1
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Rodríguez-Kessler PL, Muñoz-Castro A. Intermediate Intercluster Bond Orders. Electronic Communication in Au 38(SR) 24 Superatomic Molecules. Chemphyschem 2024:e202400183. [PMID: 38831496 DOI: 10.1002/cphc.202400183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2024] [Revised: 04/23/2024] [Accepted: 06/03/2024] [Indexed: 06/05/2024]
Abstract
Ligand-protected gold clusters remain potential building blocks for envisaged molecular materials. The archetypal Au38(SR)24 cluster can be viewed as a robust template for the fusion of two Au25(SR)18 - cluster units, retaining a bi-icosahedral Au23 core. Via electrochemical properties, the overall charge state can be selectively tuned, enabling the access of 14 valence electron (ve) species featuring a single intercluster bond and nearby charge from -1 to +3, achieving related species bearing 15- to 11-ve with variable intercluster bond orders. Here, we explore the characteristics of intermediate intercluster bond orders in order to provide insights into the plausible electron communication between the constituent building blocks, with Au38(SR)24, as a representative template. Our results denote a small structural variation along -1 to +3 charge states, provided by the core-protecting ligand interaction, which is enhanced towards more oxidized species. The remaining unpaired electron from intermediate intercluster bond orders of 1.5 for Au38(SR)24 1-, 1.5 for Au38(SR)24 1+, and 2.5 for Au38(SR)24 3+, holds delocalized characteristics between the building block units, favoring electron communication for conductive and cooperative cluster aggregates. Such features are relevant for the formation of molecular electronic device applications, favoring the rationalization prior to engaging in explorative synthesis of larger ligand-protected cluster aggregates.
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Affiliation(s)
- Peter L Rodríguez-Kessler
- Centro de Investigaciones en Óptica A.C., Loma del Bosque 115, Col. Lomas del Campestre, León, Guanajuato, 37150, Mexico
| | - Alvaro Muñoz-Castro
- Facultad de Ingeniería, Arquitectura y Diseño, Universidad San Sebastián, Bellavista 7, Santiago, 8420524, Chile
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2
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Pavlak I, Matasović L, Buchanan EA, Michl J, Rončević I. Electronic Structure of Metalloporphenes, Antiaromatic Analogues of Graphene. J Am Chem Soc 2024; 146:3992-4000. [PMID: 38294407 PMCID: PMC10870706 DOI: 10.1021/jacs.3c12079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2023] [Revised: 01/13/2024] [Accepted: 01/17/2024] [Indexed: 02/01/2024]
Abstract
Zinc porphene is a two-dimensional material made of fully fused zinc porphyrins in a tetragonal lattice. It has a fully conjugated π-system, making it similar to graphene. Zinc porphene has recently been synthesized, and a combination of rough conductivity measurements and infrared and Raman spectroscopies all suggested that it is a semiconductor (Magnera, T.F. et al. Porphene and Porphite as Porphyrin Analogs of Graphene and Graphite, Nat. Commun.2023, 14, 6308). This is in contrast with all previous predictions of its electronic structure, which indicated metallic conductivity. We show that the gap-opening in zinc porphene is caused by a Peierls distortion of its unit cell from square to rectangular, thus giving the first account of its electronic structure in agreement with the experiment. Accounting for this distortion requires proper treatment of electron delocalization, which can be done using hybrid functionals with a substantial amount of exact exchange. Such a functional, PBE38, is then applied to predict the properties of many first transition row metalloporphenes, some of which have already been prepared. We find that changing the metal strongly affects the electronic structure of metalloporphenes, resulting in a rich variety of both metallic conductors and semiconductors, which may be of great interest to molecular electronics and spintronics. Properties of these materials are mostly governed by the extent of the Peierls distortion and the number of electrons in their π-system, analogous to changes in aromaticity observed in cyclic conjugated molecules upon oxidation or reduction. These results give an account of how the concept of antiaromaticity can be extended to periodic systems.
