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Paper | Special issue | Vol 74, No. 1, 2007, pp.913-925
Published online, 7th December, 2007
DOI: 10.3987/COM-07-S(W)86
Synthesis and Characterization of 1-(2H-Tetrazol-5-yl)-1,4,7,10-tetraazacyclododecane and Its Zn(II), Ni(II) and Cu(II) Complexes

Kristina Woinaroschy, Andrei Ursu, and Burkhard König*

*Department of Chemistry, University of Regensburg, Universitätsstraße 31, D-93040 Regensburg, Germany

Abstract

As part of an ongoing effort to develop new metal complexes of tetraazamacrocycles with novel properties in coordination or functionalization we report here the synthesis of a new derivative of 1,4,7,10-tetraazacyclododecane (cyclen) with a tetraazole moiety directly bound to the azamacrocycle. The new ligand was obtained by reaction with cyanogen bromide giving the cyanamide, followed by a [2+3] cycloaddition with NaN3 to yield the tetraazole. The ligand and its Zn(II), Ni(II) and Cu(II) complexes were fully characterized by analytical methods. X-ray structure analysis of the Ni(II) compound shows the formation of a stable dimer by coordination of each of the two tetraazole substituents to the neighboring metal cation. Potentiometric titrations of the metal complexes indicate a possible conversion of the monomer to the dimeric structure in solution and show the pKa of the NH-atom on the tetraazole substituent to be between 4.03 and 5.3 depending on the metal ion coordinated by cyclen.