Research Interest Updated 27/03/2015
The group's research interests focus on the electronic structure of inorganic systems. We apply a variety of computational methods to a range of problems drawn from both transition-metal and main-group chemistry. The vast majority of our work involves close collaboration with experimental groups involved in the study of structure, magnetochemistry, electrochemistry and reactivity.
The Jigsaw model for metal cluster compound
Metal cluster compounds present a significant challenge to models of structure and bonding - the work of Wade and Mingos in the 1970's, for example, revolutionised our understanding of electron-deficient boranes and their transition metal analogues. More recently, endohedrally encapsulated clusters, where a transition metal sits inside a cluster cage, have provoked interest, in part because they represent the smallest models for transition metal impurities in bulk semiconductors like silicon or germanium. In many cases the metal and cage are essentially independent units: 60-electron [Ni@Pb12]2-, for example, can be thought of as a closed-shell d10 metal inside a 'closo' [Pb12]2- icosahedron (4n + 2 = 50 valence electrons). In work with Prof Jose Goicoechea's group, we have explored a relatively new class of cluster where the vertices of the cluster are 3-connected rather than 4- or 5-connected, as is typical of deltahedral structures. 3-connected vertices are generally associated with electron precise (5n) electron counts, but if 5n electrons are assigned to the cage in e.g. [Ru@Ge12]3-, the metal is left in an unreasonably high oxidation state. The key to understanding these systems is to note that pairs of electrons can play a dual role, satisfying the valence requirements of the metal and the cluster simultaneously. This 'jigsaw' model emphasises the importance of interpenetration of the electron density at the metal and on the cluster.
On the structural landscape in endohedral silicon and germanium clusters, M@Si12 and M@Ge12, J. Goicoechea and J. E. McGrady, Dalton Trans., 2015, 1, 468.
Synthesis and Characterization of [Ru@Ge12]3-: An Endohedral 3-Connected Cluster, G. Espinoza-Quintero, J. C. A. Duckworth, W. K. Myers, J. E. McGrady and J. M. Goicoechea, J. Am. Chem. Soc., 2014, 136, 1210.
Coherent transport through metal-metal bonded molecular wires
Another main interest of the group is to understand the link between electronic structure and electron transport properties of extended metal atom chain (EMAC) complexes, where hlical array of oligo-α-pyridyl ligands is used to support a chain of metal centres. These systems have been the subject of a protracted debate in the inorganic chemistry community due to their polymorphism – they exist is symmetric and unsymmetic forms. Our current objective is to relate the fundamental electronic structure of these EMAC complexes to their conductance as measured, for example, by STM. Ultimately, an understanding of these phenomena will be essential to the development of new computer architectures based on molecular-scale components.
In search of structure-function relationships in transition-metal based rectifiers, T. Weng, D. DeBrincat, V. Arcisauskaite and J. E. McGrady, Inorganic Chemistry Frontiers, 2014, 1, 468.
Low-symmetry distortions in extended metal atom chains: origins and consequences for electron transport, V. P. Georgiev, P. J. Mohan, D. DeBrincat and J. E. McGrady, Coord. Chem. Rev., 2013, 290.
Attenuation of conductance in cobalt extended metal atom chains, V. P. Georgiev. W.M.C. Sameera and J. E. McGrady, J. Phys. Chem. C, 2012, 20163.
Influence of Low-Symmetry Distortions on Electron Transport through Metal Atom Chains: When Is a Molecular Wire Really "Broken"?, V. P. Georgiev and J. E. McGrady, J. Am. Chem. Soc., 2011, 132, 12590.
A three-state model for the polymorphism in linear tricobalt compounds, D. A. Pantazis and J. E. McGrady, J. Am. Chem. Soc., 2006, 128, 4128.
