Hexanuclear Wheel‐Shaped Lithium N‐(2,6‐Diisopropylphenyl)‐N′‐(2‐pyridylethyl)benzamidinate

Lithiation of N‐(2,6‐diisopropylphenyl)‐N′‐(2‐pyridylethyl)benzamidine ( 1 ) with LiN(SiMe₃)₂ in a solvent mixture of toluene and TMEDA yields hexameric lithium N‐(2,6‐diisopropylphenyl)‐N′‐(2‐pyridylethyl)benzamidinate ( 2 ), which can be purified by recrystallization from a solvent mixture of toluene and THF. The three‐coordinate lithium ions have T‐shaped coordination spheres. The negative charge is delocalized within the 1,3‐diazaallylic system, which adopts a (syn‐Z)‐arrangement.     

Reactivity of 2,2′‐Bis(2N‐(1,1′,3,3′‐tetramethyl‐guanidino))diphenylene‐amine with CuI and [Cu(MeCN)4][PF6]: Benzimidazole Formation vs. Cu Oxidation

The reaction of 2,2′‐Bis(2N‐(1,1′,3,3′‐tetramethyl‐guanidino))diphenylene‐amine (TMG₂PA) ( 1 ) with CuI in MeCN results in the formation of [Cu^II(TMG₂PA^amid)I] ( 2 ) indicatingthat Cu^I is the target of an oxidative attack of the N‐H proton of the ligand which itself is converted to molecular hydrogen. In contrast, if [Cu(MeCN)₄][PF₆] is used as the Cu^I source, [Cu^I₂(TMGbenz)₂][PF₆]₂ ( 3 ) is obtained instead. The use of the non‐coordinating counterion [PF₆]^– apparently prevents Cu^I from oxidation but induces itself a cyclisation reaction within the ligand which results in the formation of a benzimidazole‐guanidine ligand.     

Enantiotropic Nematics From Cross‐Like 1,2,4,5‐Tetrakis(4′‐alkyl‐4‐ethynylbiphenyl)benzenes and Their Biaxiality Studies

The theoretically predicted optimum length/breadth/width ratio for maximizing shape biaxiality was investigated experimentally by the facile and successful synthesis of cross‐shaped compound 3 , which showed enantiomeric nematic phase behavior. This cross‐like core structure could alternatively be viewed as two fused V‐shaped mesogens, which have recently immerged as a new direction in biaxial nematic research, at the bending tips that can act as a new structure for biaxial investigations. Whilst the thermal analysis data of compound 3 did not meet the expected theoretical values for biaxial nematics, surface‐induced biaxiality was evidenced by optical studies. Cluster‐size analysis within the nematic phase of compound 3 revealed the formation of meta‐cybotactic nematics, which approached the cluster sizes of cybotactic nematics. The split small‐angle 2D X‐ray diffraction patterns of magnetic‐field‐aligned samples indicated that the nematic phase was composed of small smectic C‐like clusters with the tilting of molecules within the clusters. The wide‐temperature‐range enantiomeric nematic phase of cross‐like compound 3 enabled the molecular skeleton to serve as an alternative skeleton to bent‐rod mesogens, which exhibited nematic phases with the potential competition of transitions to higher‐order liquid‐crystalline phases and crystallization, for future biaxial investigations.     

Single‐Crystal‐to‐Single‐Crystal Transition in an Enantiopure [7]Helquat Salt: The First Observation of a Reversible Phase Transition in a Helicene‐Like Compound

Here it is reported that crystals of an enantiopure [7]helquat salt undergo reversible thermal solid–solid phase transition at 404 K. Differential scanning calorimetry (DSC), capillary electrophoresis (CE), and X‐ray diffraction analysis were used to unravel the mechanistic details of this process. The single‐crystal‐to‐single‐crystal course enabled direct monitoring of the structural changes by in situ variable‐temperature X‐ray diffraction, thus providing the first direct evidence of a solid phase transition in a helicene‐like compound.     

Tetra(N,N′‐tetramethylharnstoff)‐Beryllium‐Triiodid, [Be(TMH)4](I3)2

Tetra(N,N′‐tetramethylurea)‐beryllium‐triiodide, [Be(TMU)₄](I₃)₂ ( 1 ) was prepared from beryllium powder and iodine in N,N′‐tetramethylurea to give orange crystals, which were characterized by X‐ray diffraction and IR spectroscopy. Compound 1 crystallizes monoclinically in the space group C2/c with four formula units per unit cell. Lattice dimensions at 100(2) K: a = 1906.6(1), b = 1185.7(1), c = 1895.0(1) pm, β = 113.60(1) °, R₁ = 0.0291. The structure of 1 consists of distorted tetrahedral cations [Be(TMU)₄]²⁺ with Be–O bond lengths of 162.5(5) and 160.8(5) pm and triiodide ions without site symmetry.     

