Rare examples of diphenoxido-bridged trinuclear NiII2FeIII complexes with a reduced salen type Schiff base ligand: Structures and magnetic properties

Abstract Three new trinuclear hetero-metallic complexes, [(NiL R ) 2 Fe(N 3 ) 3 ] ( 1 ), [(NiL R (H 2 O)) 2 Fe(C 6 H 5 CH 2 CO 2 ) 2 ]·(HSO 4 ) ( 2 ) and [(NiL R (H 2 O)) 2 Fe(C 6 H 5 CO 2 ) 2 ]·(HSO 4 )·(H 2 O)·(CH 2 Cl 2 ) ( 3 ) have been synthesized using [NiL R ] as a “metalloligand” (where H 2 L R  = N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine). All complexes have been characterized by elemental analysis, spectroscopic methods, single crystal XRD and magnetic study. In the angular trinuclear units of 1 , the two terminals [NiL R ] coordinate through double phenoxido bridges to the central Fe III ion which is penta-coordinated having terminally coordinated azide ion. The two terminal Ni II centers are connected to each other and also to neighbouring units through μ 1,3 -azido bridges to form an alternating chain. On the other hand, complexes, 2 and 3 are linear discrete trinuclear species [Ni II –Fe III –Ni II ] in which two terminal octahedral [NiL R ] units coordinate to the central octahedral Fe III ion, located on a crystallographic centre of symmetry, through a μ 2 -phenoxido oxygen atom and a bridging carboxylato ion. Variable temperature magnetic susceptibility measurements show the presence of antiferromagnetic exchange interactions in 1 mediated through the phenoxido bridges ( J 1  = −33.2 cm −1 ,) and μ 1,3 -N 3 single bridges ( J 2  = −19.9 cm −1 and J 3  = −16.7 cm −1 ). On the other hand, compounds 2 and 3 show ferromagnetic coupling interactions mediated through the double phenoxido bridges with J values of +4.9 and +3.0 cm −1 for 2 and 3 , respectively.