Homo‐ and Hetero‐Dinuclear Anion Complexes

The tripodal system 4 , in which urea fragments are appended to the three terminal amine nitrogen atoms of a tris(2‐aminoethyl)amine (tren) subunit, includes a Cu II ion and two anions X − , according to a cascade mechanism through three well defined stepwise equilibria in a DMSO solution. The first anion X − (halide, N 3 − , NCS − , NO 2 − , H 2 PO 4 − ) seeks the Cu II centre coordinated by the tren moiety; the second anion X − interacts with the trisurea cavity, but this occurs only if the stronger H‐bond acceptors, such as N 3 − and H 2 PO 4 − , are used. Binding of the second X − ion is favoured by the preorganising effect exerted by the metal and disfavoured by the steric and electrostatic repulsions between the anions. Under the appropriate conditions, heterodinuclear complexes of formula [Cu II ( 4 )(Cl)(H 2 PO 4 )] can be obtained in solution, in which Cl − is bound to the metal centre and H 2 PO 4 − interacts with the trisurea compartment.