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Ward AFM, Reber AC, Khanna SN. Periodic Trends in the Infrared and Optical Absorption Spectra of Metal Chalcogenide Clusters. J Phys Chem A 2023; 127:38-45. [PMID: 36548146 DOI: 10.1021/acs.jpca.2c05955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
We have investigated the optical absorption, infrared spectra, binding energies, and other cluster properties to investigate whether periodic trends can be observed in the electronic structure of transition metal chalcogenide clusters ligated with CO ligands. Our studies demonstrate the existence of several periodic trends in the properties of pure and mixed octahedral metal chalcogenide clusters, TM6Se8(CO)6 (TM = W-Pt). We find that octahedral metal chalcogenide clusters with 96, 100, and 114 valence electrons have larger excitation energies, consistent with these clusters having closed electronic shells. Periodic trends were observed in the infrared spectra, with the CO bond stretch having the highest energy at 100 and 114 valence electrons due to the closed electronic shell minimizing back-bonding with the CO molecule. A periodic trend in the antisymmetric TM-C stretch was also observed, with the vibrational energy increasing as the valence electron count increased. This is due to decrease in the TM-C bond length, resulting in a larger force constant. These results reveal that periodic trends seen earlier in simple or noble-metal clusters can be observed in symmetric transition metal chalcogenide clusters, showing that the superatom concept in metal chalcogenide clusters goes beyond electronic excitations, and can be seen in other observable properties.
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Affiliation(s)
- Alain F M Ward
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia23284-2000, United States
| | - Arthur C Reber
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia23284-2000, United States
| | - Shiv N Khanna
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia23284-2000, United States
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Reber AC, Sengupta T, Bista D, Khanna SN. Magic Numbers in Octahedral Ligated Metal-Chalcogenide Superatoms. Inorg Chem 2022; 61:16003-16008. [PMID: 36149274 DOI: 10.1021/acs.inorgchem.2c02361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The attainment of the superatomic state offers a unifying framework for the periodic classification of atomic clusters. Metallic clusters attain the superatomic state via the confined nearly free electron gas model that leads to groupings of quantum states marked by radial and angular momentum quantum numbers. We examine ligated octahedral metal-chalcogenide clusters where the nearly free electron gas model is invalid; however, the high symmetry can also lead to the bunching of electronic states. For octahedral TM6E8L6 clusters (TM = transition metal; E = chalcogen; L = ligand), the electronic shells are filled for valence electron counts of 96, 100, and 114 electrons. These magic electron counts are marked by large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps, high ionization energies, and low electron affinity─all classic signatures of the superatomic state. We also find that clusters with electron counts differing from the magic counts show periodic patterns reminiscent of those observed in the periodic table of elements.
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Affiliation(s)
- Arthur C Reber
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, United States
| | - Turbasu Sengupta
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, United States
| | - Dinesh Bista
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, United States
| | - Shiv N Khanna
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, United States
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Reed DA, Hochuli TJ, Gadjieva NA, He S, Wiscons RA, Bartholomew AK, Champsaur AM, Steigerwald ML, Roy X, Nuckolls C. Controlling Ligand Coordination Spheres and Cluster Fusion in Superatoms. J Am Chem Soc 2021; 144:306-313. [PMID: 34937334 DOI: 10.1021/jacs.1c09901] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
We show that reaction pathways from a single superatom motif can be controlled through subtle electronic modification of the outer ligand spheres. Chevrel-type [Co6Se8L6] (L = PR3, CO) superatoms are used to form carbene-terminated clusters, the reactivity of which can be influenced through the electronic effects of the surrounding ligands. This carbene provides new routes for ligand substitution chemistry, which is used to selectively install cyanide or pyridine ligands which were previously inaccessible in these cobalt-based clusters. The surrounding ligands also impact the ability of this carbene to create larger fused clusters of the type [Co12Se16L10], providing underlying information for cluster fusion mechanisms. We use this information to develop methods of creating dimeric clusters with functionalized surface ligands with site specificity, putting new ligands in specific positions on this anisotropic core. Finally, adjusting the carbene intermediates can also be used to perturb the geometry of the [Co6Se8] core itself, as we demonstrate with a multicarbene adduct that displays a substantially anisotropic core. These additional levels of synthetic control could prove instrumental for using superatomic clusters for many applications including catalysis, electronic devices, and creating novel extended structures.
