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

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 [M2(biq)2(μ1,1-N3)2(N3)2] (M = Ni (1), M = Co (2)), [M2(biq)2(μ1,1-N3)2Cl2] (M = Ni (3), M = Co (4)), [M2(dmbpy)2(μ1,1-N3)2(N3)2] (M = Ni (5), M = Co (6)) and one end-to-end thiocyanato-bridged polymeric [Ni(dmbpy)(μ1,3-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 JNiNi and JCoCo of ca. 23 or 13 cm−1 based on the Hamiltonian H^=-2JS^1S^2 (S1 = S2 = 1 for Ni2, or 3/2 for Co2). 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^=-2J∑i=1(SˆiS^i+1)-D∑i=1[(S^iZ)2-2/3]). Magneto-structural correlationship has been investigated.

The employment of bulky ligands has been shown to be an effective approach to produce five-coordinate transition metal complexes. Ferromagnetic coupling exists in the end-on azide-bridged Co2 or Ni2 complexes and the novel end-to-end thiocyanate-bridged 1D Ni(II) complex. Significant structural-magneto correlationship has been investigated.Figure optionsDownload as PowerPoint slide