On the Persistence of Molecular Symmetry in the Solid State and the Role of Molecular Group Dipole Moments. Centrosymmetry in Bis‐(Chloromethyl)benzenes

Abstract

The crystal structures and the 35Cl NQR spectra of 1,4‐bis(chloromethyl)‐2,3,5,6‐tetrachlorobenzene, 1,4‐(CH2Cl)2C6Cl4; 1,4‐bis(chloromethyl)‐2,3,5,6‐tetramethyl‐benzene, 1,4‐(CH2Cl)2C6(CH3)4; 1,4‐bis(chloromethyl)benzene, 1,4‐(CH2Cl)2C6H4; 1,2‐bis(chloromethyl)benzene, 1,2‐(CH2Cl)2C6H4 are reported. – The compounds 1,4‐(CH2Cl)2C6Cl4 and 1,4‐(CH2Cl)2(CH3)4 are isostructural, space group C–P1, Z = 1. 1,4‐(CH2Cl)2C6Cl4: a = 893.1(4) pm, b = 655.1(3) pm, c = 494.5(2) pm, α = 98.32(2)°, β = 96.87(2)°, γ = 103.60(2) 92°; 1,4‐(CH2Cl)2C6(CH3)4: α = 902.3(4) pm, b = 809.4(4) pm, c = 442.5(2) pm, α = 87.38(2)°, β = 83.02(2)°, γ = 65.00(2)°. 1,4‐(CH2)2C6H4 crystallizes monoclinic, C–P21/c, Z = 2, a = 848.8(4) pm, b = 465.0(2) pm, c = 1042.2(5) pm, β = 99.21(2)°. 1,2‐(CH2Cl)2C6H4 is noncentrosymmetric, orthorhombic, C–Fdd2, Z = 8, a = 1562.0(4) pm, b = 1358.0(3) pm, c = 790.4(2) pm. – The 35Cl NQR spectra of 1,4‐(CH2Cl)2C6(CH3)4, 1,4‐(CH2Cl)2C6H4, and 1,2‐(CH2Cl)2C6H4 are singlets, with negative temperature coefficients dν(35Cl)/dT over the temperature range 77 K–Tmelt and the frequencies are in the range 34.4 ≥ ν(35Cl)/MHz ≥ 31.8. 1,4‐(CH2Cl)2C6Cl4 shows a 35Cl NQR triplet, with negative temperature coefficients for 77 ≤ T/K ≤ 420, 37.5 ≥ ν(35Cl)/MHz ≥ 33.8, too. In this compound a phase transition occurs, with a wide hysteresis, Tc, up = 366 K, Tc, down = 328 K. The inductive effect on the 35Cl NQR in the CH2Cl group is strong. – In molecular crystals the complete symmetry of the free molecule seldom persists in the solid state. The molecular symmetry in the condensation process is fully or partially lost due to the van der Waals interaction of neighboring molecules. The compensation of the partial dipole moments of the two chloromethyl group in para position retains the molecular symmetry Ī in the solid phases. It will be discussed that in benzene derivatives either Ī, m or 2 are the “hard” symmetry elements, preserved in the solid state.

Can simple ‘molecular’ corrections outperform projector augmented‐wave density functional theory in the prediction of 35Cl electric field gradient tensor parameters for chlorine‐containing crystalline systems?

“…This molecule is also commonly referred to as α , α ′‐dichloro‐ o ‐xylene. At the time of writing, only one crystal structure for this chemical appears in the CSD, which is listed under the refcode JUZDIR 44 . There are two chlorine atoms in the molecular building block, but they are symmetry related in the crystal structure (i.e., Z ′ = 0.5), and so therefore, only one set of EFG tensor parameters can be measured when using powdered samples of this material.…”

“…At the time of writing, only one crystal structure for this chemical appears in the CSD, which is listed under the refcode JUZDIR. 44 There are two chlorine atoms in the molecular building block, but they are symmetry related in the crystal structure (i.e., Z 0 = 0.5), and so therefore, only one set of EFG tensor parameters can be measured when using powdered samples of this material. The crystal structure was determined using XRD data at room temperature and resulted in an R-factor of 4.04%.…”

“…For example, CLACAM03 43 is the CSD refcode that specifies the crystal structure selected for the α form of 2‐chloroacetamide. Similarly, the crystal structures for the other systems considered herein are JUZDIR 44 for 1,2‐bis(chloromethyl)benzene, EWUZED 45 for 4‐chloro‐ dl ‐phenylalanine, FUYTEY 46 for trichloroborazine, WERNUF 47 for 2,4′‐dichloroacetophenone, QQQAUG09 48 for chlorothiazide, CSUCIM 49 for N ‐chlorosuccinimide, BAWNOC 50 for p ‐tetrachlorodicyanobenzene and AKUVUA 51 for transplatin. The crystal structure of WCl 6 was taken from the ICSD, and the numeric code representing this structure is 425147 52 …”