Ambient-Temperature Spin-State Switching Achieved by Protonation of the Amino Group in [Fe(H₂Bpz₂)₂(bipy-NH₂)]

Magnetism of a complex [Fe­(H₂Bpz₂)₂(bipy-NH₂)] (H₂Bpz₂ = dihydrobis­(1-pyrazolyl)­borate, bipy-NH₂ = 4,4′-diamino-2,2′-bipyridine) has been altered from paramagnetic to spin-crossover (SCO) behavior, through protonation of one amino group of bipy-NH₂ with CF₃SO₃H. Complete SCO transition, both in solid state and in solution, occurs at ambient temperature

Ambient-Temperature Spin-State Switching Achieved by Protonation of the Amino Group in [Fe(H₂Bpz₂)₂(bipy-NH₂)]

Magnetism of a complex [Fe­(H₂Bpz₂)₂(bipy-NH₂)] (H₂Bpz₂ = dihydrobis­(1-pyrazolyl)­borate, bipy-NH₂ = 4,4′-diamino-2,2′-bipyridine) has been altered from paramagnetic to spin-crossover (SCO) behavior, through protonation of one amino group of bipy-NH₂ with CF₃SO₃H. Complete SCO transition, both in solid state and in solution, occurs at ambient temperature

Multiredox Active [3 × 3] Copper Grids

A nonanuclear copper grid complex, [Cu^II₉(L)₆]­(BF₄)₆·1-PrOH·5H₂O (<b>1</b>·1-PrOH·5H₂O; L = 2,6-bis­[5-(2-pyridinyl)-1<i>H</i>-pyrazol-3-yl]­pyridine), was synthesized with a [3 × 3] grid structure consisting of nine Cu^II ions and six deprotonated ligands and displayed four-step quasi-reversible redox behavior from [Cu^II₉] to [Cu^I₄Cu^II₅]. The corresponding heterovalent complex [Cu^I₂Cu^II₇(L)₆]­(PF₆)₄·3H₂O (<b>2</b>·3H₂O) was successfully isolated and had a distorted core structure that radically changed the intramolecular magnetic coupling pathways

Chiral Single-Chain Magnet: Helically Stacked [Mn^III₂Cu^II] Triangles

The one-dimensional complex [Mn^III₂Cu^II(μ₃-O)­(Cl-sao)₃(EtOH)₂]·EtOH (Mn₂Cu) was obtained by the metal replacement reaction of the trinuclear manganese complex (Et₃NH)­[Mn^III₃(μ₃-O)­Cl₂(Cl-sao)₃(MeOH)₂(H₂O)₂] with [Cu­(acac)₂]. The Mn₂Cu chain exhibits single-chain-magnet behavior with finite-size effects due to its large magnetic anisotropy

Cyanide-Bridged Decanuclear Cobalt–Iron Cage

A cyanide-bridged decanuclear [Co₆Fe₄] cluster was synthesized by a one-pot reaction, and the magnetic properties and electronic configuration were investigated. The complex displayed thermally controlled electron-transfer-coupled spin transition (ETCST) behavior between Co^III low-spin–NC–Fe^II low-spin and Co^II high-spin–NC–Fe^III low-spin states, as confirmed by single-crystal X-ray, magnetic, and Mössbauer analyses

X‑ray Magnetic Circular Dichroism Investigation of the Electron Transfer Phenomena Responsible for Magnetic Switching in a Cyanide-Bridged [CoFe] Chain

