Pseudohalide-bridged five-coordinate Ni(II) or Co(II) complexes with bulky bidentate ligands: Magneto-structural correlationship

Abstract

Bidentate ligands 2,2′-biquinoline (biq) and 6,6′-dimethyl-2,2′-bipyridine (dmbpy) with steric hindrance substituents cis to the nitrogen atoms have been used in the synthesis of transition metal complexes. Six new doubly end-on azido-bridged binuclear complexes [M 2(biq) 2(μ 1,1-N 3) 2(N 3) 2] (M = Ni ( 1), M = Co ( 2)), [M 2(biq) 2(μ 1,1-N 3) 2Cl 2] (M = Ni ( 3), M = Co ( 4)), [M 2(dmbpy) 2(μ 1,1-N 3) 2(N 3) 2] (M = Ni ( 5), M = Co ( 6)) and one end-to-end thiocyanato-bridged polymeric [Ni(dmbpy)(μ 1,3-SCN)(NCS)] n ( 7) have been synthesized and characterized by single crystal X-ray diffraction analysis and magnetic studies. Complexes 1– 6 comprise five-coordinate M(II) ions bridged by two end-on azide ligands. The bridging M–N–M bond angles are in the small range 104.1–105.2°. Complex 7 consists of a singly thiocyanate-bridged Ni(II) chain in which Ni(II) ions are five-coordinate. This research suggests that the bulky ligands play a key role in the formation of five-coordinate coordination structure. All complexes display intramolecular intermetallic ferromagnetic coupling with J NiNi and J CoCo of ca. 23 or 13 cm −1 based on the Hamiltonian H ^ = - 2 J S ^ 1 S ^ 2 ( S 1 = S 2 = 1 for Ni 2, or 3/2 for Co 2). The singly SCN −-bridged chainlike complex 7 shows intrachain ferromagnetic interaction with J = 3.96(2) cm −1 and D = −4.55(8) cm −1 ( H ^ = - 2 J ∑ i = 1 ( S ˆ i S ^ i + 1 ) - D ∑ i = 1 [ ( S ^ iZ ) 2 - 2 / 3 ] ) . Magneto-structural correlationship has been investigated.