1
|
Staab JK, Rahman MK, Chilton NF. Intramolecular bridging strategies to suppress two-phonon Raman spin relaxation in dysprosocenium single-molecule magnets. Phys Chem Chem Phys 2024; 26:17539-17548. [PMID: 38885049 PMCID: PMC11202312 DOI: 10.1039/d4cp01716a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Accepted: 06/06/2024] [Indexed: 06/20/2024]
Abstract
Dy(III) bis-cyclopentadienyl (Cp) sandwich compounds exhibit extremely strong single-ion magnetic anisotropy which imbues them with magnetic memory effects such as magnetic hysteresis, and has put them at the forefront of high-performance single-molecule magnets (SMMs). Owing to the great success of design principles focused on maximising the anisotropy barrier, ever higher Ueff values have been reported leading to significant slow down of single-phonon Orbach spin relaxation. However, anisotropy-based SMM design has largely ignored two-phonon Raman spin relaxation, which is still limiting the temperatures at which a memory effect can be observed. In this work, we study the suppression of Raman relaxation through covalent bridging of the Cp ligands by alkyl chains, testing the hypothesis that increasing the rigidity of the ligand framework results in a blue shift of low frequency vibrations in the first coordination sphere of the Dy(III) ion. This reshaping of the vibrational low-energy density of states (DOS) results in lower occupation of pseudo-acoustic phonons available to drive Raman relaxation at low temperatures. We simulate Orbach and Raman spin relaxation in a series of zero-, mono-, di- and tri-bridged [Dy(Cpttt)2]+ analogues fully ab initio, using a quantum mechanics (QM)/molecular mechanics (MM) condensed phase embedding protocol in a periodic solvent matrix as a generic and experimentally testable environment model that can include (pseudo-)acoustic phononic degrees of freedom. We show that this approach can simulate magnetic relaxation dynamics in the condensed phase for the existing non-bridged [Dy(Cpttt)2]+ compound with quantitative experimental accuracy. Subsequently, we find a significant slowing down of Raman relaxation can be achieved for the singly-bridged SMM, while the introduction of further bridges leads to faster relaxation. A key result being that we find the two-phonon Raman rates correlate with the purity of the first-excited Kramers doublet in terms of its mJ = ±13/2 content. Even though the bridging design principle is successful at progressively reshaping the low-energy DOS, the introduction of linker atoms in the equatorial plane successively degrades magnetic anisotropy, suggesting the importance of refined design of the linker chemistry. The accuracy of our results emphasises the value of a generic periodic solvent embedding model, such that it permits the modelling of molecular spin dynamics in the condensed phase without knowledge of a crystal structure. This allows the study of hypothetical molecules or aggregates under real-world conditions, which we expect to have utility beyond the field of molecular magnetism.
Collapse
Affiliation(s)
- Jakob K Staab
- Department of Chemistry, The University of Manchester, Manchester M13 9PL, UK
| | - Md Kholilur Rahman
- Department of Chemistry, The University of Manchester, Manchester M13 9PL, UK
| | - Nicholas F Chilton
- Department of Chemistry, The University of Manchester, Manchester M13 9PL, UK
- Research School of Chemistry, The Australian National University, Canberra 2601, ACT, Australia.
| |
Collapse
|
2
|
Corner S, Gransbury GK, Vitorica-Yrezabal IJ, Whitehead GFS, Chilton NF, Mills DP. Halobenzene Adducts of a Dysprosocenium Single-Molecule Magnet. Inorg Chem 2024; 63:9552-9561. [PMID: 38359351 PMCID: PMC11134494 DOI: 10.1021/acs.inorgchem.3c04105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 01/18/2024] [Accepted: 01/23/2024] [Indexed: 02/17/2024]
Abstract
Dysprosium complexes with strong axial crystal fields are promising candidates for single-molecule magnets (SMMs), which could be used for high-density data storage. Isolated dysprosocenium cations, [Dy(CpR)2]+ (CpR = substituted cyclopentadienyl), have recently shown magnetic hysteresis (a memory effect) above the temperature of liquid nitrogen. Synthetic efforts have focused on reducing strong transverse ligand fields in these systems as they are known to enhance magnetic relaxation by spin-phonon mechanisms. Here we show that equatorial coordination of the halobenzenes PhX (X = F, Cl, Br) and o-C6H4F2 to the cation of a recently reported dysprosocenium complex [Dy(Cpttt)(Cp*)][Al{OC(CF3)3}4] (Cpttt = C5H2tBu3-1,2,4; Cp* = C5Me5) reduces magnetic hysteresis temperatures compared to that of the parent cation. We find that this is due to increased effectiveness of both one- (Orbach) and two-phonon (Raman) relaxation mechanisms, which correlate with the electronegativity and number of interactions with the halide despite κ1-coordination of a single halobenzene having a minimal effect on the metrical parameters of [Dy(Cpttt)(Cp*)(PhX-κ1-X)]+ cations vs the isolated [Dy(Cpttt)(Cp*)]+ cation. We observe unusual divergent behavior of relaxation rates at low temperatures in [Dy(Cpttt)(Cp*)(PhX)][Al{OC(CF3)3}4], which we attribute to a phonon bottleneck effect. We find that, despite the transverse fields introduced by the monohalobenzenes in these cations, the interactions are sufficiently weak that the effective barriers to magnetization reversal remain above 1000 cm-1, being only ca. 100 cm-1 lower than for the parent complex, [Dy(Cpttt)(Cp*)][Al{OC(CF3)3}4].
