Supplemental Material - ChatGPT Hallucinates Non-existent Citations: Evidence from Economics

Supplemental Material for ChatGPT Hallucinates Non-existent Citations: Evidence from Economics by Joy Buchanan, Stephen Hill and Olga Shapoval in The American Economist</p

Diversity of New Structural Types in Polynuclear Iron Chemistry with a Tridentate N,N,O Ligand

The syntheses, crystal structures, and magnetochemical characterization of four new iron clusters [Fe7O4(O2CPh)11(dmem)2] (1), [Fe7O4(O2CMe)11(dmem)2] (2), [Fe6O2(OH)4(O2CBut)8(dmem)2] (3), and [Fe3O(O2CBut)2(N3)3(dmem)2] (4) (dmemH = Me2NCH2CH2N(Me)CH2CH2OH) = 2-{[2-(dimethylamino)ethyl]methylamino}ethanol) are reported. The reaction of dmemH with [Fe3O(O2CR)6(H2O)3](NO3) (R = Ph (1), Me (2), and But (3)) gave 1, 2, and 3, respectively, whereas 4 was obtained from the reaction of 3 with sodium azide. The complexes all possess rare or novel core topologies. The core of 1 comprises two [Fe4(μ3-O)2]8+ butterfly units sharing a common body Fe atom. The core of 2 consists of a [Fe3O3] ring with each doubly bridging O2- ion becoming μ3 by also bridging to a third, external Fe atom; a seventh Fe atom is attached on the outside of this core via an additional μ3-O2- ion. The core of 3 consists of a [Fe4(μ3-O)2]8+ butterfly unit with an Fe atom attached above and below this by bridging O atoms. Finally, the core of 4 is an isosceles triangle bridged by a μ3-O2- ion with a rare T-shaped geometry and with the azide groups all bound terminally. Variable-temperature, solid-state dc, and ac magnetization studies were carried out on complexes 1−4 in the 5.0−300 K range. Fitting of the obtained magnetization (M) vs field (H) and temperature (T) data by matrix diagonalization and including only axial anisotropy (zero-field splitting) established that 1, 2, and 4 each possess an S = 5/2 ground state spin, whereas 3 has an S = 5 ground state. As is usually the case, good fits of the magnetization data could be obtained with both positive and negative D values. To obtain more accurate values and to determine the sign of D, high-frequency EPR studies were carried out on single crystals of representative complexes 1·4MeCN and 3·2MeCN, and these gave D = +0.62 cm-1 and |E| ≥ 0.067 cm-1 for 1·4MeCN and D = −0.25 cm-1 for 3·2MeCN. The magnetic susceptibility data for 4 were fit to the theoretical χM vs T expression derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, and this revealed the pairwise exchange parameters to be antiferromagnetic with values of Ja = −3.6 cm-1 and Jb = −45.9 cm-1. The combined results demonstrate the ligating flexibility of dmem and its usefulness in the synthesis of a variety of Fex molecular species

Identification of an X‑Band Clock Transition in Cp′₃Pr^– Enabled by a 4f²5d¹ Configuration

Molecular qubits offer an attractive basis for quantum information processing, but challenges remain with regard to sustained coherence. Qubits based on clock transitions offer a method to improve the coherence times. We propose a general strategy for identifying molecules with high-frequency clock transitions in systems where a d electron is coupled to a crystal-field singlet state of an f configuration, resulting in an MJ = ±1/2 ground state with strong hyperfine coupling. Using this approach, a 9.834 GHz clock transition was identified in a molecular Pr complex, [K(crypt)][Cp′3PrII], leading to 3-fold enhancements in T2 relative to other transitions in the spectrum. This result indicates the promise of the design principles outlined here for the further development of f-element systems for quantum information applications

Slow Magnetic Relaxation Induced by a Large Transverse Zero-Field Splitting in a Mn^IIRe^IV(CN)₂ Single-Chain Magnet

