Model Bridging Effects of Asymmetrical Triblock Copolymers

Summary: We have performed Monte Carlo simulations to study the bridging of symmetrical or asymmetrical triblock copolymers confined between two similar or different solid surfaces based on a simple lattice model. The influence of the molecular structure, surface separation, adsorption energy, chain composition, and the chain concentration on the fractions of chains with bridge, loop and dangling configurations are reported in detail. The results show that the largest bridging fraction is given only when symmetrical triblock copolymers are confined between two parallel surfaces with the same adsorption energy. The bridge fraction is decreased so long as the asymmetry of the copolymers or the difference between the two surfaces is enhanced. It was found also that the bridging fraction increases as the adsorption energy increases. The bridging fraction Ω_bridge under different separations, L_z, can be expressed as in various situations. On the other hand, by introducing a symmetry index ν, the influence of molecular structure of copolymers on the bridges can be illustrated approximately by a relation when the two surfaces are similar and the adsorption energy is not too high. Combining the two expressions, data of the bridge fractions for copolymers of different symmetries confined between surfaces with different separations can be described with a single equation, which, in some occasion, can be used for prediction.

Influence of molecular structure on the bridging fraction for .     

Thermal stability of polybenzoxazines with lanthanum chloride and their crosslinked structures

Lanthanum chloride (LaCl₃) was incorporated into five kinds of benzoxazines by different preparation methods. The thermal stability and the structures of polybenzoxazines were characterized by thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The evolved gases from the degradation process of polybenzoxazines were analyzed by FTIR. The results showed that the thermal stability and char yields of three kinds of polybenzoxazines containing LaCl₃ can be improved obviously. LaCl₃ has an important effect on the polymerization reactions of benzoxazines. More stable arylamine Mannich bridges were observed in the chemical structures of the polybenzoxazines. It is these structures that can effectively retard the volatilization of aniline derivatives and result in the improvement of the thermal stability of the polybenzoxazines.     

Halfsandwich Complexes Containing the Tetrathiotungstate Chelate Ligand. Crystal and Molecular Structure of Cp*Rh(PMe3)[(μ‐S)2WS2] (Cp* = η5‐Pentamethylcyclopentadienyl)

The reactions of Cp*M(PMe₃)Cl₂ (M = Rh ( 1a ), Ir ( 1b )) with (NEt₄)₂[WS₄] led to the heterodimetallic sulfido‐bridged complexes Cp*M(PMe₃)[(μ‐S)₂WS₂] (M = Rh ( 2a ), Ir ( 2b )), whereas the dimers [Cp*MCl(μ‐Cl)]₂ (M = Rh ( 4a ), Ir ( 4b )) reacted with (NEt₄)₂[WS₄) to give the known trinuclear compounds [Cp*M(Cl)]₂(μ‐WS₄) (M = Rh ( 5a ), Ir ( 5b )). Hydrolysis of the terminal W=S bonds converts 2a, b into Cp*M(PMe₃)[(μ‐S)₂WO₂] (M = Rh ( 3a ), Ir ( 3b )). Salts of a heterodimetallic anion, A[CpMo(I)(NO)(WS₄)] ( 6 ) (A⁺ = NEt₄⁺, NPh₄⁺) were obtained by reactions of [CpMo(NO)I₂]₂ with tetrathiotungstates, A₂[WS₄]. The complexes were characterized by IR and NMR (¹H, ¹³C, ³¹P) spectroscopy, and the X‐ray crystallographic structure of Cp*Rh(PMe₃)[(μ‐S)₂WS₂] ( 2a ) has been determined. The bond lengths and angles in the coordinations spheres of Rh and W in 2a (Rh···W 288.5(1) pm) are compared with related complexes containing terminal [WS₄^2—] chelate ligands.     

