Di- and trinuclear complexes with the mono- and dianion of 2,6-bis(phenylamino)pyridine: High-field displacement of chemical shifts due to the magnetic anisotropy of quadruple bonds

The monoanion of 2,6-bis(phenylamino)pyridine (HBPAP(-)) has been found to support quadruply bonded Cr-2(4+) and Mo-2(4+) units in Cr-2(HBPAP)(4) (1) and Mo-2(HBPAP)(4) (2). The corresponding dianion BPAP(2-) was able to stab ilize the trinuclear complexes, (TBA)(2)Cr-3(BPAP)(4) (3) and (TBA)(2)Ni-3( BPAP)(4) (4), where TBA is the tetrabutylammonium cation. The dinuclear com plexes have the typical paddlewheel configuration with Cr-Cr distances of a bout 1.87 Angstrom and a Mo-Mo distance of 2.0813(5) Angstrom and exhibit a high-field displacement of the corresponding N-H signals caused by the mag netic anisotropy of the quadruple bonds. For the trinuclear complexes, 3 ha s a linear chain of three chromium atoms arranged in an unsymmetrical fashi on with two chromium atoms paired to give a quadruply bonded unit (Cr-Cr di stance: 1.904(3) Angstrom) and an isolated, square planar Cr-II unit at 2.5 89(3) Angstrom from the dimetal unit. On the other hand, the three nickel a toms in 4 are evenly spaced, having Ni...Ni distances of 2.3682(8) Angstrom . The trinuclear compounds show a twisted conformation with an overall tors ion angle of about 30 degrees.