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Affiliation(s)
- Ivan Pavlak
- Department
of Chemistry, Faculty of Science, University
of Zagreb, Horvatovac 102A, Zagreb 10000, Croatia
| | - Lujo Matasović
- Cavendish
Laboratory, Department of Physics, University
of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, U.K.
| | - Eric A. Buchanan
- Department
of Chemistry and Biochemistry, University
of Colorado, Boulder, Colorado 80309-0215, United States
| | - Josef Michl
- Department
of Chemistry and Biochemistry, University
of Colorado, Boulder, Colorado 80309-0215, United States
- Institute
of Organic Chemistry and Biochemistry of the CAS, Flemingovo nám. 2, Prague 6 16610, Czech Republic
| | - Igor Rončević
- Institute
of Organic Chemistry and Biochemistry of the CAS, Flemingovo nám. 2, Prague 6 16610, Czech Republic
- Department
of Chemistry, University of Oxford, Chemistry Research Laboratory, Oxford OX1 3TA, U.K.
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3
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Roger C, Schmiedel A, Holzapfel M, Lukzen NN, Steiner UE, Lambert C. The influence of hindered rotation on electron transfer and exchange interaction in triarylamine-triptycene-perylene diimide triads. Phys Chem Chem Phys 2024; 26:4954-4967. [PMID: 38277181 DOI: 10.1039/d3cp05785b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2024]
Abstract
Stretched electron-donor-bridge-acceptor triads that exhibit intramolecular twisting degrees of freedom are capable of modulating exchange interaction (J) as well as electronic couplings through variable π-overlap at the linear bond links, affecting the rate constants of photoinduced charge separation and recombination. Here we present an in-depth investigation of such effects induced by methyl substituents leading to controlled steric hindrance of intramolecular twisting around biaryl axes. Starting from the parent structure, consisting of a triphenyl amine donor, a triptycene (TTC) bridge and a phenylene-perylene diimide acceptor (Me0), one of the two phenylene linkers attached to the TTC was ortho-substituted by two methyl groups (Me2, Me3), or both such phenylene linkers by two pairs of methyl groups (Me23). Photoinduced charge separation (kCS) leading to a charge-separated (CS) state was studied by fs-laser spectroscopy, charge recombination to either singlet ground state (kS) or to the first excited local triplet state of the acceptor (kT) by ns-laser spectroscopy, whereby kinetic magnetic field effects in an external magnetic field were recorded and analysed using quantum dynamic simulations of the spin dependent kinetics of the CS state. Kinetic spectra of the initial first order rate constants of charge recombination (k(B)) exhibited characteristic J-resonances progressing to lower fields in the series Me0, Me2, Me3, Me23. From the quantum simulations, the values of the parameters J, kS, kT and kSTD, the singlet/triplet dephasing constant, were obtained. They were analysed in terms of molecular dynamics simulations of the intramolecular twisting dynamics based on potentials calculated by density functional theory. Apart from kT, all of the parameters exhibit a clear correlation with the averaged cosine square products of the biaryl angles.
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Affiliation(s)
- Chantal Roger
- Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
| | - Alexander Schmiedel
- Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
| | - Marco Holzapfel
- Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
| | - Nikita N Lukzen
- International Tomography Center, Russia and Novosibirsk State University, Institutskaya 3a, Novosibirsk, Novosibirsk 630090, Russia
| | - Ulrich E Steiner
- Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany.
| | - Christoph Lambert
- Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
- Center for Nanosystems Chemistry, Universität Würzburg, Theodor-Boveri-Weg, D-97074 Würzburg, Germany
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4
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Miller PD, Shultz DA, Mengell J, Kirk ML, Wojtas L. Variation from closed-shell to open shell electronic structures in oligothiophene bis(dioxolene) complexes. Chem Sci 2023; 14:12264-12276. [PMID: 37969598 PMCID: PMC10631215 DOI: 10.1039/d3sc02341a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Accepted: 10/07/2023] [Indexed: 11/17/2023] Open
Abstract
A series of oligothiophene bis(dioxolene) complexes, SQ-Thn-SQ (SQ = S = ½TpCum,MeZnII(3-tert-butyl-orthosemiquinonate); TpCum,Me = tris(5-cumenyl-3-methylpyrazolyl)borate anion) have been synthesized, structurally characterized, and studied as a function of the number of thiophene bridging units, n (n = 0-3) using a combination of variable-temperature (VT) electronic absorption and EPR spectroscopies, and VT magnetic susceptibility measurements. The thiophene bridge bond lengths determined by X-ray crystallography display dramatic differences across the SQ-Thn-SQ series. Bridge bond deviation values (Σ|Δi|) display a progressive change in the nature of the bridge fragment bonding as the number of thiophene groups increases, with quinoidal bridge character for n = 1 (SQ-Th-SQ) and biradical character with "aromatic" bridge bond lengths for n = 3 (SQ-Th3-SQ). Remarkably, for n = 2 (SQ-Th2-SQ) the nature of the bridge fragment is intermediate between quinoid and biradical aromatic, which we describe as having open-shell character as opposed to biradicaloid since the open-shell biradical configuration does not have the correct symmetry to mix with the quinoidal ground-state configuration. This bridge bonding character is reflected in the energies of the lowest lying open-shell states for these three molecules. The SQ-Th-SQ molecule is diamagnetic at all temperatures studied, and we provide evidence for SQ-SQ antiferromagnetic exchange coupling and population of triplet states in SQ-Th2-SQ and SQ-Th3-SQ, with JSQ-SQ(ave) = -279 cm-1 (VT EPR/electronic absorption/magnetic susceptibility) and JSQ-SQ = -117 cm-1 (VT EPR/electronic absorption/magnetic susceptibility), respectively. The results have been interpreted in the context of state configurational mixing within a simplified 4-electron, 3-orbital model that explicitly contains contributions of a bridge fragment. Variable-temperature spectroscopic- and magnetic susceptibility data are consistent with two low-lying open-shell states for SQ-Th3-SQ, but three low-lying states (one closed-shell and two open-shell) for SQ-Th2-SQ. This model provides a simple symmetry-based framework to understand the continuum of electronic and geometric structures of this class of molecules as a function of the number of thiophene units in the bridge.
