Crystal structure and C—Cl bond properties of 2,6-dichloroacetanilide, 2,6-Cl2C6H3NHCOCH3, phase I and phase II. An X-ray and 35Cl nuclear quadrupole resonance single-crystal study

Abstract

The crystal structures of 2,6-dichloroacetanilide, 2,6-Cl₂C₆H₃NHCOCH₃, in the low-temperature phase II and high-temperature phase I have been determined at 295 K. [Phase II: C⁵_2h(P2₁/c); Z= 4; ρ_calc= 1.475 Mg m^–3; a= 783.4(2) pm, b= 1531.9(4) pm, c= 897.5(2) pm, β= 121.45(1)°; R_W= 0.041. Phase I: D⁴₂(P2₁2₁2₁); Z= 4; ρ_calc= 1.416 Mg m^–3; a= 1726.8(4) pm, b= 1167.4(3) pm, c= 474.9(2) pm; R_W= 0.055.] The molecular geometry is very little influenced by the difference in packing between phase I and phase II. ν(³⁵Cl)=f(T) was determined for both phases from 77 K up to the melting point/transition point. Single-crystal Zeeman split ³⁵Cl n.q.r. investigations at T= 295 K revealed for (³⁵Cl⁽²⁾)_II: e²ϕ_zzQh^–1= 70.435(4)MHz; η= 0.1214(15); for (³⁵Cl⁽⁶⁾)_II: e²ϕ_zzQh^–1= 70.244(4)MHz; η= 0.1031(15); for (³⁵Cl⁽²⁾)_I: e²ϕ_zzQh^–1= 69.674(4)MHz; η= 0.1293(15); for (³⁵Cl⁽⁶⁾)_I: e²ϕ_zzQh^–1= 68.890(4)MHz; η= 0.1307(15). The principal axes ϕ^(j)_zz nearly coincide with the bond directions C^(j)—Cl^(j) in both phases. There is a small widening of the angle [ϕ_zz(³⁵Cl⁽²⁾), ϕ_zz(³⁵Cl⁽⁶⁾)] in comparison with the value of the angle (C⁽²⁾—Cl⁽²⁾, C⁽⁶⁾—Cl⁽⁶⁾) of the crystal structure. The influence of the —NHCOCH₃ group on η and on the orientation of the axes ϕ_xx and ϕ_yy is discussed for both phases and is compared with the results reported for 2,3,6-Cl₃C₆H₂OCOCH₃.