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Affiliation(s)
- Douglas A Reed
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Taylor J Hochuli
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Natalia A Gadjieva
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Shoushou He
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Ren A Wiscons
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | | | - Anouck M Champsaur
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Michael L Steigerwald
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Xavier Roy
- Department of Chemistry, Columbia University, New York, New York 10027, United States
| | - Colin Nuckolls
- Department of Chemistry, Columbia University, New York, New York 10027, United States
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Shen J, He H, Sengupta T, Bista D, Reber AC, Pandey R, Khanna SN. Electron transport properties of PAl 12-based cluster complexes. NANOSCALE ADVANCES 2021; 3:6888-6896. [PMID: 36132360 PMCID: PMC9418132 DOI: 10.1039/d1na00355k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/15/2021] [Accepted: 09/10/2021] [Indexed: 06/15/2023]
Abstract
The electronic transport properties of PAl12-based cluster complexes are investigated by density functional theory (DFT) in combination with the non-equilibrium Green's function (NEGF) method. Joining two PAl12 clusters via a germanium linker creates a stable semiconducting complex with a large HOMO-LUMO gap. Sequential attachment of an electron-donating ligand, N-ethyl-2-pyrrolidone, to one of the two linked clusters results in the shifting of the electronic spectrum of the ligated cluster while the energy levels of the unligated cluster are mostly unchanged. Using this approach, one can eventually align the HOMO of the ligated cluster to the LUMO of the non-ligated cluster, thereby significantly reducing the HOMO-LUMO gap of the complex. As a result, the transport properties of the complex are highly dependent on the number of attached ligands. Although a single ligand is observed to generally decrease the current, the inclusion of two or more ligands shows a significant increase in the amount of current at most voltages. The resulting increase of the current can be attributed to two factors, first the reduction in the HOMO-LUMO gap due to ligand attachment which has moved the transmission orbitals into the bias window. Secondly, when two or more ligands are attached to the complex, the HOMOs become delocalized across the scattering region, and this significantly enhances the currents.
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Affiliation(s)
- John Shen
- Department of Physics and Astronomy, Valparaiso University Valparaiso Indiana 46383 USA
| | - Haiying He
- Department of Physics and Astronomy, Valparaiso University Valparaiso Indiana 46383 USA
| | - Turbasu Sengupta
- Department of Physics, Virginia Commonwealth University Richmond Virginia 23284 USA
| | - Dinesh Bista
- Department of Physics, Virginia Commonwealth University Richmond Virginia 23284 USA
| | - Arthur C Reber
- Department of Physics, Virginia Commonwealth University Richmond Virginia 23284 USA
| | - Ravindra Pandey
- Department of Physics, Michigan Technological University Houghton Michigan 49931 USA
| | - Shiv N Khanna
- Department of Physics, Virginia Commonwealth University Richmond Virginia 23284 USA
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Bista D, Sengupta T, Reber AC, Khanna SN. Interfacial magnetism in a fused superatomic cluster [Co 6Se 8(PEt 3) 5] 2. NANOSCALE 2021; 13:15763-15769. [PMID: 34528648 DOI: 10.1039/d1nr00876e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
An isolated Co6Se8(PEt3)6 cluster is non-magnetic; however, we find that a magnetic unit can be formed by fusing two Co6Se8(PEt3)5 superatoms into a [Co6Se8(PEt3)5]2 dimer. Theoretical studies indicate that the dumbbell-shaped [Co6Se8(PEt3)5]2 dimer has a spin moment of 2μB, and the spin density is primarily localized at the interfacial Co-sites where two clusters are fused into a dimer. The dimer has a low ionization energy of 4.17 eV, allowing the dimer to donate charge to C70 during the formation of a cluster assembled material, as seen in recent experiments by Nuckolls and co-workers. The donation of charge causes the dimer's magnetic moment to drop from 2μB to 1μB. We hypothesize that adding electrons to the dimer, such as doping impurities to the crystal lattice, may enhance the magnetic moment by neutralizing the charged cluster. This reveals a strategy for stabilizing magnetic moments in ligated cluster assemblies.
