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Santokh Tandon

Santokh Tandon

Office/Department: Department of Chemistry
Location: 2491 SR 45 S
Phone: 330-385-3805
Area(s) of Expertise:

Ph.D., Guru Nanak Dev University (India), 1979.

Our present research is in the broad area of coordination chemistry of metallosupramolecular architectures of transition and lanthanide metals with multidentate polynucleating macrocyclic and non-cyclic organic ligands, with potential applications in magnetic materials.  Such magnetic materials are often referred to as molecule-based magnets in which the magnetism arises from a molecule rather than a single atom.  Some of the recently discovered examples in this class of magnets include low-dimensional magnetic systems such as single-molecule magnets (SMMs), single-chain magnets (SCMs), and a number of spin clusters that act as "single-molecular magnets" (SMMs) displaying slow magnetization relaxation at low temperature.  The burgeoning interest in this area is due to their potential applications in magnetic refrigeration, quantum computing, and in the highly competitive area of nanotechnology.  The unique behavior of some spin coupled clusters has been attributed to the molecular properties of a large ground-spin state and easy-axis type magnetic anisotropy.  Our research involves the following research areas:

  1. Macrocyclic polymetallic clusters:
    Design, synthesis, structural characterization, and magneto-strcutural investigations of spin-coupled metallosupramolecular architectures of paramagnetic transition and lanthanide metals with polynucleating macrocyclic ligands using template and/or self-assembly processes.  These macrocycles have the potential to act as ditopic to hexatopic ligands holding two to six metal centers in the macrocyclic cavity.  Using 20 and 24 membered macrocyclic ligands we have reported, mononuclear, dinuclear, tetranuclear, and dimeric octanuclear complexes of Ba(II), Cu(II), mixed valence Co(II)/Co(III), Mn(II)/Mn(III), Ni(II), Pb(II) metal ions.  Up to this point, we have reported dimeric dodecanuclear and tetradecanuclear coordination clusters of only copper(II) ions of 30 membered hexanucleating hexatopic macrocyclic ligands which have six pre-organized coordination pockets (N2O) to hold six metal centers in close proximity for very effective magnetic exchange interactions.  Magnetic, electrochemical, and catalytic properties of these complexes will be investigated to find their potential applications in magnetic materials and catalysis.  These studies may also provide a better insight into complex biological process where paramagnetic transition metal centers are closely placed for spin interactions.  It is also planned to trap symmetrical species like BO33-, CO32-, No3- etc. in the central cavity bonded to all metal centers for effective magnetic exchange interactions.
  2. Metallosupramolecular coordination clusters of non-cyclic Schiff-based ligands
    We are also interested in the generation of discrete multimetallic and polymeric coordination clusters with one-dimensional single chains, two-dimensional sheets and three-dimensional structures of polynucleating multidentate non-cyclic Schiff-based ligands in conjunction with doubly or triply bridging anions like N3-,. NCS-, N(CN)s-, CN-, C2H3O2-, C6H5CO2-, C6H5O-, OH- etc. to create extended networks.  In coordination clusters the nature and magnitude of the magnetic exchange interactions between the metal centers depend on a number of factors, the most important of these are the type of bridging ligands and the bridge angles.  Among all, azido and hydroxo (phenoxide and alkoxide) bridges are the most versatile mediators of magnetic exchange interactions between paramagnetic ions due to their flexidentate nature and different modes of coordination.  In most of the reported complexes, azide bridges propagate antiferromagnetic (end-to-end, μ-1,3 bridges) or ferromagnetic interactions (end-on, μ-1,1 bridges) depending upon the nature of the bridges.  The number of complexes in which azide ions exhibit novel triply bridging (μ3-1,1,1 and μ3-1,1,3) and quadruple bridging (μ4-1,1,1,1 and μ4-1,1,3,3) modes is relatively linked.
  3. Metallosupramolecular coordination grid systems
    The third important area of our research is the synthesis and structural characterization of polytopic ligands capable of generating discrete 2D and polymeric guide architectures.  To date, in our group, the crystal structures and magnetic properties of [2x2], [3x3], and [4x4] transition metal polymetallic grids and [2x2] lanthanide grids based on 2,6-piclinic dihydrazone and 3,6-pyridazine dihydrazone have been reported.  a [5x5] Mn25 grid system has been isolated but crystals suitable for x-ray diffraction studies could not be obtained after repeated trials.  The identity of the Mn(II)25 grid was established by STM/CITS measurements.  We are interested in the generation of two-dimensional discrete and polymeric polymetallic coordination grid systems [nxn] (n=2-6) of transition and lanthanide metal ions.

The following techniques are used to characterize the organic polynucleating macrocyclic and non-cyclic ligands and supramolecular coordination clusters: 2D FT-NMR (1H & 13C), FT-IR, UV/Vis, EPR, atomic absorption and mass spectrometry (FAB), Thermogravimetric analysis (TGA) and differential thermal analysis (DTA), electrochemical investigations, x-ray diffraction studies, and variable temperature magnetic studies for magneto-structural investigations.

