Unexpected Self‐Assembly of a Homochiral Metallosupramolecular M4L4 Catenane

Two enantiomerically pure 9,9′‐spirobifluorene‐based bis(pyridine) ligands 1 and 2 were prepared to study their self‐assembly behavior upon coordination to cis‐protected palladium(II) ions. Whereas the sterically more demanding ligand, 2 , gave rise to the expected dinuclear metallosupramolecular M₂L₂ rhombi, the sterically less demanding ligand, 1 , acts as a template to give rise to a homochiral metallosupramolecular M₄L₄ catenane.     

Synthesis and Antibacterial Activities of 2‐(1‐Aryl‐5‐Methyl‐1,2,3‐triazol‐4‐yl)‐1,3,4‐Oxadiazole Derivatives

Eighteen novel 2‐(1‐aryl‐5‐methyl‐1,2,3‐triazol‐4‐yl)‐1,3,4‐oxadiazole derivatives and two acylhydrazone intermediate compounds were synthesized by various pathways starting from 1‐aryl‐5‐methyl‐1,2,3‐triazol‐4‐formhydrazide ( 1 ). All products were identified by spectroscopic analysis, and 2‐(1‐aryl‐5‐methyl‐1,2,3‐triazol‐4‐yl)‐5‐benzalthio‐1,3,4‐oxadiazole was further validated by X‐ray crystallography. Results from primary antibacterial activity tests indicated that most of the compounds were effective against E. coli, P. aeruginosa, B. subtilis and S. aureus.     

A New Structural Motif for an Enantiomerically Pure Metallosupramolecular Pd4L8 Aggregate by Anion Templating

An enantiomerically pure BINOL‐based bis(3‐pyridyl) ligand 1 assembles into a homochiral [Pd₄( 1 )₈] complex upon coordination to tetravalent Pd^II ions. The formation of this aggregate is templated by two tetrafluoroborate counterions that are encapsulated in two peripheral cavities. The resulting structure is a new structural motif for this kind of metallosupramolecular assemblies that arranges the palladium ions in a distorted tetrahedral fashion and forces ligand 1 to adopt two different conformations. Both phenomena are unique and cause an overall three‐dimensional structure that has another confined, chiral, and hydrophilic central cavity.     

Facile synthesis of pyridinium aryltetrachlorotellurates: crystal and molecular structure of [C5H6N][RTeCl4] (R = m‐O2NC6H4, p‐NCC6H4)

Arylation of TeCl₄ with arylboroxine–pyridine complexes [(RBO)₃·C₅H₅N, where R = m‐O₂NC₆H₄ ( 1 ), p‐O₂NC₆H₄ ( 2 ), m‐NCC₆H₄ ( 3 ), p‐NCC₆H₄ ( 4 )] and advantageous moisture provided good yields of the pyridinium aryltetrachlorotellurates [C₅H₆N][RTeCl₄] [R = m‐O₂NC₆H₄ ( 5 ), p‐O₂NC₆H₄ ( 6 ), m‐NCC₆H₄ ( 7 ), p‐NCC₆H₄ ( 8 )]. Compounds 5 and 8 have been investigated by X‐ray crystallography. Key features of both crystal structures are intermolecular secondary Te???Cl interactions between the aryltetrachlorotellurate anions and weak association of the cations and anions. Electrospray mass spectra of compound 5 reveal that the associative interactions also play a role in solution. Copyright © 2005 John Wiley & Sons, Ltd.     

The Structure of 2‐[(1S)‐(+)‐10‐camphorsulfonamino]‐6‐aminopyridine in the Solid State and in Solution; Unprecedented Cocrystallization of Four Stereoisomers

The solid and solution structures of a new optically active aminopyridine compound, 2‐[(1S)‐(+)‐10‐camphorsulfonamino]‐6‐aminopyridine [(S)‐csaap], 1 , are reported. Crystal data: space group P2₁, a = 8.9729 (5), b = 10.9447 (6), c = 36.693 (2) Å, β = 96.435 (1)°, V = 3580.8 (3) ų, Z = 8, R₁ = 0.0673 and wR₂ = 0.1600 with I > 2σ(I). This chiral compound shows an unprecedented cocrystallization of four stereoisomers, which are characterized by X‐ray crystallography and NMR spectroscopy.     

