A Versatile Series of Nickel(II) Complexes Derived from Tetradentate Imine/Pyridyl Ligands and Various Pseudohalides: Azide and Cyanate Compared

The chemical reactions of a family of tetradentate pyridyl/imine ligands, L1, L2, and L3 (L1 = [N,N′-bis(2-pyridinylmethylene)]ethane-1,2-diamine; L2 = [N,N′-bis(pyridin-2-yl)benzylidene]ethane-1,2-diamine; L3 = [N,N′-bis(2-pyridinylmethylene)]propane-1,3-diamine), with NiII in the presence of various pseudohalides (N3−, SCN−, and NCO−) have served to prepare six different complexes, [Ni2(L1)2(N3)2](ClO4)2·H2O (1), [Ni2(L2)2(N3)2](ClO4)2 (2), [Ni2(L2)2(NCS)4] (3), [Ni2(L2)2(NCO)2](ClO4)2 (4), [Ni2(L3)2(NCO)2](ClO4)2 (5), and [Ni(L3)(N3)2] (6), which have been characterized by X-ray crystallography. Interestingly, four of these complexes are dinuclear and exhibit end-on (EO) pseudohalide bridges (1, 2, 4, and 5), one is dinuclear and bridged exclusively by the tetradentate ligand (3), and one is mononuclear (6). The bulk magnetization of the complexes bridged by EO pseudohalides has been studied, revealing these ligands to mediate ferromagnetic coupling between the NiII ions, with modeled coupling constants, J, of +31.62 (1), +28.42 (2), +2.81 (4), and +1.72 (5) cm−1 (where the convention H = −2JS1S2 was used). The striking difference in the coupling intensity between N3− and NCO− has prompted an investigation by means of density functional theory calculations, which has confirmed the experimental results and provided insight into the reasons for this observation.