Indolenine meso-Substituted Dibenzotetraaza[14]annulene and Its Coordination Chemistry toward the Transition Metal Ions MnIII, FeIII, CoII, NiII, CuII, and PdII
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A new dibenzotetraaza[14]annulene bearing two 3,3-dimethylindolenine fragments at the meso positions (LH2), has been synthesized through a nontemplate method. X-ray crystallography shows that the whole molecule is planar. The basicity of the indolenine ring permits the macrocycle to be protonated external to the core and form LH42+·2Cl–. Yet another structural modification having strong C–H···π interactions was found in the chloroform solvate of LH2. The latter two modifications are accompanied by a degree of nonplanar distortion. The antiaromatic core of the macrocycle can accommodate a number of metal ions, MnIII, FeIII, CoII, NiII and CuII, to form complexes of [Mn(L)Br], [Mn(L)Cl], [Fe(LH2)Cl2]+·Cl–, [Co(L)], [Ni(L)], and [Cu(L)]. In addition, the reaction of LH2 with the larger PdII ion leads to the formation of [Pd2(LH2)2(OAc)4] wherein the macrocycle acts as a semiflexible ditopic ligand to coordinate pairs of metal ions via its indolenine N atoms into dinuclear metallocycles. The compounds LH2, [Co(L)], and [Ni(L)] are isostructural and feature close π-stacking as well as linear chain arrangements in the case of the metal complexes. Variable temperature magnetic susceptibility measurements showed thermally induced paramagnetism in [Ni(L)].