Synthesis and Characterization of Tetrahedral Zinc(II) Complexes with 3, 6,7‐Triamino‐7H‐[1, 2,4]triazolo[4, 3‐b][1, 2,4]triazole as Nitrogen‐Rich Ligand

Triaminotriazolotriazole (TATOT) was used as a nitrogen‐rich ligand for the formation of the energetic Zn^II complexes [ZnCl₂(TATOT)₂] · H₂O ( 2 ), [Zn(H₂O)(TATOT)₃](NO₃)₂ · 2H₂O ( 3 ), and [Zn(TATOT)₄](ClO₄)₂ · 2H₂O ( 4 ). The zinc species were prepared in a straightforward and inexpensive synthesis. The complexes 2 – 4 were structurally characterized using X‐ray diffraction. Additionally, the compounds were characterized using elemental analysis and infrared (IR) spectroscopy. Finally, the sensitivities toward thermal and mechanical stimuli were determined by differential thermal analysis (DTA) and BAM (Bundesanstalt für Materialforschung und ‐prüfung) methods.     

Synthesis,Crystal Structure and Magnetic Properties of [Fe(bpe)4(H2O)2](TCNQ)2 (bpe = trans‐1,2‐bis(4‐pyridyl)ethane and TCNQ = tetracyanoquinodimethane)

The synthesis, structure and magnetic properties of [Fe(bpe)₄(H₂O)₂](TCNQ)₂ ( 1 ) are reported. 1 crystallizes in the triclinic P space group, a = 13.481(5), b = 14.887(3), c = 16.663(4) Å, α = 101.048(18), β = 112.84(2), γ = 90.92(2)°, V = 3009.6(14) ų, Z = 2. The iron atom defines a compressed octahedron with the equatorial positions occupied by the bpe molecules which act as monodentate ligands and the two axial positions occupied by water molecules. The TCNQ^? radical counterions are uncoordinated and interact by pairs defining (TCNQ)₂^2? units strongly coupled antiferromagnetically. The iron(II) atoms are in the high spin state and its magnetic behaviour indicates the occurrence of zero‐field splitting of the S = 2 ground state.     

Dynamic Phenomena in Self‐Complementary {2}‐Metallocryptates Probed by Solution 133Cs‐NMR. New Insights into Ion Pairing Processes: X‐Ray Structure and Solid‐State NMR Spectra of a Meandering Species

Two self‐complementary {2}‐metallocryptates, differing in methyl and phenyl substituents, respectively, have been studied by X‐ray analysis, and solid‐state and solution NMR. Mixed Mg/Cs metal methyl complex 2 is a linear polymer in the solid state. The two different Cs sites are confirmed by ¹³³Cs‐solid‐state NMR. By contrast, the analog mixed Mg/Cs metal phenyl complex 4 is a meandering polymer as shown by an actual X‐ray analysis. The four non‐equivalent Cs‐sites in 4 are reflected in the solid‐state NMR spectra. Solution ¹³³Cs‐NMR spectra of 4 reveal two independent dynamic processes: a fast exchange of Cs within contact ion‐pairs and solvent‐separated ion‐pairs (CIP, SSIP), and a slower exchange of ‘inside’ endo Cs, surrounded by three ligands, and ‘outside’ exo Cs involved in the CIP/SSIP equilibrium. Complete line‐shape analysis of variable‐temperature ¹³³Cs‐NMR spectra of 4 yield kinetic parameters of =10.8 kcal/mol for the fast SSIP‐CIP exchange and =13.2 kcal/mol for the slower endo/exo exchange of Cs. DOSY‐NMR Measurements confirm the monomeric nature of 4 in solution.     

Crystallographic report: Crystal structure of tetra(4‐methyl‐5‐imidazole‐carboxyaldehyde)zinc(II) diperchlorate

The central zinc(II) atom in the title complex is tetrahedrally coordinated by four nitrogen atoms derived from 4‐methyl‐5‐imidazolecarboxyaldehyde ligands with Zn? N in the range 2.007(3) to 2.026(4) Å. Copyright © 2003 John Wiley & Sons, Ltd.     

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.     

From a Si3‐Cyclopropene to a Si3S‐Bicyclo[1.1.0]butane to a Si3S‐Cyclopropene to a Si3S2‐Bicyclo[1.1.0]butane: Back‐and‐Forth,and In‐Between

Compact and highly reactive bicyclo[1.1.0]butanes constitute one of the most fascinating classes of organic compounds. Furthermore, interplay of bicyclo[1.1.0]butanes with their valence isomers, such as buta‐1,3‐dienes and cyclobutenes, is among the fundamental pericyclic transformations in organic chemistry. Herein we report the back‐and‐forth interconversion between the cyclotrisilenes and thiatrisilabicyclo[1.1.0]butanes, allowing for the synthesis of novel representatives of such classes of highly reactive organometallics. The peculiar structural and bonding features of the newly synthesized compounds, as well as the mechanism of their isomerization, were verified both experimentally and computationally.     

