Spectroscopic Properties and Crystal Structure of a tetraaza[14]annulene Nickel(II) Complex Containing a Strapped Pyridine Group

Abstract

The reaction between a tetraaza[14]annulene (H₂tmtaa) and 3.3′-(2.6-pyridyldimethyleneoxy)dibenzoylchloride hydrochloride (Pydbe) led to the corresponding compound (H₂stmtaa) with a strapped pyridine group. The nickel(II) complex (Ni(stmtaa)) has been prepared from H₂stmtaa and nickel(H) acetate. The mass spectra exhibit the molecular ion peaks caused by the strapped products, respectively. The infrared spectra reveal the strong stretching modes of C[dbnd]O in the range of 1645–1660 cm⁻¹. The structure of Ni(stmtaa) has been determined by X-ray single crystal diffraction. The crystal belongs to a monoclinic system and the space group is C2/m. The nickel(II) is coordinated through four nitrogen atoms of stmtaa to form a four-coordinate square-planar configuration. The complex has a large cavity. The average bond length of Ni to the four nitrogen atoms of stmtaa is 1.854(4) A and is very short. The displacement of the nickel(II) relative to she plane of the four nitrogen atoms of stmtaa is 0.010(1) A which is effectively coplanar. The ¹H and ¹³C NMR spectra also confirm the structures of the strapped compounds.