The model compounds (NBu₄)₂[ReCl₄(CN)₂] (<b>1</b>), (DMF)₄ZnReCl₄(CN)₂ (<b>2</b>), and [(PY5Me₂)₂Mn₂ReCl₄(CN)₂]­(PF₆)₂ (<b>3</b>) have been synthesized to probe the origin of the magnetic anisotropy barrier in the one-dimensional coordination solid (DMF)₄MnReCl₄(CN)₂ (<b>4</b>). High-field electron paramagnetic resonance spectroscopy reveals the presence of an easy-plane anisotropy (<i>D</i> > 0) with a significant transverse component, <i>E</i>, in compounds <b>1</b>–<b>3</b>. These findings indicate that the onset of one-dimensional spin correlations within the chain compound <b>4</b> leads to a suppression of quantum tunneling of the magnetization within the easy plane, resulting in magnetic bistability and slow relaxation behavior. Within this picture, it is the transverse <i>E</i> term associated with the Re^IV centers that determines the easy axis and the anisotropy energy scale associated with the relaxation barrier. The results demonstrate for the first time that slow magnetic relaxation can be achieved through optimization of the transverse anisotropy associated with magnetic ions that possess easy-plane anisotropy, thus providing a new direction in the design of single-molecule and single-chain magnets

Binding of Higher Alcohols onto Mn₁₂ Single-Molecule Magnets (SMMs): Access to the Highest Barrier Mn₁₂ SMM

Two new members of the Mn12 family of single-molecule magnets (SMMs), [Mn12O12(O2CCH2But)16(ButOH)(H2O)3]·2ButOH (3·2ButOH) and [Mn12O12(O2CCH2But)16(C5H11OH)4] (4) (C5H11OH is 1-pentanol), are reported. They were synthesized from [Mn12O12(O2CMe)16(H2O)4]·2MeCO2H·4H2O (1) by carboxylate substitution and crystallization from the appropriate alcohol-containing solvent. Complexes 3 and 4 are new members of the recently established [Mn12O12(O2CCH2But)16(solv)4] (solv = H2O, alcohols) family of SMMs. Only one bulky ButOH can be accommodated into 3, and even this causes significant distortion of the [Mn12O12] core. Variable-temperature, solid-state alternating current (AC) magnetization studies were carried out on complexes 3 and 4, and they established that both possess an S = 10 ground state spin and are SMMs. However, the magnetic behavior of the two compounds was found to be significantly different, with 4 showing out-of-phase AC peaks at higher temperatures than 3. High-frequency electron paramagnetic resonance (HFEPR) studies were carried out on single crystals of 3·2ButOH and 4, and these revealed that the axial zero-field splitting constant, D, is very different for the two compounds. Furthermore, it was established that 4 is the Mn12 SMM with the highest kinetic barrier (Ueff) to date. The results reveal alcohol substitution as an additional and convenient means to affect the magnetization relaxation barrier of the Mn12 SMMs without major change to the ligation or oxidation state

Diversity of New Structural Types in Polynuclear Iron Chemistry with a Tridentate N,N,O Ligand

The syntheses, crystal structures, and magnetochemical characterization of four new iron clusters [Fe7O4(O2CPh)11(dmem)2] (1), [Fe7O4(O2CMe)11(dmem)2] (2), [Fe6O2(OH)4(O2CBut)8(dmem)2] (3), and [Fe3O(O2CBut)2(N3)3(dmem)2] (4) (dmemH = Me2NCH2CH2N(Me)CH2CH2OH) = 2-{[2-(dimethylamino)ethyl]methylamino}ethanol) are reported. The reaction of dmemH with [Fe3O(O2CR)6(H2O)3](NO3) (R = Ph (1), Me (2), and But (3)) gave 1, 2, and 3, respectively, whereas 4 was obtained from the reaction of 3 with sodium azide. The complexes all possess rare or novel core topologies. The core of 1 comprises two [Fe4(μ3-O)2]8+ butterfly units sharing a common body Fe atom. The core of 2 consists of a [Fe3O3] ring with each doubly bridging O2- ion becoming μ3 by also bridging to a third, external Fe atom; a seventh Fe atom is attached on the outside of this core via an additional μ3-O2- ion. The core of 3 consists of a [Fe4(μ3-O)2]8+ butterfly unit with an Fe atom attached above and below this by bridging O atoms. Finally, the core of 4 is an isosceles triangle bridged by a μ3-O2- ion with a rare T-shaped geometry and with the azide groups all bound terminally. Variable-temperature, solid-state dc, and ac magnetization studies were carried out on complexes 1−4 in the 5.0−300 K range. Fitting of the obtained magnetization (M) vs field (H) and temperature (T) data by matrix diagonalization and including only axial anisotropy (zero-field splitting) established that 1, 2, and 4 each possess an S = 5/2 ground state spin, whereas 3 has an S = 5 ground state. As is usually the case, good fits of the magnetization data could be obtained with both positive and negative D values. To obtain more accurate values and to determine the sign of D, high-frequency EPR studies were carried out on single crystals of representative complexes 1·4MeCN and 3·2MeCN, and these gave D = +0.62 cm-1 and |E| ≥ 0.067 cm-1 for 1·4MeCN and D = −0.25 cm-1 for 3·2MeCN. The magnetic susceptibility data for 4 were fit to the theoretical χM vs T expression derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, and this revealed the pairwise exchange parameters to be antiferromagnetic with values of Ja = −3.6 cm-1 and Jb = −45.9 cm-1. The combined results demonstrate the ligating flexibility of dmem and its usefulness in the synthesis of a variety of Fex molecular species