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Affiliation(s)
- Paul D Miller
- Department of Chemistry, North Carolina State University Raleigh North Carolina 27695-8204 USA
| | - David A Shultz
- Department of Chemistry, North Carolina State University Raleigh North Carolina 27695-8204 USA
| | - Joshua Mengell
- Department of Chemistry and Chemical Biology, The University of New Mexico MSC03 2060, 1 University of New Mexico Albuquerque NM 87131-0001 USA
| | - Martin L Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico MSC03 2060, 1 University of New Mexico Albuquerque NM 87131-0001 USA
- The Center for High Technology Materials, The University of New Mexico Albuquerque New Mexico 87106 USA
- Center for Quantum Information and Control (CQuIC), The University of New Mexico Albuquerque New Mexico 87131-0001 USA
| | - Lukasz Wojtas
- Department of Chemistry, University of South Florida 4202 E. Fowler Avenue, CHE 205 Tampa FL 33620-5250 USA
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Yu H, Heine T. Magnetic Coupling Control in Triangulene Dimers. J Am Chem Soc 2023; 145:19303-19311. [PMID: 37610306 PMCID: PMC10485925 DOI: 10.1021/jacs.3c05178] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Indexed: 08/24/2023]
Abstract
Metal-free magnetism remains an enigmatic field, offering prospects for unconventional magnetic and electronic devices. In the pursuit of such magnetism, triangulenes, endowed with inherent spin polarization, are promising candidates to serve as monomers to construct extended structures. However, controlling and enhancing the magnetic interactions between the monomers persist as a significant challenge in molecular spintronics, as so far only weak antiferromagnetic coupling through the linkage has been realized, hindering their room temperature utilization. Herein, we investigate 24 triangulene dimers using first-principles calculations and demonstrate their tunable magnetic coupling (J), achieving unprecedented strong J values of up to -144 meV in a non-Kekulé dimer. We further establish a positive correlation between bandgap, electronic coupling, and antiferromagnetic interaction, thereby providing molecular-level insights into enhancing magnetic interactions. By twisting the molecular fragments, we demonstrate an effective and feasible approach to control both the sign and strength of J by tuning the balance between potential and kinetic exchanges. We discover that J can be substantially boosted at planar configurations up to -198 meV. We realize ferromagnetic coupling in nitrogen-doped triangulene dimers at both planar and largely twisted configurations, representing the first example of ferromagnetic triangulene dimers that cannot be predicted by the Ovchinnikov rule. This work thus provides a practical strategy for augmenting magnetic coupling and open up new avenues for metal-free ferromagnetism.
