X-RAY AND N-14, CL-35 NQR STUDY OF CRYSTALLINE DICHLOROANILINES AND DIMETHYLANILINES

To study intermolecular interactions in hydrogen bond systems, the cry stal structures of i,j-Cl2C6H3NH2, i,j = 2,3; 2,4; 2,6; 3,4; 3,5 and o f 3,4-(CH3)2C6H3NH2 have been determined. 2,3-Cl2C6H3NH2: tetragonal, I4(1)/a, Z=16, a=1930 pm, c=743 pm; 2,4-Cl2C6H3NH2: orthorhombic, P2(1 )2(1)2(1), Z=4, a=1554 pm, b=1126 pm, c=393 pm; 2,6-Cl2C6H3NH2: monocl inic, P2(1)/c, Z=4, a=1132 pm, b=410 pm, c=1543 pm, beta=99.97-degrees ; 3,4-Cl2C6H3NH2: orthorhombic, Pbca, Z=8, a=1527 pm, b=1592 pm, c=574 pm; 3,5-Cl2C6H3NH2, orthorhombic, P2(1)2(1)2(1), Z=4, a=1376 pm, b=12 20 pm, c=400 pm; 3,4-(CH3)2C6H3NH2: monoclinic, P2(1)/c, Z=8, a=639 pm , b=2747 pm, c=837 pm, beta=96.54-degrees. Cl-35 and N-14 nuclear quad rupole resonance (NQR) spectra were investigated by pulse and CW NQR e xperiments from 77 K up to the melting point. None of the studied subs tances shows a phase transition within the temperature range covered b y NQR. In all compounds the hydrogen bond scheme N-H..H is such, that the molecules are connected to chains and only one hydrogen atom of ea ch NH2 group participates in this formation. Many related compounds, f or which the structure is known, follow this rule. In the dichloroanil ines, the second hydrogen atom of the NH2 group forms a weak bond N-H. .Cl. In this way the chains are interconnected. Finally, Cl..Cl van de r Waals interactions are also present. Applying the free energy relati onship of Hammett to the NOR data, the interplay of NQR frequencies or nuclear quadrupole coupling constants, respectively, and hydrogen bon d distances is discussed.