ic980131p_si_001.cif (69.96 kB)
First Examples of Dinickel Complexes Containing the N3Ni(μ2-SR)3NiN3 Core. Synthesis and Crystal Structures of [L2Ni2][BPh4]2 and [L3Ni2][BPh4]2 (L = 2,6-Di(aminomethyl)-4-tert-butyl-thiophenolate)
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posted on 1998-07-07, 00:00 authored by Berthold Kersting, Dieter SiebertA coordinatively unsaturated dinuclear NiII complex of the tridentate ligand 2,6-di(aminomethyl)-4-tert-butyl-thiophenol (HL) has been synthesized and investigated in the context of ligand binding and oxidation state changes.
The starting complex [L2Ni2][BPh4]2 (1) is readily prepared from NaL, NiCl2·6H2O, and NaBPh4 in methanol.
Compound 1·CH3CN·CH3OH crystallizes from an acetonitrile/methanol mixed-solvent system in monoclinic space
group P21/n with a = 21.940(4) Å, b = 13.901(3) Å, c = 23.918(5) Å, β = 110.00(3)°, and Z = 4. The structure
consists of dinuclear [L2Ni2]2+ cations with two distorted planar cis-N2S2Ni coordination units joined by the
thiophenolate sulfur atoms. The molecule has idealized C2v symmetry. Complex 1 readily adds another 1 equiv
of HL to afford the pale green complex [L3Ni2]Cl (2). The dinuclear structure and its formulation as a 3:2
complex (six-coordinate Ni ions) is derived from UV spectroscopy, cyclic voltammetry, and single-crystal X-ray
diffraction of its oxidation product, [L3Ni2]2+. The dication was prepared by chemical oxidation of 2 with iodine
in DMF and isolated as the dark brown BPh4- salt, [L3Ni2][BPh4]2·CH3OH (3), which crystallizes in monoclinic
space group P21/c with a = 23.678(5) Å, b = 20.090(4) Å, c = 16.797(3) Å, β = 106.16(3)°, and Z = 4.
Complex 3 is the first structurally characterized example that features a bioctahedral N3Ni(μ2-SR)3NiN3 core.
Distortions from D3h symmetry suggest that 3 is a trapped-valence NiIINiIII compound. The Ni−S and Ni−N
bond lengths vary from 2.2975(9) to 2.4486(12) Å and from 2.027(3) to 2.120(3) Å, respectively. On the CV
time scale complex 2 undergoes two reversible electron-transfer reactions at E1/2 = −0.02 and +0.44 V vs SCE,
affording 3 and the transient dark green trication [L3Ni2]3+ (τ1/2 ≈ 15 min at 295 K), respectively. While 2 is
EPR silent, the EPR spectrum of a powdered sample of 3 reveals g⊥ = 4.0 and g∥ = 2.09 at 77 K, consistent with
an S = 3/2 spin state of the mixed-valent NiIINiIII complex.
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UV spectroscopyoxidation state changescyclic voltammetryL 2 Ni 2N 2 S 2 Ni coordination units3 NiN 3 coreOHL 3 Ni 2dinuclear structureDMFHLligand bindingSCEEPR spectrumthiophenolate sulfur atomsDinickel Complexes ContainingComplex 1chemical oxidationNaBPh 44. Complex 3Crystal StructuresCHCN77 Kdinuclear Ni IICV time scaleSRD 3 h symmetryBPh 43 NiN 3 CoreIII1 equivFirst ExamplesC 2 v symmetryoxidation product
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