and thermal methods and their molecular structures determined by single-crystal XRD. All complexes have a distorted octahedral Sn[N]6 coordination geometry and possess greater thermal stability than their Si and Ge homologues. The nitrogen content of the adducts of up to 44% exceed any Sn(IV) compound known hitherto.

Dehydration of raffinose pentahydrate: structures of raffinose 5-, 4.433-, 4.289- and 4.127-hydrate at 93 K

Raffinose [or O-α-D-galactopyranosyl-(1→6)-α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside] pentahydrate, C18H32O16·5H2O, (I), and three lower hydrates, namely the 4.433-, (II), 4.289-, (III), and 4.127-hydrated, (IV), forms, obtained in the course of the dehydration of (I), have been studied. The unit cells in the space group P2₁2₁2₁ are of similar dimensions for all the crystals. The conformation of the raffinose molecules remains almost the same across the four crystal structures. The raffinose molecules are linked into a three-dimensional hydrogen-bonded network involving all the -OH groups, the ring and glycosidic O atoms, and the water molecules. Six water sites were identified in the structures of (II), (III) and (IV), of which W1, W4 and W6 (W = water) are partially occupied with their populations coupled. W1, W4 and one of the -OH groups of the galactose ring form an infinite hydrogen-bonding chain around a 2₁ axis parallel to the a axis (denoted chain A), and W6 and the same -OH group form a similar chain (chain A') disordered with chain A. The occupancy ratio of chain A to chain A' for N-hydrates (N is a hydration number between 4 and 5) is (N - 4):(5 - N). The transformation of chain A to chain A' as part of the dehydration process has little effect on the rest of the structure. Thus, the dehydration proceeds without significant impact on the crystal structure.

Isolation of Uranyl Dicyanamide Complexes from N-Donor Ionic Liquids

An ionic liquid (IL) approach for soft-donor f-element chemistry has been demonstrated by the isolation of several new uranyl dicyanamide complexes through reactions of UO2(NO3)2·6H2O with dicyanamide ([N(CN)2](-))-containing ILs. The [N(CN)2](-) ions are able to rapidly substitute uranium's O-donor ligands, as evidenced by single-crystal X-ray diffraction studies on two anhydrous adducts of UO2(NO3)2 with [N(CN)2](-) ILs as well as by IR and NMR spectroscopic studies on solutions of UO2(NO3)2 in these ILs. By contrast, the slow reaction of UO2(OAc)2·2H2O with a nitrile-functionalized imidazolium dicyanamide IL in solvent and the reaction of UO2(NO3)2·6H2O with NaN(CN)2 at elevated temperature resulted in irreversible hydrolysis. The reaction of UO2SO4 with [N(CN)2](-) ions in an acidified aqueous solution resulted in the crystallization of a [UO2](2+) complex with biuret, a N(CN)2](-) hydrolysis product. [N(CN)2](-) ions in the form of ILs react rapidly with [UO2](2+) at room temperature, allowing ligand substitution with [N(CN)2](-) to out-compete the slower hydrolysis reaction, enabling the isolation of uranyl dicyanamide complexes and challenging assumptions regarding the affinity of uranium for O-donors.

Crystal structure of di-μ-iodido-bis-[bis(aceto-nitrile-κN)copper(I)]

The title compound, [Cu2I2(CH3CN)4], exhibits a centrosymmetric Cu2I2 core [Cu⋯Cu distance = 2.7482 (11) Å], the Cu(I) atoms of which are further coordinated by four mol-ecules of aceto-nitrile. The Cu(I) atom has an overall distorted tetra-hedral coordination environment evidenced by L-Cu-L angles (L = N or I) ranging from 100.47 (10) to 117.06 (2)°. The coordination geometries of the aceto-nitrile ligands deviate slightly from linearity as shown by Cu-N-C angles of 167.0 (2) and 172.7 (2)°. In the crystal, there are no significant hydrogen-bonding inter-actions present, so the crystal packing seems to be formed predominantly by van der Waals forces.

