Selective Formation of Dinuclear and Heptanuclear Zn(II), Ni(II), and Co(II) Metal Clusters from a Simple Dialdehyde

Abstract Herein, the selective formation of dinuclear and hexagonal disk-shape heptanuclear metal cluster complexes is reported. The reaction of 4-tert-butyl-2,6-diformylphenol (L) and M(ClO4)2, where M is Zn (II), Co (II), or Ni (II), in the presence of a strong base resulted in the formation of heptanuclear metal cluster complexes. Treatment of M(ClO4)2.6H2O (M= Zn, and Ni) in the presence of NaOCH3 in MeOH at the elevated temperature afforded [Zn2(L)2(CH3O)4].ClO4 (1) and [Ni2(L)2(CH3O)2].ClO4 (2). Furthermore, treatment of M(ClO4)2.6H2O (M= Zn, Co, and Ni) in the presence of NaOH in MeOH at the elevated temperature yielded heptanuclear metal cluster complexes [Zn7(L)6(µ3-CH3O)6].2ClO4 (3), [Co7(L)6(µ3-CH3O)6].2ClO4 (4), and [Ni7(L)6(µ3-OH)6].2ClO4 (5). These were characterized using elemental analysis, infrared spectroscopy, and X-ray crystallography. Zinc complexes 1 and 3 were also characterized using 1H NMR spectroscopy. In the crystal structures of heptanuclear cluster complexes 3–5, six ligand molecules were aligned to hold six metal centers that were in hexagonal positions. The central metal atom was connected by the bridging of the oxygen atom of methoxy and hydroxy groups with the remaining metal atoms. The photophysical properties of complexes were studied and zinc complexes 1 and 3 showed strong fluorescence in PL spectra. The heptanuclear metal cluster complexes 3–5 were employed as catalysts in the cycloaddition reaction of CO2 to epoxide, exhibiting moderate activities.