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Affiliation(s)
- Dinesh Bista
- Department of Physics, Virginia Commonwealth University, Richmond, VA, 23284-2000, USA.
| | - Turbasu Sengupta
- Department of Physics, Virginia Commonwealth University, Richmond, VA, 23284-2000, USA.
| | - Arthur C Reber
- Department of Physics, Virginia Commonwealth University, Richmond, VA, 23284-2000, USA.
| | - Shiv N Khanna
- Department of Physics, Virginia Commonwealth University, Richmond, VA, 23284-2000, USA.
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Khanna SN, Reber AC, Bista D, Sengupta T, Lambert R. The superatomic state beyond conventional magic numbers: Ligated metal chalcogenide superatoms. J Chem Phys 2021; 155:120901. [PMID: 34598575 DOI: 10.1063/5.0062582] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The field of cluster science is drawing increasing attention due to the strong size and composition-dependent properties of clusters and the exciting prospect of clusters serving as the building blocks for materials with tailored properties. However, identifying a unifying central paradigm that provides a framework for classifying and understanding the diverse behaviors is an outstanding challenge. One such central paradigm is the superatom concept that was developed for metallic and ligand-protected metallic clusters. The periodic electronic and geometric closed shells in clusters result in their properties being based on the stability they gain when they achieve closed shells. This stabilization results in the clusters having a well-defined valence, allowing them to be classified as superatoms-thus extending the Periodic Table to a third dimension. This Perspective focuses on extending the superatomic concept to ligated metal-chalcogen clusters that have recently been synthesized in solutions and form assemblies with counterions that have wide-ranging applications. Here, we illustrate that the periodic patterns emerge in the electronic structure of ligated metal-chalcogenide clusters. The stabilization gained by the closing of their electronic shells allows for the prediction of their redox properties. Further investigations reveal how the selection of ligands may control the redox properties of the superatoms. These ligated clusters may serve as chemical dopants for two-dimensional semiconductors to control their transport characteristics. Superatomic molecules of multiple metal-chalcogen superatoms allow for the formation of nano-p-n junctions ideal for directed transport and photon harvesting. This Perspective outlines future developments, including the synthesis of magnetic superatoms.
