Synthesis and Characterization of Trinuclear NiII3 and CuII3 Triplesalophen Complexes: Evaluation of Ligand Folding and Heteroradialene Formation and their Impact on the Magnetic Properties



The coordination chemistry of the triplesalophen ligands H6baronR (R = Me, Cl, Br) with CuII and NiII has been studied. The triplesalophen ligand system is an extension of the triplesalen ligand system and is composed of a bridging phloroglucinol ring with three meta-phenylene salophen coordination compartments. The completely sp2 hybridized backbone of the triplesalophen ligands should favor a more planar molecular structure of the trinuclear complexes in comparison to the triplesalen complexes. Reaction of the ligands with the metal acetates in n-butanol/CHCl3 provided the complexes [(baronMe)Ni3]a, [(baronCl)Ni3]a, [(baronBr)Ni3]a, [(baronMe)Cu3], [(baronCl)Cu3], and [(baronBr)Cu3]. For the NiII complexes, recrystallization from pyridine or performing the reaction in pyridine provided the compounds [(baronMe)Ni3]b and [(baronCl)Ni3]b, whereas for the bromo derivative the complex [(baronBr){Ni(py)2}2Ni] with one four-coordinate and two six-coordinate NiII ions have been obtained. In contrast, for the CuII complexes, two [(baronR){Cu(py)}2Cu] (R = Me, Cl, Br) units dimerize via bridging of a coordinated phenolate. The structural analysis reveals a strong tendency for π stacking of the trinuclear complexes resulting in a planarization of the complexes. The trinuclear triplesalophen complexes exhibit the four signatures of heteroradialene formation, which were extracted from single-crystal X-ray diffraction, NMR, FTIR, and UV/Vis spectroscopy. Analysis of these experimental data with regard to the respective data of the free ligands H6baronR (R = Me, Cl, Br) and the mononuclear analogue H2carlCl and its complexes [(carlCl)Ni] and [(carlCl)Cu] clearly demonstrates that the heteroradialene resonance structure, which has been established as the dominant resonance structure for the free ligands, still has a strong but smaller contribution in the trinuclear triplesalophen complexes. The magnetic properties demonstrate weak intramolecular ferromagnetic interactions mediated by the triplesalophen ligands in the trinuclear CuII3 complexes, which are experimentally difficult to determine due to intermolecular antiferromagnetic interactions of the same order of magnitude.