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Affiliation(s)
- Hongde Yu
- Faculty
of Chemistry and Food Chemistry, Technische
Universität Dresden, Bergstraße 66c, 01062 Dresden, Germany
| | - Thomas Heine
- Faculty
of Chemistry and Food Chemistry, Technische
Universität Dresden, Bergstraße 66c, 01062 Dresden, Germany
- Institute
of Resource Ecology, Helmholtz Zentrum Dresden-Rossendorf, Permoserstraße 15, 04318 Leipzig, Germany
- Department
of Chemistry, Yonsei University, Seodaemun-gu, Seoul 120-749, Republic of Korea
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6
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Quantum interference effects elucidate triplet-pair formation dynamics in intramolecular singlet-fission molecules. Nat Chem 2023; 15:339-346. [PMID: 36585444 DOI: 10.1038/s41557-022-01107-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Accepted: 11/03/2022] [Indexed: 12/31/2022]
Abstract
Quantum interference (QI)-the constructive or destructive interference of conduction pathways through molecular orbitals-plays a fundamental role in enhancing or suppressing charge and spin transport in organic molecular electronics. Graphical models were developed to predict constructive versus destructive interference in polyaromatic hydrocarbons and have successfully estimated the large conductivity differences observed in single-molecule transport measurements. A major challenge lies in extending these models to excitonic (photoexcited) processes, which typically involve distinct orbitals with different symmetries. Here we investigate how QI models can be applied as bridging moieties in intramolecular singlet-fission compounds to predict relative rates of triplet pair formation. In a series of bridged intramolecular singlet-fission dimers, we found that destructive QI always leads to a slower triplet pair formation across different bridge lengths and geometries. A combined experimental and theoretical approach reveals the critical considerations of bridge topology and frontier molecular orbital energies in applying QI conductance principles to predict rates of multiexciton generation.
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7
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Yue Z, Liu J, Baumgarten M, Wang D. Spirobifluorene Mediating the Spin-Spin Coupling of Nitronyl Nitroxide Diradicals. J Phys Chem A 2023; 127:1565-1575. [PMID: 36627248 DOI: 10.1021/acs.jpca.2c06648] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
To investigate the mechanism of this spiro conjugation magnetic behavior, we designed and synthesized three diradicals─22'SBF-NN, 44'SBF-NN, and 27SBF-NN. They are bridged by spirobifluorene and nitronyl nitroxide (NN) diradicals as the spin centers. Notably, by SQUID and electron paramagnetic resonance (EPR) zero-field splitting data analyses, the 22'SBF-NN and 27SBF-NN diradicals exhibit intramolecular, distinctly antiferromagnetic (AF) coupling, with 2J(22'SBF-NN)/kB = -5.86 K and 2J(27SBF-NN)/kB = -24.6 K, respectively. The AF of 22'SBF-NN is opposite to that predicted by the spin density alternation rule based on Hund's rule. Diradical intramolecular conjugation coupling bridged by spiro-carbon conjugation is discussed, in which the 22'SBF-NN is smaller than that of 27SBF-NN, corresponding to the room-temperature EPR characterization. This spiro conjugation is weaker than the traditional planar conjugation and generally leads to a weaker spin-spin coupling in the helical biradical molecule. The EPR spectrum of the 44'SBF-NN diradical shows a deformed nine-line curve, indicating intramolecular exchange coupling. The density functional theory calculation gives a very weak coupling constant of 2Jcalc/kB = 0.06 K, with ferromagnetic (FM) interaction as the proof, which is consistent with the spin-polarized prediction. Further analysis of magnetic susceptibility χm and VT-EPR data shows that there is indeed an extremely weak FM interaction in the 44' position diradical. We find the bridge, which is a 44' substituted SBF structure, blocks the conjugation and contains a larger twist in steric hindrance, which also hampers sufficient spin density delocalization, resulting in a much weaker spin coupling interaction. Combined with the analysis of molecular orbital calculation results, the anomalous intramolecular AF coupling mechanism of 22'SBF-NN is further explained.
