Heterodinuclear Cu^IIPb^II and Cu^IIM^II (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes of Macrocycles with Dissimilar 4- and 5-Coordination Sites: Synthesis, Structures, and Properties

Heterodinucleating macrocycles with two 2,6-bis(iminomethyl)-4-methylphenolate entities combined through two lateral chains, -(CH₂)₂- and -(CH₂)_mNH(CH₂)_m-(m = 2,3), at the imino nitrogens have been prepared as Cu^IIPb^II complexes of the formula [CuPb(L)]XY (L²⁻ = L1 for m = 2 and L2 for m = 3; XY = (C1O₄)2, (NO₃)(PF₆), (AcO)(BPh₄)). [CuPb(L1)](AcO)(BPh₄)·DMF crystallizes in the monoclinic crystal system, space group P2₁/n, with Z = 4, a = 18.890(3) Å, b = 19.968(3) Å, c = 12.704(2) Å, β = 91.61(1)°, and F= 4790(1) ų. The refinement converges with R = 0.0697 and R_w = 0.0863 for 4945 reflections with |F| > 3σ-(|F_o|). The crystal consists of a dimeric cation {CuPb(L1)(Ac)}2²⁺ bridged by acetate groups, tetraphenylborate ions, and DMF molecules. The Cu is located at the 4-coordination site formed with the ethylene chain and assumes a planar environment. The Pb is at the 5-coordination site formed with the -(CH₂)₂NH(CH₂)₂- chain and assumes an eight-coordinate structure also involving three acetate oxygen atoms. The Cu- -Pb separation, bridged by two phenolic oxygens, is 3.577(2) Å. In the crystal, the dimeric cations further interact through out-of-plane bonding between the {CUN₂O₂} entities forming a column along the a axis. The [CuPb(Ll)]XY complexes react with metal(II) sulfates to form a series of Cu^IIM^II complexes, [CuM(L1)]XY (M = Mn, Fe, Co, Ni, Cu, Zn). [CuMn(L1)](AcO)(BPh₄) crystallizes in the monoclinic space group P2₁/n, with Z = 4, a = 17.508(8) Å, b = 15.539(5) Å, c = 16.515(5) Å, β= 106.30(3)°, and V = 4312(3) ų. The refinement converges with R = 0.0689 and R_w = 0.0563 for 2935 reflections with |F_o| > 3σ(|F_o|). The Cu(II) and Mn(II) ions reside at the 4- and 5-coordination sites of the macrocycle, respectively, and the acetate group bridges the two metal ions providing a nearly square-pyramidal geometry for the Cu and a highly distorted six-coordinate environment for the Mn. The Cu-Mn separation is 3.122(2) Å. The cryomagnetic investigations (4.2–300 K) for the CuMn, CuFe, CuCo, CuNi, and CuCu complexes reveal the operation of an antiferromagnetic spin-exchange interaction within each molecule. The cyclic voltammograms of the CuM complexes show Cu(II)/Cu(I) reduction near −0.8 V (vs SCE) and oxidation at the ligand center near +1.3 V. The oxidation of the Fe(II) of the CuFe complex occurs at +0.64 V whereas the Mn(II) ion of the CuMn complex and the Co(II) ion of the CuCo complex are hardly oxidized.