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Conformation and Crystal and Molecular Structure of N-2-biphenyl-(2-hydroxy-1-salicylaldimine) and its Ni(II) Complex

Schiff base class of compounds as well as their transition metal complexes have been comprehensively investigated for years due to their role in the biological systems, apprehension of the conformational polymorphism, their properties as liquid crystals etc. The type of the substituent - alkyl or aryl - on the azomethine nitrogen of salicylaldimine is crucial for the stereochemistry of either free ligands or metal complexes. Salicylaldimines having as bulk as possible aryl substituent derived from amines with NH2 group in an "awkward" position, as in the case of 2-aminobiphenyl, are of special interest. The N-substituent can effect remarkably the magnetic, dielectric, spectral, thermal and other ligand and metal complex physical and chemical properties. The most pronounced influence to the stereochemistry of the ligand upon coordination to the metal centre displays in the N-substituent spatial orientation in relation to the chelate plane. An additional feature typical for 2-biphenyl is the existence of two steps of conformational freedom. The impact to the metal centre coordination sphere alternation should be taken in consideration as well. Compound 1: C19H15NO, Mr = 261.33, Monoclinic, Space group P 21/n, a = 11.922(3) A, b = 10.147(3) A, c = 24.547(7) A, beta = 93.51(3)o, V = 2963.9(14) A 3, Z = 8, Dx = 1.171 gcm-3, lambda(MoKa) = 0.7107 A. Final uncertainty factors were: R = 0.058, wR = 0.082 and S = 1.03 for 2206 unique observed reflections with Inet gt 2s(Inet) and 379 variable parameters. Compound 2: C38H28N2NiO2, Mr = 603.36, Triclinic, Space group P-1, a = 8.131(6) A, b =9.951(7) A, c = 10.983(3) A, alpha = 111.05(7)o, beta = 111.04(4)o, gamma = 95.31(8)o, V = 748.6(8) A3, Z = 1, Dx = 1.338 gcm-3, lambda(MoKa) = 0.7107 A, mi(MoKa) = 0.68 mm-1 R = 0.048 for 1197 reflections with Inet gt 2s(Inet). Final uncertainty factors were: R = 0.039, wR = 0.069 and S = 1.05 for 2774 unique observed reflections with Inet gt 2s(Inet) and 196 variable parameters. Compound 1 asymmetric unit contains two crystallographically independent molecules A and B with 2-biphenyl interplanar benzene rings angles 57.7(3)o (molecule A) and 41.4(4)o (molecule B). Both A and B molecules are present in the form of an enol/imine tautomer. The molecule of compound 2 has imposed crystallographic symmetry with nickel atom laying in the inversion centre, and O and N chelate ring donor atoms and corresponding symmetry depending ones being positioned trans to each other. The form of the metal atom coordination polyhedron is square-planar. The compound 2 molecules possess the stepped conformation with chelate rings perpendicular separation amounting 0.74 A.

N-biphenylsalycilaldimine; nickel; crystal structure

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