Synthesis and Some First‐Row Transition‐Metal Complexes of the 1,2,4‐Triazole‐Based Bis(terdentate) Ligands TsPMAT and PMAT

The employment of a strategy based on nucleophilic substitution, rather than Schiff base condensation, for the preparation of 1,2,4‐triazole‐based ligands has been investigated and has led to the synthesis of two new ligands, 4‐amino‐3,5‐bis{[ N ‐(2‐pyridylmethyl)‐ N ‐(4‐toluenesulfonyl)amino]methyl}‐4 H ‐1,2,4‐triazole (TsPMAT, 14 ) and 4‐amino‐3,5‐bis{[(2‐pyridylmethyl)amino]methyl}‐4 H ‐1,2,4‐triazole (PMAT, 15 ). These are the first examples of bis(terdentate) ligands incorporating the 1,2,4‐triazole unit. TsPMAT ( 14 ) forms a dinuclear 2:2 complex with Co(BF 4 ) 2 ⋅ 6 H 2 O even when reacted in a metal‐to‐ligand molar ratio of 2:1. Similarly, the reaction of PMAT ( 15 ) with Mn(ClO 4 ) 2 ⋅ 6 H 2 O or M(BF 4 ) 2 ⋅ 6 H 2 O (M=Fe, Co, Ni, Zn) in a ligand‐to‐metal molar ratio of 1:1 has afforded a series of complexes with the general formula [M II 2 (PMAT) 2 ]X 4 . The metal centres in these complexes of TsPMAT ( 14 ) and PMAT ( 15 ) are encapsulated by two ligand molecules and doubly bridged by the N 2 units of the 1,2,4‐triazole moieties, which gives rise to N 6 coordination spheres that are strongly distorted from octahedral, as evidenced by the X‐ray crystal structure analyses of [Co II 2 (TsPMAT) 2 ](BF 4 ) 4 ⋅ 6 MeCN ( 24⋅ 6 MeCN) and [Fe II 2 (PMAT) 2 ](BF 4 ) 4 ⋅ DMF ( 27⋅ DMF). Studies of the magnetic properties of [Co II 2 (TsPMAT) 2 ](BF 4 ) 4 ⋅ 4 H 2 O ( 24⋅ 4 H 2 O), [Mn II 2 (PMAT) 2 ](ClO 4 ) 4 ( 26 ), and [Co II 2 (PMAT) 2 ](BF 4 ) 4 ( 28 ) have revealed weak antiferromagnetic coupling ( J =−3.3, −0.16, and −2.4 cm −1 , respectively) between the two metal centres in these complexes.