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C19H25N7O7, triclinic, P1 (no. 2), a = 6.969(2) Å, b = 9.300(3) Å, c = 17.214(5) Å, α = 98.231(5)°, β = 96.842(6)°, γ= 90.945(5)°, V = 1095.7 Å3, Z = 2, Rgt(F) = 0.0501, wRref(F2) = 0.1415, T = 273 K. [ABSTRACT FROM AUTHOR]

An unexpected polyhydroxyl-bridged tetranuclear ZnII complex and a benzoquinone compound derived from metal-ion promoted reactivity of Schiff base ligands were synthesized and characterized. The reaction of zinc(II) acetate dihydrate with oxime-type Schiff base ligand HL1 [HL1 = 1-(3-((3,5-dibromosalicylaldehyde)amino)phenyl) ethan-1-one O-benzyl oxime] in methanol, acetone and acetonitrile resulted in the chemoselective cleavage of the C=N bond of the Schiff base HL1 and then the further addition of acetone to two salicylaldehyde molecules derived from cleavage of the C=N bond in situ α,α double aldol reaction promoted by ZnII ions. The newly formed ligands H4L2 coordinate to four ZnII ions forming a defect-dicubane core structure [ZnII 4(H2L2)2(μ3-OCH3)2(μ-OCH3)2(CH3OH)2] (1) bridged exclusively by oxygen-based ligands. The similar ligand HL3 [HL3 = 1-(3- ((3,5-dichlorosalicylaldehyde)amino)phenyl)ethan-1-one O-benzyl oxime)] was employed to react with CdII acetate dihydrate under the same reaction conditions. No aldol addition occurred but a unexpected benzoquinone compound 2,5-bis(((3-(1-((benzyloxy)imino)ethyl) phenyl)imino)methyl)-1,4-benzoquinone (2) formed. The results provided interesting insights into one-pot routes involving in situ reactions act as a strategy for obtaining a variety of polymeric/polynuclear complexes which are inconvenient to obtain from directly presynthesizing the ligands. [ABSTRACT FROM AUTHOR]

• The Schiff base binuclear Zn(II) complex, [Zn 2 (L) 2 ∙(H 2 O) 2 ]∙2DMF (1) and its coordination polymer, [Zn 2 (L) 2 ∙(4,4′-bpy) 2 ] n (2) by introducing auxiliary ligand 4,4′-bpy. • The fluorescence spectrum showed the complex 2 containing 4,4′-bpy was substantially quenching of the fluorescence as compared with the complex 1. • The LUMO and HOMO orbits of the complex 2 were occupied by the 4,4′-bpy, which is different from complex 1 , resulting in 1 and 2 had different spectral properties. The Schiff base binuclear Zn(II) complexes, [Zn 2 (L) 2 ∙(H 2 O) 2 ]∙2DMF (1) and its coordination polymer [Zn 2 (L) 2 ∙(4,4′-bpy) 2 ] n (2) (H 2 L = 3-[(5-chloro-2-hydroxy-benzylidene)-amino]-4-hydroxy-chromen-2-one, 4,4′-bpy = 4,4′-bipyridine), were synthesized under the same experimental condition without or with the auxiliary ligand 4,4′-bpy, respectively. The structural analysis revealed that complexes 1 and 2 have different crystal structures. The complex 1 was a centrosymmetric binuclear structure. It is noteworthy that the linker 4,4′-bpy was introduced during the synthesis of complex 2 , so that two water molecules in complex 1 were replaced by two 4,4′-bpy linkers to form one-dimensional (1D) chain-like coordination polymer. The central Zn(II) ions in complex 1 were penta-coordinated distorted square pyramid geometry with τ = 0.42. However, the Zn(II) ions of complex 2 were hexa-coordinated distorted octahedral geometry. The fluorescence spectrum showed the complex 2 containing 4,4′-bpy was substantially quenching of the fluorescence as compared with the complex 1. In addition, it could be seen from the DFT calculation the energy gaps of the complexes 1 and 2 were both reduced compared to the ligand H 2 L. However, the LUMO and HOMO orbits of the complex 2 were occupied by the 4,4′-bpy, which is different from complex 1 , resulting in 1 and 2 had different spectral properties. [ABSTRACT FROM AUTHOR]