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Affiliation(s)
- Zheng Yue
- Anhui Key Laboratory of Advanced Building Materials, School of Materials Science and Chemical Engineering, Anhui Jianzhu University, Hefei 230601, China
| | - Jin Liu
- Anhui Key Laboratory of Advanced Building Materials, School of Materials Science and Chemical Engineering, Anhui Jianzhu University, Hefei 230601, China
| | - Martin Baumgarten
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Di Wang
- Anhui Key Laboratory of Advanced Building Materials, School of Materials Science and Chemical Engineering, Anhui Jianzhu University, Hefei 230601, China
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8
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Zilberg S, Stekolshik Y, Palii A, Tsukerblat B. Controllable Electron Transfer in Mixed-Valence Bridged Norbornylogous Compounds: Ab Initio Calculation Combined with a Parametric Model and Through-Bond and Through-Space Interpretation. J Phys Chem A 2022; 126:2855-2878. [PMID: 35537213 DOI: 10.1021/acs.jpca.1c09637] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In the context of a computationally guided approach to the controllable electron transfer in mixed-valence (MV) systems, in this article, we study the electron transfer (ET) in the series of oxidized norbornadiene C7H8 (I) and its polycyclic derivatives, C12H12 (II), C17H16, (III), C27H24 (IV), and C32H28 (V), with variable lengths of the bridge connecting redox sites. The work combines an ab initio CASSCF evaluation of the electronic structure of systems I-V with the parametric description in the framework of the biorbital two-mode vibronic model. The model involves coupling with the "breathing" mode and intercenter vibration modulating the distances between the redox fragments. The ab initio calculations were performed for two types of optimized structures of I-V: (a) charge-localized global minimum (Cs) and (b) symmetric configuration (C2v) with the delocalized charge. This allows one to estimate the potential barrier separating charge-localized configurations as well as vibronic coupling parameters and the electron transfer integral. Along with the adiabatic approach, the quantum-mechanical analysis of the vibronic levels has been applied to precisely estimate the quantum effect of tunneling splitting. We estimate the "through-space" and "through-bond" contributions to the parameters interrelated with the charge transfer (CT). The through-space effect proves to be a major factor of ET at a short distance between the redox centers, whereas the through-bond contribution is dominant at a long distance. Vibronic coupling under the condition of through-space ET leads to the localization of the positive charge on the π-chromophore, while the through-bond component of ET results in compensating σ-shifts and subsequent charge delocalization over the bridge. The limitations of the parametric approach were discussed in the context of the two components contributing to the ET. Particularly, the bridge polarization in the course of through-bond ET proves to be beyond the basis of the employed parametric model.
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Affiliation(s)
- Shmuel Zilberg
- Department of Chemical Sciences, Materials Research Center, Ariel University, 40700 Ariel, Israel
| | - Yaniv Stekolshik
- Department of Chemical Sciences, Materials Research Center, Ariel University, 40700 Ariel, Israel
| | - Andrew Palii
- Laboratory of Molecular Magnetic Nanomaterials, Institute of Problems of Chemical Physics, Academician Semenov Avenue 1, Chernogolovka, Moscow Region 142432, Russian Federation
| | - Boris Tsukerblat
- Department of Chemical Sciences, Materials Research Center, Ariel University, 40700 Ariel, Israel.,Department of Chemistry, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel
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9
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Hewitt P, Shultz DA, Kirk ML. Rules for Magnetic Exchange in Azulene-Bridged Biradicals: Quo Vadis? J Org Chem 2021; 86:15577-15587. [PMID: 34644082 DOI: 10.1021/acs.joc.1c02085] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Electronic coupling through organic bridges facilitates magnetic exchange interactions and controls electron transfer and single-molecule device electron transport. Electronic coupling through alternant π-systems (e.g., benzene) is better understood than the corresponding coupling through nonalternant π-systems (e.g., azulene). Herein, we examine the structure, spectroscopy, and magnetic exchange coupling in two biradicals (1,3-SQ2Az and 1,3-SQ-Az-NN; SQ = the zinc(II) complex of spin-1/2 semiquinone radical anion, NN = spin-1/2 nitronylnitroxide; Az = azulene) that possess nonalternant azulene π-system bridges. The SQ radical spin density in both molecules is delocalized into the Az π-system, while the NN spin is effectively localized onto the five-atom ONCNO π-system of NN radical. The spin distributions and interactions are probed by EPR spectroscopy and magnetic susceptibility measurements. We find that J = +38 cm-1 for 1,3-SQ2Az and J = +9 cm-1 for 1,3-SQ-Az-NN (H=-2JS^SQ·S^SQorNN). Our results highlight the differences in exchange coupling mediated by azulene compared to exchange coupling mediated by alternant π-systems.
