Studies on the metalamide bond. XIX. A comparison of molecular distortions in the crystal structures of [N,N′-bis(2′-pyridinecarboxamido)-1,2-benzene] nickel(II) with its 6′-methyl-substituted Analogue

Frederick S. Stephens*, Robert S. Vagg

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)

Abstract

[N,N′-Bis(pyridine-2′-carboxamide)-1,2-benzene]nickel(II) monohydrate, C18H14N4O3Ni, crystallizes in the monoclinic space group C2/c with a = 14.240(4), b = 20.071(3), c = 16.275(2) Å,β = 97.25(2)o, Z = 12 and its crystal structure has been refined to R = 0.033 for 3597 diffractometer data. [N,N′-Bis(6′-methylpyridine-2′-carboxamide)-1,2- benzene]nickel(II) monohydrate, C20H18N4O3Ni, crystallizes in the orthorhombic space group Pbca with a = 10.14(2) b = 17.12(2), c= 21.11(5) Å, Z = 8 and its crystal structure has been refined to R = 0.088 for 1979 photographic data. In both structures the nickel atoms are four coordinate with the ligands acting as N4 tetradentates. For the first mentioned complex the structure consists of two independent molecules one of which is constrained, by space group requirements, to have C2 (2) symmetry. These two molecules are closely similar and both exhibit nearly planar molecular arrangements with a small tetrahedral twist of up to 4o at the nickel atoms. In the second complex the methyl substitution at the 6′-pyridyl positions causes severe steric strain in the molecule which gives rise to a 14.9o tetrahedral twist at the nickel atom and approximately 25% pyramidal distortion at both amide nitrogen atoms. The resulting methyl-methyl separation of 3.26(1) Å is considerably less than the sum of the van der Waals radii for two such groups. This close separation leads to carbon-acid character for the methyl group protons which are shown to exchange for deuterons in NMR studies. A full analysis of the out-of-plane distortions and torsion angles of the two structures and a comparison with the previously reported analogous copper structures are made.

Original languageEnglish
Pages (from-to)165-171
Number of pages7
JournalInorganica Chimica Acta
Volume120
Issue number2
DOIs
Publication statusPublished - 15 Oct 1986

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