35Cl NQR, Crystal Structure, and Pyroelectricity of 2,3-Dichloro-1,4-naphthoquinone

The Cl NQR spectra of the two phases (phases I and II) of 2,3-dichloro-1,4-naphthoquinone were studied from 77 to 394 K. The crystal structure determination of the triclinic phase (phase I) was refined by single crystal X-ray diffraction. Phase I crystallizes in the space group C -P1̄. The unit cell (Z = 4) has the dimensions a = 1614.3(4) pm, 6 = 828.1 (3) pm, c = 733.2(3) pm, α = 67.02(1)°, β = 82.55(1)°, γ = 89.77(1)°. In the temperature range 439≦ TI /K≦447 a unidirectional phase transition I → II is observed. Phase II is orthorhombic, space group C -Pb2 a. The bond distances d and the Cl NQR frequencies correlate quite well according to the theory: v( Cl) (d( )) The multiplicity of the Cl NQR spectra is discussed. Pyroelectricity studies on phase II are reported. The pyroelectric coefficient depends little on the temperature, 8.3≦p /μCm ≦10.7 in 103 ≦T/K≦343.