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.