Crystal structure of [μ2-3,3-dimethyl-4-(propan-2-yl-idene)thietane-2,2-dithiol-ato-κ(4) S:S':S:S']bis[tricarbonyl-iron(I)](Fe-Fe)

The title complex, [Fe2(C8H12S3)(CO)6] or [{Fe(CO)3}2(μ-L)] [L = 3,3-dimethyl-4-(propan-2-yl-idene)thietane-2,2-bis-(thiol-ato)], consists of two Fe(CO)3 moieties double-bridged by a di-thiol-ate ligand. Each of the two Fe(I) atoms has a distorted anti-prismatic coordination environment consisting of three carbonyl groups, two S atoms of the di-thiol-ate ligand and the neighboring Fe(I) atom [Fe-Fe = 2.4921 (4) Å]. Weak C-H⋯O inter-molecular inter-actions result in the formation of dimers. This is the second crystal structure reported with the 3,3-dimethyl-4-(propan-2-yl-idene)thietane-2,2-bis-(thiol-ate) ligand and the first in which it bridges two metal atoms.

Crystal structure of tris-(3-methyl-1H-pyrazol-1-yl)methane

The title mol-ecule, C13H16N6, crystallizes from hexane as a mol-ecular crystal with no strong inter-molecular inter-actions (the shortest C-H⋯N contact is longer than 3.38 Å). A relatively short intra-molecular contact (3.09 Å) has a C-H⋯N angle of 118° which is quite small to be still considered a hydrogen bond. The three pyrazole rings form a propeller-like motif, with one methylpyrazole unit almost perpendicular to the mean plane of the three rings [82.20 (6)°]. The other two methylpyrazole units, with nitrogen donor atoms oriented in opposite directions, are oriented at 67.26 (6) and 72.53 (6)° to the mean plane.

Crystal structure of 3,4'-diphenyl-3'-p-tolyl-4'H-spiro-[indan-2,5'-[1,2]oxazol]-1-one

In the title compound, C30H23NO2, the five-membered rings are both in envelope conformations with the same spiro C atom as the flap. The benzene ring and the two phenyl rings are inclined to the mean plane of the indene ring system by 83.98 (8), 81.46 (8) and 72.31 (7)°. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds into inversion dimers. The dimers are further connected by C-H⋯N inter-actions, forming layers parallel to (10-1).

Crystal structure of [5-n-butyl-10-(2,5-di-meth-oxy-phen-yl)-2,3,7,8,13,12,17,18-octa-ethyl-porphyrin-ato]nickel(II)

The asymmetric unit of the title nickel(II) porphyrin, [Ni(C48H60N4O2)], contains one independent mol-ecule. The average Ni-N bond length is 1.917 (13) Å. The mol-ecules are arranged in a closely spaced lattice structure in which neighbouring porphyrins are oriented in inversion-related dimers. The nickel(II) porphyrin is characterized by a significant degree of a ruffled (B 1u ) conformation with small contributions from saddle (B 2u ) and wave (y) [Eg (y)], as determined using normal structural decomposition. Disorder in the 2,5-di--meth-oxy-phenyl substituent was modelled over two positions with a 60% occupancy for the major moiety. One of the ethyl groups is also disordered over two positions and was modelled with the major moiety being present in 51.3% occupancy.

Crystal structure of 5-hy-droxy-5-propyl-barbituric acid

Mol-ecules of the title compound, C7H10N2O4, systematic name 5-hy-droxy-5-propyl-pyrimidine-2,4,6(1H,3H,5H)-trione, form a hydrogen-bonded framework which is based on three independent hydrogen bonds, N-H⋯O(carbon-yl), N-H⋯O(hy-droxy) and O-H⋯O(carbon-yl). This framework has the topology of the 5-connected nov net. Each mol-ecule is linked to five other mol-ecules via six hydrogen bonds, and the descriptor of the hydrogen-bonded structure is F65[4(4).6(6)-nov]. The crystal packing is isostructural with that of the previously reported 5-hy-droxy-5-ethyl analogue.

Spectroscopic and theoretical studies of some 4′-substituted-phenyl 2-(ethanesulfonyl)acetates. Structure of 4′-nitrophenyl 2-(ethanesulfonyl)acetate