Experimental and quantum chemical calculational studies on N‐[4‐(3‐Methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐N′‐pyridin‐3ylmethylene‐hydrazine

The title molecule, N‐[4‐(3‐Methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐N′‐pyridin‐3ylmethylene‐ hydrazine (C₂₀ H₂₀ N₄ S₁), was characterized by ¹H‐NMR, ¹³C‐NMR, IR, UV‐visible, and X‐ray determination. In addition to the molecular geometry from X‐ray experiment, the molecular geometry, vibrational frequencies and gauge including atomic orbital ¹H‐ and ¹³C‐NMR chemical shift values of the title compound in the ground state have been calculated using the Hartree‐Fock and density functional method (B3LYP) with 6‐31G(d, p) basis set. The calculated results show that optimized geometries can well reproduce the crystal structural parameters. By using time‐dependent density functional theory method, electronic absorption spectrum of the title compound has been predicted. © 2011 Wiley Periodicals, Inc.     

Synthesis and Conformation of Fluorinated β‐Peptidic Compounds

Experimental and theoretical data indicate that, for α‐fluoroamides, the F? C? C(O)? N(H) moiety adopts an antiperiplanar conformation. In addition, a gauche conformation is favoured between the vicinal C? F and C? N(CO) bonds in N‐β‐fluoroethylamides. This study details the synthesis of a series of fluorinated β‐peptides ( 1 – 8 ) designed to use these stereoelectronic effects to control the conformation of β‐peptide bonds. X‐ray crystal structures of these compounds revealed the expected conformations: with fluorine β to a nitrogen adopting a gauche conformation, and fluorine α to a C?O group adopting an antiperiplanar conformation. Thus, the strategic placement of fluorine can control the conformation of a β‐peptide bond, with the possibility of directing the secondary structures of β‐peptides.     

Two polymorphs of N‐(2‐methoxyphenyl)‐4‐oxo‐4H‐chromone‐3‐carboxamide

The title compound, C₁₇H₁₃NO₄, crystallizes in two polymorphic forms, each with two molecules in the asymmetric unit and in the monoclinic space group P2₁/c. All of the molecules have intramolecular hydrogen bonds involving the amide group. The amide N atoms act as donors to the carbonyl group of the pyrone and also to the methoxy group of the benzene ring. The carbonyl O atom of the amide group acts as an acceptor of the β and β′ C atoms belonging to the aromatic rings. These intramolecular hydrogen bonds have a profound effect on the molecular conformation. In one polymorph, the molecules in the asymmetric unit are linked to form dimers by weak C—H...O interactions. In the other, the molecules in the asymmetric unit are linked by a single weak C—H...O hydrogen bond. Two of these units are linked to form centrosymmetric tetramers by a second weak C—H...O interaction. Further interactions of this type link the molecules into chains, so forming a three‐dimensional network. These interactions in both polymorphs are supplemented by π–π interactions between the chromone rings and between the chromone and methoxyphenyl rings.     

Conformational Change from a Twisted Figure‐Eight to an Open‐Extended Structure in Doubly Fused 36π Core‐Modified Octaphyrins Triggered by Protonation: Implication on Photodynamics and Aromaticity

