Multinuclear Ni(ii), Cu(ii) and Zn(ii) complexes of chiral macrocyclic nonaazamine

Abstract

The chiral macrocyclic amines R-L and S-L derived from the 3 + 3 condensation of 2,6-diformylpyridine and (1R,2R)-1,2-diaminocyclohexane or (1S,2S)-1,2-diaminocyclohexane form enantiopure trinuclear Ni(II) and Cu(II) complexes [Ni₃(L)(H₂O)₂Cl₅]Cl and [Cu₃(L)Cl₄]Cl₂ and form the dinuclear complex [Zn₂(L)Cl₂](ZnCl₄) with Zn(II). The X-ray crystal structures of these complexes indicate remarkably different conformations of the ligand and different binding modes of the chloride anions. The structure of the copper(II) derivative [Cu₃(R-L)Cl₄]Cl₂·CH₃CN·7.5(H₂O) indicates unsymmetrical conformation of the macrocycle with three dissimilar pentacoordinate copper(II) ions bridged by chloride; the structure of [Ni₃(R-L)(H₂O)₂Cl₅]Cl·0.4CH₃CN·4.2H₂O is somewhat more symmetrical, with three Ni(II) ions of distorted octahedral geometry, also bridged by a common chloride anion. On the other hand, the macrocycle is highly folded in [Zn₂(R-L)Cl₂](ZnCl₄)·CHCl₃·0.8CH₃OH·3.7H₂O, forming a cleft where the third Zn(II) ion is held via electrostatic interactions as the ZnCl₄²⁻ anion. The magnetic data for [Cu₃(R-L)Cl₄]Cl₂ indicate the coexistence of antiferromagnetic and ferromagnetic interactions within the quasi isosceles tricopper(II) core (J = −85.6 cm⁻¹, j = 77.1 cm⁻¹). Compound [Ni₃(R-L)(H₂O)₂Cl₅]Cl shows the presence of weak antiferromagnetic coupling (J = −2.56 cm⁻¹, j = −1.54 cm⁻¹) between the three Ni(II) ions.