Syntheses and characterization of mono- and di- N-hydroxyethylated tetraaza macrocycles containing eight C-methyl groups and their nickel(II) and copper(II) complexes

Abstract

New partially N-hydroxyethylated 14-membered tetraaza macrocycles 1,8-bis(2-hydroxyethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L 2) and 1-(2-hydroxyethyl))-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L 3) have been synthesized selectively by the one-step reaction of 2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L 1) with 2-hydroxyethyl bromide. The complexes [NiL 3] 2+, [CuL 2] 2+, and [CuL 3] 2+ have been prepared and characterized. The complex [CuL 2](ClO 4) 2 has a square-pyramidal coordination geometry with one apical oxygen atom; only one of the two hydroxyethyl groups is coordinated to the metal ion. Electronic absorption spectra of [CuL 3](ClO 4) 2 containing one hydroxyethyl pendant arm indicate that the geometry is similar to that of [CuL 2](ClO 4) 2. Unexpectedly, the nickel(II) complex [NiL 3](ClO 4) 2 has a severely distorted trigonal bipyramidal coordination geometry with the oxygen atom of the pendant arm at the equatorial position. The NiO bond distance of the nickel(II) complex is shorter, or not longer, than the NiN bond distances. The ligand in [CuL 2] 2+ is in the RRSS ( trans-III) configuration, as usual, whereas that in [NiL 3] 2+ has the RRRR ( trans-V) conformation. The coordination geometry and properties of [NiL 3] 2+ are quite different from those reported for other related nickel(II) complexes containing one functional pendant arm.