Two examples of core‐modified 36π doubly fused octaphyrins that undergo a conformational change from a twisted figure‐eight to an open‐extended structure induced by protonation are reported. Syntheses of the two octaphyrins (in which Ar=mesityl or tolyl) were achieved by a simple acid‐catalyzed condensation of dipyrrane unit containing an electron‐rich, rigid dithienothiophene (DTT) core with pentafluorobenzaldehyde followed by oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). The single‐crystal X‐ray structure of the octaphyrin (in which Ar=mesityl) shows a figure‐eight twisted conformation of the expanded porphyrin skeleton with two DTT moieties oriented in a staggered conformation with a π‐cloud distance of 3.7 Å. Spectroscopic and quantum mechanical calculations reveal that both octaphyrins conform to a [4n]π nonaromatic electronic structure. Protonation of the pyrrole nitrogen atoms of the octaphyrins results in dramatic structural change, which led to 1) a large redshift and sharpening of absorption bands in electronic absorption spectrum, 2) a large change in chemical shift of pyrrole β‐CH and ? NH protons in the ¹H NMR spectrum, 3) a small increase in singlet lifetimes, and 4) a moderate increase in two‐photon absorption cross‐section values. Furthermore, nucleus‐independent chemical shift (NICS) values calculated at various geometrical positions show positive values and anisotropy‐induced current density (AICD) plots indicate paratropic ring‐currents for the diprotonated form of the octaphyrin (in which Ar=tolyl); the single‐crystal X‐ray structure of the diprotonated form of the octaphyrin shows an extended structure in which one of the pyrrole ring of each dipyrrin subunit undergoes a 180 ° ring‐flip. Four trifluoroacetic acid (TFA) molecules are bound above and below the molecular plane defined by meso‐carbon atoms and are held by N? H ??? O, N? H ??? F, and C? H ??? F intermolecular hydrogen‐bonding interactions. The extended‐open structure upon protonation allows π‐delocalization and the electronic structure conforms to a [4n]π Hückel antiaromatic in the diprotonated state.     

Ionic Liquids as Unique Solvents in One‐Pot Synthesis of 4‐(N,2,2,2‐Tetranitroethylamino)‐3‐R‐Furazans

An efficient two‐step one‐pot protocol for the synthesis of N‐nitrated trinitroethylamino furazans in an ionic liquid has been developed involving the condensation of aminofurazans with trinitroethanol and the N‐nitration of an intermediate Mannich base. Trinitroethylnitramino derivatives have been synthesized and characterized by multinuclear NMR spectroscopy and X‐ray crystallography. A role of the N,2,2,2‐tetranitroethylamino group for stabilization of the high‐density crystal‐packing motif is described. The performance calculations gave detonation pressures and velocities for the furazan derivatives in a range of about 31–36 GPa and 8330–8745 ms^?1, respectively, which makes them competitive energetic materials. Furthermore, due to the positive oxygen balance, the compounds could be potential oxidizers for energetic formulations.     

Stereoselective Synthesis of [5‐[4,4,4,4′,4′,4′‐Hexafluoro‐N‐(2‐hydroxyethoxy)‐D‐valine]]‐ and [5‐[4,4,4,4′,4′,4′‐Hexafluoro‐N‐(2‐hydroxyethoxy)‐L‐valine]cyclosporin A

Addition of various amines to the 3,3‐bis(trifluoromethyl)acrylamides 10a and 10b gave the tripeptides 11a – 11f , mostly as mixtures of epimers (Scheme 3). The crystalline tripeptide 11f ₂ was found to be the N‐terminal (2‐hydroxyethoxy)‐substituted (R,S,S)‐ester HOCH₂CH₂O‐D ‐Val(F₆)‐MeLeu‐Ala‐O^tBu by X‐ray crystallography. The C‐terminal‐protected tripeptide 11f ₂ was condensed with the N‐terminus octapeptide 2b to the depsipeptide 12a which was thermally rearranged to the undecapeptide 13a (Scheme 4). The condensation of the epimeric tripeptide 11f ₁ with the octapeptide 2b gave the undecapeptide 13b directly. The undecapeptides 13a and 13b were fully deprotected and cyclized to the [5‐[4,4,4,4′,4′,4′‐hexafluoro‐N‐(2‐hydroxyethoxy)‐D ‐valine]]‐ and [5‐[4,4,4,4′,4′,4′‐hexafluoro‐N‐(2‐hydroxyethoxy)‐L ‐valine]]cyclosporins 14a and 14b , respectively (Scheme 5). Rate differences observed for the thermal rearrangements of 12a to 13a and of 12b to 13b are discussed.     

