Molecules NAr3 with planar stereochemistry at N and canted Ar rings can form the intermolecular sixfold aryl embrace (6AE). The presence of 3-methyl groups on the aryl groups enhances the stabilisation of the 6AE, by contributing to the EF motifs which comprise it. Analysis of the crystal packing of four tritolylamines, N,N,N-tris(4-methylphenyl)amine [444TTA], N-(3-methylphenyl)-N,N-bis(4-methylphenyl)amine [344TTA], N,N-bis-(3-methylphenyl)-N-(4-methylphenyl)amine [334TTA] and N,N,N-tris(3-methylphenyl)amine [333TTA], reveals the presence of (333TTA)2 dimers maintained by an excellent 6AE, an unprecedented almost linear chain of repeated 6AE in 334TTA (cryst), and poorly formed embrace motifs in 344TTA (cryst), and 444TTA (cryst). Calculated intermolecular potentials for the actual or possible 6AE embraces formed by 333TTA, 334TTA and 444TTA confirm the stabilisation of the 6AE by 3-methyl groups, and it is estimated that each such methyl group augments the stabilisation of the underlying 6AE embrace by ca 5 kJ mol−1. The dominant dimerisation that occurs in crystalline 333TTA is reflected in the phase change enthalpies for the four isomers. The enthalpy of sublimation of 333TTA (51 kJ mol−1) is ca 45 kJ mol−1 less than the enthalpies of sublimation of 334TTA (97 kJ mol−1), 344TTA (98 kJ mol−1) and 444TTA (93 kJ mol−1), which leads to the hypothesis that (333TTA)2 dimers occur in the gas phase at ambient pressure. Mass spectrometric attempts to detect (333TTA)2(g), as [(333TTA)2]+, were unsuccessful, possibly due to dissociation under high vacuum. The unknown crystal packing of tris(3,5-dimethylphenyl)amine is predicted to be dominated by linear chains of methyl-stabilised 6AE.
