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

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 (L2) and 1-(2-hydroxyethyl))-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L3) have been synthesized selectively by the one-step reaction of 2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L1) with 2-hydroxyethyl bromide. The complexes [NiL3]2+, [CuL2]2+, and [CuL3]2+ have been prepared and characterized. The complex [CuL2](ClO4)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 [CuL3](ClO4)2 containing one hydroxyethyl pendant arm indicate that the geometry is similar to that of [CuL2](ClO4)2. Unexpectedly, the nickel(II) complex [NiL3](ClO4)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 [CuL2]2+ is in the RRSS (trans-III) configuration, as usual, whereas that in [NiL3]2+ has the RRRR (trans-V) conformation. The coordination geometry and properties of [NiL3]2+ are quite different from those reported for other related nickel(II) complexes containing one functional pendant arm.