Periodic Reporting for period 1 - MMQIP (Molecular Magnets: Coordination Cages, Frameworks and Multifunctional Materials)
Reporting period: 2020-04-14 to 2022-04-13
Specific Research Objectives: To build coordination cages and molecule-based framework materials possessing permanent cavities, and to do so with both diamagnetic and paramagnetic metal centres. Further, employ both experimental (NMR, EPR, SQUID magnetometry, single crystal XRD, powder XRD, heat capacity, INS) and theoretical characterisation to identify the appropriate host-guest combinations for attractive magnetic/redox/photo-active behaviours.
Importance for Society: Magnetic materials are ubiquitous in modern life, used in technologies as diverse as computers, smartphones and tablets, medical equipment, hybrid cars, wind turbines, and security and communications equipment. They are also of enormous importance in cutting-edge academic chemistry, physics and materials science research, since molecules proffer better, faster, smaller, cleaner, greener, cheaper, and more controllable alternatives to traditional solid-state materials. As such they have the potential to transform, for example, how we store information and how we compute - industries worth $billions to the world economy, where advances in fundamental science can have a transformative technological and economic impact
Overall Objective: the aim of the proposal is to construct and fully characterise magnetic coordination capsules, develop magneto-structural relationships and identify candidates suitable for employment in quantum mechanical devices.
Importance for Society: Magnetic materials are ubiquitous in modern life, used in technologies as diverse as computers, smartphones and tablets, medical equipment, hybrid cars, wind turbines, and security and communications equipment. They are also of enormous importance in cutting-edge academic chemistry, physics and materials science research, since molecules proffer better, faster, smaller, cleaner, greener, cheaper, and more controllable alternatives to traditional solid-state materials. As such they have the potential to transform, for example, how we store information and how we compute - industries worth $billions to the world economy, where advances in fundamental science can have a transformative technological and economic impact
Overall Objective: the aim of the proposal is to construct and fully characterise magnetic coordination capsules, develop magneto-structural relationships and identify candidates suitable for employment in quantum mechanical devices.
We have designed and synthesised a series of organic ligands as well as used commercially available ligands (Figure 2) to make a series of polymetallic clusters/cages.
1. We for the first time have reported Mn18 wheel, complex 1, which consists of two square [MnIII6MnII2] wheels linked via two MnII ions. An interesting magnetic feature along with available empty spaces in the centre makes complex 1 a suitable guest for large host cages and a suitable host for small organic molecules (Figure 3).
2. We have reported the first example of a heterometallic [Mn2Gd] triangle, Complex 2, containing Mn in the III+ and II+ oxidation states. Susceptibility, magnetisation and detail DFT and ab initio studies highlighting the importance of MnIII/MnII-O-GdIII angle and the rigidity of the 2,2’-bis-p-tBu-calix[4]arene (L2H8) ligand in governing the sign and magnitude of the exchange interactions (Figure 4).
3. It is somewhat unusual for synthetic chemists to employ two different metal salts for the formation of homometallic cluster compounds and we were able to do so by making (complex 3 [Fe15]) cage where the high symmetry of the metallic skeleton leads to the presence of competing for antiferromagnetic exchange interactions and spin frustration. Combined experimental and computational studies reflect the presence of a large density of low-lying spin states (Figure 5).
4. We for the first time have reported complex 4, where the bpptz•- radical ligand enwraps two CoII centres within quasi-TPR geometries, which are further bridged by the tetrazine radical in trans mode. The magnetic and theoretical studies revealed that the interaction between the Co centres and the tetrazine radical is strongly antiferromagnetic with typical SMM behaviour with an attractive effective energy barrier for spin reversal, among the largest for polynuclear transition metal SMMs. Apparently, the presence of strong exchange effectively suppresses the QTM effect (Figure 6).