Diversity of New Structural Types in Polynuclear Iron Chemistry with a Tridentate N,N,O Ligand

The syntheses, crystal structures, and magnetochemical characterization of four new iron clusters [Fe7O4(O2CPh)11(dmem)2] (1), [Fe7O4(O2CMe)11(dmem)2] (2), [Fe6O2(OH)4(O2CBut)8(dmem)2] (3), and [Fe3O(O2CBut)2(N3)3(dmem)2] (4) (dmemH = Me2NCH2CH2N(Me)CH2CH2OH) = 2-{[2-(dimethylamino)ethyl]methylamino}ethanol) are reported. The reaction of dmemH with [Fe3O(O2CR)6(H2O)3](NO3) (R = Ph (1), Me (2), and But (3)) gave 1, 2, and 3, respectively, whereas 4 was obtained from the reaction of 3 with sodium azide. The complexes all possess rare or novel core topologies. The core of 1 comprises two [Fe4(μ3-O)2]8+ butterfly units sharing a common body Fe atom. The core of 2 consists of a [Fe3O3] ring with each doubly bridging O2- ion becoming μ3 by also bridging to a third, external Fe atom; a seventh Fe atom is attached on the outside of this core via an additional μ3-O2- ion. The core of 3 consists of a [Fe4(μ3-O)2]8+ butterfly unit with an Fe atom attached above and below this by bridging O atoms. Finally, the core of 4 is an isosceles triangle bridged by a μ3-O2- ion with a rare T-shaped geometry and with the azide groups all bound terminally. Variable-temperature, solid-state dc, and ac magnetization studies were carried out on complexes 1−4 in the 5.0−300 K range. Fitting of the obtained magnetization (M) vs field (H) and temperature (T) data by matrix diagonalization and including only axial anisotropy (zero-field splitting) established that 1, 2, and 4 each possess an S = 5/2 ground state spin, whereas 3 has an S = 5 ground state. As is usually the case, good fits of the magnetization data could be obtained with both positive and negative D values. To obtain more accurate values and to determine the sign of D, high-frequency EPR studies were carried out on single crystals of representative complexes 1·4MeCN and 3·2MeCN, and these gave D = +0.62 cm-1 and |E| ≥ 0.067 cm-1 for 1·4MeCN and D = −0.25 cm-1 for 3·2MeCN. The magnetic susceptibility data for 4 were fit to the theoretical χM vs T expression derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, and this revealed the pairwise exchange parameters to be antiferromagnetic with values of Ja = −3.6 cm-1 and Jb = −45.9 cm-1. The combined results demonstrate the ligating flexibility of dmem and its usefulness in the synthesis of a variety of Fex molecular species

Slow Magnetic Relaxation Induced by a Large Transverse Zero-Field Splitting in a Mn^IIRe^IV(CN)₂ Single-Chain Magnet

The model compounds (NBu₄)₂[ReCl₄(CN)₂] (<b>1</b>), (DMF)₄ZnReCl₄(CN)₂ (<b>2</b>), and [(PY5Me₂)₂Mn₂ReCl₄(CN)₂]­(PF₆)₂ (<b>3</b>) have been synthesized to probe the origin of the magnetic anisotropy barrier in the one-dimensional coordination solid (DMF)₄MnReCl₄(CN)₂ (<b>4</b>). High-field electron paramagnetic resonance spectroscopy reveals the presence of an easy-plane anisotropy (<i>D</i> > 0) with a significant transverse component, <i>E</i>, in compounds <b>1</b>–<b>3</b>. These findings indicate that the onset of one-dimensional spin correlations within the chain compound <b>4</b> leads to a suppression of quantum tunneling of the magnetization within the easy plane, resulting in magnetic bistability and slow relaxation behavior. Within this picture, it is the transverse <i>E</i> term associated with the Re^IV centers that determines the easy axis and the anisotropy energy scale associated with the relaxation barrier. The results demonstrate for the first time that slow magnetic relaxation can be achieved through optimization of the transverse anisotropy associated with magnetic ions that possess easy-plane anisotropy, thus providing a new direction in the design of single-molecule and single-chain magnets

