Experimental and theoretical investigation of a new non-symmetric salamo-like ligand and its tri-nuclear Zn(II) and Ni(II) complexes

Abstract

Neutral homotrinuclear complexes [{Zn3(L)2(μ-OAc)2}2]·5EtOH and [Ni3(L)2(μ-OAc)2(MeOH)2]·2MeOH were obtained in the reactions of a new non-symmetric salamo-like ligand H2L (5-(N,N′-diethylamino)-2,2′-[ethylenedioxybis(nitrilomethylidyne)]phenolnaphthol) with the respective salts of M(OAc)2·2H2O (M = Zn(II) and Ni(II)), respectively. Single crystals of the ligand were also obtained. All the Zn(Ⅱ) and Ni(Ⅱ) complexes were structurally characterized by single crystal X-ray diffraction. Both Zn(Ⅱ) and Ni(Ⅱ) complexes are composed of two (L)2− units combined with three metal(Ⅱ) ions, where a pair of μ-OAc− ions bridging Zn1⋯Zn2 and Zn2⋯Zn3 or Ni1⋯Ni2 and Ni2⋯Ni1#1 neutralize the charge of the Zn(II) and Ni(II) complexes and stabilize the trinuclear structure. The two μ-OAc− ions are located on the same side of the Zn(Ⅱ) complex, while on different sides of the Ni(Ⅱ) complex. In addition, there are two methanol molecules in the Ni(Ⅱ) complex involved in the coordination. UV–vis absorption spectral analyses showed that the ligand (L)2− units have coordinated with Zn(Ⅱ) and Ni(Ⅱ) atoms. DFT calculations exhibited that the Zn(II) and Ni(II) complexes have higher kinetic stability and lower chemical reactivity. Fluorescence spectrum analyses indicated that the electrons of the ligand have transferred to the empty orbitals (LMCT) of the Zn(Ⅱ) and Ni(Ⅱ) atoms. Furthermore, to discern the interactions in the crystal structures, Hirshfeld surfaces analyses were evaluated. Molecular electrostatic potentials were calculated in order to find electrophilic and nucleophilic sites favorable for hydrogen bonds.