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Affiliation(s)
- Patrick Hewitt
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
| | - David A Shultz
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
| | - Martin L Kirk
- Department of Chemistry, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States
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10
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Sarbadhikary P, Misra A. Magnetic Modulation in Heteroallene and Heterocumulene Based tert-butyl Nitroxide Diradicals: Spin Delocalization and Conformation Play Crucial Roles. Chemphyschem 2021; 22:1379-1388. [PMID: 33977620 DOI: 10.1002/cphc.202100161] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Revised: 04/27/2021] [Indexed: 11/11/2022]
Abstract
We have theoretically investigated the magnetic properties of heteroallene (>C=C=X-) and heterocumulene (>C=C=C=X-) based tert-butyl nitroxide diradicals (X is P/As). Calculation of magnetic exchange coupling constant (J) shows ferromagnetic interaction in heteroallene based diradicals. Whereas, in heterocumulene based diradicals, tuning of J value from antiferro- to ferro-magnetic state is observed from Z- to E- isomer. Delocalization of spin density from radical site to the coupler (in planar arrangement) is observed in spin distribution analysis which is also advocated by molecular orbital analysis. The typical feature of tert-butyl nitroxide radical creates spin delocalization along with spin polarization within the coupler. The J values of all the diradicals strongly depend on the dihedral angle between radical center and coupler. Magneto-structural correlation shows that the change in dihedral angle tunes the magnetic property for both the Z- and E- isomers of heterocumulenes depending on the spin accumulation on two nearby magnetic centers. The extent of spin delocalization and conformation of spin centers on the molecular axis are important for the different J values observed in our designed systems.
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Affiliation(s)
| | - Anirban Misra
- Department of Chemistry, University of North Bengal, Dist-Darjeeling, 734013, India
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11
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Abstract
Applications of density-functional theory (DFT) in computational chemistry rely on an approximate exchange-correlation (xc) functional. However, existing approximations can fail dramatically for open-shell molecules, in particular for transition-metal complexes or radicals. Most importantly, predicting energy differences between different spin-states with approximate exchange-correlation functionals remains extremely challenging. Formally, it is known that the exact xc functional should be spin-state dependent, but none of the available approximations feature such an explicit spin-state dependence [C. R. Jacob and M. Reiher, Int. J. Quantum Chem., 2012, 112, 3661-3684]. Thus, to find novel approximations for the xc functional for open-shell systems, the development of spin-state dependent xc functionals appears to be a promising avenue. Here, we set out to shed light on the spin-state dependence of the xc functional by investigating the underlying xc holes, which we extract from configuration interaction calculations for model systems. We analyze the similarities and differences between the xc holes of the lowest-energy singlet and triplet states of the dihydrogen molecule, the helium atom, and the lithium dimer. To shed further light on the spin-state dependence of these xc holes we also discuss exact conditions that can be derived from the spin structure of the reduced two-electron density matrix. Altogether, our results suggest several possible routes towards the construction of explicitly spin-state dependent approximations for the xc functional.
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Affiliation(s)
- Julia Brüggemann
- Technische Universität Braunschweig, Institute of Physical and Theoretical Chemistry, Gaußstraße 17, 38106 Braunschweig, Germany.
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12
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When Molecular Magnetism Meets Supramolecular Chemistry: Multifunctional and Multiresponsive Dicopper(II) Metallacyclophanes as Proof-of-Concept for Single-Molecule Spintronics and Quantum Computing Technologies? MAGNETOCHEMISTRY 2020. [DOI: 10.3390/magnetochemistry6040069] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Molecular magnetism has made a long journey, from the fundamental studies on through-ligand electron exchange magnetic interactions in dinuclear metal complexes with extended organic bridges to the more recent exploration of their electron spin transport and quantum coherence properties. Such a field has witnessed a renaissance of dinuclear metallacyclic systems as new experimental and theoretical models for single-molecule spintronics and quantum computing, due to the intercrossing between molecular magnetism and metallosupramolecular chemistry. The present review reports a state-of-the-art overview as well as future perspectives on the use of oxamato-based dicopper(II) metallacyclophanes as promising candidates to make multifunctional and multiresponsive, single-molecule magnetic (nano)devices for the physical implementation of quantum information processing (QIP). They incorporate molecular magnetic couplers, transformers, and wires, controlling and facilitating the spin communication, as well as molecular magnetic rectifiers, transistors, and switches, exhibiting a bistable (ON/OFF) spin behavior under external stimuli (chemical, electronic, or photonic). Special focus is placed on the extensive research work done by Professor Francesc Lloret, an outstanding chemist, excellent teacher, best friend, and colleague, in recognition of his invaluable contributions to molecular magnetism on the occasion of his 65th birthday.