Nitridorhenium(V)‐Komplexe mit Dimercaptobernsteinsäuredimethylester. Präparation,Charakterisierung und Kristallstruktur von [Re{NC(CH3)2PPhMe2}(DMSMe2)2]

Nitridorhenium(V) Complexes with Dimercapto Succinic Acid Dimethylester. Preparation, Characterization, and Crystal Structure of [Re{NC(CH₃)₂PPhMe₂}(DMSMe₂)₂] Reaction of [ReNCl₂(Me₂PhP)₃] 1 with two equivalents of dimercaptosuccinic acid dimethylester (DMSMe₂) results in the formation of a neutral, diamagnetic rhenium(V)‐DMSMe₂ complex with a phenyldimethylphosphinoisopropyl group at the nitrido ligand as a consequence of a nucleophilic attack of the coordinated nitrido ligand on the solvent molecule. The formed complex 2 of the composition [Re{NC(CH₃)₂(Me₂PhP)}(DMSMe₂)₂] crystallizes in the triclinic space group P 1, a = 12.334(7), b = 12.412(7), c = 12.414(8) Å; α = 60.14(3)°, β = 67.98(3)°, γ = 80.63(6)°; Z = 2. Rhenium is located in a square‐pyramidal configuration of the donor atoms. The two meso‐DMSMe₂ ligands are in a syn‐endo conformation. The rhenium‐nitrogen bond (1.697(12) Å) is only slightly longer than typical Re–N bonding distances in nitrido complexes and comparable with other Re–N–C bonding distances. The addition of a solvent molecule is observed in acetone ( 2 ) as well as in methylethylketone ( 3 ). Moreover, a reaction of the nitrido group with the condensation product of ketone is found by mass spectrometry ([ReN{C(CH₃)(C₂H₅)CH₂C(O)C₂H₅(Me₂PhP)}(DMSMe₂)₂] 4 ).     

The Nitrido Borates Ln3B2N4 (Ln = La–Nd) and La5B4N9: Syntheses,Structures, and Properties

Single crystals of the lanthanoide nitrido borates Ln₃B₂N₄ (Ln = La–Nd) and La₅B₄N₉ have been obtained from reactions of lanthanoide metal powder, lanthanoide nitride powder, and hexagonal boron nitride in calcium chloride melts. The isotypic compounds Ln₃B₂N₄ belong to the space group Immm (#71), Z = 2, with the lattice parameters for La₃B₂N₄: a = 362.94(3), b = 641.25(6), c = 1097.20(8) pm; Ce₃B₂N₄: a = 356.20(3), b = 631.90(6), c = 1071.91(8) pm; Pr₃B₂N₄: a = 353.46(4), b = 630.04(13), c = 1079.04(23) pm and Nd₃B₂N₄: a = 351.52(4), b = 627.01(15), c = 1075.59(23) pm. The structure of La₅B₄N₉ has been determined in the space group Pbcm (#57), Z = 4, with a = 988.25(5); b = 1263.48(7), c = 770.33(4) pm. These two structure types resemble three kinds of nitrido borate anions, the oxalate analogue B₂N₄ of Ln₃B₂N₄, and the carbonate analogue BN₃ together with the six‐membered ring system B₃N₆ of La₅(BN₃)(B₃N₆). In contrast to the valence compound La₅B₄N₉ the compounds (Ln³⁺)₃(B₂N₄)^8–(e^–) contain one electron in the conduction band, yielding temperature independent paramagnetism for La₃B₂N₄. The calculated electronic structure is developed through the formation of B₂N₄^8– ions by dimerisation of two BN₂ units.     

Azido-Derivate des Pentamethylcyclopentadienyl-Vanadium(IV)-Fragments. Molekülstrukturen der Zweikernkomplexe [Cp*VCl(N3)(μ-N3)]2 und [Cp*V(N3)2(μ-N3)]2

Azido Derivatives of the Pentamethylcyclopentadienyl Vanadium(IV)-Fragment. Molecular Structures of the Binuclear Complexes [Cp*VCl(N₃)(μ-N₃)]₂ and [Cp*V(N₃)₂(μ-N₃)]₂ The stepwise reaction of Cp*VCl₃ with excess trimethylsilyl azide (Me₃Si–N₃) in solution leads to the paramagnetic, azido-bridged complexes [Cp*VCl₂(μ-N₃)]₂ ( 3 ), [Cp*VCl(N₃)(μ-N₃)]₂ ( 4 ) and [Cp*V(N₃)₂(μ-N₃)]₂ ( 5 ) which were characterized by their IR and mass spectra. The azide-rich binuclear complex 5 is also formed if a pentane solution of Cp*V(CO)₄ is stirred in the presence of excess Me₃Si–N₃ in an open vessel. According to the X-ray structure analyses both 4 and 5 are centrosymmetric molecules with a planar V(N)₂V four-membered ring. In the absence of free trimethylsilyl azide, solutions of 3 – 5 lose dinitrogen slowly; in the presence of traces of air, 5 is thereby converted to the diamagnetic, oxo-bridged complex [Cp*V(O)(N₃)]₂(μ-O) ( 6 ).     

