3-(2-Pyrazyl)-[1,2,4]triazolo[4,3-a]pyridine – A versatile ligand: Ambidenticity and coordination isomerism in mono- and polynuclear 3d transition metal complexes

The coordination behaviour of the new ligand 3-(2-pyrazyl)-[1,2,4]triazolo[4,3-a]pyridine (L2) has been studied. In the course of this investigation 12 complexes have been structurally characterised by single crystal X-ray diffraction, namely the discrete mononuclear complexes [FeII(L2)3](ClO4)2·1.25MeCN·1.25H2O (1·1.25MeCN·1.25H2O) and [FeII(L2)3](BF4)2·2MeCN·0.5H2O (2·2MeCN·0.5H2O), the 2D polymeric complex [CuII(L2)2](ClO4)2 (3), the 1D chain compounds [FeII2(L2)2(H2O)6(MeSO3)2](MeSO3)2 (6), [CoII(L2)2Cl2] (7a), [FeII(L2)2Cl2] (9) and [FeII(L2)2(NCS)2]·MeCN (13·MeCN) as well as the hydrogen-bonded and π–π-stacked mononuclear complexes [FeII(L2-κNpz4)2(NCS)2(MeOH)2] (10a), [FeII(L2-κNtp1)2(NCS)2(MeOH)2] (10b), [FeII(L2-κNpz4)2(NCSe)2(MeOH)2] (11), [FeII(L2-κNpz4)2(NCBH3)2(MeOH)2] (12a) and [FeII(L2-κNtp1)2(NCBH3)2(MeOH)2] (12b). The structural characterisation revealed a multitude of coordination modes for L2, which has been found to utilise all of its four potential donor atoms. Thus L2, acts as a unidentate ligand coordinating via Ntp1 or Npz4, as a bidentate Npz1,Ntp2-chelating ligand, as a bidentate Ntp1,Npz4-bridging ligand or as a terdentate ligand coordinating via Npz1,Ntp2,Npz4. Coordination isomerism has been observed in complexes 10 and 12.

Ligand 3-(2-pyrazyl)-[1,2,4]triazolo[4,3-a]pyridine (L2) forms a multitude of coordination modes by utilising all of its four potential donor atoms. It acts as a unidentate ligand coordinating via Ntp1 or Npz4, as a bidentate Npz1,Ntp2-chelating ligand, as a bidentate Ntp1,Npz4-bridging ligand or as a terdentate ligand coordinating via Npz1,Ntp2,Npz4.Figure optionsDownload as PowerPoint slide