Neutron diffraction and vibrational spectroscopic study of single crystals of KH(D)(CHCl2COO)2

The hydrogen atoms in the short (2.498 Å) hydrogen bonds of potassium hydrogen bis-dichloroacetate are placed asymmetrically with respect to the oxygen atoms. The geometric mass effect (R 0.02 Å) is well within the range observed with this type of hydrogen bond. The thermal ellipsoids of the bridging protons are slightly elongated, the longer axis being at 40 ° with respect to the O(2)-O(4) direction. This coincides with the direction of the transition dipole moment of thev _a OH vibration. The two infrared components of this vibration are rather different, one (A_u) being very broad and intense and the other (B_u) only moderately broad. Thev _a OH/v _a OD ratio is small (1.05).     

Komplexe des zweiwertigen Molybdäns,Derivate des Oktahalodimolybdat(II)-Ions, 4. Mitt.: Darstellungen und Kristallstrukturen von zwei neutralen Komplexen mit 4-Methylpyridin

Mo₂Cl₄ Pic ₄·CHCl₃ (A) (Pic=4-methylpyridine) and Mo₂Br₄ Pic ₄ (B) crystallize in the monoclinic space group.A inC2/c (No. 15) witha=15.175 (4),b=10.847 (2),c=19.946 (6) and =104.52 (2)°;D _o=1.71 (2),D _c =1.72 gcm^–3 forZ=4.B inP2_l/n (No. 14) witha=9.270 (3),b=16.614 (5),c=9.305 (3) and =91.96 (5)°;D _o=2.03 (3),D _c =2.05 gcm^–3 forZ=2.Two halogens and 4-methylpyridines of the MoX ₂ Pic ₂ group are in the trans position. Mo–Mo bond lengths are 2.153 96) forA and 2.150 92) forB. Both molecules are situated on the inversion center resulting in the eclipsed configuration of the ligands around the molybdenum pair. The structure ofB has been refined to the conventionalR factors of 0.08 and 0.098. Disorder on the part of 4-methylpyridines and chloroform molecules stopped the refinement ofA at the endR value of 0.175.Mean Mo–X and Mo–N bonding distances are 2.40 (2), 2.25 (5) forA and 2.53 (3), 2.25 (1) forB.

     

Preparation,Chemical and Structural Characterization of Tungsten(III) Coordination Compounds: WCl3Pic3, WCl3Pic3 · 1/2 Pic,and (Pic)2HWCl4Pic2 (Pic = 4-methylpyridine)

(Pic)₂HWCl₄Pic₂ (Pic = 4-methylpyridine, C₅H₇N) was prepared by reduction of WCl₄Pic₂ with NaBH₄ in isopropanol. The compound crystallizes in the triclinic P1 space group with: a = 9.931(3), b = 14.127(5), c = 10.010(3) Å, α = 83.71(2), β = 99.35(2), γ = 99.90(2)°, Z = 2. The unit cell contains trans-WCl₄Pic₂^? octahedra and (Pic)₂H⁺. Hydrogen bond N? H…N within the cation is 2.71(2) Å. W? Cl and W? N(Pic) bonds (average) are 2.419(5) and 2.165(10) Å. (Pic)₂HWCl₄Pic₂ is very unstable towards oxidation. The first product is WCl₄Pic₂. (Pic)₂HWCl₄Pic₂ reacts further with 4-methylpyridine. The product is WCl₃Pic₃ which crystallizes from the cooled solutions of the ligand as WCl₃Pic₃ · 1/2 Pic. WCl₃Pic₃ and WCl₃Pic₃ · 1/2 Pic are isostructural with the corresponding molybdenum and chromium compounds with the mer structures. WCl₃Pic₃ is triclinic and WCl₃Pic₃ · 1/2 Pic monoclinic. WCl₃Pic₃ · 1/2 Pic decomposes in the inert atmosphere before 140°C to WCl₃Pic₃. Both neutral compounds are more stable towards oxidation compared to (Pic)₂HWCl₄Pic₂.     

New compounds in ring‐opening reaction of 5‐substituted epoxyisoindolines

Methoxy or nitro group present in the furan ring of tertiary alkenylfurfurylamine changes the expected results of both, the intramolecular [4+2]cycloaddition and the acid catalyzed ring‐opening reaction of the derived oxatricycloadduct. With a 5‐methoxy group, in addition to the expected 5‐methoxyisoindoline 3 , the corresponding hydroxy derivative 5 was obtained. On the other hand a 5‐nitro group changes the outcome of the reaction even more profoundly. Instead of the expected 5‐nitroisoindoline 12 , 5‐nitro‐substituted epoxy‐isoindoline 6 submitted to ring‐opening reaction with the mixture of hydrobromic and acetic acid, yielded the mixture of bromo‐substituted epoxy compounds 7,8, 9 and/or bromo‐substituted isoindolines 10 and 11 .     

Experimental analysis of contact for the indentation of a flat rounded punch

The ‘plane vs. plane’ contact involving flat punches has been the subject of many investigations, even in recent years, mainly due to the crucial role that such components play in phenomena, such as fretting fatigue and indentation tests. While the problem has been deeply approached from a theoretical point of view, there is a noteworthy lack of experimental verifications due to the limited number of laboratory techniques capable of supplying detailed information about contact parameters. In order to make a partial contribution towards gaining an understanding of such problems, this study proposes the investigation of flat rounded punch contact with an ultrasound-based technique, which exploits the properties of ultrasonic waves to be differently reflected by a contact interface depending on its stress state. A suitable setup was built in such a way as to ensure a good level of control of contact conditions, and the interface was scanned with a high-frequency ultrasonic transducer so as to acquire the reflection data. While the graphic processing of the ultrasonic coefficient of reflection may easily be displayed as a ‘contact map’, the quantitative accuracy of the method was also investigated by comparing experimental results with those obtained from a Finite Element model of the system. The results show a good level of agreement between the two approaches, thus confirming that the ultrasonic technique can be effectively employed to investigate many contact problems which to date have never (or scarcely) been experimentally validated.     

X-ray diffraction and vibrational spectra of the guanidine:maleic acid (1:1) complex—two crystal forms

From an equimolar mixture of guanidine and maleic acid, two different crystal modifications of guanidinium hydrogen maleate, CH₆N ₃ ⁺ ·C₄H₃O ₄ ^– , were isolated and their crystal structures determined using three-dimensional diffractometer data. Crystals of both forms are orthorhombic:Pca2₁,a=19.012(8)b=3.758(1),c=11.119(5) Å,Z=4 for form I;Fdd2,a=18.505(2),b=20.007(3),c=8.406(2) Å,Z=16 for form II. The structures were solved by direct methods and refined by full-matrix least squares to conventionalR values of 0.064 for form I and 0.043 for form II, with 488 and 605 reflections respectively. The structures consist of planar guanidinium cations C(NH₂) ₃ ⁺ and hydrogen-maleate residues C₄H₃O ₄ ^– . There are no significant differences in distances and angles within the guanidinium and hydrogen-maleate units. However, a substantial difference appears in the length and geometry of the intramolecular hydrogen bond OHO. The packing of cations and anions is also completely different in the two forms. Infrared and Raman spectra of the title compound are presented, and salient differences between them and the spectrum of the symmetrically bonded potassium hydrogen maleate are discussed briefly.