Diversity of New Structural Types in Polynuclear Iron Chemistry with a Tridentate N,N,O Ligand

The syntheses, crystal structures, and magnetochemical characterization of four new iron clusters [Fe7O4(O2CPh)11(dmem)2] (1), [Fe7O4(O2CMe)11(dmem)2] (2), [Fe6O2(OH)4(O2CBut)8(dmem)2] (3), and [Fe3O(O2CBut)2(N3)3(dmem)2] (4) (dmemH = Me2NCH2CH2N(Me)CH2CH2OH) = 2-{[2-(dimethylamino)ethyl]methylamino}ethanol) are reported. The reaction of dmemH with [Fe3O(O2CR)6(H2O)3](NO3) (R = Ph (1), Me (2), and But (3)) gave 1, 2, and 3, respectively, whereas 4 was obtained from the reaction of 3 with sodium azide. The complexes all possess rare or novel core topologies. The core of 1 comprises two [Fe4(μ3-O)2]8+ butterfly units sharing a common body Fe atom. The core of 2 consists of a [Fe3O3] ring with each doubly bridging O2- ion becoming μ3 by also bridging to a third, external Fe atom; a seventh Fe atom is attached on the outside of this core via an additional μ3-O2- ion. The core of 3 consists of a [Fe4(μ3-O)2]8+ butterfly unit with an Fe atom attached above and below this by bridging O atoms. Finally, the core of 4 is an isosceles triangle bridged by a μ3-O2- ion with a rare T-shaped geometry and with the azide groups all bound terminally. Variable-temperature, solid-state dc, and ac magnetization studies were carried out on complexes 1−4 in the 5.0−300 K range. Fitting of the obtained magnetization (M) vs field (H) and temperature (T) data by matrix diagonalization and including only axial anisotropy (zero-field splitting) established that 1, 2, and 4 each possess an S = 5/2 ground state spin, whereas 3 has an S = 5 ground state. As is usually the case, good fits of the magnetization data could be obtained with both positive and negative D values. To obtain more accurate values and to determine the sign of D, high-frequency EPR studies were carried out on single crystals of representative complexes 1·4MeCN and 3·2MeCN, and these gave D = +0.62 cm-1 and |E| ≥ 0.067 cm-1 for 1·4MeCN and D = −0.25 cm-1 for 3·2MeCN. The magnetic susceptibility data for 4 were fit to the theoretical χM vs T expression derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, and this revealed the pairwise exchange parameters to be antiferromagnetic with values of Ja = −3.6 cm-1 and Jb = −45.9 cm-1. The combined results demonstrate the ligating flexibility of dmem and its usefulness in the synthesis of a variety of Fex molecular species

Binding of Higher Alcohols onto Mn₁₂ Single-Molecule Magnets (SMMs): Access to the Highest Barrier Mn₁₂ SMM

Two new members of the Mn12 family of single-molecule magnets (SMMs), [Mn12O12(O2CCH2But)16(ButOH)(H2O)3]·2ButOH (3·2ButOH) and [Mn12O12(O2CCH2But)16(C5H11OH)4] (4) (C5H11OH is 1-pentanol), are reported. They were synthesized from [Mn12O12(O2CMe)16(H2O)4]·2MeCO2H·4H2O (1) by carboxylate substitution and crystallization from the appropriate alcohol-containing solvent. Complexes 3 and 4 are new members of the recently established [Mn12O12(O2CCH2But)16(solv)4] (solv = H2O, alcohols) family of SMMs. Only one bulky ButOH can be accommodated into 3, and even this causes significant distortion of the [Mn12O12] core. Variable-temperature, solid-state alternating current (AC) magnetization studies were carried out on complexes 3 and 4, and they established that both possess an S = 10 ground state spin and are SMMs. However, the magnetic behavior of the two compounds was found to be significantly different, with 4 showing out-of-phase AC peaks at higher temperatures than 3. High-frequency electron paramagnetic resonance (HFEPR) studies were carried out on single crystals of 3·2ButOH and 4, and these revealed that the axial zero-field splitting constant, D, is very different for the two compounds. Furthermore, it was established that 4 is the Mn12 SMM with the highest kinetic barrier (Ueff) to date. The results reveal alcohol substitution as an additional and convenient means to affect the magnetization relaxation barrier of the Mn12 SMMs without major change to the ligation or oxidation state