Neutron and X-ray diffraction, inelastic neutron scattering, and solid-state ¹³C NMR investigations of polymorphic p-chlorophenylformamide: Absence of proton transfer along the intermolecular N-H⋯O hydrogen bond

Neutron and X-ray crystal structures of p-chlorophenylformamide (ClC ₆H₄NHCHO, 1) have been determined after recrystallization from methanol and acetone solvents. Acetone and methanol grown samples are polymorphic, where the central layer of a three layer asymmetric unit is partially (0.37:0.63) reversed within the acetone grown crystal. All structures reveal that the formamide group is essentially coplanar with the chlorophenyl ring. The possibility of hydrogen atom transfer between amide and iminol tautomers has been ruled out on the basis of crystallographic results and additional ¹³C CPMAS NMR and inelastic neutron scattering investigations. Only infinite chains of hydrogen-bonded formamide units are found in the crystal. Compound 1 crystallizes from methanol in the orthorhombic space group P2₁2₁2₁ (Mo Kα radiation; 173 K; Z = 4; a = 6.1356(2) Å, b = 9.5362(3) Å, c = 11.8990(4) Å; V = 696.2 ų) and (neutron radiation; 20 K; Z = 4; a = 6.0873(10) Å, b = 9.5095(15) Å, c = 11.814(5) Å; V= 683.9 ų). From acetone, a supercell is observed for crystalline 1, where 3a = c (P2₁2₁2₁; Mo Kα radiation; 173 K; Z = 12; a = 9.5704(2) Å, b = 11.9479(1) Å, c = 18.4555(2) Å; V= 2110.3 ų).