An analysis of carbonyl bands in the infrared spectra of some 2-ethylsulfonyl 4′-substituted phenylacetates bearing substituents NO2 (1), H (2) and OMe (3), supported by B3LYP/6-31G(d,p) and SM5.42R at PM3 level calculations, along with natural bond orbital analysis (NBO) and X-ray diffraction (for 1) was performed. Theoretical data indicated the existence of two stable gauche conformations (g 1 and g 2). The g 1 conformer is the most stable, least polar and has the lowest νCO frequency. The more intense, lower frequency carbonyl doublet component found in CCl4 solution is assigned to the g 1 conformer. As the solvent dielectric constant increases (going from CCl4 to MeCN) the higher frequency νCO doublet increases in intensity. This behaviour is reproduced by the solvation free energy calculations, supporting the conformer assignments. NBO calculations indicate that the most important orbital interaction is LPO9 → π*C7=O8 for both conformers, which corresponds to [C=O ↔ C+–O-] conjugation. This stabilises the g 1 conformer to a greater extent and is responsible for the lower νCO frequency. The sum of the selected NBO delocalisation energies for 1–3 indicates that the g 1 conformer is more stable. It is concluded that the calculated greater stability of the g 1 conformer is due to a balance of attractive electrostatic and orbital interactions along with relevant hydrogen bonds. The X-ray crystal structure analysis of 1 shows the presence of two crystallographic independent but almost superimposable molecules each which adopt a cis geometry. The molecules are consolidated into the three-dimensional crystal packing by C–H…O interactions as well as by nitro- N–O…π(phenyl) contacts.

Crystal structure of hexa-kis-(urea-κO)chromium(III) dichromate bromide monohydrate from synchrotron X-ray data

The title bromide salt, [Cr{CO(NH2)2}6](Cr2O7)Br·H2O, is isotypic to the corresponding chloride salt. Within the complex cation, the Cr(III) atom is coordinated by six O atoms of six urea ligands, displaying a slightly distorted octa-hedral coordination environment. The Cr-O bond lengths involving the urea ligands are in the range 1.9534 (13)-1.9776 (12) Å. The Cr2O7 (2-) anion has a nearly staggered conformation, with a bridging angle of 130.26 (10)°. The individual components are arranged in rows extending parallel to [100]. The Br(-) anion links the complex cation, as well as the solvent water mol-ecule, through N-H⋯Br and O-H⋯Br hydrogen-bonding inter-actions. The supra-molecular architecture also includes N-H⋯O and O-H⋯O hydrogen bonding between urea N-H and water O-H donor groups and the O atoms of the Cr2O7 (2-) anion as acceptor atoms, leading to a three-dimensional network structure.

Crystal structure of (E)-4-meth-oxy-2-{[(5-methyl-pyridin-2-yl)imino]-meth-yl}phenol

The mol-ecule of the title Schiff base compound, C14H14N2O2, displays an E conformation with respect the imine C=N double bond. The mol-ecule is approximately planar, with the dihedral angle formed by the planes of the pyridine and benzene rings being 5.72 (6)°. There is an intra-molecular hydrogen bond involving the phenolic H and imine N atoms.

Crystal structure of di-μ-iodido-bis{[bis(piperidin-1-yl)methane-κ(2) N,N']copper(I)}

The title compound, [Cu2I2(C11H22N2)2], crystallizes as a symmetric dimer with one quarter of the mol-ecule in the asymmetric unit. The copper(I) atom, the iodine atom and the central methyl-ene C atom of the di(piperidin-1-yl)methane ligand lie on a mirror plane and the complete molecule exhibits point group symmetry 2/m. To the best of our knowledge it is the first di-amine copper(I) complex containing a four-membered chelate ring. Compared to other di-amine copper(I) iodide dimers, the title compound has a short Cu⋯Cu distance of 2.5137 (11) Å, but a long Cu-N bond length of 2.213 (3) Å. The I-Cu-I angle [121.84 (2)°] is large, and the N-Cu-N angle = 66.61 (13)° is the smallest one found for copper(I) di-amine complexes. As a result of the four-membered ring, the ligands around the copper(I) atom have an extremely distorted tetra-hedral arrangement. In the crystal, there are no significant inter-molecular inter-actions present.

Crystal structure of 2-cyano-1-methyl-pyridinium perchlorate

The asymmetric unit of the title salt, C7H7N2 (+)·ClO4 (-), comprises two independent formula units. The solid-state structure comprises corrugated layers of cations and of anions, approximately parallel to (010). The supra-molecular layers are stabilized and connected by C-H⋯O hydrogen bonding to consolidate a three-dimensional architecture. A close pyridin-ium-perchlorate N⋯O contact [2.867 (5) Å] is noted. The crystal was refined as an inversion twin.

Crystal structure of 3-bromo-pyridine N-oxide

In the title compound, C5H4BrNO, there are two mol-ecules in the asymmetric unit that are related by a pseudo-inversion center. The two independent mol-ecules are approximately planar, with an observed (ring-ring) angle of 5.49 (13)°. The crystal structure exhibits a herringbone pattern with the zigzag running along the b-axis direction. The least-squares plane containing the rings of both asymmetric molecules and the plane containing the symmetrically related mol-ecules make a plane-plane angle of 66.69 (10)°, which makes the bend of the herringbone pattern. The bromo group on one mol-ecule points to the bromo group on the neighboring mol-ecule, with a Br⋯Br inter-molecular distance of 4.0408 (16) Å. The herringbone layer-to-layer distance is 3.431 (4) Å with a shift of 1.742 (7) Å. There are no short contacts, hydrogen bonds, or π-π inter-actions.

