Structural consequences of the introduction of 2,2′-bipyrimidine as auxiliary ligand in triazolopyrimidine-based transition metal complexes. In vitro antiparasitic activity

Abstract Five new metal complexes containing 1,2,4-triazolo[1,5- a ]pyrimidine derivatives and the chelating-bridging ligand 2,2′-bipyrimidine have been synthesized and structurally characterized for Cu(II), Zn(II) and Cd(II) ions. Three different 1,2,4-triazolo[1,5- a ]pyrimidine ligands have been used: the unsubstituted (tp), 5,7-dimethylated (dmtp) and 7-amine substituted (7atp) derivatives. In all metal complexes, triazolopyrimidines coordinate monodentately via N3, while the versatile binding behaviour of 2,2′-bipyrimidine ligand (bpym) leads to mononuclear units [Cd(tp)(bpym) 2 (H 2 O)](ClO 4 ) 2 ( 2 ) and [Cu(dmtp) 2 (bpym)(H 2 O) 2 ](ClO 4 ) 2 ·H 2 O ( 3 ), dinuclear species [Cu 2 (tp) 2 (bpym) 2 (μ-bpym)(ClO 4 ) 2 ](ClO 4 ) 2 ( 1 ) and [Zn 2 (7atp) 4 (μ-bpym)(H 2 O) 4 ](ClO 4 ) 4 ·2(7atp) ( 5 ) and the helicoidal chain-like complex {[Cd(dmtp)-(H 2 O)(μ-bpym) 2 Cd(dmtp) 2 ](ClO 4 ) 4 ·dmtp·H 2 O} n ( 4 ). Different supramolecular motifs are originated in the crystal structures of compounds 2 , 3 and 5 by hydrogen bonds formation and π–π interactions, being the latter especially relevant. A weak antiferromagnetic coupling occurs across bpym-bridge for copper(II) dimer 1 ( J  = −7.2 cm −1 ). In order to evaluate the chemotherapeutic potential of the non-cadmium complexes ( 1 , 3 and 5 ), they have been tested in vitro against Leishmania infantum , Leishmania braziliensis and Trypanosoma cruzi , which cause leishmaniasis and Chagas disease, respectively.