5. We have reported a series of novel lantern-like guest⸦[M2L44]4+ coordination cages (here, M = CuII and PdII) through simple self-assembly of four molar equivalents of the ligand molecule (L4 = 1,3-bis(3-ethynylpyridyl)benzene) with two molar equivalents of the corresponding metal salt, followed by one molar equivalent of guest, forming [CuII2L44(H2O)(OTf)3](OTf)·MeCN (complex 5), ReBr6⸦ [PdII2L44](BF4)2 (complex 6) and ReBr6⸦[CuII2L44(OTf)2] (complex 7), respectively. Complex formation was confirmed by ESI–MS and 1H NMR, both revealing solution stability. Magnetic measurements combined with theoretical calculations show that: (a) there is no magnetic interaction between the CuII ions in the “empty” [Cu2L44]4+ cage, complex 5. (b) The geometry of the encapsulated [ReBr6]2- ion remains essentially unchanged with respect to its metal salt and thus the axial zero-field splitting parameter, DRe, also remains the same. (c) The ingress of the ReBr62- ion induces a magnetic exchange interaction between the ReIV guest and the CuII host (Figure 7).
6. We have synthesised a smaller member of this molecular iron oxide family, an [Fe8] cage (complex 8· 3H2O·2MeO-Py). For complex 8, the metallic skeleton conforms to a hexagonal bipyramid with metal-oxygen core related to the mineral magnetite. Magnetic and theoretical studies reveal an S = 10 ground state (Figure 8).
7. We have synthesised a series of molecular cages, Co2L44X4 Cages (X = NCS (complex 9), F(complex 10), Cl(complex 11), Br(complex 12)). The atomic-level fine-tuning results in fascinating anisotropy parameters with the D values ranging between -80 ≤ D ≥ +100 cm-1. To the best of our knowledge, this is the first-ever report where atomic-scale fine-tuning on cages has been performed to get such a huge change in the D parameter, which is essential for many magnetic applications (Figure 9).
1. We for the first time have reported Mn18 wheel, complex 1, which consists of two square [MnIII6MnII2] wheels linked via two MnII ions. An interesting magnetic feature along with available empty spaces in the centre makes complex 1 a suitable guest for large host cages and a suitable host for small organic molecules (Figure 3).
2. We have reported the first example of a heterometallic [Mn2Gd] triangle, Complex 2, containing Mn in the III+ and II+ oxidation states. Susceptibility, magnetisation and detail DFT and ab initio studies highlighting the importance of MnIII/MnII-O-GdIII angle and the rigidity of the 2,2’-bis-p-tBu-calix[4]arene (L2H8) ligand in governing the sign and magnitude of the exchange interactions (Figure 4).
3. It is somewhat unusual for synthetic chemists to employ two different metal salts for the formation of homometallic cluster compounds and we were able to do so by making (complex 3 [Fe15]) cage where the high symmetry of the metallic skeleton leads to the presence of competing for antiferromagnetic exchange interactions and spin frustration. Combined experimental and computational studies reflect the presence of a large density of low-lying spin states (Figure 5).
4. We for the first time have reported complex 4, where the bpptz•- radical ligand enwraps two CoII centres within quasi-TPR geometries, which are further bridged by the tetrazine radical in trans mode. The magnetic and theoretical studies revealed that the interaction between the Co centres and the tetrazine radical is strongly antiferromagnetic with typical SMM behaviour with an attractive effective energy barrier for spin reversal, among the largest for polynuclear transition metal SMMs. Apparently, the presence of strong exchange effectively suppresses the QTM effect (Figure 6).
5. We have reported a series of novel lantern-like guest⸦[M2L44]4+ coordination cages (here, M = CuII and PdII) through simple self-assembly of four molar equivalents of the ligand molecule (L4 = 1,3-bis(3-ethynylpyridyl)benzene) with two molar equivalents of the corresponding metal salt, followed by one molar equivalent of guest, forming [CuII2L44(H2O)(OTf)3](OTf)·MeCN (complex 5), ReBr6⸦ [PdII2L44](BF4)2 (complex 6) and ReBr6⸦[CuII2L44(OTf)2] (complex 7), respectively. Complex formation was confirmed by ESI–MS and 1H NMR, both revealing solution stability. Magnetic measurements combined with theoretical calculations show that: (a) there is no magnetic interaction between the CuII ions in the “empty” [Cu2L44]4+ cage, complex 5. (b) The geometry of the encapsulated [ReBr6]2- ion remains essentially unchanged with respect to its metal salt and thus the axial zero-field splitting parameter, DRe, also remains the same. (c) The ingress of the ReBr62- ion induces a magnetic exchange interaction between the ReIV guest and the CuII host (Figure 7).
