Spin Crossover in Fe(II) and Co(II) Complexes with the Same Click-Derived Tripodal Ligand

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• 作者：David Schweinfurth ; Serhiy Demeshko ; Stephan Hohloch ; Marc Steinmetz ; Jan Gerit Brandenburg ; Sebastian Dechert ; Franc Meyer ; Stefan Grimme ; Biprajit Sarkar
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：August 18, 2014
• 年：2014
• 卷：53
• 期：16
• 页码：8203-8212
• 全文大小：518K
• ISSN：1520-510X

文摘

The complexes [Fe(tbta)₂](BF₄)₂路2EtOH (1), [Fe(tbta)₂](BF₄)₂路2CH₃CN (2), [Fe(tbta)₂](BF₄)₂路2CHCl₃ (3), and [Fe(tbta)₂](BF₄)₂ (4) were synthesized from the respective metal salts and the click-derived tripodal ligand tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (tbta). Structural characterization of these complexes (at 100 or 133 K) revealed Fe鈥揘 bond lengths for the solvent containing compounds 1鈥?b>3 that are typical of a high spin (HS) Fe(II) complex. In contrast, the solvent-free compound 4 show Fe鈥揘 bond lengths that are characteristic of a low spin (LS) Fe(II) state. The Fe center in all complexes is bound to two triazole and one amine N atom from each tbta ligand, with the third triazole arm remaining uncoordinated. The benzyl substituents of the uncoordinated triazole arms and the triazole rings engage in strong intermolecular and intramolecular noncovalent interactions. These interactions are missing in the solvent containing molecules 1, 2, and 3, where the solvent molecules occupy positions that hinder these noncovalent interactions. The solvent-free complex (4) displays spin crossover (SCO) with a spin transition temperature T_1/2 near room temperature, as revealed by superconducting quantum interference device (SQUID) magnetometric and M枚ssbauer spectroscopic measurements. The complexes 1, 2, and 3 remain HS throughout the investigated temperature range. Different torsion angles at the metal centers, which are influenced by the noncovalent interactions, are likely responsible for the differences in the magnetic behavior of these complexes. The corresponding solvent-free Co(II) complex (6) is also LS at lower temperatures and displays SCO with a temperature T_1/2 near room temperature. Theoretical calculations at molecular and periodic DFT-D3 levels for 1鈥?b>4 qualitatively reproduce the experimental findings, and corroborate the importance of intermolecular and intramolecular noncovalent interactions for the magnetic properties of these complexes. The present work thus represents rare examples of SCO complexes where the use of identical ligand sets produces SCO in Fe(II) as well as Co(II) complexes.