Single Crystal C1 NQR of 2,3,4,4-Tetrachloro-l-oxo-l,4-dihydronaphthaline and of 2,2,3,4-Tetr achloro-1 -oxo-1,2-dihy dronaphthaline *

2,3,4,4-Tetrachloro-l-oxo-l,4-dihydronaphthaline, ß-TKN, crystallizes in the orthorhombic space group D ^ P n m a with Z = 4, and the C1 N Q R spectrum consists of three lines with an intensity ratio of 2:1:1. The crystal structure of 2,2,3,4-tetrachloro-l-oxo-l,2-dihydronaphthaline, a-TKN, is described in literature as belonging to the polar space group C ^ P ^ with Z = 2. In contradiction to the reported space group and Z, we observed a three line C1 NQR spectrum with an intensity ratio of 2:1:1. Therefore, the crystal structure of a -TKN was redetermined at 7 = 296 K: space group C^ h -P2 1 /m, Z = 2, a = 888.4 (2) pm, b = 692.3 (2) pm, c = 869.6 (2) pm, >3 = 91.483 (5)°. The nuclear quadrupole coupling tensors have been investigated using a 4 n Zeeman NQR goniometer and FT NQR for tracing the zero splitting cones. According to the crystal structure of ß-TKN, two symmetry related zero splitting cones have been found for Cl, two for Cl, and four for Cl (4 ) ( 7 = 2 9 7 K). From the single crystal Zeeman split NQR measurements of a -TKN one zero splitting cone has been found for Cl, one for Cl, and two for CI (2) ( 7 = 2 9 0 K). The asymmetry parameters t] and the direction cosines of the principal axes <PXX, and & : z of the nuclear quadrupole coupling tensors have been determined. The results are: CI", v (C1), e 2 Q q h 1 (C1), rj (C1) for ß T K N (at 7 = 2 9 7 K): Cl, 37.442 MHz, 74.469 MHz, 0.184; Cl, 36.854 MHz, 73.083 MHz, 0.160; Cl , 4 ) , Cl , 4 , 38.685 MHz, 77.307 MHz, 0.070 and for a -TKN (at 7 = 290 K): Cl, CI' ' ' , 38.297 MHz, 76.501 MHz, 0.086; Cl, 36.943 MHz, 73.700 MHz, 0.123; Cl, 36.311 MHz, 72.314 MHz, 0.160. By comparing the crystal structures and the C1 NQR results, the C C l bonds in the title compounds are discussed.