Dinuclear Cu^IIM^II complexes of a phenol-based macrocycle with N(amine)₂O₂ and N(imine)₂O₂ metal-binding sites: The effect of chloride ligation upon the site selectivity of metal ions

A phenol-based dinucleating macrocycle, L^2-, comprising two 2-(N-methyl)aminomethyl-6-iminomethyl-4-bromophenolate moieties combined by a -(CH₂)₂-chain at the amino nitrogens and by a -(CH₂)₃-chain at the imino nitrogens and having dissimilar N(amine)₂O₂ and N(imine)₂O₂ metal-binding sites sharing the phenolic oxygens, is obtained as the mononuclear Cu^II complex [Cu(L)]. The 2-propanol adduct, [Cu(L)]·2-PrOH, crystallizes in a triclinic crystal system, space group P1̄ (No. 2) with Z=2, a=11.621(6), b= 14.17(1), c=9.390(4) Å, a=96.59(6), β=107.78(3), γ=103.78(5)°, V=1400(1) ų. The crystallography reveals that the Cu^II resides in the N(imine)₂O₂ site and has a nearly planar geometry. A series of dinuclear Cu^IIM^II complexes CuM(L)Cl₂ (M=Mn, Co, Ni, Cu, Zn) are obtained by reacting [Cu(L)] with metal(II) chloride salts. The methanol adduct of the CuNi complex, [CuNi(L)Cl₂] · MeOH, crystallizes in a monoclinic crystal system, space group P2₁/a (No. 14) with Z=4, a= 14.495(4), b=13.034(4), c=14.978(3) Å, β=91.89(2)°, V=2828(1) ų. The methanol adduct of the CuZn complex, [CuZn(L)Cl₂] · MeOH, crystallizes in a monoclinic crystal system, space group P2₁/a (No. 14) with Z=4, a=14.680(4), b=12.942(3), c=15.149(4) Å, β=91.25(2)°, V=2877(1) Å3. The X-ray crystallography for the two complexes reveal that the Cu^II ion resides in the N(imine)₂O₂ site with the M^II (Ni^II or Zn^II) ion in the N(amine)₂O₂ site. In each complex the Cu^II and M^II ions have nearly square-pyramidal geometry with the chloride ion occupying apical positions. Cryomagnetic studies (4.2-300 K) indicate a significant antiferromagnetic interaction within each dinuclear unit except for the case of the CuZn complex.