Three Polyhydroxyl-Bridged Defective Dicubane Tetranuclear MnIII Complexes: Synthesis, Crystal Structures, and Spectroscopic Properties

Hao-Ran Jia,Jian Chang,Jing Li,Hong-Jia Zhang,Yin-Xia Sun

doi:10.3390/cryst8070272

Abstract

Three polyhydroxyl-bridged tetranuclear MnIII complexes [Mn4(L1a)2(μ3-OMe)2(μ2-OMe)2(MeOH)2] (1), [Mn4(L2a)2(μ3-OMe)2(μ2-OMe)2(H2O)2] (2), and [Mn4(L3a)2(μ3-OMe)2(μ2-OMe)2(H2O)2] (3) derived from Mnn+-promoted reactivity of Schiff base ligands (HL1 = 1-(4-{[(E)-3,5-dichlorine-2-hydroxybenzylidene]amino}phenyl)ethanone O-benzyloxime, HL2 = 1-(4-{[(E)-3-bromine-5-chloro-2-hydroxybenzylidene]amino}phenyl) ethanone O-benzyloxime, and HL3 = 1-(4-{[(E)-3,5-dibromine-2-hydroxybenzylidene]amino}phenyl)ethanone O-benzyloxime) have been synthesized and characterized. In the MnIII complexes 1, 2, and 3, the newly formed ligands (L1a)4−, (L2a)4−, and (L3a)4− are derived from the chemoselective cleavage of the C=N bond in the original Schiff base ligands HL1, HL2, and HL3 to form corresponding halogenated salicylaldehyde, 3,5-dichlorosalicylaldehyde, 3-bromine-5-chlorosalicylaldehyde, and 3,5-dibrominesalicylaldehyde, respectively. Then, the further addition of acetone to two halogenated salicylaldehyde molecules in situ α,α double aldol reaction promoted by Mnn+ ions in the presence of base to give the new ligands ((Lna)4−. X-ray crystallographic analyses of the MnIII complexes 1, 2, and 3 show that the three complexes are all tetranuclear structure and crystallizes in the triclinic system, space group P-1. The four MnIII ions and bridging alkoxido groups are arranged in a face-shared dicubane-like core with two missing vertices. In the three MnIII complexes, the asymmetric unit contains two kinds of different MnIII ions (Mn1 and Mn2), where the MnIII ions are all hexacoordinated with slightly distorted octahedral geometries. Simultaneously in the synthesis of multinuclear Mnn+ complexes above, we explored the crystal structure, spatial configuration, and spectroscopic properties of the multinuclear MnIII complexes with different halogen substituents.

Highlights

There is a wide range of research space in aldol condensation reactions, in particular, in its asymmetric and catalytic field, via an asymmetric organic catalyst or chelating agent of the metal complex unit
Synthesis of MnIII complexes [1, 2], and 3 consisting of the addition of Schiff base ligands (HL1, and HL3 ) to the acetone solution containing a small amount of triethylamine, respectively, followed by addition of a solution of Mn(OAc)2 ·4H2 O in methanol (5 mL)
It is worth noticing that the C=N bond of the original Schiff base ligands HL1, H18 BrClN2 O2 (HL2), and HL3 have chemoselectively cleaved due to the hydrolytic action and gave the corresponding halogenated salicylaldehyde derivatives, 3,5-dichlorosalicylaldehyde, 3-bromine-5-chlorosalicylaldehyde, and 3,5-dibrominesalicylaldehyde, respectively

Summary

Introduction

There is a wide range of research space in aldol condensation reactions, in particular, in its asymmetric and catalytic field, via an asymmetric organic catalyst or chelating agent of the metal complex unit. The B, Ti, or Sn ions because of their specific Lewis acid properties are used for promoting enolization followed by aldol addition [1–3]. The other first row of transition metal Zr, Co, Ni, Cu, or Zn ions have been used [4–6]. We have recently reported a tetranuclear ZnII complex using a double aldol ligand formed in situ by α,α-double aldol addition of acetone to 3,5-dichlorosalicylaldehyde promoted by ZnII ion in the presence of base [7]. In efforts to design new multidentate ligands which can form novel polynuclear complexes with attractive structural features, we are probing into this reaction using Lewis acid metal assistance.

Methods

Results

Conclusion