School of Chemistry
Our research focuses on the synthesis of inorganic magnetic materials towards applications in fields such as:
My research is based in the field of molecular magnetism which details the design, synthesis and study of novel polynuclear paramagnetic materials whose properties are inherited from their parent mononuclear building blocks and may be tuned by structural variation at the molecular level. More detailed descriptions of my research interests are documented below:
Single-Molecule Magnets (SMMs) and Paramagnetic complexes
An important subgroup of this large research field are Single-Molecular Magnets (SMMs), which are discrete polymetallic transition metal complexes (i.e. Fig. 1) and are distinguished by their ability to exhibit magnetic hysteresis of molecular origin. This barrier (Ueff) to magnetization reversal (Ueff = S2D) stems from possession of large ground spin states (S) and significant and negative magnetic anisotropy parameters (D). This discovery spawned a new and exciting area of research in the fields of information storage devices, quantum computing and more recently as potential molecular spintronic devices (i.e. molecular transistors and switches) and as magnetic coolant materials arising from the Magnetic Caloric Effects (MCE).
Figure 1 Crystal structure of a [Co8] cage recently produced by the Jones group
Magnetic Coolant Materials
Magnetic refrigerants are complexes / materials capable of causing a significant decrease in their temperature (mK) as a result of exposure to a large fluctuating magnetic field. Paramagnetic transition metal complexes which posses extremely large ground states (S) and negligible zero-field splitting parameters (D) may as a result exhibit the Magnetic Caloric Effect (MCE) and may be addressed as magnetic coolant materials. When a magnetic coolant complex is placed in an adiabatic bath at low temperatures (< 10 K) and introduced to a large external magnetic field, the large magnetic moment of the complex becomes polarised and results in a large drop in magnetic entropy (Sm). In an adiabatic system the total entropy (magnetic + lattice) must remain constant and therefore when the external magnetic field is removed (adiabatic demagnetisation), the spins again randomise and the magnetic entropy increases, thus resulting in an equal but opposite decrease in the lattice entropy which necessitates a substantial drop in temperature (reaching mK). Recent MCE studies on high-spin paramagnetic complexes show that they compete well with conventionally used low T magnetic refrigerant materials.
Figure 2 Crystal structure of a mixed metal [Gd2Cu9] cluster (part of a chain)
1, 2 and 3-D coordination polymers
Although the ability of SMMs to exhibit molecular magnetic hysteresis is remarkable, this phenomenon currently only functions at temperatures approaching absolute zero. An alternative approach would be to utilise magnetic polymers, which have significantly higher operating temperatures, but lack the immediate possibility of miniaturisation to molecular scale. 1, 2 and 3-D coordination polymers (a.k.a: Metal-Organic Frameworks, MOFs) comprise metal centres (nodes) linked into extended arrays through rigid organic linker ligands. Our interest lies in utilising paramagnetic polymetallic complexes (i.e. SMMs) as building blocks in the construction of pre-designed 2 and 3-D extended architectures in order to improve their function as potential magnetic materials.
Figure 3 A 1-D chain of H-bonded alternating Mn(III) (purple) and Na(I) (yellow) mononuclear units
Magnetic Cages as Supramolecular Hosts
The design and synthesis of self-assembled molecular flasks and containers capable of encapsulating smaller guest molecules continues to fascinate the scientific community. This is due to their potential applications in both the solution and solid state. Examples of their use in solution include anion sensing, catalytic organic transformations and medical diagnostics. In the solid state, interests lie in their potential as gas storage and separation vessels, and as containers for magnetic nanoparticles towards imaging. Recently the Jones group described the structural and magnetic characterisation of a large family of heptanuclear [M(II/III)7(OH)6(L)6](NO3)2 (M = Ni(II), Zn(II), Co(II/III)) complexes, each member comprising pseudo metallocalixarene double-bowl topologies, derived from partial (pseudo) Calix[n]arene Schiff base ligands such as 2-iminomethyl-6-methoxy-phenol (Fig. 4a). More specifically these complexes possess metallic skeletons describing planar hexagonal discs. Their organic exteriors form double bowl shaped topologies which (due to their crystal packing) result in the formation of molecular cavities in the solid state. These confined spaces are shown to behave as host units in the solid state for guests including small organic molecules and charge balancing counter anions, depending on the exact ligand utilised during construction (i.e. Fig. 4b and c). We are currently extending and extrapolation upon this body of work by producing new host materials with pre-meditated molecular cavities via strategic ligand design towards the accommodation of more pertinent guests.
Figure 4 (a) General structure of the Schiff base ligands used to form [M7] (M = Co(II/III), Ni(II), Zn(II)) double-bowl metallocalixarenes as shown in (b) and (c).
List of Peer Reviewed Publications (since 2010)
Total Publications to date: 56
The Jones group has particular expertise in the exploration of various synthetic methodologies towards producing novel magnetic materials. If you are interested in working within the Jones group, please do not hesitate to contact me at the email address provided.
Current PhD students:
Previous PhD students:
We have a broad range of collaborators as listed below.