Carboxylate Bridge Controlled Formation of Tetra‐ and Pentanuclear Nickel(II) Complexes: Synthesis, Crystal Structure, Spectroscopy and Magnetic Properties

A carboxyamine functionalized tridentate ligand in combination with three different carboxylate bridging groups (RCO 2 − ; R=CH 3 , C 2 H 5 and CF 3 ) has been utilized to prepare tetra‐ and pentanuclear nickel(II) complexes, [Ni 4 (L) 2 ( μ 3 ‐OCH 3 ) 2 ( μ 1,1 ‐O 2 CCH 3 ) 2 ( μ 1,3 ‐O 2 CCH 3 ) 2 (CH 3 OH) 2 ] ( 1 ), [Ni 4 (L) 2 ( μ 3 ‐OCH 3 ) 2 ( μ 1,1 ‐O 2 CC 2 H 5 ) 2 ( μ 1,3 ‐O 2 CC 2 H 5 ) 2 (CH 3 OH) 2 ] ( 2 ) and [Ni 5 (L) 4 ( μ 3 ‐OH) 2 ( μ 1,3 ‐O 2 CCF 3 ) 2 ]Br 2 ⋅ 3H 2 O ( 3 ) (HL=3‐[(2‐pyridylmethyl)‐amino]‐propionic acid). The complexes have been characterized using several techniques such as elemental analysis, solution electrical conductivity, FTIR and UV‐Vis spectroscopy, and low temperature magnetic measurements. While complex 1 and 3 were further characterized using single crystal X‐ray diffraction, molecular structure of complex 2 has been optimized using DFT calculation. Whereas the acetate/propionate groups deliver Ni 4 cluster, the trifluoroacetate group provides Ni 5 assembly. Molecular structures of complexes 1 and 2 comprise a central [Ni 4 O 6 ] core that could be described as a distorted face‐shared dicubane with two missing vertices. On the other hand, the [Ni 5 ( μ 3 ‐OH) 2 ( μ 1,3 ‐O 2 CCF 3 ) 2 ] 6+ structural core of complex 3 contains five coplanar nickel(II) ions in a rectangular organization. Variable‐temperature magnetic susceptibility studies reveal the interesting magnetic properties of complexes 1 and 3 . While complex 1 shows both ferro‐ and antiferromagnetic interactions with J 1 =−1.10 cm −1 , J 2 =+2.40 cm −1 and J 3 =−0.65 cm −1 , complex 3 exhibits only ferromagnetic interactions with J 1 =+2.0 cm −1 and J 2 =+1.0 cm −1 .