Kompleksy metali przejściowych z 2,3,5,6-tetrakis(2-pirydylo)pirazyną w aspekcie badań strukturalnych, spektroskopowych oraz magnetycznych

The research subject of my thesis concerns mono- and polynuclear transition metal coordination compounds incorporating 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and halide or pseudohalide ligands. The main goal of this work was to synthesize new coordination compounds with promising photoluminescent, catalytic and magnetic properties. In the first part of my thesis based on the literature data, I showed that transition metal compounds containing tppz may be functional materials in many fields, such as molecular magnetism, catalysis and photoluminescence. Compared to the related complexes incorporating 2,2';6',2"-terpyridine derivatives, however, the number of transition metal coordination compounds of tppz is still limited. Therefore, the results of these studies also allow us to understand factors which determine the type of biding modes of tppz as well as allow us to predict the structure and properties of new coordination compounds with 2,3,5,6-tetrakis(2-pyridyl)pyrazine in future. As a result of my studies, I have obtained 21 new coordination compounds, among which there are compounds of Mn(II), Co(II), Cd(II), Ni(II), Re(IV) and Re(III). For all the examined systems, X-ray structural analysis was performed in order to determine coordination modes of tppz and inorganic ions. It is worth mentioning that I have synthesized a completely new type of coordination polymers ([Cd(NCS)2(-tppz)]n or [Co(μ-1,3-NCS)(NCS)(tppz)]n) with Cd ions linked by tppz and single, thiocyanate anion, respectively. Most importantly, my research confirmed that the complexes incorporating tppz are promising inorganic materials due to their catalytic, spectroscopic and magnetic properties. Magnetic susceptibility measurements of the complexes of general formula [M(tppz)2]Xn (where X = dca, tcm, [Co(NCS)4]2– or [Co(NCO)4]2–, n = 1 lub 2) revealed the occurrence of an incomplete spin crossover behavior 1/2 (LS) 3/2 (HS). On the other hand, the isomorphous coordination polymers [MII(μ-1,3-NCS)(NCS)(tppz)]n (where MII = Co(II) or Ni(II)), which are made up of zigzag chains of cobalt(II) and nickel(II) bridged by single end-to-end thiocyanate groups, exhibited intrachain ferromagnetic interactions. Measurements of temperature-dependent magnetic susceptibility for [H2tppz][ReCl4] revealed that the Re(IV) centers are magnetically isolated. In turn, the magnetic susceptibility of [ReCl3(tppz)]·CH3CN can be attributed to the second-order Zeeman effect between the non-magnetic ground state (MJ = 0) and higher energy levels (MJ ≠ 0). The compounds [Mn(NO3)2(tppz)(H2O)] and [Mn(N3)(NO3)(tppz)(H2O)] turned out to be effective and selective catalysts in oxidation reactions of alcohol to aldehydes/ketones and oxidation reactions of sulfides to sulfoxides. All the obtained Cd(II) compounds were emissive in solid state. Most importantly, the ladder-like coordination polymer [Cd2(1,3-NCS)2(NO3)2(-tppz)]n exhibited long lifetime photoluminescence at room temperature with large separation between excitation and emission luminescence, which indicates phosphorescence nature of the emission

Single ion magnet behaviour in a two-dimensional network of dicyanamide-bridged cobalt(II) ions

A novel two-dimensional coordination polymer of the formula [Co(dca)2(atz)2]n (1) resulted from assembling trans-bis(2-amino-1,3,5-triazine)cobalt(II) motifs by dicyanamide spacers. Variabletemperature dc and ac magnetic susceptibility measurements of 1 show that the high-spin cobalt(II) ions act as single ion magnets (SIMs)

Vanadium(IV) complexes with methyl-substituted 8-hydroxyquinolines : catalytic potential in the oxidation of hydrocarbons and alcohols with peroxides and biological activity