Transition metal clusters
Open-shell transition metal systems, where the presence of one or more unpaired electron presents a considerable challenge to theory, are a major theme within the group. Many of the highlights in this area involve transition metal ions and clusters, where the presence of multiple metal centres further complicates matters. Through a careful consideration of the electronic states that arise from the coupling of these unpaired electrons, we have unravelled the complex and previously unexplained structural phenomena in a number of cluster systems. In collaboration with Prof. Raphael Raptis (University of Puerto Rico), we investigate the nature of the mixed valency (localised or delocalised) in reduced ferric/ferrous clusters.
Double exchange in a mixed-valent octanuclear iron cluster, [Fe8(μ4-O)4(μ-4-Cl-pz)12Cl4]-, E. M. Zueva, R. Herchel, S. Borshch, E. Govor, W. M. C. Sameera, R. McDonald, J. Singleton, J. Krystek, Z. Travnicek, Y. Sanakis, J. E. McGrady and R. G. Raptis, Dalton Trans., 2014, 43, 11269.
Experimental and Theoretical Mossbauer Study of an Extended Family of Fe8(mu4-O)4(mu-4-R-px)12X4 Clusters. E. M. Zueva, W. M. C. Sameera, D. M. Pinero, I Chakraborty, E. Devlin, P. Baran, K. Lubruskova, Y. Sanakis, J. E. McGrady and R. G. Raptis, Inorg. Chem., 2011, 50, 1021.
The role of Synthesis, Characterization, and Study of Octanuclear Iron-Oxo Clusters Containing a Redox-Active Fe4O4-Cubane Core, P. Baran, R. Boca, I. Chakraborty, J. Giapintzakis, R. Herchel, Q. Huang, J. E. McGrady, R. G. Raptis, Y. Sanakis, A. Simopoulos, Inorg. Chem., 2008, 47, 645.
Redox-active ligands
We also have a strong interest in exploring the ways in which electrons are transferred between transition metals (and metal clusters) and redox-active coordinated ligands. Recent highlights include the study of redox-noninnocent complexes of ipyridyl (with Dr Jose Goicoechea, Oxford and Prof Sreebrata Goswami, IACS, Kolkata) reactions of Mn-, Fe- and Cu-based biomimetic clusters in collaboration with Prof. Christine McKenzie (University of Southern) and Prof. Paul Walton (University of York). Our studies have illustrated that the open-shell character plays a defining role in controlling the direction of electron transfer processes.
A Homologous Series of First-Row Transition-Metal Complexes of 2,2 '-Bipyridine and their Ligand Radical Derivatives: Trends in Structure, Magnetism, and Bonding, M. Irwin, L.R. Doyle, T. Kramer, R. Herchel, J.E. McGrady and J.M. Goicoechea, Inorg. Chem., 2012, 51, 12301.
On the mechanism of water oxidation by a bimetallic manganese catalyst: A density functional study. W. M. C. Sameera, C. J. McKenzie and J. E. McGrady, Dalton Trans., 2011, 40, 3859.
Catalytic alcohol oxidation by an unsymmetrical triaminocyclohexane copper complex: electronic structure and mechanism, Ekaterina Zueva, P. H. Walton, J. E. McGrady, Dalton Trans., 2006, 159.
Mechanistic Organometallic Chemistry
We have a longstanding interest in the mechanisms of organometallic reactions. A recent highlight has been the discovery of an unexpected role for phosphine ligands in C-F activation chemistry by zerovalent nickel and platinum complexes. Classic oxidative addition chemistry dominates the thinking of most chemists involved in bond activation, but in the presence of phosphine ligands, C-F bonds can be activated by transferring the fluoride not to the metal, but rather to the phosphine, forming a metallophosphorane. In collaboration with Prof. Robin Perutz (University of York) and Prof. Stuart Macgregor (Heriot-Watt University) we have rationalised a variety of previously puzzling experimental observations regarding C-F activation at pentafluoropyridine using this framework. Perhaps most remarkable is that in the nickel systems the phosphine-assisted pathway allows the pyridyl nitrogen to act as a neighbouring group, stabilising the unsaturated metal centre. This neighbouring group effect only operates if the bond ortho to the pyridyl nitrogen is activated, thus causing a switch in regioselectivity relative to the platinum analogues, where para selectivity is observed.
