Synthesis, structures and reactivity of cobalt(II) complexes supported by N,N,N′,N″-tetradentate N′-substituted bis((1H-pyrazol-1-yl)methyl)amine.

Novel Co(II) complexes supported by N,N,N ′ ,N ″-tetradentate N ′-substituted bis((1H-pyrazol-1-yl)methyl)amines) have been synthesized and characterized by X-ray diffraction method. Notably, anion exchange reaction was found to be highly selective; only the substitution of NO 3 − by BPh 4 − was achieved, whereas attempted anion exchange of NO 3 − with BPh 4 − proved unsuccessful. In addition, the presences of methyl substituents at pyrazole moieties play an influential role in determining the anionic exchange capabilities of these complexes. Thus, the counter anion exchange reaction depends on the size and nature of anions but also the geometry of cationic complexes. • Synthesis of Co(II) complexes with bis((1H-pyrazol-1-yl)methyl)amine derivatives. • [L n Co(NO 3)]BPh 4 (L n = L A , L B, L D) showed distorted trigonal bipyramidal geometries. • [L C Co(NO 3)]NO 3 exhibited distorted octahedral geometry around the Co(II) centre. • The substitution of NO 3 − anion by BPh 4 − anion was achieved successfully. A series of cobalt(II) complexes, namely [L n Co(NO 3)]+Y− (L n = L A –L D ; Y = NO 3 −, BPh 4 −) was prepared by the reaction of the corresponding metal starting materials with N , N -bis((1 H -pyrazol-1-yl)methyl)-2-(piperidin-1-yl)ethanamine (L A), N , N -bis((1 H -pyrazol-1-yl)methyl)-2-morpholinoethanamine (L B), N , N -bis((3,5-dimethyl-1 H -pyrazol-1-yl)methyl)-2-(piperidin-1-yl)ethanamine(L C) and N , N -bis((3,5-dimethyl-1 H -pyrazol-1-yl)methyl)-2-morpholinoethanamine (L D), respectively. X-ray diffraction studies revealed that the coordination geometry around the Co(II) centre in [L n Co(NO 3)]BPh 4 (L n = L A , L B and L D) can be best described as distorted trigonal bipyramidal, whereas [L C Co(NO 3)]NO 3 showed a distorted octahedral geometry around the Co(II) centre due to the bidentate binding mode of the ligand NO 3 −. Specifically, the presence of methyl substituents at the pyrazole moieties plays an influential role in determining the anionic exchange capabilities of these complexes. The anion exchange reaction was found to be highly selective; the substitution of the smaller anion NO 3 − to the bigger anion BPh 4 − was achieved easily, whereas the attempted anion exchange of BPh 4 − with NO 3 − proved unsuccessful. [ABSTRACT FROM AUTHOR]