Polynuclear Complexes of Ligands Containing in Situ Formed Oxazinane and Oxazolidine Rings with Appended Alkoxyl and Phenol Groups

In situ formation of ligands is an efficient approach to synthesizing novel complexes with unique coordinating moieties. Oxazolidines and oxazinanes are 1,3-N,O-containing five-membered and six-membered heterocycles, respectively. Metal complexes of ligands derived from these two heterocycles are rather rare. In this work, we designed and synthesized a novel multihydoxy ligand, 2-((2,3-dihydroxypropylamino)­methyl)­phenol (H₃L¹). It contains both aminoethanol and aminopropanol units, which may be employed to react with aldehydes to afford oxazolidines and oxazinanes, respectively. Thus, H₃L¹ was reacted with metal salts in the absence or presence of aldehydes to afford complexes [Cu­(HL¹)]₂ (1), [CuL²]₄·4CH₃OH (2) [Zn₅Na₂(L³)₄­(DMSO)_2.65­(DMF)_1.35]­·DMF (3), and [Ni­(HL⁴)]₂ (4). Complex 1 is a dialkoxo-bridged binuclear Cu­(II) complex. The coordination moieties are linked by intermolecular C–H···O hydrogen bonds to afford a 1D double-chain supramolecular structure. Interestingly, in complexes 2–4, H₃L¹ has been reacted with formaldehyde, salicylaldehyde, and 2,6-diformyl-4-cresol to afford novel ligands H₂L², H₃L³, and H₃L⁴, respectively. The combination of in situ formed oxazinane or oxazolidine rings with appended alkoxyl and phenol functionalities in these ligands has been demonstrated to form a rich diversity of coordination structures. Thus, 2 is a tetranuclear Cu­(II) complex with a face-sharing double defective cubane core structure. In this complex, (L²)^2– ligands coordinate in two different bridging modes with the Harris notations of 3.1₁2₁₂2₁₃1₁ and 3.1₁3₁₂₃1₁1₁, respectively. Complex 3 has an interesting heptanuclear Zn₅Na₂ core structure. A central Zn­(II) is coordinated with four alkoxo O atoms from four (L³)^3– ligands. Each of the O atom further bridges another Zn­(II) atom, resulting in a Zn₅ moiety, which is then connected to two Na⁺ by phenoxo O bridges, finally affording the Zn₅Na₂ core. The bridging mode of (L³)^3– can be designated as 4.2₁₂2₁₃1₁3₁₂₄1₁. And Complex 4 is a binuclear Ni­(II) complex containing di-μ₂-phenoxo bridges. The coordination moieties are linked by intermolecular C–H···π, C–H···O, and π···π interactions to afford a two-dimensional supramolecular network. These results indicate that the combination of in situ formed oxazinane and oxazolidine rings with appended phenol and alkoxyl functionalities is an efficient approach to developing novel ligands and complexes with a rich structural diversity. Variable temperature magnetic data measurements revealed that medium antiferromagnetic interaction exists between the Cu­(II) centers in complex 1 with a −2J value of 278 cm^–1. And in complex 4, weak antiferromagnetic coupling occurs between the Ni­(II) centers, with a −2J value of 9.36 cm^–1.