Synthesis and X‐Ray Single Crystal Structure of Two New Copper Complexes with the Redox Active Ligand 1,10‐Phenanthroline‐5,6‐dione

The synthesis and the crystal structures of the complexes [Cu(L^I)₂](ClO₄) ( 1 ) and [Cu(L^I)(CH₃CN)₂(ClO₄)₂] ( 2 ) are reported. 1 crystallizes in the monoclinic space group C2/c with the unit cell dimensions a = 13.169(4), b = 12.289(3), c = 14.732(3) Å, β = 109.03(2)° and Z = 4. Copper(I) is coordinated to four N atoms of the two 1,10‐Phenanthroline‐5,6‐dione (L^I) ligands with a two‐fold axis passing between the ligands. The copper(II) compound 2 crystallizes in the orthorhombic space group Pbn2₁ with unit cell dimensions of a = 7.498(5), b = 23.492(7), c = 12.363(4) Å and Z = 4. Copper(II) coordination can be described as a distorted octahedron with the N donor atoms of one L^I ligand and of two molecules of CH₃CN occupying the equatorial positions completed by two oxygen atoms of the two perchlorate molecules in the axial positions.     

Electron‐Deficient Tetrabenzo‐Fused Pyracylene and Conversions into Curved and Planar π‐Systems Having Distinct Emission Behaviors

Polycyclic aromatic compounds containing fully unsaturated five‐membered ring(s) have been intensively studied because of their unique properties, which include high electron affinity and reactivity. Reported herein is an efficient route for the synthesis of tetrabenzo‐fused pyracylene, which comprises pyracylene and tetracene segments, using intramolecular oxidative C? H coupling. It was shown to possess high electron affinity and was found to undergo addition reactions with n‐butyllithium or benzyne. These reactions led to either a 1,4‐addition compound or triptycene‐type adduct with a curved or planar π‐system, respectively. Although these compounds exhibited similar sky‐blue emissions in a dilute solution, the emission band of the 1,4‐addition compound was significantly red‐shifted in the solid state and exhibited intense yellow emission attributable to the excimer, while the triptycene‐type adduct retained the intense blue color emission in the solid state.     

Cyclic Hydroboration – The Structure of Perhydro‐9b‐boraphenalenes

Complete hydroboration of cyclododecatrienes was reported to give two isomers, depending on conditions. The assignment of their structure had been attempted without unequivocal proofs. We have now used NMR spectroscopy (¹¹B, ¹³C, ¹⁵N and ²³Na NMR) to study the sodium amides of these two polycyclic boranes. In addition, one of the isomeric borates could be crystallized, and the X‐ray analysis revealed a cis‐,cis‐,trans configuration of the six‐membered rings reversing the original structural assignment.     

Hybridization of Long Pyridine‐Dicarboxamide Oligomers into Multi‐Turn Double Helices: Slow Strand Association and Dissociation,Solvent Dependence,and Solid State Structures

Oligoamides of 2,6‐diaminopyridine and 2,6‐pyridinedicarboxylic acid comprised of 5, 7, 9, 11, or 13 units and bearing 4‐isobutoxychains on all pyridine rings and tert‐butyl‐carbamate terminal groups have been synthesized stepwise, along with an 11 mer having benzyl‐carbamate terminal groups. The crystal structure of all five Boc‐terminated compounds has been obtained and shows a highly regular and conserved double helical hybridization motif of up to 3 complete turns for the 13 mer. Four pyridine units span one helical turn and define a helix pitch of ca 7 Å. Solution studies in CDCl₃ demonstrated that the Boc‐terminated oligomers strongly hybridize in this solvent, and that K_dim values increase with oligomer length. The K_dim values are 31000 and 7×10⁵ L mol^?1 for the 7 mer and the 9 mer, respectively, and are too high to be measured by NMR for the 11 mer and the 13 mer. Hybridization and dissociation kinetics at 2 mM proceed at decreasing rates upon increasing oligomer length. The rate was faster than minutes for the 7 mer, of the order of hours for the 9 mer, and days for the 11 mer and 13 mer. The same trend was observed in [D₅]pyridine but with considerably lower K_dim values and faster kinetics. The benzylcarbamate 11 mer was also found to hybridize into a double helix but with reduced K_dim values and faster kinetics compared to its Boc‐terminated analogue. Combined with previous studies, the results presented here frame a global understanding of the hybridization of these pyridinecarboxamide oligomers and provide useful guidelines for the design of other artificial double helices.