Cobalt(II) complexes containing N′-substituted N,N′,N-bis((1H-pyrazol-1-yl)methyl)amine ligands: The formation of four-coordinate or five-coordinate complexes as a function of the N′-substitution group in N,N′,N-bis((1H-pyrazol-1-yl)methyl)amine

N,N-bis((1H-pyrazol-1-yl)methyl)(cyclohexyl)methanamine (L_A), N,N-bis((1H-pyrazol-1-yl)methyl)-2,6-diethylbenzenamine (L_B), N,N-bis((1H-pyrazol-1-yl)methyl)-4-bromobenzenamine (L_C), N,N-bis((1H-pyrazol-1-yl)methyl)cyclohexanamine (L_D), N,N-bis((1H-pyrazol-1-yl)methyl)(furan-2-yl)methanamine (L_E), N,N-bis((1H-pyrazol-1-yl)methyl)-2-methoxyethanamine (L_F), and N,N-bis((1H-pyrazol-1-yl)methyl)-3-(methylthio)propan-1-amine (L_G) with [CoCl₂·6H₂O] in ethanol yield a novel series of Co(II) chloride complexes; i.e. [L_nCoCl₂] (L_n = L_A-L_G), respectively. The molecular structures of [L_nCoCl₂] (L_n = L_A-L_C) and [L_nCoCl₂] (L_n = L_D-L_G) exist as monomeric four-coordinated and five-coordinated complexes, respectively. [L_nCoCl₂] (L_n = L_A-L_C) showed a distorted tetrahedral geometry involving non-coordination of the nitrogen atom of the N′-substitution amine moiety and the Co(II) centre, resulting in the formation of an eight-membered chelate ring. The geometry at each Co(II) centre in [L_nCoCl₂] (L_n = L_D-L_G) were best described as a distorted trigonal bipyramid involving coordination of the nitrogen atom of the N′-substitution amine group and the Co(II) centre. Specifically, a distorted trigonal bipyramid was achieved in [L_DCoCl₂] through a coordinative interaction of the nitrogen atom of the cyclohexylamine unit and the Co(II) atom with an σ plane of symmetry based on the bond length of Co-N_{cyclcohexylamine} [2.466(4) Å]. Moreover, [L_DCoCl₂] showed the highest activity for methyl methacrylate (MMA) polymerization in the presence of modified methylaluminoxane (MMAO) at 60 °C and yielded poly(methylmethacrylate) (PMMA) with a high molecular weight (M_w) and narrower polydispersity index (PDI) compared to the other Co(II) complexes. However, all Co(II) complexes produced syndiotactic (PMMA), characterised using ¹H NMR spectroscopy, with ca. 0.70.