Scholarly, Creative & Professional Activities
  1. Muhammad Anwar, Louise Dawe, Stewart Parsons, Santokh Tandon, Laurence Thompson, Subrata Dey, Valeriu Mereacre, William Reiff, and Scott D. Bunge. Oligo-nuclear Fe complexes (Fe, Fe4, Fe6, Fe9) derived from tritopic pyridine bis-hydrazone ligands – structural, magnetic and Mössbauer studies. Inorg. Chem., 2014, 53, 04655-4668.
  2. Marcus W. Drover, Santokh S. Tandon, Muhammad U. Anwar, Konstantin V. Shuvaev, Louise N. Dawe, Julie L. Collins, Laurence K. Thompson. Polynuclear complexes of a series of hydrazone and hydrazone–oxime ligands – M2 (Fe), M4 (Mn, Ni, Cu), and Mn (Cu) examples. Polyhedron, 2014, 68, 94-102.
  3. Marcus W. Drover, Santokh S. Tandon, Muhammad U. Anwar, Konstantin V. Shuvaev, Louise N. Dawe, Julie L. Collins, Laurence K. Thompson. Polynuclear complexes of a series of hydrazone and hydrazone–oxime ligands – M2 (Fe), M4 (Mn, Ni, Cu), and Mn (Cu) examples. Polyhedron, 2014, 68, 94-102.
  4. Muhammad U. Anwar, Louise N. Dawe, Santokh S. Tandon, Scott D. Bunge, Laurence K. Thompson. Polynuclear Lanthanide (Ln) complexes of a tri-functional hydrazone ligand - mononuclear (Dy), dinuclear (Y,Tm), tetranuclear (Gd), and hexanuclear (Gd, Dy, Tb) examples. Dalton Trans. 2013, 42, 7781-7794.
  5. Santokh S. Tandon, Scott D. Bunge, Joaquin Sanchiz, and Laurence K. Thompson. Structures and Magnetic Properties of an Antiferromagnetically Coupled Polymeric Copper(II) Complex and Ferromagnetically Coupled Hexanuclear Nickel(II) Clusters. Inorg. Chem. 2012, 51, 3270-3282.
  6. Muhammad U. Anwar, Santokh S. Tandon, Louise N. Dawe, Fatemah Habib, Muralee Murugesu,and Laurence K. Thompson. Lanthanide Complexes of Tritopic Bis(hydrazone) Ligands: Single-Molecule Magnet Behavior in a Linear Dy(III) Complex. Inorg. Chem. 2012, 51, 1028-1034.
  7. Santokh S. Tandon, Marie-Claire Dul, John L. Lee, Louise N. Dawe, Muhammad U. Anwar and Laurence K. Thompson. Complexes of ditopic carbo- and thio-carbohydrazone ligands – mononuclear, 1D chain, dinuclear and tetranuclear examples. Dalton Trans., 2011, 40, 3466.
  8. Kontantin V. Shuvaev, Santokh S. Tandon, Louise N. Dawe, and Laurence K. Thompson. Unexpected Ni(II) and Cu(II) polynuclear assemblies- a balance between ligand and metal ion coordination preferences. Chem. Commun. 2010, 46, 4755-4757.
  9. Santokh Singh Tandon, Scott D. Bunge, Douglas Motry, José Sánchez Costa , Guillem Aromí, Jan Reedijk and Laurence K. Thompson. Copper Coordination Polymers based on Single Chain or Sheet Structures Involving Dinuclear and Tetranuclear Copper(II) Units: Synthesis, Structures, and Magnetostructural Correlations. Inorg. Chem., 2009, 48, 4873-4881.
  10. Santokh S. Tandon, Scott D. Bunge, Robert Rakosi, Zhiqiang Xu and Laurence K. Thompson. Self-assembly of mixed-valence cobalt (II, III) and nickel(II) clusters: azide-bridged one-dimensional single chain coordination polymers [Co2IICo2III]n comprised of tetranuclear units, tetranuclear cobalt [Co2IICo2III] complexes, ferromagnetically coupled azide-bridged tetranuclear, and hexanuclear nickel(II) complexes: synthesis, structural, and magnetic properties. Dalton Trans., 2009, 6536-6551.
  11. Santokh S. Tandon, Scott D. Bunge, Neil Patel, and Laurence K. Thompson. The Synthesis, Structure, and Magnetic Properties of a Novel Copper (II) Cluster with H-bonding Directed 3D-Structure Comprised of Interconnected Double Stranded Ladders. Inorg. Chem. Commun. 2009, 12, 1077-1080.
  12. Santokh S. Tandon and Robert C. Lucas. Metal-induced facile synthesis of a tricyclic system: 10-methyl-12-thia-2,9-diaza-tricyclo[,8]tetradeca-3, 5, 7-triene-1-carbonitrile. Formation of an intramolecular carbon-carbon bond. Canadian J. Chem. 2008, 86, 912-917.
  13. Virginie Niel, Victoria A. Milway, Louise N. Dawe, Hilde Grove, Santokh S. Tandon, Tarque S. M. Abedin, Timpthy L. Kelly, Elinor C. Spencer, Judith A. K. Howard, Julie L. Collins, David O. Miller, and Laurence K. Thompson. Coordination “oligomers” in self-assembly reactions of some “tritopic” picolinic dihydrazone ligands-mononuclear, dinuclear, hexanuclear, heptanuclear and nonanuclear examples. Inorg. Chem., 2008, 47, 176-189.
  14. Santokh S. Tandon, Scott D. Bunge, and Laurence K. Thompson. A Tetradecanuclear-Copper Dimeric Macrocyclic Complex with a Body Centred Heptanuclear Core-Structure and Magnetism. Chem. Commun., 2007, 798-800.
  15. Santokh S. Tandon, Lousie N. Dawe, Victoria A. Milway, Julie L. Collins, and Laurence K. Thompson. Linear Copper ‘chain’ complexes with bulky tritopic hydrazone ligands-structural and magnetic studies. Dalton Trans., 2007, 1948-1953.
  16. Subrata K. Dey, Tareque S. M. Abedin, Louice N. Dawew, Santokh S. Tandon, Julie L. Collins, Laurence K. Thompson, Andrei V. Postnikov, Mohammad Sahabul Alam, Paul Muller. ‘Supramolecular’ self-assembled polynuclear complexes from tritopic, tetratopic and pentatopic ligands-structural, magnetic and surface studies. Inorg. Chem., 2007, 46(19), 7767-7781.