Evidence of protonation induced intra-molecular metal-to-metal charge transfer in a highly symmetric cyanido bridged {Fe₂Ni₂} molecular square

Abstract

A highly symmetric cyanido bridged tetranuclear square shaped [NiII2FeIII2] aggregate exhibits protonation induced intra-molecular electron transfer in solution and switching between [NiII2FeIII2] and [NiIII2FeII2] states.

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

“…The protonation-induced shifting of the Fe III /Fe II redox couple in 2 toward a more positive electrode potential is observed in case of a tricyanido iron(III) precursor complex as well as in the dinuclear Fe-Co aggregate prepared by employing this precursor. 28,35 Due to the shifting of Fe III /Fe II redox couples in 2 toward more positive electrode potential, the difference in redox potential, ΔE (ΔE = E Fe − E Co ) between Fe and Co centers in 2 is reduced and becomes optimum to trigger ETCST in accordance with Marcus−Hush theory. 50 It may be noted that the ΔE value for pristine 2 is −1.03 V, which is considerably above the limit for the observation of ETCST in a tetranuclear Fe-Co PBA.…”

“…However, only three molecular PB analogues reported so far display protonationinduced ETCST behavior. 26,28,33,35 Herein, we employed a tricyano Fe(III) linker that undergoes considerable redox variation upon protonation to construct a cyanido-bridged Fe-Co square-shaped tetranuclear aggregate. The self-assembly of The FT-IR spectrum of 2 shows intense peaks at ∼1619 and ∼1557 cm −1 which correspond to the CN and CC stretching vibration of N-heterocyclic rings, respectively (Figure S2).…”

“…In this regard, protonation of N-donor blocking ligands present on the constituent Fe-Co fragments has emerged as an elegant tool to tune the redox potential difference and thereby facilitate ETCST. However, only three molecular PB analogues reported so far display protonation-induced ETCST behavior. ,,, Herein, we employed a tricyano Fe­(III) linker that undergoes considerable redox variation upon protonation to construct a cyanido-bridged Fe-Co square-shaped tetranuclear aggregate. The self-assembly of [Co­(MeTPyA)­(CH 3 COO)]­PF 6 ( 1 ) with the cyanometalate linker [Fe­(bbp)­(CN) 3 ] 2– has resulted in the successful isolation of a tetranuclear cyanido-bridged square aggregate, [{Co­(MeTPyA)­(μ 2 -NC) 2 Fe­(bbp)­(CN)} 2 ]·3H 2 O ( 2 ).…”

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

“…Homoleptic [M(CN) x ] n– metalloligands ( x = 4, 6, and 8 and n = 2 and 3) with multiple coordination sites, rarely generate cyanido-bridged square-like molecules when are combined with 3 d -based species whose coordination sphere is partially blocked. − Even though the cyanido-based [M III (CN) 6 ] 3– metalloligands (M = Fe, Cr, and Co) are largely available, only a few examples of cyanido-bridged d - d ′ squares were reported involving hexacyanoferrate­(III) ion as an assembling unit (Scheme ). − The preformed [Cu­(bpca/bpcam)­(H 2 O) x ] + species [Hbpca = bis­(2-pyridylcarbonyl)­amine and Hbpcam = bis­(2-pyrimidylcarbonyl)­amide with x = 2 and 3, respectively], where three of the equatorial sites at the Cu II ion are occupied by the tridentate bpca/bpcam ligands and the remaining sites are filled by coordinated water molecules, assembled into two cyclic square-shaped molecules when reacting with K 3 [Fe(CN) 6 ] .…”

Thermally induced charge transfer in a quinoid-bridged linear Cu3compound

“…1 Metal-metal or metalligand charge transfer always occurs in molecular valence tautomers, leading to the redistribution of electron density and exhibiting electrical, optical, and magnetic properties, and can be further controlled by multiple external stimuli such as temperature, light, and electric field. [2][3][4][5][6][7][8] Therefore, molecular valence tautomers have potential application in molecular switches, displays, memory devices, and sensors. [9][10][11] The redox-active quinone ligand is one of the typical ligands for building metal-ligand charge transfer valence tautomerism.…”