1,4,7-Triazacyclononane-N,N',N''-triacetate (TCTA), a new hexadentate ligand for divalent and trivalent metal ions. Crystal structures of [CrIII(TCTA)], [FeIII(TCTA)], and Na[CuII(TCTA)].bul.2NaBr.bul.8H2O