Synthesis and crystal structure of a second polymorph of N,N′-bis(salicylidene)-3,5,3′,5′-tetramethyl-biphenyl-4, 4′-diamine

The Schiff base compound N,N′-bis(salicylidene)-3,5,3′, 5′-tetramethyl-biphenyl-4,4′-diamine was synthesized and crystal structure was determined by single-crystal X-ray diffractometry. The result shows that there is another polymorphic form (B) in structure besides published one (A) [1]. In structure B, there are four aromatic rings. The dihedral angles between the phenol rings and the adjacent dimethylbenzene rings are distinctly larger than that formed by the dimethylbenzene rings, possibly as a result of the steric hindrance of the methyl groups and the presence of intramolecular O-H...N hydrogen bonds. The remarkable defference between A and B lies in the angles of C1-C6 ring and C25-C30 ring, which are 51.64(13)° and 7.40(7)° in B and A, respectively. Crystal data for the title compolex C ₃₀H₂₇N₂O₂: Monoclinic, P2(1)/c, a = 14.346(3) Å, b = 12.258(2) Å, c = 14.265(3) Å; β = 99.515(4)°, V = 2474.1(7) ų, Z = 4.