In Situ Ligand Formation in the Synthetic Processes from Mononuclear Dy(III) Compounds to Binuclear Dy(III) Compounds: Synthesis, Structure, Magnetic Behavior, and Theoretical Analysis

Abstract

Guided by the self-assembled process and mechanism, the strategy of in situ Schiff base reaction would be capable of bringing a feasible method to construct and synthesize lanthanide compounds with distinct structures and magnetic properties. A mononuclear Dy(III) compound was synthesized through a multidentate Schiff base ligand and a chelating β-diketonate ligand, which was named as [Dy(L)(bppd)]·CH3OH [1; H2L = N,N′-bis(2-hydroxy-5-methyl-3-formylbenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine and bppd = 3-bis(pyridin-2-yl)propane-1,3-dione]. Furthermore, a new binuclear Dy(III) compound, [Dy2(H2Lox)(bppd)3]·8CH3OH [2; H4Lox = N,N′-bis[2-hydroxy-5-methyl-3-(hydroxyiminomethyl)benzyl]-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine], was obtained via an in situ synthetic process. Under similar synthetic conditions, [Dy(L)(ctbd)] [3; ctbd = 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione] and [Dy2(H2Lox)(ctbd)3]·CH3OH·C4H10O (4) were synthesized by modifying the β-diketonate ligand and in situ Schiff base reaction. Compound 3 is a mononuclear configuration, while compound 4 exhibits a binuclear Dy(III) unit. Therein, formylbenzyl groups of H2L in 1 and 3 were changed to (hydroxyiminomethyl)benzyl groups in 2 and 4, respectively. In isomorphous 2 and 4, two Dy(III) centers are connected through two phenol O– atoms of the H2Lox2– ligand to form a binuclear structure. Eight-coordinated Dy(III) ions with different distortions can be observed in 1–4. The crystals of 1 and 3 suffered dissolution/precipitation to obtain 2 and 4, respectively. The relationship between the structure and magnetism in compounds 1–4 was discussed through the combination of structural, experimental, and theoretical investigations. Especially, the rates of quantum tunneling of magnetization of 1–4 were theoretically predicted and are consistent with the experimental results. For 2 and 4, the theoretically calculated dipolar parameters Jdip are consistent with the experimental observation of weak ferromagnetic coupling.

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