The research work is mainly focused on:
- Preparation of layered materials containing guests having nonlinear optical properties. Phosphates or phosphonates of tetravalent metals, especially of zirconium and titanium, have excellent thermal and acid-base stability and are able to accommodate guest molecules into their interlayer space by means of an intercalation reaction. Moreover, phosphonates could be further modified by functional groups useful for grafting of guest molecules. In this way, an intercalation of organic push-pull molecules featuring intramolecular charge-transfer will be studied. Restricted geometry in the interlayer space of layered inorganic solids helps to organize the incorporated species in a way favorable for the improvement of their optical properties.
- Synthesis and characterization of new functionalized layered metal phosphonates and their intercalation with organic guests. The description of the arrangement and orientation of the functional groups in the interlayer space using molecular simulations and quantum calculation helps us to understand the structure-properties relationships in the studied materials. Molecular modeling is also a useful and reliable method for studying the bonding geometry and shape of intercalated molecules, mutual interaction energies, charge distribution and complete arrangement of the guest species. Knowledge of the arrangement of functional groups and/or guest molecules will be used for design and synthesis of new hosts and their intercalation with compounds with interesting optical or electrical properties. The work is focused on the following three types of materials: tetravalent metal (Ti, Ce, Sn, Zr) and alkaline-earth metal phosphonates as hosts, their intercalates, and composite polymer-host materials.
- Preparation and characterization of other metal phosphonates, not only the layered ones, with the aim to obtain materials interesting from the point of their porosity, their optical and electronic properties. The goal is to obtain materials which could have potential applications in gas storage, catalysis, as components of sensors (due to their ionic conductivity), components of optical devices (due to their luminescence properties), or as ionic exchangers. Structures of some of these materials (coordination polymers) were determined from their single-crystal X-ray data.
Background of our work:
The term intercalation denotes a process in which a molecule or an ion (guest) is placed into a host lattice. The structure of the host remains unchanged or is only slightly altered in the guest-host complex that is in the intercalation compound (intercalate).
The intercalation reaction is usually chemically or thermally reversible. Other terms like insertion, inclusion or topotactic reaction are often used for the intercalation reactions, but all of them correspond to the above given definition. Intercalation chemistry is one of the field of supramolecular chemistry. Intercalation reactions offer the way for the synthesis of new solids and allow controlled systematic changes of their physical properties. These materials have many applications, for instance as catalysts, sorbents, electrochromic displays, electrodes for secondary batteries (Li-ion batteries) and components for fuel cells.
Our team has a long-lasting experience in the study of the intercalation of inorganic and organic guests into various layered host materials like vanadyl phosphate (VOPO4),[1] layered double hydroxides (LDH), tetravalent and divalent metal organophosphonates, especially those containing functional groups.
In our work, we are looking for new compounds which can serve as host materials. In this effort, we focused on functionalized layered organophosphonates which can be applied as catalysts, ion exchangers, sorbents and in molecular recognition. We prepared new inorganic-organic hybrid materials, namely arylphosphonates and alkylphosphonates of metals. Especially proton conductive organophosphonates in which the organic part is functionalized with carboxyl or sulfonic groups are considered as prospective materials as they can be applied as membranes in fuel cells.
We successfully used these host materials for intercalation of optically active species.[2] As an example a schematic structure of the intercalate with tris[4-(pyridin-4-yl)phenyl]amine, a tripodal Y shaped push‑pull system, is shown below
For the characterization of the prepared compounds and the study of their chemical and physical properties we are using the following characterization methods: powder X-ray diffraction, single-crystal X-ray diffraction, thermogravimetric analysis, infrared and Raman spectroscopy, energy-dispersive X-ray analysis, differential thermal analysis, ac and dc conductivity and solid-state NMR. For the study of interconversions of arylphosphonates of alkaline-earth metals we developed a method of computer-controlled additions of reagents to phosphonate suspensions using an automated burette.
We also solved structures of several phosphonates by single-crystal X-ray diffraction, when suitable crystal were prepared, for instance a structure of several functionalized copper arylphosphonates.[3]
As an example there is shown a structure of Cu(C12H8N2)(O3PC6H4COOH)·H2O, which consists of one-dimensional helical motifs. These motifs are alternately right-handed (A) and left-handed.
References:
[1] L. Benes, K. Melanova, J. Svoboda and V. Zima, J. Incl. Phenom. Macrocycl. Chem. 2012, 73, 33-53.
[2] K. Melánová, D. Cvejn, F. Bureš, V. Zima, J. Svoboda, L. Beneš, T. Mikysek, O. Pytela and P. Knotek, Dalton Trans. 2014, 43, 10462 - 10470.
[3] V. Zima, J. Svoboda, Y.-C. Yang and S.-L. Wang, Crystengcomm 2012, 14, 3469-3477.
