Home   Members   Publications   Publications   News   23 July 2019
  อ.ไฉนพร ด่านวิรุทัย
  อ.ขวัญใจ กนกเมธากุล
  อ.อารยัน จันศรี
  อ.อัจฉรา ศิริมังคลา
  อ.ชูศักดิ์ พูนสวัสดิ์
  อ.พิทักษ์ นาสมใจ
  อ.พนาวัลย์ หมู่โสภณ
  นายกิติศักดิ์ ภูผาสิทธิ์

Department of Chemistry, Faculty of Science, Khon Kaen University

Khon Kaen University


The Royal Golden Jubilee Ph.d Program

The Thailand Research Fund
Coordination Chemistry, X-ray Crystallography, Crystal Engineering & Molecular Functional Materials
1) Magneto-structural chemistry of copper(II) coordination compounds
Our main area of research concerns the magneto-structural chemistry of copper(II) coordination compounds containing different bridging ligands both in the experimental and theoretical points of view. During the past decade, we have designed and synthesized a number of complex systems based on the nature of the bridging ligands. Each complex system involves a number of compounds with diverse structural topologies and geometries. Some of these show unique properties, for instance, two phase transitions clearly visible from thermal and magnetic behaviors in a dihydroxo-bridged copper(II) dimer [Cu(dpyam)(OH)]2(ClO4)2 (dpyam = di-2-pyridylamine) and strong ferromagnetism in a series of the triply-bridged dinuclear compounds.
The theoretical study for the latter system leads to strong conclusion about the role of the pentacoordination geometry and the nature of the third bridging ligand in determining the final value of the magnetic exchange constant. Analysis of the structural factors that influence the magnitude of magnetic interactions allows tuning the magnetic exchange interaction (J values). Therefore the appropriate design of new magnetic materials with improved features requires knowledge of magneto-structural correlations.
2) Crystal Engineering of novel metal-organic frameworks (MOFs)
Current research is focused on the design and synthesis of novel metal-organic frameworks (MOFs) with desired functional properties. As it has well known, the potential applications of MOFs include molecular adsorption and separation processes, ion-exchange, catalysis, sensors technology, optoelectronics and molecular magnetism. This project emphasizes on the crystal engineering of these molecular materials and the investigation of their functional properties. As a representative complexes system, Zn(II)-4,4'-bipyridine-carboxylato compounds are good heterogeneous catalysts for the high yield cyanosilylation of acetaldehyde in dichloromethane and the anion-exchange among zinc(II) compounds is found to be highly selective. The removal and reintroduction of water guest molecules is accompanied by a crystalline-to-crystalline structural transformation of the material, which exhibits rigid vacant host channels.
Another complex system is the flexible and dynamic non-coordination supramolecular cobalt(II)/iron(II)-2-aminopyrazine-sulfate frameworks [M(H2O)4(ampyz)2][M(H2O)6](SO4)2(H2O)2 (M = CoII, FeII and mixed CoII/FeII, ampyz = 2-aminopyrazine) which exhibit water-induced reversible crystal-to-amorphous transformations with chromotropism and a Cd(II) coordination polymer [Cd(ampyz)(H2O)2(SO4)]n(H2O)n which exhibit water-induced reversible structural crystalline phase transformation.
3) Molecule-Based Magnetic materials
More recently, we have also studied on the crystal engineering of molecular magnetic materials including 1D to 3D coordination polymers, which aims to control the spins in molecules and molecular assemblies. They usually reveal magnetic orders accompanying with various fascinating architectures and exhibit remarkable magnetic properties, such as spin-canting and metamagnetism, etc. As a representative example, the [Co3(N3)6(OH2)2(2,2′-bpe)2]n(2,2′-bpe)n (2,2′-bpe = 1,2-bis(2-pyridyl)ethylene) shows remarkable 1D chain comprised of the alternating distinctive cobalt(II) geometries in a unique [-5-5-6-]n sequence of coordination number, which shows overall metamagnetic behavior having magnetic ordering at 6 K. In contrast, [Co(N3)2(2,2′-bpe)2]n has 2D wavy layers which exhibits weak ferromagnetism due to spin canting below TN of 12 K.
Another complex system is 2D layer [Co(N3)2(ampyz)]n and 3D framework [Co(N3)2(ampyz)]n of azido-bridged CoII coordination networks. The layered diffusion reaction in ambient temperature gave the high symmetric 2D square-grid structure of [Co(N3)2(ampyz)]n whereas the hydrothermal reaction at 90 C for 1 day yielded the 3D framework of [Co(N32(ampyz)]n. Although both compounds are similar in local coordination environments but somewhat different in structural symmetries, dimensionalities and bridging parameters, consequently, their magnetic behaviors at low temperature reveal the significant disparities. The magnetic investigation of 2D layer [Co(N3)2(ampyz)]n shows the coexistence of big spin canting angle and metamagnetism having magnetic ordering at 10 K, whereas the magnetic behavior of another one simply exhibits spin-canted antiferromagnetism below TN of 16 K.
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