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13
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Kirk ML, Dangi R, Habel-Rodriguez D, Yang J, Shultz DA, Zhang J. Transferrable property relationships between magnetic exchange coupling and molecular conductance. Chem Sci 2020; 11:11425-11434. [PMID: 34094385 PMCID: PMC8162509 DOI: 10.1039/d0sc04350h] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 09/14/2020] [Indexed: 01/12/2023] Open
Abstract
Calculated conductance through Au n -S-Bridge-S-Au n (Bridge = organic σ/π-system) constructs are compared to experimentally-determined magnetic exchange coupling parameters in a series of TpCum,MeZnSQ-Bridge-NN complexes, where TpCum,Me = hydro-tris(3-cumenyl-1-methylpyrazolyl)borate ancillary ligand, Zn = diamagnetic zinc(ii), SQ = semiquinone (S = 1/2), and NN = nitronylnitroxide radical (S = 1/2). We find that there is a nonlinear functional relationship between the biradical magnetic exchange coupling, J D→A, and the computed conductance, g mb. Although different bridge types (monomer vs. dimer) do not lie on the same J D→A vs. g mb, curve, there is a scale invariance between the monomeric and dimeric bridges which shows that the two data sets are related by a proportionate scaling of J D→A. For exchange and conductance mediated by a given bridge fragment, we find that the ratio of distance dependent decay constants for conductance (β g) and magnetic exchange coupling (β J) does not equal unity, indicating that inherent differences in the tunneling energy gaps, Δε, and the bridge-bridge electronic coupling, H BB, are not directly transferrable properties as they relate to exchange and conductance. The results of these observations are described in valence bond terms, with resonance structure contributions to the ground state bridge wavefunction being different for SQ-Bridge-NN and Au n -S-Bridge-S-Au n systems.
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Affiliation(s)
- Martin L Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico MSC03 2060, 1 University of New Mexico Albuquerque New Mexico 87131-0001 USA
- Center for High Technology Materials, The University of New Mexico Albuquerque New Mexico 87106 USA
| | - Ranjana Dangi
- Department of Chemistry and Chemical Biology, The University of New Mexico MSC03 2060, 1 University of New Mexico Albuquerque New Mexico 87131-0001 USA
| | - Diana Habel-Rodriguez
- Department of Chemistry and Chemical Biology, The University of New Mexico MSC03 2060, 1 University of New Mexico Albuquerque New Mexico 87131-0001 USA
| | - Jing Yang
- Department of Chemistry and Chemical Biology, The University of New Mexico MSC03 2060, 1 University of New Mexico Albuquerque New Mexico 87131-0001 USA
| | - David A Shultz
- Department of Chemistry, North Carolina State University Raleigh North Carolina 27695-8204 USA
| | - Jinyuan Zhang
- Department of Chemistry, North Carolina State University Raleigh North Carolina 27695-8204 USA
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Bahlke MP, Mogos N, Proppe J, Herrmann C. Exchange Spin Coupling from Gaussian Process Regression. J Phys Chem A 2020; 124:8708-8723. [DOI: 10.1021/acs.jpca.0c05983] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Marc Philipp Bahlke
- Department of Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany
| | - Natnael Mogos
- Department of Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany
| | - Jonny Proppe
- Institute of Physical Chemistry, Georg-August University, Tammannstr. 6, 37077 Göttingen, Germany
| | - Carmen Herrmann
- Department of Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany
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15
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Zheng R, Bevacqua GM, Young NR, Allison TC, Tong YJ. Site-Dependent Spin Delocalization and Evidence of Ferrimagnetism in Atomically Precise Au 25(SR) 180 Clusters as Seen by Solution 13C NMR Spectroscopy. J Phys Chem A 2020; 124:7464-7469. [PMID: 32819099 DOI: 10.1021/acs.jpca.0c02915] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
We report a simple but detailed solution 13C nuclear magnetic resonance spectroscopic study of atomically precise neutral Au25(SR)180 (SR = alkyl thiolate) clusters. The paramagnetic 13C Knight shift of alkyl chain carbons, which is proportional to the local electron spin density, exhibits an electron spin delocalization that exponentially decays along the alkyl chain. The magnitude and decay constant of the observed electron spin delocalization, although largely independent of alkyl chain length, depend on where, that is, "in" versus "out" (vide infra) position, the alkyl chain is bound, in agreement with density functional theory calculations. Notably, the determined position-dependent decay constants, 1.70/Å and 0.41/Å for "in" and "out" ligands, respectively, not only could have important ramifications in molecular spintronics but are also comparable to measured decay constants in molecular electrical conductance of alkyl chains, potentially offering an alternative, simple method for estimating the latter. Moreover, the negative intercept temperatures of linear fits of reciprocal 13C (as well its bound 1H) Knight shift versus temperature strongly suggest the existence of local ferrimagnetism in individual Au25(SR)180 clusters.