Dinuclear Dysprosium and Ytterbium Complexes Incorporating N,N‐Bis(pyrrolyl‐α‐methyl)‐N‐methylamine Ligand: Syntheses and Structures

Reaction of DyCl₃ with two equivalents of NaN(SiMe₃)₂ in THF yielded {Dy(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 1 ). X‐ray crystal structure analysis revealed that 1 is a centrosymmetric dimer with asymmetrically bridging chloride ligands. The metal coordination arrangement can be best described as distorted trigonal bipyramid. The bond lengths of Ln–Cl and Ln–N showed a decreasing trend with the contraction of the size of Ln³⁺. Treatment of N,N‐bis(pyrrolyl‐α‐methyl)‐N‐methylamine (H₂dpma) with 1 and known compound {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂, respectively, led to the formations of [Dy(μ‐Cl)(dpma)(THF)₂]₂ ( 2 ) and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 3 ). Compounds 2 and 3 were fully characterized by single‐crystal X‐ray crystallography, elemental analysis, and ¹H NMR spectroscopy. Structure determination indicated that 2 and 3 exhibit as centrosymmetric dimers with asymmetrically bridging chloride ligands. One pot reactions involving LnCl₃ (Ln = Dy and Yb), LiN(SiMe₃)₂, and H₂dpma were explored and desired products 2 and 3 were not yielded, which indicated that 1 and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ are the demanding precursors to synthesize Dysprosium and Ytterbium complexes supported by dpma^2– ligand. Compounds 2 and 3 are the first reported lanthanide complexes chelated by dpma^2– ligand.     

Regioselective Cage Opening of La2@D2(10611)‐C72 with 5,6‐Diphenyl‐3‐(2‐pyridyl)‐1,2,4‐triazine

The thermal reaction of the endohedral metallofullerene La₂@D₂(10611)‐C₇₂, which contains two pentalene units at opposite ends of the cage, with 5,6‐diphenyl‐3‐(2‐pyridyl)‐1,2,4‐triazine proceeded selectively to afford only two bisfulleroid isomers. The molecular structure of one isomer was determined using single‐crystal X‐ray crystallography. The results suggest that the [4+2] cycloaddition was initiated in a highly regioselective manner at the C? C bond connecting two pentagon rings of C₇₂. Subsequent intramolecular electrocyclization followed by cycloreversion resulted in the formation of an open‐cage derivative having three seven‐membered ring orifices on the cage and a significantly elongated cage geometry. The reduction potentials of the open‐cage derivatives were similar to those of La₂@D₂‐C₇₂ whereas the oxidation potentials were shifted more negative than those of La₂@D₂‐C₇₂. These results point out that further oxidation could occur easily in the derivatives.     

4‐Nitro‐3‐(5‐tetrazole)furoxan and Its Salts: Synthesis,Characterization, and Energetic Properties

A series of new energetic salts based on 4‐nitro‐3‐(5‐tetrazole)furoxan (HTNF) has been synthesized. All of the salts have been fully characterized by nuclear magnetic resonance (¹H and ¹³C), infrared (IR) spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). The crystal structures of neutral HTNF ( 3 ) and its ammonium ( 4 ) and N‐carbamoylguanidinium salts ( 9 ) have been determined by single‐crystal X‐ray diffraction analysis. The densities of 3 and its nine salts were found to range from 1.63 to 1.84 g cm^?3. Impact sensitivities have been determined by hammer tests, and the results ranged from 2 J (very sensitive) to >40 J (insensitive). Theoretical performance calculations (Gaussian 03 and EXPLO 5.05) provided detonation pressures and velocities for the ionic compounds 4 – 12 in the ranges 25.5–36.2 GPa and 7934–8919 m s^?1, respectively, which make them competitive energetic materials.     

Synthesis,characterization and antibacterial activity of 3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoic acid and di‐isopropylammonium [3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoato] triphenylstannate(IV). The crystal structure of [HQ][SnPh3(o‐mpspa)]

Reaction of 3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoic acid [H₂(o‐mpspa)] with SnPh₃OH in the presence of di‐isopropylamine resulted in the formation of the complex [HQ][SnPh₃(o‐mpspa)] (where HQ = di‐isopropylammonium cation and o‐mpspa = 3‐(2‐methoxyphenyl)‐2‐sulfanylpropenoato), which was characterized by mass spectrometry and vibrational spectroscopy, as well as by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. The single‐crystal X‐ray structural analysis of the new complex shows a trigonal‐bipyramidal coordination geometry around the Sn atom where o‐mpspa behaves as a bidentate chelating ligand. Dimeric units arise from the existence of N? H…O hydrogen bonds between the NH₂ group of the di‐isopropylammonium cation and the oxygen atoms of the two neighbouring carboxylato groups. The bacteriostatic activity of the complex is also reported. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and Characterization of 5‐(1,2,4‐Triazol‐3‐yl)tetrazoles with Various Energetic Functionalities

