Syntheses, Crystal Structures, and Magnetic Properties of Two Heterobridged Butterfly‐Type Tetranickel(II)‐Azido Systems Derived From Acyclic Compartmental Schiff Base Ligands: Experimental and Theoretical Exploration

This investigation deals with the syntheses, single crystal X‐ray structures and the experimental as well as density functional theory (DFT) magnetic properties of two tetranuclear complexes of composition [Ni II 4 (L 1 ) 2 (μ 1,1 ‐N 3 ) 2 (μ 1,1,1 ‐N 3 ) 2 (MeOH) 2 ] ( 1 ) and [Ni II 4 (L 2 ) 2 (μ 1,1 ‐N 3 ) 2 (μ 1,1,1 ‐N 3 ) 2 (MeOH) 2 ] ( 2 ). These complexes are derived from two bi‐compartmental ligands, H 2 L 1 and H 2 L 2 , which are 1:2 condensation products of 3‐methoxysalicylaldehyde and 3‐ethoxysalicylaldehyde, respectively, with 1,4‐diaminobutane. In terms of coordination to the metal ions, the N(imine) 2 O(phenoxido) 2 compartment behaves as two subcompartments. The tetranuclear 10‐atom core is a defective dicubane (butterfly‐type) where the bridging pattern is as follows: μ‐phenoxido‐μ 1,1 ‐azido for two pairs, μ 1,1 ‐azido‐μ 1,1,1 ‐azido for two pairs, and bis(μ 1,1,1 ‐azido) for one pair. Variable‐temperature and variable‐field magnetic measurements reveal overall ferromagnetic interaction in both 1 and 2 . A three‐ J model has been utilized to fit the two sets of magnetic data, giving weak to moderate values of all three exchange integrals. DFT calculations have been carried out to model the observed magnetic properties. The observed and DFT‐computed J values are well matched. Observed/DFT J values (in cm −1 ): 18.75/20.35, 1.88/3.88, and 8.60/10.10 in 1 and 21.80/25.24, 1.21/3.31, and 9.15/9.98 in 2 . The nature of interaction has been enlightened from the spin density values and nonorthogonal magnetic orbitals. Rare/unique features in the titled compounds have been discussed.