Observation of Protonation-Induced Spin State Switching in a Cyanido-Bridged {Fe₂Co₂} Molecular Square

Abstract

The self-assembly of [Co(MeTPyA)(CH 3 COO)]-PF 6 (1) and [Fe(bbp)(CN) 3 ] 2− affords a cyanido-bridged squareshaped {Fe 2 Co 2 } tetranuclear complex, [{Co(MeTPyA)(μ 2 -NC) 2 Fe(bbp)(CN)} 2 ]•3H 2 O (2; MeTPyA = tris((3,5-dimethylpyrazol-1-yl)methyl)amine and H 2 bbp = bis(2-benzimidazolyl)pyridine). The possibility of inducing an intramolecular electron transfer coupled spin transition in 2 by employing protonation as an external stimulant is explored. UV−visible spectrophotometric measurements, electrochemical and 1 H NMR studies establish that a reversible intramolecular electron transfer coupled spin transition can be triggered in 2 upon addition of either acid or base.

Cyanido-Bridged Heterobimetallic Molecular Squares: Low-Dimensional Models of Prussian Blue Analogues and Beyond

“…The planar configuration of the tridentate bbp 2− dianion [H 2 bbp = bis(2-benzimidazolyl)-pyridine] was exploited to assemble another type of tricyanido-based metalloligand of formula mer-[(bbp)Fe III (CN) 3 ] 2− where the three peripheral cyanide ligands are mer-positioned (Scheme 8). 105,106 The cyanido-bridged {[Ni(tren)] 2 [Fe(bbp)(CN) 3 ] 2 }• 7MeOH complex with a square-like arrangement was obtained when the mer-[(bbp)Fe III (CN) 3 ] 2− bulding-block was reacted with the preformed [Ni II (tren)] 2+ species [tren = tris(2aminoethyl)amine], the magnetic studies revealing a ferromagnetic interaction between Fe III and Ni II ions through the (ii) The majority of the Ln III ions exhibit high axial or prolate magnetic anisotropy due to the spin−orbit coupling that is a prerequisite to attain slow relaxation of the magnetization. 107 Because of the practically isotropic character of the Gd III center and the diamagnetic La III / Lu III ions, they are exceptions and the analysis of the magnetic data of their nd/4f derivatives are more accessible for theoretical approaches.…”

“…The planar configuration of the tridentate bbp 2– dianion [H 2 bbp = bis­(2-benzimidazolyl)-pyridine] was exploited to assemble another type of tricyanido-based metalloligand of formula mer -[(bbp)­Fe III (CN) 3 ] 2– where the three peripheral cyanide ligands are mer -positioned (Scheme ). , …”

“…Also, the [Co­(MeTPyA)­(μ-NC) 2 Fe­(bbp)­(CN)] 2 ·3H 2 O square-like molecule (Figure ) resulted when using the same tricyano species as a ligand toward the [Co­(MeTPyA)­(CH 3 COO)] + complex cation [MeTPyA = tris­((3,5-dimethylpyrazol-1-yl)­methyl)­amine]. This last compound was shown to be a rare case of a molecular switch responsive to a chemical stimulus, the ETCST process being induced by protonation …”

“…Schematic representation of the pH influence on the oxidation state of cobalt and iron ions within the [Co­(MeTPyA)­(μ-NC) 2 Fe­(bbp)­(CN)] 2 ] molecular square …”

pH-Switching of the luminescent, redox, and magnetic properties in a spin crossover cobalt(ii) molecular nanomagnet

“…Coordination compounds of transition metal ions with noninnocent ligands have attracted much attention in diverse areas of nanoscience due to their unusual combination of chemical (Brønsted or Lewis acidity, redox, and catalytic) and physical properties (optical or luminescent, conducting, and magnetic) resulting from the metal and its ligand counterpart. [1][2][3][4][5][6] The ongoing crucial step towards new nanotechnologies is to successfully modulate their physicochemical properties through a variety of internal factors, either electronic (metal oxidation and spin states) or steric ones (ligand substituents and conformation), and eventually to switch them under the presence of external stimuli, either of chemical (pH and chemical analytes) or physical nature (temperature, hydrostatic pressure, light, electric and magnetic elds). [3][4][5][6] This goal has been successfully achieved using mononuclear rst-row transition metal complexes as both synthetic and theoretical models of dynamic molecular systems (DMS).…”