The cyanide-bridged [CoFe] one-dimensional chain, [Co^II((<i>R</i>)-pabn)]­[Fe^III(Tp)­(CN)₃]­(BF₄)·MeOH·2H₂O, where (<i>R</i>)-pabn = (<i>R</i>)-<i>N</i>2,<i>N</i>(2′)-bis­(pyridin-2-ylmethyl)-1,1′-binaphthyl-2,2′-diamine and Tp = hydrotris­(pyrazolyl)­borate, exhibits magnetic and electric bistabilities originating from an electron transfer coupled spin transition between Fe–CN–Co pairs. The use of L-edge X-ray absorption spectroscopy (XAS) in combination with L-edge X-ray magnetic circular dichroism (XMCD) is explored for the investigation of the electronic structure and magnetization of Co and Fe ions separately, in both diamagnetic and paramagnetic states. It has been established from susceptibility results that the switching between diamagnetic and paramagnetic phases emanates from electron transfer between low spin Fe­(II) and Co­(III), resulting in low spin Fe­(III) (<i>S</i> = 1/2) and high spin Co­(II) (<i>S</i> = 3/2). The XAS and XMCD results are consistent with the bulk susceptibility measurements, where greater detail regarding the charge transfer process is determined. The Fe–CN–Co electron transfer pathway is highlighted by a strongly XMCD dependent transition to a cyanide back bonding orbital, giving evidence for strong hybridization with Fe­(III) t_2g orbitals. In addition to thermally induced and photoinduced switching, [CoFe] is found to exhibit a switching by grinding induced dehydration. Analysis of XAS shows that on grinding diamagnetic [CoFe], 75% of metal ions lock into the magnetic Co­(II)­Fe­(III) phase. Density functional theory calculations based on the [CoFe] crystal structure in the magnetic and nonmagnetic phases aid the spectroscopic results and provide a complementary insight into the electronic configuration of the [CoFe] 3d shells, quantifying the change in ligand field around Co and Fe centers on charge transfer

Intermediate-Spin Iron(III) Complexes Having a Redox-Noninnocent Macrocyclic Tetraamido Ligand

An iron­(III) complex having a dibenzotetraethyltetraamido macrocyclic ligand (DTTM^4–), (NEt₄)₂[Fe^III(DTTM)­Cl] (<b>1</b>), was synthesized and characterized by crystallographic, spectroscopic, and electrochemical methods. Complex <b>1</b> has a square-pyramidal structure in the <i>S</i> = ³/₂ spin state. The complex exhibited two reversible redox waves at +0.36 and +0.68 V (vs SCE) in the cyclic voltammogram measured in CH₂Cl₂ at room temperature. The stepwise oxidation of <b>1</b> using chemical oxidants allowed us to observe clear and distinct spectral changes with distinct isosbestic points for each step, in which oxidation occurred at the phenylenediamido moiety rather than the iron center. One-electron oxidation of <b>1</b> by 1 equiv of [Ru^III(bpy)₃]­(ClO₄)₃ (bpy = 2,2′-bipyridine) in CH₂Cl₂ afforded square-pyramidal (NEt₄)­[Fe­(DTTM)­Cl] (<b>2</b>), which was in the <i>S</i> = 1 spin state involving a ligand radical and showed a slightly distorted square-pyramidal structure. Complex <b>2</b> showed an intervalence charge-transfer band at 900 nm, which was assigned on the basis of time-dependent density functional theory calculations, to indicate that the complex is in a class IIA mixed-valence ligand-radical regime with <i>H</i>_ab = 884 cm^–1. Two-electron oxidation of <b>1</b> by 2 equiv of [(4-Br-Ph)₃N^•+]­(SbCl₆) in CH₂Cl₂ afforded two-electron-oxidized species of <b>1</b>, [Fe­(DTTM)­Cl] (<b>3</b>), which was in the <i>S</i> = ¹/₂ spin state; complex <b>3</b> exhibited a distorted square-pyramidal structure. X-ray absorption near-edge structure spectra of <b>1</b>–<b>3</b> were measured in both CH₃CN solutions and BN pellets to observe comparable rising-edge energies for the three complexes, and Mössbauer spectra of <b>1</b>–<b>3</b> showed almost identical isomer shifts and quadruple splitting parameters, indicating that the iron centers of the three complexes are intact to be in the intermediate-spin iron­(III) state. Thus, in complexes <b>2</b> and <b>3</b>, it is evident that antiferromagnetic coupling is operating between the unpaired electron(s) of the ligand radical(s) and those of the iron­(III) center