Chemistry and Biochemistry

Stephen M. Holmes

 

HolmesProfessor Holmes received his B.S. degree from Southwest Texas State University in 1992 and Ph.D. from the University of Illinois at Urbana-Champaign in 1999. He was a Postdoctoral Scholar at Cornell University from 1999-2001. He served on the faculty at the University of Kentucky before joining the Department of Chemistry & Biochemistry at UM-St. Louis in 2008. He is currently an NSF CAREER Awardee (2007-2012).

holmesst@umsl.edu
Office: B418
Phone: (314) 516-4382
FAX: (314) 516-5342

http://www.umsl.edu/~holmesst/Site/Home.html

Research Interests

Magnetic Materials. 
Understanding the physical origins of single-molecule magnetic behavior in a series of structurally related cyanometalate clusters is an active area of study. Cyanometalatesare excellent building blocks for constructing molecule-based clusters because cyanides generally form linear M(m-CN)M´ linkages between two metal centers, stabilize a variety of transition metal centers and oxidation states, and efficiently communicate spin density information. Furthermore the sign and magnitude of the local exchange interactions can be controlled via substitution and predicted using simple orbital symmetry arguments. We have developed a synthetic methodology for preparing several well-defined clusters containing a variety of tricyanide complexes (building blocks). The building blocks exhibit significant orbital contributions to their magnetic moments, apparently a necessary feature for the observation of slow magnetic relaxation. Current efforts are focused on how late transition metal centers alter the magnetic (and optical) properties of structurally related clusters.

 

Photoresponsive Materials.
Compounds that change their optical, magnetic, and electrical properties as a function of external stimuli is an exciting area of study in materials science. We recently reported that two polynuclear cyanometalate complexes exhibit reversible changes their optical and magnetic properties with temperature (up to 250 K) and light. If this is a general phenomenon, then substitution of the metal ions and ligands present may extend the operable switching temperatures of these materials above 300 K. Current efforts are directed at understanding the factors necessary for tuning thephotoresponsive behavior in these clusters and one-dimensional networks.

Molecule-Based Devices.
The increasing demand for higher information density and circuit miniaturization is rapidly approaching the limits of device scaling technologies, with potential cost and performance limits being realized within a decade. An overarching goal of molecule-based electronics is to insert easily modified molecules that function as switching elements into electronic devices, in principle allowing for information storage at the molecular level. Key challenges of this collaborative research effort are to (1) fabricate nm-scale electrode gaps that correspond to molecular length scales and (2) engineer tunable molecules for study. Recent measurements suggest that we have successfully integrated a series of magnetic clusters into electrical junctions. Future efforts will investigate how the clusters and metal ions present tune the electrical transport behavior of assembled devices.

Selected Publications

"Pyrazolylborates and their Importance in tuning Single Molecule Magnet Properties of (FeIII2NiII} Complexes", Y-Z.. Zhang, U. P Mallik, N. P Rath, R. Clerac and S. M Holmes,  Inorg. Chem. 2011, 50, 10537

"Controlling Thermally Induced Electron Transfer in Cyanp-Bridged Molecular Squares from Solid State to Solution", D. Siretanu, D. Li, L. Buisson, D. M. Bassani, S. M Holmes, C. Mathoniere and R. Clerac, Chem. A Eur. J. 2011, 17, 11704.

“Irreversible Solvent-Driven Conversion in Cyanometalate {Fe2Ni}n (n = 2, 3) Single-Molecule Magnets,” Y. Zhang, U. P. Mallik, R. Clérac, N. P. Rath and S. M. Holmes,Chem. Commun. 2011, 47, 7194 .

“Synthesis and Characterization of Di- and Trivalent Pyrazolylborate b-Diketonates and Cyano­metalates,” M. Tang, D. Li, U. P. Mallik, Y.-Z. Zhang, R. Clérac, G. T. Yee, M.-H. Whangbo and S. M. Holmes, Inorg. Chem. 2011, 50, 5153.

"A cyano-based octanuclear {FeIII4NiII4} single-molecule magnet". Y. Zhang, U. P. Mallik, N. P. Rath, T. Gordon R. Clérac, and S. M. Holmes, Chem. Commun. 2010, 46, 4953.

"Reversible Thermally and Photoinduced Electron Transfer in a Cyano-Bridged {Fe2Co2} Square Complex", Y. Zhang, D. Li, R. Clérac, , M. Kalisz, C. Mathonière and S. M. Holmes, Angew. Chem., Int.l Ed. 2010, 49, 3752.

"First Structurally Characterized Tricyanomanganate(III) and its Magnetic {MnIII2MII2} Complexes (MII = Mn, Ni", M. Tang, D. Li, U. P. Mallik, J. R. Withers, S. Brauer, M. R. Rhodes, R. Clérac, , G. T. Yee, M-H. Whangbo and S. M. Holmes, Inorg. Chem. 2010, 49, 4753.

"Magnetic and Optical Bistability Driven by Thermally and Photoinduced IntramolecularElectron Transfer in a Molecular Cobalt-Iron Prussian Blue Analogue," D. Li, R.Clérac, O. Roubeau, E. Harté, C. Mathonière, R. Le Bris and S. M. Holmes, J. Am. Chem. Soc.2008, 130, 252.

"Structural Distortion and Magnetic Behavior in Cyanide-Bridged FeIII2NiII2 Single-Molecule Magnets," D. Li, S.Parkin, R. Clérac, G. Wang, G. T Yee and S. M. Holmes,.Eur. J. Inorg. Chem. 2007, 1341.

"Molecular Electrodes at the Exposed Edge of Metal-Insulator-Metal TrilayerStructures," P. Tyagi, L. Li, D. S. M. Holmes and B. J. Hinds, J. Am. Chem. Soc. 2007,128, 4929.

"Synthesis and characterization of one- and two-dimensional octacyanometalate(V) networks: {[trans-MII(DMF)4][cis-MII(DMF)4]2[MV(CN)8]2}n (MII = Mn, Fe, Ni; MV = Mo, W)," J. R. Withers, D. Li, J. Triplet, C. Ruschman, S. Parkin, G. Wang, G. T. Yee and S. M. Holmes, Polyhedron , 2007, 26, 2353.

"Exchange coupling and contribution of induced orbital angular momentum of low-spin Fe3+ ions to magnetic anisotropy in cyanide-bridged Fe2M2 molecular magnets: Spin-polarized density-functional calculations," K. Park and S. M. Holmes, Phys. Rev. B2006, 74, 224440.

"Syntheses, Structures, and Magnetic Characterization of Dicyanometalate(II) Building Blocks: [NEt4][(Tp*)MII(CN)2] [MII = Cr, Co, Ni; Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate]," D. Li, C. Ruschman, R. Clérac, and S. M. Holmes,Chem. Commun. 2006, 4036.

"Ancillary Ligand Functionalization of Cyanide-Bridged S = 6 FeIII4NiII4 Complexes for Molecule-Based Electronics," D. Li, S. Parkin, R. Clérac and S. M. Holmes, Inorg. Chem.2006, 45, 7569.

"A Two-Dimensional Octacyanomolybdate(V)-Based Ferrimagnet: {[MnII(DMF)4]3[MoV(CN)8]2}n," J. R. Withers, D. Li, J. Triplett, C. Ruschmann, S.Parkin, G. Wang, G. T. Yee and S. M. Holmes, Inorg. Chem. 2006, 45, 4307..