C-F and C-H Bond Activation of Fluorobenzenes and Fluoropyridines at Transition Metal Centers: How Fluorine Tips the Scales, E. Clot, O. Eisenstein, N. A. Jasim, S. A. Macgregor, J. E. McGrady and R. N. Perutz, Acc. Chem. Res., 2011, 44, 333.
Selective Activation of the ortho C-F Bond in Pentafluoropyridine by Zerovalent Nickel: Reaction via a Metallophosphorane Intermediate Stabilized by Neighboring Group Assistance from the Pyridyl Nitrogen, A. Nova, M. Reinhold, R.N. Perutz, S.A. Macgregor and J.E. McGrady, Organometallics, 2010, 29, 1824.
Competing C-F activation Pathways in the reaction of Pt(0) with fluoropyridines: Phosphine-assistance versus oxidative addition, A. Nova, S. Erhardt, N. A. Jasim, R. N. Perutz, S. A. Macgregor, J. E. McGrady, A. C. Whitwood, J. Am. Chem. Soc., 2008, 130, 15499.
A comparison of C-F and C-H bond activation by zerovalent Ni and Pt: A density functional study, Meike Reinhold, John E. McGrady, Robin N. Perutz, J. Am. Chem. Soc., 2004, 126, 5268.
Weak interactions in organometallic chemistry
The nature of agostic interactions is also an area of considerable interest in the group. In collaboration with Prof. Michel Etienne (LCC, Toulouse) and Prof. Feliu Maseras (ICIQ, Tarragona), we have shown that the interplay between steric and electronic factors in TpMe,MeNbCl(R)(alkyne) (where R = alkyl) leads to an unprecedented diversity of α- and β-C-H agostic interactions. Most recently, we have discussed the remarkable structure of the cyclopropyl derivative, which shows evidence for a very unusual α-C-C agostic bond.
Critical role of the correlation functional in DFT descriptions of an agostic niobium complex, D. A. Pantazis, J. E. McGrady, F. Maseras, M. Etienne, Chem. Theory and Comput., 2007, 3, 1329.
On the origin of α- and β-agostic distortions in early-transition-metal alkyl complexes, D. A. Pantazis, J. E. McGrady, M. Besora, F. Maseras, M. Etienne, Organometallics, 2008, 27, 1128.
Agostic interactions in alkyl derivatives of sterically hindered tris(pyrazolyl)borate complexes of niobium, J. E. McGrady, F. Maseras, M. Etienne, Coord. Chem. Rev., 2009, 235, 635
Main group chemistry
Not all the work in the group is related to transition metal chemistry. In collaboration with Dr. Chris Russell and Prof. Michael Green (Bristol) and Dr. Jason Lynam (York), we have explored the mechanisms of nucleophilic substitution at phosphorus clusters. In principle these reactions are direct analogues of the well-known SN2 process in carbon chemistry, but the P-P bonded framework provides a sink for electron density, leading to an unexpectedly complex potential energy landscape. We have also recently worked on problems of bond activation by main group compounds (phosphabenzenes)
Hydrogen Activation by an Aromatic Triphosphabenzene,L. E. Longobardi, C. A. Russell, M. Green, N. S. Townsend, K. Wang, A. J. Holmes, S. B. Duckett, J. E. McGrady and D. W. Stephan, J. Am. Chem, Soc., 2014, 136, 13453.
A New Reaction Pathway in Organophosphorus Chemistry: Competing SN2 and AE Pathways for Nucleophilic Attack at a Phosphorus-Carbon Cage Compound, C. Fish, M. Green, R. J. Kilby, J. M. Lynam, J. E. McGrady, D. A. Pantazis, C. A. Russell, A. C. Whitwood, C. E. Willans, Angew. Chem. Int. Ed., 2008, 27, 1128.