Single-Molecule and Single-Ion-Magnets with emphasis on 4f ions
Synthesizing soluble models for silicate and phosphate materials and building designer zeolites through a hierarchical synthesis protocol
Developing synthetic strategies for thermally unstable precursors for ceramic phosphates
Unraveling coordination behavior of heavier s-block elements
C3 Symmetric Organic Electron rich systems and COFs derived from them
Area (a): Single ion magnets (SIM), that exhibit magnetization blockade below a critical temperature (TB), represent the ultimate size limit for future spin based devices. Raising TB is an ongoing unresolved challenge in this area and lanthanide ions are found to be the most appealing candidates. A strategy to circumvent this challenge is to quench the prominent deactivating quantum tunneling of magnetization (QTM) through appropriately designed molecules with higher order symmetry. We have recently reported air-stable Dy(III) and Er(III) complexes possessing pseudo-D5h symmetry where the Dy(III) complex is found to possess record anisotropy barriers (Ueff) of 735.4 K, while the magnetization studies reveal opening up of the hysteresis at least up to 12 K (TB) even at zero field. The combination of both high Ueff and TB is the best observed for any SIMs. Ab initio calculations have been used to establish the connection between higher-order symmetry and quenching of QTM effects.
Area (b): The beginning of independent research career of Murugavel had an accidental coincidence with the emergence of metal-organic-frameworks (MOFs) in the literature. Only years before that, there has been a lot of activity around the world to understand the formation of zeolitic structures and to this effect several model compounds have been synthesized to understand complicated silicate structures. In this direction, Murugavel’s research group significantly contributed to the development of suitable organic-soluble building blocks or SBUs by synthesizing a multitude of siloxanes, phosphonates, and more recently phosphates. Among the building blocks unraveled, structurally diverse D4R cubanes (with varying coordination numbers on the metal on the alternate vertices of the cubane) and extremely rare examples of S4R, S6R, and S8R SBUs need special mention. An outstanding contribution to this area is the demonstration of the fact that the transition metal phosphonates need not necessarily be always layered solids. The 2007 report of Murugavel on transition metal phosphonates with cubic cores opened up a new channel for investigations in metal-phosphonate chemistry including the possible use of these clusters as SMMs. An offshoot of these efforts was the report of 2001 concerning the only example of an organic soluble silicophosphonate by diligently combining silanol and phosphazane chemistry.
No doubt that the efforts of Murugavel’s group on synthesizing models for zeoltic materials mentioned above are noteworthy, but what made a great impact of his contributions is the further perusal by his team to really make use of these molecules as real building blocks and just not treat them as model compounds. Taking a single zinc based di-isopropylphenyl phosphate D4R cluster as a typical example, and using H-bonding, coordinate bonding, and covalent bonding as the glue to combine these SBUs, Murugavel’s group has demonstrated a novel approach to develop porous solids at room temperature and atmospheric pressure. The impact of these results of Murugavel is already evident from the large number of citations his recent published work is receiving. His group is already expanding this approach for room temperature synthesis of COFs (covalent organic frameworks).
Area (c): Soft Chemistry (Chimie Douce) was successfully applied to the preparation of a large number of metal oxides by solid state chemists in the 1990s; these reactions were typically carried out under moderate conditions (typically T < 500 oC), and were primarily used for stabilizing / isolating metastable phases. A parallel development in this area was to prepare thermally unstable metal precursor complexes such as beta-diketonates and decompose them at fairly low temperatures to prepare metal oxides. However this methodology could not be extended for the synthesis of non metal oxide materials such as metal silicates and phosphates mainly due to the lack of good synthons that decompose at fairly low temperatures. Tilley et al. had in fact developed an organometallic approach to prepare fine particle metal phosphates. This approach for example is only applicable to metals for which stable / commercial organometallic precursors are available (e.g. zinc phosphate from Me2Zn) and not for metals such as Mn, Cu, Hg, etc.
In 2001, Murugavel’s group started to successfully address this problem by developing a non-organometallic strategy. A thermally and hydrolytically unstable diester of phosphoric acid, di-tert-butylphosphate, was identified as the most suitable precursor for this purpose in view of its high solubility in water as well as lipophilic solvents such as hexane. Exploiting its solubility in protic solvents and high thermal instability, Murugavel’s group demonstrated its utility to produce ceramic phosphates at temperatures much below 300 oC, in some cases even at 175 oC. This work published in a serried of articles starting from 2001 has made a huge impact which is evident from a large number of citations for this work (at least minimum of 30 for each of the top ten articles published); the early results on this area were also reviewed by Murugavel in an Acc. Chem. Res. Article in 2004 and a Chem. Rev. article in 2008.
Area (d): Another area where he has made significant contributions deals with the understanding of the fundamental coordination chemistry of alkaline earth metal ions with particular emphasis to the understanding of calcium ions biology. A work which initially commissioned to just understand the interaction of aminoacids / amino carboxylic acids with calcium ions in aqueous medium under physiological pH conditions, late percolated to a deeper understanding of fundamental coordination chemistry of group 2 metal ions, modulation of the hard/soft character of group 2 elements, and inclusion of pyridinic bases in the coordination sphere. Close to 20 papers published by Murugavel in this area are the best cited amongst all his publications. Three of these articles have already been cited some 70 times each. This body of research on s-block elements is comprehensive and probably the most exhaustive among all the research groups in this area.