Comparative Structural Study of Three Tetrahalophthalic Anhydrides: Recognition of X···O(anhydride) Halogen Bond and πh···O(anhydride) Interaction

Structures of three tetrahalophthalic anhydrides (TXPA: halogen = Cl (TCPA), Br (TBPA), I (TIPA)) were studied by X-ray diffraction, and several types of halogen bonds (HaB) and lone pair···π-hole (lp···πh) contacts were revealed in their structures. HaBs involving the central oxygen atom of anhydride group (further X···O(anhydride) were recognized in the structures of TCPA and TBPA. In contrast, for the O(anhydride) atom of TIPA, only interactions with the π system (π-hole) of the anhydride ring (further lp(O)···πh) were observed. Computational studies by a number of theoretical methods (molecular electrostatic potentials, the quantum theory of atoms in molecules, the independent gradient model, natural bond orbital analyses, the electron density difference, and symmetry-adapted perturbation theory) demonstrated that the X···O(anhydride) contacts in TCPA and TBPA and lp(O)···πh in TIPA are caused by the packing effect. The supramolecular architecture of isostructural TCPA and TBPA was mainly affected by X···O(acyl) and X···X HaBs, and, for TIPA, the main contribution provided I···I HaBs.

Chalcone single crystals with red emission and photodimerization-triggered hopping behavior: the substituent effect and molecular packing effect

Chalcone single crystals with distinctively different emission color and photoinduced mechanical response are designed and fabricated via fine-tuning the donor substituents.

Three differently coloured polymorphs of 3,6-bis(4-chlorophenyl)-2,5-dipropyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione

In this paper, the conformational polymorphism of a chlorinated diketopyrrolopyrrole (DPP) dye having flexible substituents in a non-hydrogen-bonding system is reported. The propyl-substituted DPP derivative (PR3C) has three polymorphic forms, each showing a different colour (red, orange and yellow). All polymorphs could be obtained concomitantly under various crystallization conditions. The results of the crystal structure analysis indicate that PR3C adopts different conformations in each polymorph. The packing effect caused by the difference in the arrangement of neighbouring molecules was found to play an important role in the occurrence of the observed polymorphism. The thermodynamic stability relationship between the three polymorphs was identified by thermal analysis and indicates that the yellow polymorph is the thermally stable form. The results indicate that the yellow form and orange form are enantiotropically related, and the other polymorph is monotropically related to the others.

Investigation of the Optimal Percentage from Polyvinyl Alcohol on Flexural Strength of Cement Mortar Composite

Polyvinyl alcohol solution(PVA) proveded potential enhancement of the properties of cement mortar composite. This work investigated the effect of (w/c) and polymer-cement ratios (p/c) on the flexural strength of type I Portland cement mortar. A sand-cement ratio (s/c) of 1.25 and 0.5 by mass was used, and PVA powder was dispersed in water at (0.7%, 1%, 2%, and 3%) by weight of cement. The p/c solution was adjusted at five different values of 0.008, 0.012, 0.016, 0.020 and 30% covering relatively low and high values. Two types of curing were used; wet and dry curing. The study results demonstrated that flexural strength and significant water absorption properties of Portland cement mortar, as well as workability can be basically enhanced by the addition of PVA. Composite was prepared with optimum (p/c) 1.6% at concentration of 1% by mass under dry curing. The highest flexural strength was above twice the flexural strength of unmodified mortar. Also modified mortar samples illustrated that increasing of (p/c) causes reducing water absorption due to the packing effect caused by PVA, while mortar prepared at 0.1 and 0.3 w/c and (p/c) respectively, exhibited an increase in flexural strength which was more than the strength of unmodified mortar.

Beam Web-Side-Plate Connection Axial Performance

A number of beam web side plate connection configurations are analyzed under monotonic axial force. Parameters investigated include (i) gravity loads causing a beam shear up to 60% of the capacity, (ii) column lateral drift, (iii) beam lateral restraint along the length, (iv) packing effect represent the practice when plates do not align perfectly, and (v) cope length. For the analyses conducted, gravity shear forces up to 0.6 times of the cleat plate gross shear capacity, reduced the connection compressive axial strength by up to 15% compared to connections without gravity loads. The connection axial strength varied by 10% with lateral drifts of up to 2% and the increase or decrease depended on the relative directions of drift and axial force. Also, axial strength of double-coped WSP connection decreased linearly with increasing the cope length. Other parameters were found to have less than 2% effect on the web side plate axial strength. A general simple design method to assess axial strength of these connections is proposed.