Stereochemistry of metal tetramethylcyclam complexes directed by an unexpected anion effect

Metal(TMC) complexes (TMC = tetramethylcyclam) exclusively form trans-I diastereoisomers; thus, little is known about the trans-III isomers. Herein, we report a new method to prepare the trans-III-[Cu(TMC)](2+) complex via an anion effect. Our crystallo-graphic, spectroscopic, and computational analyses validated that [Cu(TMC)](NO3)(2) produced the trans-III complex, different from the trans-I structure of [Cu(TMC)](ClO4)(2).