Preparation and crystal structures of an ionic triple-hydrogen-bridged derivative of 9-BBN hydroborate zirconium(IV)

An ionic dinuclear triple-hydrogen-bridged 9-BBN hydroborate zirconium complex, [K(Et₂O)₄][{(μ-H)₂BC₈H₁₄}₃Zr(μ-H)₃Zr{(μ-H)₂BC₈H₁₄}₃] (1) was formed from the reaction of Zr{(μ-H)₂BC₈H₁₄}₄ with KH and aniline in diethyl ether. The molecular structure of compound 1 was determined by single-crystal X-ray diffraction analysis. Six 9-BBN hydroborate ligands are coordinated to two Zr atoms via two bridging H atoms, and two Zr atoms are connected by three bridging hydrogens in the anion part of this molecule. The distance of Zr?Zr is 3.1025(5) Å. The crystal structure of 1 suggests that agostic interactions between the zirconium metal center and α-C-H of the 9-BBN hydroborate ligand exist in the solid state. The Zr?H distances corresponding to the α-C-H?Zr agostic interactions are 2.579(4) Å and 2.743(4) Å.     

Synthesis, Structure and Fluorescent Pr.operty of a Novel 2-D Sheet Inorganicorganic Hybrid Cadmium Polymer [CdBr2（bpdo）]n

A novel 2-D sheet inorganic-organic hybrid cadmium polymer,[CdBr2(bpdo)]n (bpdo=N,N'-O,O-4,4'-bipyridine) has been hydrothermally synthesized and characterized by elemental analysis,IR and single-crystal X-ray diffraction. The crystal crystallizes in monoclinic,space group C2/c,with a=16.336(3),b=3.9904(5),c=18.479(3),β=91.640(6)°,Mr= 460.40,V=1204.1(3)3,Z=4,Dc=2.540 g/cm3,μ=8.439 mm-1,F(000)=864,R=0.0314 and wR=0.0733 for 1069 observed reflections (I > 2σ(I)). X-ray diffraction reveals that the title compound consists of the 2-D inorganic-organic hybrid sheet constructed from [CdBr2]n chains and bpdo bridges in the packing motif of…ABAB….The title compound exhibits intense blue photoluminescence in the solid state at room temperature.     

5-Arylmethylene-2,4-imidazolidinediones and 5-arylmethylene-2-thioxo-4-imidazolidinones derivatives: stereochemistry elucidation by H and C NMR

Derivatives of 5-arylmethylene-2,4-imidazolidinediones and 5-arylmethylene-2-thioxo-4-imidazolidinones were synthesized as potential aldose reductase inhibitors (ARI). The Z/E configuration was elucidated by homonuclear NOE difference spectra and by proton-carbon coupling constant measurement from ¹³C coupled spectra using GATEDEC and SFDEC programs.     

MNE Nitrido Bridges with Transition Metal Nitrogen Multiple Bonds and E = Phosphorus,Sulfur, and Chlorine

A compilation is given on new syntheses, properties, and structures of complexes with M≡N—E ? M=N=E nitrido bridges with transition metal nitrogen multiple bonds and participation of the main group elements E of phosporus, sulfur, and chlorine. 1. MNP: This atomic sequence is realized in phosphoraneiminato complexes with transition metals in high oxidation states and termal bond of the (NPR₃^—) ligand. A series of new complexes of this type is reported with M = zirconium, hafnium, molybdenum, tungsten, and rhenium, among these the homoleptic species [Hf(NPPh₃)₄] and [M(NPPh₃)₄]²⁺ with M = Mo and W. Therefrom the isolobal complexes [:N≡Mo(NPPh₃)₃], [:O≡W(NPPh₃)₃]⁺, [(O)₂Mo(NPPh₃)₂], and [(O)₃Re(NPPh₃)] are derived. 2. MNS: Adding to compounds with this atomic sequence, new complexes were developed on the basis of the functional ligand groups thionitrosyl ( a ), dinitridosulphate(II) ( b ), dinitridosulphate(IV) ( c ), and cyclothiazeno ( d ) (cyclo‐3, 5‐dithia‐2, 4, 6‐triazino):