6. We have synthesised a smaller member of this molecular iron oxide family, an [Fe8] cage (complex 8· 3H2O·2MeO-Py). For complex 8, the metallic skeleton conforms to a hexagonal bipyramid with metal-oxygen core related to the mineral magnetite. Magnetic and theoretical studies reveal an S = 10 ground state (Figure 8).
7. We have synthesised a series of molecular cages, Co2L44X4 Cages (X = NCS (complex 9), F(complex 10), Cl(complex 11), Br(complex 12)). The atomic-level fine-tuning results in fascinating anisotropy parameters with the D values ranging between -80 ≤ D ≥ +100 cm-1. To the best of our knowledge, this is the first-ever report where atomic-scale fine-tuning on cages has been performed to get such a huge change in the D parameter, which is essential for many magnetic applications (Figure 9).
We have built coordination capsules possessing permanent cavities and do so with both diamagnetic and paramagnetic metal centres. Latter we have characterized them with 1H NMR, including their solution host-guest behaviour. All these cages/clusters are unique from both the structural and the magnetic points of view. Later we used a variety of paramagnetic guests, including redox- and photoactive species and later examined the magnetic behaviour of these complexes using magnetometry, EPR spectroscopy, heat capacity and INS.
To elucidate their solid-state structures via single-crystal X-ray crystallography, and later investigated their magnetic behaviour with a battery of techniques, including magnetometry (DC and AC), EPR spectroscopy (CW and pulsed), heat capacity and INS to obtain complete electronic structure information. For all the synthesised cages and clusters, we have employed theoretical tools (DFT and ab initio calculations) to compute the spin-Hamiltonian parameters and correlated these properties to those from the experiment.
Based on systematic experimental/theoretical studies, we have explored and exploited the controlled switching (on/off) of the spin-spin interactions between host and guest ion via the charge state of the guest. We have for the first time performed atomic-scale fine-tuning on cages to fine-tune an enormous change of ZFS parameters, to achieve practically applicable magnetic devices.
We have employed theoretical tools (DFT and ab initio calculations) to compute the nature of the interaction between host and guest molecule and fully comprehend the nature of bonding and energetic cost associated with this effect.
We have performed detailed Molecular Orbitals (MOs) analysis and magneto-structural correlations to achieve a suitable host-guest combination which later can be used for end-on-application for magnetic material-based application devices.
To elucidate their solid-state structures via single-crystal X-ray crystallography, and later investigated their magnetic behaviour with a battery of techniques, including magnetometry (DC and AC), EPR spectroscopy (CW and pulsed), heat capacity and INS to obtain complete electronic structure information. For all the synthesised cages and clusters, we have employed theoretical tools (DFT and ab initio calculations) to compute the spin-Hamiltonian parameters and correlated these properties to those from the experiment.
Based on systematic experimental/theoretical studies, we have explored and exploited the controlled switching (on/off) of the spin-spin interactions between host and guest ion via the charge state of the guest. We have for the first time performed atomic-scale fine-tuning on cages to fine-tune an enormous change of ZFS parameters, to achieve practically applicable magnetic devices.
We have employed theoretical tools (DFT and ab initio calculations) to compute the nature of the interaction between host and guest molecule and fully comprehend the nature of bonding and energetic cost associated with this effect.
We have performed detailed Molecular Orbitals (MOs) analysis and magneto-structural correlations to achieve a suitable host-guest combination which later can be used for end-on-application for magnetic material-based application devices.