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)
† Institut für Anorganische Chemie, Universität Leipzig, Johannisallee 29, 04103 Leipzig, Germany
‡ Institut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB), UMR 6302, CNRS, Université de Bourgogne-Franche Comté, 9 avenue Alain Savary, BP 47870, 21078 Dijon Cedex, France
§ Research Institute for Physical Chemical Problems of Belarusian State University, Leningradskaya 14, 220030 Minsk,Belarus
∥ Belarusian State University, 4 Nezavisimisti Avenue, 220050 Minsk, Belarus
Inorg. Chem., Article ASAP
DOI: 10.1021/acs.inorgchem.5b02743
Publication Date (Web): February 2, 2016
Copyright © 2016 American Chemical Society
*E-mail: michel.meyer@u-bourgogne.fr. Fax: +33/(0)3 80 39 61 17., *E-mail: b.kersting@uni-leipzig.de. Fax: +49/(0)341-97-36199.
The dinuclear NiII 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)(μ1,1-N3)][ClO4] (7) or [Ni2(L2)(μ1,1-N3)][BPh4] (8), while the previously reported complex [Ni2L1(μ1,3-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 3to 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(μ1,3-N3)][ClO4] (2), which features a S = 0 ground state, [Ni2(L2)(μ1,1-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).
The binuclear Ni(II) complex binds the N3− ion end-on, which is in striking contrast to the end-to-end coordination encountered for the related azido complex of the smaller macrocycle in previous work. This can be traced to a more preorganized binding pocket, which controls the azide binding mode by repulsive CH···π interactions. the spin ground state changes from S = 0 to S = 2.
The binuclear Ni(II) complex binds the N3− ion end-on, which is in striking contrast to the end-to-end coordination encountered for the related azido complex of the smaller macrocycle in previous work. This can be traced to a more preorganized binding pocket, which controls the azide binding mode by repulsive CH···π interactions. the spin ground state changes from S = 0 to S = 2.
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