Steric constraints imposed by triazamacrocyclic ligands. Crystal and molecular structure of two copper(II) complexes with triazamacrocyclic ligands : μ-chloro-μ-hydroxo-bis(1,5,9-triazacyclododecane)dicopper(II) perchlorate and bromo-(1,5,9-triazacyclotetradecane)copper(II) perchlorate