This dissertation presents the investigation of magnetic exchange and anisotropy in novel metal-organic complexes containing minimum number of magnetic ions. Such complexes can serve as a model system to understand the exciting magnetic phenomena in such class of materials and also can put forward as candidates for the so called molecular nanomagnets. A direct assessment of the effective magnetic moment and the effective interaction between the metal ions in the complex can be done using magnetization measurements. Here the magnetization studies are performed as a function of temperature and field using a SQUID magnetometer. Yet another powerful tool to characterize and determine the spin levels, the ESR spectroscopic methods, has also been exploited. The study of the dynamical properties of this class of materials was relevant to understand the relaxation mechanism in the low temperatures. For this a new ac susceptometer has been built in house which was another main objective of this dissertation work. The design, fabrication, calibration and automation done on this device is presented in this thesis. The device has been tested using the known molecular magnet Mn12 acetate, and the antiferromagnet Dy2PdSi3. The present work is mainly focused on the magnetic properties of Mn, Ni and Fe based organometallic complexes. The studied Mn dimer with different acceptor and donor ligands exhibit the fine tuning of the electron density at the core of molecular complex by variation in ligands. This in turn shows that the change in peripheral ligands can control the magnetism of the molecule. The influence of the change in Ni-S-Ni bond angle in the magnetic exchange interaction is studied in a Ni(2) dimer and a Ni(2) trimer complex. The Ni dimer complex shows a ferromagnetic interaction (J = -42K) whereas trimer shows an antiferromagnetic interaction (J = 140K). Another Ni based complex bridged via phosphorous has been studied which shows the existence of glassy nature at low temperature. Also a polymeric chain compound based on Fe is studied and presented. All these phosphorous or sulphur bridged complexes are novel materials and these are the first data on these complexes.

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In the past decade there has been a growing interest in one-dimensional (1D) nanostructures, such as nanowires, nanotubes and nanorods, owing to their size-dependent optical and electronic properties and their potential application as building blocks, interconnects and functional components for assembling nanodevices. One of the ways to obtain such architectures is a template-directed synthesis which is practically a straightforward route to 1D nanostructures. In this approach, the template simply serves as a scaffold, within (or around) which a different material is generated in situ and shaped into a nanostructure with its morphology complementary to that of the template. It is generally accepted that template-directed synthesis provides a simple, high-throughput, and cost-effective procedure that also allows the complex topology present on the surface of a template to be duplicated in a single step. In the current work, utilization of the molecular bottle brushes as templates is proposed for the fabrication of conductive nanorods. Their non-spherical macromolecular geometries and lengths up to a few hundred nanometers allow the application of these structures in nanowire synthesis. The variety of molecular bottle brush architectures and their composition enables the adjustment of appropriate conditions for the preparation of conductive materials. Moreover, the ability of the brushes to assemble on a surface under certain conditions provides their usage as building blocks for the preparation of complex conductive networks. Here, the preparation, characterization, and applications of molecular bottle brushes are discussed. Two main goals were pursued. First, to deepen the knowledge in the synthesis of molecular bottle brushes, and to investigate their behavior on the surface. Second, to explore the application of the brushes as templates or building blocks for the formation of conductive nanowires. For the purpose, new ways of molecular brush synthesis by using the “grafting to” approach had to be developed. It was found that the reaction of nucleophilic addition based on pentofluorophenol chemistry and a coupling “click chemistry” reaction can be used to fabricate molecular brushes. Both methods showed efficient results and demonstrated high reactivity of the backbone with the end groups of the side chains. The “click chemistry” approach, however, demonstrated better results considering higher thicknesses of the brushes and, therefore, higher grafting density of the side chains. The “grafting to” together with the “grafting from” methods are very powerful synthetic tools, which can be used in the fabrication of any desired molecular bottle brush architectures. Additionally, complexation of oppositely charged bottle polymer brushes at a single-molecule level using AFM and CryoTEM was experimentally investigated. It was found that polyelectrolyte complexes have “scrambled-egg” morphology, where oppositely charged polymer chains are not oriented parallel to each other but cross each other. Furthermore, molecular bottle brushes were used as templates for the preparation of conductive nanowires. Three approaches for their fabrication were tested. It was found that brushes could easily be covered with various conductive materials, for example conductive polymers or metals. It was showed that for very small, tiny objects as molecular bottle brushes, one can use FIB in order to build up electrodes at its ends. The electrodes could be sputtered with an accuracy of 500 nm and further be used in the determination of the conductivity. The molecular bottle brushes covered with palladium showed the resistance of 50 MΩ, which, regarding the size of the brush, corresponds to a conductivity of one single molecule being ~1 S*cm-1. The obtained conductivity data were in good correlation with the data found in literature. We believe that the molecular bottle brushes have high potential applicability for the building of complex conductive networks. Future refinement of the synthetic methods, combined with improvements in structuring and positioning of objects at the nanoscale, could lead to their implementation in the construction of high-performance electronic devices.

The thesis presented here is focused on the synthesis of iron-bismuth alkoxides and siloxides as precursors for multiferroic BiFeO₃ systems. Spectrum of novel cyclopentadienyl substituted iron-bismuth complexes of the general type [{Cp^y(CO)₂Fe}BiX₂], as potential precursors for cyclopentadienyl iron-bismuth alkoxides or siloxides [{Cp^y(CO)₂Fe}Bi(OR)₂] (R-O^tBu, OSiMe₂^tBu), were obtained and characterised. The use of wide range of cyclopentadienyl rings in the iron carbonyl compounds allowed for a comprehensive analysis of its influence on structure, reactivity as well as solubility of the studied complexes, which are crucial features of potential precursors. The results fill the gap in the chemistry of cyclopentadienyl iron-bismuth complexes. In this work a new method of preparation of novel alkoxides or siloxides iron-bismuth complexes has been developed. In the reaction of Fe₂(CO)₉ with Bi(O^tBu)₃ or Bi(OSiMe₂^tBu)₃ molecular precursors for preparation of heterobimetallic oxides were obtained. Moreover, characterised compounds allowed to extend the knowledge about existence of iron-bismuth clusters and open new ways for the further investigations on the carbonyl iron-bismuth siloxides and alkoxides. The resulting compounds are good single source precursors for the BiFeO₃ materials. The presented synthetic route can be generalized and other heterobimetallic compounds can be obtained. This work should also be helpful in the designing new precursors for synthesis of metal oxides.