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Affiliation(s)
- Shiv N Khanna
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, USA
| | - Arthur C Reber
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, USA
| | - Dinesh Bista
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, USA
| | - Turbasu Sengupta
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, USA
| | - Ryan Lambert
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, USA
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Bista D, Sengupta T, Khanna SN. Massive dipoles across the metal-semiconductor cluster interface: towards chemically controlled rectification. Phys Chem Chem Phys 2021; 23:18975-18982. [PMID: 34612436 DOI: 10.1039/d1cp02420e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
An interface between a metallic cluster (MgAl12) and a semiconducting cluster (Re6Se8(PMe3)5) is shown to be marked by a massive dipole reminiscent of a dipolar layer leading to a Schottky barrier at metal-semiconductor interfaces. The metallic cluster MgAl12 with a valence electron count of 38 electrons is two electrons short of 40 electrons needed to complete its electronic shells in a superatomic model and is marked by a significant electron affinity of 2.99 eV. On the other hand, the metal-chalcogenide semiconducting cluster Re6Se8(PMe3)5, consisting of a Re6Se8 core ligated with five trimethylphosphine ligands, is highly stable in the +2 charge-state owing to its electronic shell closure, and has a low ionization energy of 3.3 eV. The composite cluster Re6Se8(PMe3)5-MgAl12 formed by combining the MgAl12 cluster through the unligated site of Re6Se8(PMe3)5 exhibits a massive dipole moment of 28.38 D resulting from a charge flow from Re6Se8(PMe3)5 to the MgAl12 cluster. The highest occupied molecular orbital (HOMO) of the composite cluster is on the MgAl12 side, which is 0.53 eV below the lowest unoccupied molecular orbital (LUMO) localized on the Re6Se8(PMe3)5 cluster, reminiscent of a Schottky barrier at metal-semiconductor interfaces. Therefore, the combination can act as a rectifier, and an application of a voltage of approximately 4.1 V via a homogeneous external electric field is needed to overcome the barrier aligning the two states: the HOMO in MgAl12 with the LUMO in Re6Se8(PMe3)5. Apart from the bias voltage, the barrier can also be reduced by attaching ligands to the metallic cluster, which provides chemical control over rectification. Finally, the fused cluster is shown to be capable of separating electron-hole pairs with minimal recombination, offering the potential for photovoltaic applications.
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Affiliation(s)
- Dinesh Bista
- Department of Physics, Virginia Commonwealth University, Richmond, VA 23284-2000, USA.
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Bista D, Sengupta T, Reber AC, Khanna SN. A Magnetic Superatomic Dimer with an Intense Internal Electric Dipole Moment. J Phys Chem A 2021; 125:816-824. [DOI: 10.1021/acs.jpca.0c10262] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Dinesh Bista
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, United States
| | - Turbasu Sengupta
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, United States
| | - Arthur C. Reber
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, United States
| | - Shiv N. Khanna
- Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000, United States
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Bista D, Chauhan V, Sengupta T, Reber AC, Khanna SN. A ligand-induced homojunction between aluminum-based superatomic clusters. NANOSCALE 2020; 12:12046-12056. [PMID: 32469025 DOI: 10.1039/d0nr02611e] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
A superatomic molecule formed by joining two metallic clusters linked by an organometallic bridge can behave like a semiconductor and the addition of ligands can induce a significant energy level shift across an inter-cluster homojunction. This shift is induced by the N-ethyl-2-pyrrolidone ligands, and the placement of the ligands strongly affects the direction of the dipole moment, including the case where the dipole moment is parallel to the cluster interface. This computational study provides an alternative strategy for constructing nanometer-scale electronic interfaces between clusters mimicking semiconductor motifs. The semiconducting features in the PAl12 clusters emerge from the grouping of the quantum states in a confined nearly free electron gas that creates a substantial energy gap. An organometallic Ge(CH3)2(CH2)2 bridge links the clusters while maintaining the cluster's electronic shell structure. The amount of level shifting between the bridged clusters can be changed by controlling the number of ligands. Attaching multiple ligands can result in a broken gap energy alignment in which the HOMO level of one cluster is aligned with the LUMO level of the other bridged cluster. Furthermore, the singly ligated bridged superatomic molecule is found to exhibit promising features to separate the electron-hole pairs for photovoltaic applications.
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Affiliation(s)
- Dinesh Bista
- Department of Physics, Virginia Commonwealth University, Richmond, VA 23284-2000, USA.
| | - Vikas Chauhan
- Ramjas College, University of Delhi, Delhi-110007, India
| | - Turbasu Sengupta
- Department of Physics, Virginia Commonwealth University, Richmond, VA 23284-2000, USA.
| | - Arthur C Reber
- Department of Physics, Virginia Commonwealth University, Richmond, VA 23284-2000, USA.
| | - Shiv N Khanna
- Department of Physics, Virginia Commonwealth University, Richmond, VA 23284-2000, USA.
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