Collapse
Affiliation(s)
| | | | | | - George F. S. Whitehead
- Department of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | | | - David P. Mills
- Department of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| |
Collapse
|
3
|
Corner S, Gransbury GK, Vitorica-Yrezabal IJ, Whitehead GFS, Chilton NF, Mills DP. Synthesis and Magnetic Properties of Bis-Halobenzene Decamethyldysprosocenium Cations. Inorg Chem 2024; 63:9562-9571. [PMID: 38382535 PMCID: PMC11134500 DOI: 10.1021/acs.inorgchem.3c04106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 01/18/2024] [Accepted: 01/23/2024] [Indexed: 02/23/2024]
Abstract
The decamethyldysprosocenium cation, [Dy(Cp*)2]+ (Cp* = {C5Me5}), was a target single-molecule magnet (SMM) prior to the isolation of larger dysprosocenium cations, which have recently shown magnetic memory effects up to 80 K. However, the relatively short Dy···Cp*centroid distances of [Dy(Cp*)2]+, together with the reduced resonance of its vibrational modes with electronic states compared to larger dysprosocenium cations, could lead to more favorable SMM behavior. Here, we report the synthesis and magnetic properties of a series of solvated adducts containing bis-halobenzene decamethyldysprosocenium cations, namely [Dy(Cp*)2(PhX-κ-X)2][Al{OC(CF3)3}4] (X = F or Cl) and [Dy(Cp*)2(C6H4F2-κ2-F,F)(C6H4F2-κ-F)][Al{OC(CF3)3}4]. These complexes were prepared by the sequential reaction of [Dy(Cp*)2(μ-BH4)]∞ with allylmagnesium chloride and [NEt3H][Al{OC(CF3)3}4], followed by recrystallization from parent halobenzenes. The complexes were characterized by powder and single crystal X-ray diffraction, NMR and ATR-IR spectroscopy, elemental analysis, and SQUID magnetometry; experimental data were rationalized by a combination of density functional theory and ab initio calculations. We find that bis-halobenzene adducts of the [Dy(Cp*)2]+ cation exhibit highly bent Cp*···Dy···Cp* angles; these cations are also susceptible to decomposition by C-X (X = F, Cl, Br) activation and displacement of halobenzenes by O-donor ligands. The effective energy barrier to reversal of magnetization measured for [Dy(Cp*)2(PhF-κ-F)2][Al{OC(CF3)3}4] (930(6) cm-1) sets a new record for SMMs containing {Dy(Cp*)2} fragments, though all SMM parameters are lower than would be predicted for an isolated [Dy(Cp*)2]+ cation, as expected due to transverse ligand fields introduced by halobenzenes and the large deviation of the Cp*···Dy···Cp* angle from linearity promoting magnetic relaxation.
Collapse
Affiliation(s)
- Sophie
C. Corner
- Department of Chemistry, The
University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - Gemma K. Gransbury
- Department of Chemistry, The
University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | | | - George F. S. Whitehead
- Department of Chemistry, The
University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | | | - David P. Mills
- Department of Chemistry, The
University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| |
Collapse
|
4
|
Liu HY, Neale SE, Hill MS, Mahon MF, McMullin CL, Richards E. [{SiN Dipp}MgNa] 2: A Potent Molecular Reducing Agent. Organometallics 2024; 43:879-888. [PMID: 38665773 PMCID: PMC11041119 DOI: 10.1021/acs.organomet.4c00076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2024] [Revised: 03/17/2024] [Accepted: 03/25/2024] [Indexed: 04/28/2024]
Abstract
The bimetallic species, [{SiNDipp}MgNa]2 [{SiNDipp} = {CH2SiMe2N(Dipp)}2; (Dipp = 2,6-i-Pr2C6H3)], is shown to be a potent reducing agent, able to effect one- or two-electron reduction of either dioxygen, TEMPO, anthracene, benzophenone, or diphenylacetylene. In most cases, the bimetallic reaction products imply that the dissimilar alkaline metal centers react with a level of cooperativity. EPR analysis of the benzophenone-derived reaction and the concurrent isolation of [{SiNDipp}Mg(OCPh2)2], however, illustrate that treatment with such reducible, but O-basic, species can also result in reactivity in which the metals provide independent reaction products. The notable E-stereochemistry of the diphenylacetylene reduction product prompted a computational investigation of the PhC≡CPh addition. This analysis invokes a series of elementary steps that necessitate ring-opening via Mg+ → Na+ amido group migration of the SiNDipp ligand, providing insight into the previously observed lability of the bidentate dianion and its consequent proclivity toward macrocyclization.
