Abstract2,3,4,4-Tetrachloro-1-oxo-1,4-dihydronaphthaline, ß-TKN, crystallizes in the orthorhombic space group D1 6 2 h - Pnma with Z = 4, and the 35Cl NQR spectrum consists of three lines with an intensity ratio of 2:1:1. The crystal structure of 2,2,3,4-tetrachloro-1-oxo-1,2-dihydronaphthaline, α-TKN, is described in literature as belonging to the polar space group C22 - P 21 with Z = 2. In contradiction to the reported space group and Z, we observed a three line 35Cl NQR spectrum with an intensity ratio of 2:1:1. Therefore, the crystal structure of α-TKN was redetermined at 7 = 296 K: space group C22h-P21/m, Z = 2, a = 888.4 (2) pm, b = 692.3 (2) pm, c = 869.6 (2) pm, β = 91.483 (5)°. The nuclear quadrupole coupling tensors have been investigated using a 4 π Zeeman NQR goniometer and FT NQR for tracing the zero splitting cones. According to the crystal structure of β-TKN, two symmetry related zero splitting cones have been found for Cl(2), two for Cl(3), and four for Cl(4) ( T = 297 K). From the single crystal Zeeman split NQR measurements of α-TKN one zero splitting cone has been found for Cl(3), one for Cl(4), and two for CI(2) (T=290 K).The asymmetry parameters η and the direction cosines of the principal axes Φxx, and Φyy, and Φzz of the nuclear quadrupole coupling tensors have been determined. The results are: Cl(j), v (35Cl(j)), e2 Q q h -1 (35Cl(j)), η(35Cl(j)) for β-TKN (at T = 297 K): Cl(2), 37.442 MHz, 74.469 MHz, 0.184; Cl(3), 36.854 MHz, 73.083 MHz, 0.160; Cl(4) , Cl(4'), 38.685 MHz, 77.307 MHz, 0.070 and for α-TKN (at T = 290 K): Cl(2), CI(2'), 38.297 MHz, 76.501 MHz, 0.086; Cl(3), 36.943 MHz, 73.700 MHz, 0.123; Cl(4), 36.311 MHz, 72.314 MHz, 0.160. By comparing the crystal structures and the 35Cl NQR results, the C-Cl bonds in the title compounds are discussed.
