Phloroglucinol-bridged trinuclear complexes with three paramagnetic octahedral nickel(II) ions: Syntheses, crystal structures, and magnetic properties

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• 作者：Daniel Plaul^a ; Winfried Plass ; ^a ; ^{sekr.plass@uni-jena.de"" rel=""nofollow} ;
• 关键词：Nickel ; Bridging ligands ; Schiff-base ligands ; Magnetic properties ; Spin-polarization ; Superexchange
• 刊名：Inorganica Chimica Acta
• 出版年：2011
• 出版时间：1 August 2011
• 年：2011
• 卷：374
• 期：1
• 页码：341-349
• 全文大小：1117 K

文摘

Three new C₃-symmetric tritopic ligands with a central phloroglucinol bridging unit have been synthesized and characterized. The ligands are accessible through Schiff-base condensation of 2,4,6-triformylphloroglucinol with 2-aminomethylpyridine (H₃tfpg-ampy), N,N-bis(pyridin-2-ylmethyl)-ethylenediamine (H₃tfpg-unspenp), and benzhydrazide (H₆tfpg-bhy). These ligands differ in nature and number of the donor atoms within the resulting binding pockets. Based on these ligands the synthesis of the first trinuclear phloroglucinol-bridged nickel(II) complexes with three octahedrally coordinated nickel centers is reported. The ligands H₃tfpg-ampy and H₆tfpg-bhy, which provide tridentate binding pockets, react with nickel(II) perchlorate in the presence of bis(pyridin-2-ylethyl)-amine (bpea) as an additional tridentate capping ligand leading to the formation of the trinuclear complexes [Ni₃(tfpg-ampy)(bpea)₃](ClO₄)₃ and [Ni₃(tfpg-bhy)(bpea)₃](ClO₄)₃, respectively. Due to the pentadentate binding pocket in ligand H₃tfpg-unspenp, no additional coligand is needed and a water molecule occupies the sixth coordination site at the nickel(II) ion resulting in the complex [Ni₃(tfpg-unspenp)(H₂O)₃](ClO₄)₃. Temperature-dependent magnetic measurements reveal overall weak antiferromagnetic exchange interactions within the trinuclear complex together with a rather strong zero-field splitting (ZFS) for the nickel(II) ions. The observed isotropic coupling constants for the three complexes are in the range of 0.14 < − J < 0.37 cm⁻¹, whereas for the zero-field splitting parameter D values between 1.8 and 5.5 cm⁻¹ are found. This is indicative for competitive spin-polarization and superexchange mechanisms, with the latter prevailing the interaction between the nickel(II) ions through the meta-phenylene-linkage for the complexes reported.