Crystal structure of 2-cyano-1-methyl-pyridinium bromide

In the title mol-ecular salt, C7H7N2 (+)·Br(-), all the non-H atoms lie on crystallographic mirror planes. The packing consists of (010) cation-anion layers, with the cations forming dimeric units via very weak pairwise C-H⋯N inter-actions. Weak C-H⋯Br inter-actions link the cations to the anions.

Crystal structure of [Co(NH3)6][Co(CO)4]2

Hexaamminecobalt(II) bis-[tetra-carbonyl-cobaltate(-I)], [Co(NH3)6][Co(CO)4]2, was synthesized by reaction of liquid ammonia with Co2(CO)8. The Co(II) atom is coordinated by six ammine ligands. The resulting polyhedron, the hexa-amminecobalt(II) cation, exhibits point group symmetry -3. The Co(-I) atom is coordinated by four carbonyl ligands, leading to a tetra-carbonyl-cobaltate(-I) anion in the shape of a slightly distorted tetra-hedron, with point group symmetry 3. The crystal structure is related to that of high-pressure BaC2 (space group R-3m), with the [Co(NH3)6](2+) cations replacing the Ba sites and the [Co(CO)4](-) anions replacing the C sites. N-H⋯O hydrogen bonds between cations and anions stabilize the structural set-up in the title compound.

Structure-activity relationship studies on rhodamine B-based fluorogenic probes and their activation by anticancer platinum(II) compounds

Fluorescence microscopy has emerged as an attractive technique for imaging intracellular Pt species arising from exposure to clinical anticancer drugs such as cisplatin. A rhodamine-B based fluorogenic probe termed Rho-DDTC can be activated selectively in the presence of Pt(II) compounds, and possesses the ability to discriminate Pt(II) species from Pt(IV) carboxylate prodrug complexes, thereby providing a unique platform to investigate the reduction of these Pt(IV) complexes after cell entry. In this report, we seek to establish the mechanism of activation of Rho-DDTC through a structure-activity relationship study on its structural analogues.

A Hafnium-Based Metal-Organic Framework as a Nature-Inspired Tandem Reaction Catalyst

Tandem catalytic systems, often inspired by biological systems, offer many advantages in the formation of highly functionalized small molecules. Herein, a new metal-organic framework (MOF) with porphyrinic struts and Hf6 nodes is reported. This MOF demonstrates catalytic efficacy in the tandem oxidation and functionalization of styrene utilizing molecular oxygen as a terminal oxidant. The product, a protected 1,2-aminoalcohol, is formed selectively and with high efficiency using this recyclable heterogeneous catalyst. Significantly, the unusual regioselective transformation occurs only when an Fe-decorated Hf6 node and the Fe-porphyrin strut work in concert. This report is an example of concurrent orthogonal tandem catalysis.

Synthesis and Analysis of the Structure, Diffusion and Cytotoxicity of Heterocyclic Platinum(IV) Complexes

We have developed six dihydroxidoplatinum(IV) compounds with cytotoxic potential. Each derived from active platinum(II) species, these complexes consist of a heterocyclic ligand (HL) and ancillary ligand (AL) in the form [Pt(HL)(AL)(OH)2](2+), where HL is a methyl-functionalised variant of 1,10-phenanthroline and AL is the S,S or R,R isomer of 1,2-diaminocyclohexane. NMR characterisation and X-ray diffraction studies clearly confirmed the coordination geometry of the octahedral platinum(IV) complexes. The self-stacking of these complexes was determined using pulsed gradient stimulated echo nuclear magnetic resonance. The self-association behaviour of square planar platinum(II) complexes is largely dependent on concentration, whereas platinum(IV) complexes do not aggregate under the same conditions, possibly due to the presence of axial ligands. The cytotoxicity of the most active complex, exhibited in several cell lines, has been retained in the platinum(IV) form.

