Magneto-Structural Correlation Studies and Theoretical Calculations of a Unique Family of Single End-to-End Azide-Bridged NiII4 Cyclic Clusters

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• 作者：Sujit Sasmal ; Susanta Hazra ; Parimal Kundu ; Samit Majumder ; Nria Aliaga-Alcalde ; Eliseo Ruiz ; Sasankasekhar Mohanta
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：October 18, 2010
• 年：2010
• 卷：49
• 期：20
• 页码：9517-9526
• 全文大小：911K
• 年卷期：v.49,no.20(October 18, 2010)
• ISSN：1520-510X

文摘

The work in this paper aims to portray a complete structural, magnetic, and theoretical description of two original end-to-end (EE) μ_1,3-azide-bridged, cyclic tetranuclear Ni^II clusters, [{Ni^II(L¹)(μ_1,3-N₃)(H₂O)}₄] (1) and [{Ni^II(L²)(μ_1,3-N₃)(H₂O)}₄] (2), where the ligands used to achieve these species, HL¹ and HL², are the tridentate Schiff base ligands obtained from [1 + 1] condensations of salicylaldehyde with 1-(2-aminoethyl)-piperidine and 4-(2-aminoethyl)-morpholine, respectively. The title compounds, 1 and 2, crystallize in a monoclinic P2₁ space group. Overall, both species can be described in a similar way; where all Ni^II centers within each molecule are hexacoordinated and bound to [L¹]⁻ or [L²]⁻ through the phenoxo oxygen, imine nitrogen, and piperidine/morpholine nitrogen atoms of the corresponding ligand. The remaining coordination sites are satisfied by one molecule of H₂O and two nitrogen atoms from N₃⁻ anions. The latest act as bridges between Ni^II ions, and eventually, only four azido groups are linked to the same number of Ni^II centers resulting in the formation of cyclic Ni^II₄ systems. Interestingly, compounds 1 and 2 are the two sole examples of tetranuclear clusters generated exclusively by EE azide-bridging ligands to date. All the N(azide)−Ni−N(azide) moieties are almost linear in 1 and 2 indicating trans arrangement of the azido ligand. Variable-temperature (2−300 K) magnetic susceptibilities of 1 and 2 have been measured under magnetic fields of 0.04 T (from 2 to 30 K) and 0.7 T (from 30 to 300 K), and magneto-structural correlations have been performed. Despite the presence of both ferromagnetic and antiferromagnetic interactions in both compounds, significant differences have been observed in their magnetic behaviors directly related to the arrangement of the bridging azido ligands. Hence, compound 1 has an overall moderate antiferromagnetic behavior due to the presence of an exchange pathway with an unprecedented Ni−N···N−Ni torsion angle close to 0°, meanwhile complex 2 exhibits a predominant ferromagnetic behavior, with torsion angles between 50 and 90°. Density functional theory calculations have been performed to provide more insight into the magnetic nature of this new family of Ni^II−azido complexes and also to corroborate the fitting of the data.