In this contribution the synthesis and full structural as well as spectroscopic characterization of three 5‐(1,2,4‐triazol‐3‐yl)tetrazoles along with selected energetic moieties like nitro, nitrimino, and azido groups are presented. The main goal is a comparative study on the influence of those variable energetic moieties on structural and energetic properties. A complete characterization including IR and Raman as well as multinuclear NMR spectroscopy of all compounds is presented. Additionally, X‐ray crystallographic measurements were performed and reveal insights into structural characteristics as well as inter‐ and intramolecular interactions. The standard enthalpies of formation were calculated for all compounds at the CBS‐4M level of theory and reveal high positive heats of formation for all compounds. The calculated detonation parameters (using the EXPLO5.05 program) are in the range of 8000 m s^?1 (8097 m s^?1 ( 5 ), 8020 m s^?1 ( 6 ), 7874 m s^?1 ( 7 )). As expected, the measured impact and friction sensitivities as well as decomposition temperatures strongly depend on the energetic moiety at the triazole ring. The C? C connection of a triazole ring with its opportunity to introduce a large variety of energetic moieties and a tetrazole ring, implying a large energy content, leads to the selective synthesis of primary and secondary explosives.     

Syntheses and Structural Characterization of Four New Silver(I) Complexes with the N,N′(O)‐bidentate Bridging Ligands

Four new bridged silver(I) complexes, namely [Ag₂(μ₂‐teda)(μ₂‐fbc)₂] ( 1 ), [Ag₂(μ₂‐1,6‐dah)₂](bpdc) · 4H₂O ( 2 ), [Ag₂(μ₂‐2‐ap)(2‐ap)(bnb)] · 0.34H₂O ( 3 ), [Ag₂(μ₂‐pyc)₂(2‐apy)₂] · 0.5H₂O ( 4 ), have been synthesized and characterized by elemental analysis and crystallographic methods [fbc = 4‐fluorobenzoate, teda = triethylenediamine ( 1 ); bpdc = biphenyl‐4,4′‐dicarboxylate, 1,6‐dah = 1,6‐diaminohexane ( 2 ); bnb = 3,5‐binitrobenzoate, 2‐ap = 2‐aminopyrimidine ( 3 ); pyc = 3‐pyridinecarboxylate acid, 2‐apy = 2‐aminopyridine ( 4 )]. Complex 1 contains a 1D linear chain paralleling to the c‐axis, whereas in complex 2 silver(I) atoms were bridged by the 1,6‐dah ligand into a zigzag chain, further giving a 1D ribbon by weak Ag ··· Ag interactions. Complex 3 consists of a dinuclear silver(I) [Ag₂(μ₂‐2‐ap)(2‐ap)(bnb)] moiety and a lattice water molecule, forming a 3D network via a number of hydrogen‐bonding interactions such as N–H ··· O, N–H ··· N and C–H ··· O hydrogen bond and other weak interactions such Ag ··· Ag, Ag ··· N, N ··· O as well as O ··· O interaction. Similar to 3 , the asymmetric unit of 4 consists of one dinuclear silver(I) [Ag₂(μ₂‐pyc)₂(2‐apy)₂] moiety and half lattice water molecule, further generating a tetranuclear silver(I) {[Ag₂(μ₂‐pyc)₂(2‐apy)₂]₂ · H₂O} moiety. These moieties construct a 3D supramolecular network structure of 4 through N–H ··· O, O–H ··· O and C–H ··· O hydrogen bonds as well as other weak interactions such as Ag ··· O and N ··· O interactions.     

A one‐dimensional cobalt(II) coordination polymer based on 2,4′‐oxydibenzoic acid: poly[[[diaquabis[2‐(4‐carboxyphenoxy)benzoato‐κO1]cobalt(II)]‐μ‐4,4′‐bipyridine‐κ2N:N′] dihydrate]

The reaction of CoSO₄ with 2,4‐oxydibenzoic acid (H₂oba) and 4,4′‐bipyridine (bipy) under hydrothermal condition yielded a new one‐dimensional cobalt(II) coordination polymer, {[Co(C₁₄H₉O₅)₂(C₁₀H₈N₂)(H₂O)₂]·2H₂O}_n, which was characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, magnetic properties and single‐crystal X‐ray diffraction. The Co^II ions are connected by bipy ligands into infinite one‐dimensional chains. The Hoba⁻ ligands extend out from the two sides of the one‐dimensional chain. O—H...O hydrogen bonding extends these chains into a two‐dimensional supramolecular architecture.