Azide Binding Controlled by Steric Interactions in Second Sphere. Synthesis, Crystal Structure, and Magnetic Properties of [NiII2(L)(μ1,1-N3)][ClO4] (L = Macrocyclic N6S2 Ligand)

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• 作者：Alexander Jeremies ; Sina Gruschinski ; Michel Meyer ; Vitaly Matulis ; Oleg A. Ivashkevich ; Karolin Kobalz ; Berthold Kersting
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：February 15, 2016
• 年：2016
• 卷：55
• 期：4
• 页码：1843-1853
• 全文大小：564K
• ISSN：1520-510X

文摘

The dinuclear Ni^II complex [Ni₂(L²)][ClO₄]₂ (3) supported by the 28-membered hexaaza-dithiophenolate macrocycle (L²)^2– binds the N₃^– ion specifically end-on yielding [Ni₂(L²)(μ_1,1-N₃)][ClO₄] (7) or [Ni₂(L²)(μ_1,1-N₃)][BPh₄] (8), while the previously reported complex [Ni₂L¹(μ_1,3-N₃)][ClO₄] (2) of the 24-membered macrocycle (L¹)^2– coordinates it in the end-to-end fashion. A comparison of the X-ray structures of 2, 3, and 7 reveals the form-selective binding of complex 3 to be a consequence of its preorganized, channel-like binding pocket, which accommodates the azide anion via repulsive CH···π interactions in the end-on mode. In contrast to [Ni₂L¹(μ_1,3-N₃)][ClO₄] (2), which features a S = 0 ground state, [Ni₂(L²)(μ_1,1-N₃)][BPh₄] (8) has a S = 2 ground state that is attained by competing antiferromagnetic and ferromagnetic exchange interactions via the thiolato and azido bridges with a value for the magnetic exchange coupling constant J of 13 cm^–1 (H = −2JS₁S₂). These results are further substantiated by density functional theory calculations. The stability of the azido-bridged complex determined by isothermal titration calorimetry in MeCN/MeOH 1/1 v/v (log K₁₁ = 4.88(4) at I = 0.1 M) lies in between those of the fluorido- (log K₁₁ = 6.84(7)) and chlorido-bridged complexes (log K₁₁ = 3.52(5)). These values were found to compare favorably well with the equilibrium constants derived at lower ionic strength (I = 0.01 M) by absorption spectrophotometry (log K₁₁ = 5.20(1), 7.77(9), and 4.13(3) for N₃^–, F^–, and Cl^– respectively).