Variable genetic architectures produce virtually identical molecules in bacterial symbionts of fungus-growing ants

Small molecules produced by Actinobacteria have played a prominent role in both drug discovery and organic chemistry. As part of a larger study of the actinobacterial symbionts of fungus-growing ants, we discovered a small family of three previously unreported piperazic acid-containing cyclic depsipeptides, gerumycins A-C. The gerumycins are slightly smaller versions of dentigerumycin, a cyclic depsipeptide that selectively inhibits a common fungal pathogen, Escovopsis. We had previously identified this molecule from a Pseudonocardia associated with Apterostigma dentigerum, and now we report the molecule from an associate of the more highly derived ant Trachymyrmex cornetzi. The three previously unidentified compounds, gerumycins A-C, have essentially identical structures and were produced by two different symbiotic Pseudonocardia spp. from ants in the genus Apterostigma found in both Panama and Costa Rica. To understand the similarities and differences in the biosynthetic pathways that produced these closely related molecules, the genomes of the three producing Pseudonocardia were sequenced and the biosynthetic gene clusters identified. This analysis revealed that dramatically different biosynthetic architectures, including genomic islands, a plasmid, and the use of spatially separated genetic loci, can lead to molecules with virtually identical core structures. A plausible evolutionary model that unifies these disparate architectures is presented.

Crystal structure of 4-nitro-N-[(pyridin-2-yl)methyl-idene]aniline

The title compound, C12H9N3O2, adopts an E conformation at the imine double bond. The pyridyl ring makes a dihedral angle of 47.78 (5)° with the benzene ring, indicating the mol-ecule is twisted. In the crystal, mol-ecules are π-π stacked into columns parallel to [100], with an inter-planar separation of 3.8537 (8) Å, corresponding to the length of the a axis. The chains are further linked via weak C-H⋯O and C-H⋯N hydrogen bonds, forming two-dimensional sheets parallel to (010). The sheets interact by van der Waals inter-actions.

Crystal structure of Boc-(S)-ABOC-(S)-Ala-(S)-ABOC-(S)-Phe-OBn chloro-form monosolvate

In the title compound, phenyl (S)-2-[(S)-(1-{2-[(S)-(1-{[(tert-but-oxy)carbon-yl]amino}-bicyclo-[2.2.2]octan-2-yl)formamido]-propanamido}-bicyclo-[2.2.2]octan-2-yl)formamido]-3-phenyl-propano-ate chloro-form monosolvate, C42H56N4O7·CHCl3, the α,β-hybrid peptide contains two non-proteinogenic amino acid residues of (S)-1-amino-bicyclo-[2.2.2]octane-2-carb-oxy-lic acid [(S)-ABOC], two amino acid residues of (S)-2-amino-propanoic acid [(S)-Ala] and (S)-2-amino-3-phenyl-propanoic acid [(S)-Phe], and protecting groups of tert-but-oxy-carbonyl (Boc) and benzyl ester (OBn). The tetra-mer folds into a right-handed mixed 11/9 helix stabilized by intra-molecular i,i + 3 and i,i - 1 C=O⋯H-N hydrogen bonds. In the crystal, the oligomers are linked by N-H⋯O=C hydrogen bonds into chains along the a-axis direction. The chloro-form solvent mol-ecules are inter-calated between the folded chains via C-H⋯O=C inter-actions.

Crystal structure of benz-yl(meth-yl)phen-yl[(piperidin-1-ium-1-yl)meth-yl]silane bromide

The title compound, C20H29NSi(+)·Br(-), contains a chiral silicon atom but crystallizes as a racemate. The C-Si-C bond angles in the range of 103.64 (8)-111.59 (9)° are usual for tetra-hedral geometry. The piperidine ring shows a regular chair conformation with an equatorially positioned exocyclic N-C bond. In the crystal, there is a hydrogen bond between the ammonium cation and the bromide anion. The crystal packing shows the dominant inter-molecular inter-action to be the electrostatic attraction between the ammonium cation and the bromide anion.

Crystal structure of 2,6-di-chloro-4-nitro-pyridine N-oxide

In the title compound, C5H2Cl2N2O3, the nitro group is essentially coplanar with the aromatic ring, with a twist angle of 4.00 (6)° and a fold angle of 2.28 (17)°. The crystal structure exhibits a herringbone pattern with the zigzag running along the b axis. The herringbone layer-to-layer distance is 3.0075 (15) Å, with a shift of 5.150 (4) Å. Neighboring mol-ecules are tilted at a 57.83 (4)° (ring-to-ring) angle with each other. The nitro group on one mol-ecule points to the N-oxide group on the neighboring one, with an inter-molecular O⋯N(nitro) distance of 3.1725 (13) Å.