Dinaionic Ligand Complexes, K2[CuLn] and K2[NiLn] (n = 1, 2; H4L1 = 1,2-Bis(2-hydroxybenzamido)ethane, H4L2 = 1,2-Bis(2-hydroxybenzamido)benzene), and Their Dinuclear Cu(II)–Cu(II) and Ni(II)–Cu(II) Complexes

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Abstract
Copper(II) and nickel(II) complexes with tetraanionic quadridentate ligands, K2[CuLn] and K2[NiLn] (n = 1, 2), have been prepared. We examined whether or not they can function as “ligand complexes”, where H4L1 = 1,2-bis(2-hydroxybenzamido)ethane and H4L2 = 1,2-bis(2-hydroxybenzamido)benzene. One of the ligand complexes, K2[NiL1]·2dmf·2H2O, crystallizes in the monoclinic space group P21/n with the cell dimensions of a = 15.34(8), b = 18.99(8), c = 18.86(5) Å, β = 100.2(3), V = 5406 Å3, and Z = 8. The ligand complex assumes a unique one-dimensional structure consisting of {[KO3][K(NiL1)O]}n as the repeating unit, where each K+ ion is surrounded octahedrally by six oxygen atoms with the distances of 2.672(2)—2.866(9) Å and all the oxygen atoms act as bridging group to K+ ion. Each of the precursor complexes can function as an electrically dianionic bidentate “ligand complex” and reacts with Cu(II) ion and terminal capping ligand (cap) such as 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), ethylenediamine (en), and 1,3-diaminopropane (tn) to give di-μ-phenoxo-bridged dinuclear Cu(II)–Cu(II) and Ni(II)–Cu(II) complexes with the general formula of [(Cu or Ni)LnCu(cap)]. The molar electrical conductivities of the dinuclear complexes measured in the DMF or DMSO solutions are essentially zero, indicating that the dinuclear structures are preserved in the solutions. The electrochemical measurements for a series of [CuL2Cu(cap)] (cap = bpy, phen, tn) demonstrated that the Cu(II/III) redox process of the {CuL2} site exhibits more positive potential (−0.04 — −0.09 V) than that of the mononuclear precursor complex (−0.288 V). One of the dinuclear complexes, [CuL2Cu(phen)(DMSO)], crystallizes in the orthorhombic space group Pna21 with the cell dimensions of a = 19.702(3), b = 15.847(3), c = 9.652(2) Å, V = 3013 Å3, and Z = 4. The complex consists of a discrete di-μ-phenoxo-bridged dinuclear structure, in which two copper(II) ions assume a square planar and square pyramidal coordination geometry and the bridging core of Cu2O2 is unequivalent, as found in the distances of Cu(1)–O(1) = 1.924(4) Å, Cu(1)–O(2) = 1.908(4) Å, Cu(2)–O(2) = 1.964(4) Å and Cu(2)–O(1) = 2.249(4) Å. The magnetic susceptibility is well reproduced with the antiferromagnetic coupling parameter of J = −82 cm−1 by the Bleaney–Boweres equation.

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