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Affiliation(s)
- Rongfeng Zheng
- Department of Chemistry, Georgetown University, 37th & O Streets, NW, Washington, District of Columbia 20057, United States
| | - Gianna M Bevacqua
- Department of Chemistry, Georgetown University, 37th & O Streets, NW, Washington, District of Columbia 20057, United States
| | - Nicholas R Young
- Department of Chemistry, Georgetown University, 37th & O Streets, NW, Washington, District of Columbia 20057, United States
| | - Thomas C Allison
- Chemical Informatics Group, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8320, Gaithersburg, Maryland 20899-8320, United States
| | - YuYe J Tong
- Department of Chemistry, Georgetown University, 37th & O Streets, NW, Washington, District of Columbia 20057, United States
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16
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Garner MH, Solomon GC. Simultaneous Suppression of π- and σ-Transmission in π-Conjugated Molecules. J Phys Chem Lett 2020; 11:7400-7406. [PMID: 32787288 DOI: 10.1021/acs.jpclett.0c01727] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Molecular dielectric materials require ostensibly conflicting requirements of high polarizability and low conductivity. As previous efforts toward molecular insulators focused on saturated molecules, it remains an open question whether π- and σ-transport can be simultaneously suppressed in conjugated systems. Here, we demonstrate that there are conjugated molecules where the σ-transmission is suppressed by destructive σ-interference, while the π-transmission can be suppressed by a localized disruption of conjugation. Using density functional theory, we study the Landauer transmission and ballistic current density, which allow us to determine how the transmission is affected by various structural changes in the molecule. We find that in para-linked oligophenyl rings the σ-transmission can be suppressed by changing the remaining hydrogens to methyl groups due to the inherent gauche-like structure of the carbon backbone within a benzene ring, similar to what was previously seen in saturated systems. At the same time, the methyl groups fulfill a dual purpose as they modulate the twist angle between neighboring phenyl rings. When neighboring rings are orthogonal to each other, the transmission through both π- and σ-systems is effectively suppressed. Alternatively, breaking conjugation in a single phenyl ring by saturating two carbons atoms with two methyl substituents on each carbon, results in suppressed π- and σ-transport independent of dihedral angle. These two strategies demonstrate that methyl-substituted oligophenyls are promising candidates for the development of molecular dielectric materials.
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Affiliation(s)
- Marc H Garner
- Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark
| | - Gemma C Solomon
- Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark
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Shultz DA, Kirk ML, Zhang J, Stasiw DE, Wang G, Yang J, Habel-Rodriguez D, Stein BW, Sommer RD. Spectroscopic Signatures of Resonance Inhibition Reveal Differences in Donor-Bridge and Bridge-Acceptor Couplings. J Am Chem Soc 2020; 142:4916-4924. [PMID: 32069027 DOI: 10.1021/jacs.0c00326] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The torsional dependence of the ground state magnetic exchange coupling (J) and the corresponding electronic coupling matrix element (HDA) for eight transition metal complexes possessing donor-acceptor (D-A) biradical ligands is presented. These biradical ligands are composed of an S = 1/2 metal semiquinone (SQ) donor and an S = 1/2 nitronylnitroxide (NN) acceptor, which are coupled to each other via para-phenylene, methyl-substituted para-phenylenes, or a bicyclo[2.2.2]octane ring. The observed trends in electronic absorption and resonance Raman spectral features are in accord with a reduction in electronic and magnetic coupling between D and A units within the framework of our valence bond configuration interaction model. Moreover, our spectroscopic results highlight different orbital mechanisms that modulate coupling in these complexes, which is not manifest in the ferromagnetic JSQ-B-NN values. The work provides new detailed insight into the effects of torsional rotations which contribute to inhomogeneities in experimentally determined exchange couplings, electron transfer rates, and electron transport conductance measurements.
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Affiliation(s)
- David A Shultz
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
| | - Martin L Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States.,Center for High Technology Materials, The University of New Mexico, Albuquerque, New Mexico 87106, United States
| | - Jinyuan Zhang
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
| | - Daniel E Stasiw
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
| | - Guangbin Wang
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
| | - Jing Yang
- Department of Chemistry, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States
| | - Diana Habel-Rodriguez
- Department of Chemistry, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States
| | - Benjamin W Stein
- Department of Chemistry, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States
| | - Roger D Sommer
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
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