Stepwise complexation of Ni(II) and Cu(II) Ions by 6,6′-C-spirobi(cyclam) (cyclam = 1,4,8,11-tetraazacyclotetradecane), L₁. (see abstract)

In aqueous HClO₄, the cation [H₄(L])]⁴⁺ where L₁ is 6,6′-C-spirobi(cyclam) (cyclam = 1,4,8,11-tetraazacyclotetradecane), complexes Cu²⁺ and Ni²⁺ ions in a stepwise fashion to form [M(H₂L₁)](ClO₄)₄ (M = Cu²⁺ and Ni²⁺) from which. [CuNi(L₁)](ClO₄)₄ has been prepared selectively. The preparation and the structure of [Cu₂(Li)]-(ClO₄)₄ (empirical formula, C₁₉H₄₄N₈Cu₂Cl₄O ₁₆; space group, triclinic; P1̄; a - 8.1815(6) Å, b = 12.6098(9) Å, c = 16.6565(12) Å, a = 80.3890(10)°, β= 76.5840(10)°, γ = 87.1750(10)°, V = 1647.9(2) ų, and Z = 2; of the 9531 total reflections collected, 6779 reflections with I > 2σ(I) on least-squares refinement provided final R₁ = 0.0657 and wR₂ = 0.1424) are also reported. The cyclic voltammograms (1.0 M NaCl, 0.1 M H⁺; Pt electrodes; all E_1/2 vs NHE) of [M(H₂L₁)]⁴⁺ (M = Cu²⁺ and Ni²⁺) ions show single waves for the Cu^II/Cu^III couple (E_1/2 = 0.79 V, irreversible) and the Ni^II/Ni^III couple (E_1/2 = 0.56 V, reversible), respectively. In CH₃CN (0.1 M Et₄-NClO₄), the [Cu₂(L₁)]⁴⁺ ion shows a reversible wave for the Cu^II-Cu^II/Cu^II-Cu^III couple (¹E_1/2 = 1.120 V) and an irreversible wave for the Cu^II-Cu^III/Cu^III-Cu^III couple (²E_1/2 = 1.430 V). Similarly, a reversible wave for the Cu^II-Ni^II/Cu^II -Ni^III couple (¹E_1/2 = 0.750 V) and an irreversible wave for the NiI-CuII/NiIII-Cu^III couple (²E_1/2 = 1.20 V) are observed in the case of the [Cu^IINi^II)]⁴⁺ ion. The [Cu₂(L₁)]⁴⁺ ion (g_⊥ = 2.120, g_⊥ = 2.256 and 2.196, A_∥ = 150 G, and D_∥ = 75 G) and the mixed valent species [Cu^IINi^III(Li)]⁵⁺ (for Cu²⁺, g_⊥ = 2.060, g_∥ = 2.219, and A_∥ = 100 G; for Ni³⁺ in sulfate media, g_∥ = 2.204 and g_∥ = 1.967) and [Cu^IICu^III(L₁)]⁵⁺ (g_xx = 1.982, g_yy = 2.155, g_zz = 2.386, A_yy = 80 G, and A_zz = 120 G) show dipolar-dipolar interaction. In the mixed-valent ions, due to strong electrostatic repulsion from either the Ni(III) or Cu(III) ions, significantly smaller A_∥ (or A_zz) values are observed for the Cu²⁺ ion compared to 200 G in the mononuclear ions. Also, the [Cu^IINi^III-(L₁)]⁴⁺ in aqueous HClO₄ and the [Ni₂(Li)]⁴⁺ ion in CH₃NO₂ show a tendency to reduce perchlorate very slowly.