Collapse
Affiliation(s)
- Han-Ying Liu
- Department
of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
| | - Samuel E. Neale
- Department
of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
| | - Michael S. Hill
- Department
of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
| | - Mary F. Mahon
- Department
of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
| | - Claire L. McMullin
- Department
of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
| | - Emma Richards
- School
of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K.
| |
Collapse
|
5
|
Olding A, Lucas NT, Ho CC, Bissember AC. Acridine-based copper(I) PNP pincer complexes: catalysts for alkyne hydroboration and borylation of aryl halides. Dalton Trans 2024; 53:4471-4478. [PMID: 38348688 DOI: 10.1039/d3dt04269c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/06/2024]
Abstract
PNP pincers represent some of the most well-studied ligand systems in coordination chemistry owing to their high thermal and chemical stability, and the predictable metal coordination geometries of associated metal complexes. Examples of first-row transition metal complexes bearing acridine-based PNP pincer ligands are extremely rare. This study reports the preparation and structural authentication of acridine-based copper(I) PNP complexes, which reveal the profound effects that the steric bulk of methylene-tethered P-substituents has on metal centre coordination number and geometry. The capacity of these systems to mediate copper-catalysed alkyne hydroboration and the borylation of aryl halides is also investigated.
Collapse
Affiliation(s)
- Angus Olding
- School of Natural Sciences - Chemistry, University of Tasmania, Hobart, Tasmania, 7001, Australia.
| | - Nigel T Lucas
- Department of Chemistry, University of Otago, Dunedin, Otago 9054, New Zealand
| | - Curtis C Ho
- School of Natural Sciences - Chemistry, University of Tasmania, Hobart, Tasmania, 7001, Australia.
| | - Alex C Bissember
- School of Natural Sciences - Chemistry, University of Tasmania, Hobart, Tasmania, 7001, Australia.
| |
Collapse
|
6
|
Emerson-King J, Gransbury GK, Whitehead GFS, Vitorica-Yrezabal IJ, Rouzières M, Clérac R, Chilton NF, Mills DP. Isolation of a Bent Dysprosium Bis(amide) Single-Molecule Magnet. J Am Chem Soc 2024; 146:3331-3342. [PMID: 38282511 PMCID: PMC10859956 DOI: 10.1021/jacs.3c12427] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Revised: 01/09/2024] [Accepted: 01/10/2024] [Indexed: 01/30/2024]
Abstract
The isolation of formally two-coordinate lanthanide (Ln) complexes is synthetically challenging, due to predominantly ionic Ln bonding regimes favoring high coordination numbers. In 2015, it was predicted that a near-linear dysprosium bis(amide) cation [Dy{N(SiiPr3)2}2]+ could provide a single-molecule magnet (SMM) with an energy barrier to magnetic reversal (Ueff) of up to 2600 K, a 3-fold increase of the record Ueff for a Dy SMM at the time; this work showed a potential route to SMMs that can provide high-density data storage at higher temperatures. However, synthetic routes to a Dy complex containing only two monodentate ligands have not previously been realized. Here, we report the synthesis of the target bent dysprosium bis(amide) complex, [Dy{N(SiiPr3)2}2][Al{OC(CF3)3}4] (1-Dy), together with the diamagnetic yttrium analogue. We find Ueff = 950 ± 30 K for 1-Dy, which is much lower than the predicted values for idealized linear two-coordinate Dy(III) cations. Ab initio calculations of the static electronic structure disagree with the experimentally determined height of the Ueff barrier, thus magnetic relaxation is faster than expected based on magnetic anisotropy alone. We propose that this is due to enhanced spin-phonon coupling arising from the flexibility of the Dy coordination sphere, in accord with ligand vibrations being of equal importance to magnetic anisotropy in the design of high-temperature SMMs.
Collapse
Affiliation(s)
- Jack Emerson-King
- Department
of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - Gemma K. Gransbury
- Department
of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - George F. S. Whitehead
- Department
of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | | | | | | | - Nicholas F. Chilton
- Department
of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
- Research
School of Chemistry, The Australian National
University, Sullivans
Creek Road, Canberra, ACT 2601, Australia
| | - David P. Mills
- Department
of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| |
Collapse
|