Methyl-substituted 8-hydroxyquinolines (Hquin) were successfully used to synthetize five-coordinated oxovanadium(IV) complexes: [VO(2,6-(Me)2-quin)2] (1), [VO(2,5-(Me)2-quin)2] (2) and [VO(2-Me-quin)2] (3). Complexes 1–3 demonstrated high catalytic activity in the oxidation of hydrocarbons with H2O2 in acetonitrile at 50 C, in the presence of 2-pyrazinecarboxylic acid (PCA) as a cocatalyst. The maximum yield of cyclohexane oxidation products attained was 48%, which is high in the case of the oxidation of saturated hydrocarbons. The reaction leads to the formation of a mixture of cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone. When triphenylphosphine is added, cyclohexyl hydroperoxide is completely converted to cyclohexanol. Consideration of the regioand bond-selectivity in the oxidation of n-heptane and methylcyclohexane, respectively, indicates that the oxidation proceeds with the participation of free hydroxyl radicals. The complexes show moderate activity in the oxidation of alcohols. Complexes 1 and 2 reduce the viability of colorectal (HCT116) and ovarian (A2780) carcinoma cell lines and of normal dermal fibroblasts without showing a specific selectivity for cancer cell lines. Complex 3 on the other hand, shows a higher cytotoxicity in a colorectal carcinoma cell line (HCT116), a lower cytotoxicity towards normal dermal fibroblasts and no effect in an ovarian carcinoma cell line (order of magnitude HCT116 > fibroblasts > A2780)

Photoinduced Processes in Rhenium(I) Terpyridine Complexes Bearing Remote Amine Groups: New Insights from Transient Absorption Spectroscopy

Photophysical properties of two Re(I) complexes [ReCl(CO)3(R-C6H4-terpy-κ2N)] with remote amine groups, N-methyl-piperazinyl (1) and (2-cyanoethyl)methylamine (2), were investigated. The complexes show strong absorption in the visible region corresponding to metal-to-ligand charge transfer (1MLCT) and intraligand-charge-transfer (1ILCT) transitions. The energy levels of 3MLCT and 3ILCT excited-states, and thus photoluminescence properties of 1 and 2, were found to be strongly affected by the solvent polarity. Compared to the parent chromophore [ReCl(CO)3(C6H5-terpy-κ2N)] (3), both designed complexes show significantly prolonged (by 1–2 orders of magnitude) phosphorescence lifetimes in acetonitrile and dimethylformamide, contrary to their lifetimes in less polar chloroform and tetrahydrofuran, which are comparable to those for 3. The femtosecond transient absorption (fsTA) measurements confirmed the interconversion between the 3MLCT and 3ILCT excited-states in polar solvents. In contrast, the emissive state of 1 and 2 in less polar environments is of predominant 3MLCT nature

Ferromagnetic Coupling Through the End-to-End Thiocyanate Bridge in Cobalt(II) and Nickel(II) Chains

The preparation, spectroscopic characterization, and X-ray crystal structure of two novel one-dimensional compounds of formula [M^II(tppz)­(NCS)­(μ-1,3-NCS)]_<i>n</i> [tppz = 2,3,5,6-tetrakis­(2-pyridyl)­pyrazine and M = Co­(<b>1</b>) and Ni (<b>2</b>)] are reported. <b>1</b> and <b>2</b> are isomorphous compounds, and they crystallize in the <i>P</i>2₁/<i>n</i> space group. Their structures are made up of zigzag chains of cobalt­(II) (<b>1</b>) and nickel­(II) ions (<b>2</b>) bridged by single end-to-end thiocyanate groups with a tridentate <i>tppz</i> molecule and a terminally bound thiocyanate-<i>N</i> ligand achieving distorted MN₅S octahedral surroundings around each metal center. The main source of the distortion of the ideal octahedron is due to the geometrical constraints issued from the occurrence of two fused five-member chelate rings of the tridentate <i>tppz</i> ligand, the values of the N–M–N bond angles covering the range 75.58(9)–78.66(9)°. The M–N bond lengths vary in the range 2.025(3)–2.116­(29 (<b>1</b>) and 2.001(2)–2.079(2) Å (<b>2</b>), and they are shorter than the M–S bond distance [2.6395(10) (<b>1</b>) and 2.5225(9) Å (<b>2</b>)]. The values of the intrachain metal–metal separation are 6.4197(7) (<b>1</b>) and 6.3257(5) Å (<b>2</b>). The magnetic properties of <b>1</b> and <b>2</b> have been investigated in the temperature range 1.9–300 K. Both compounds exhibit intrachain ferromagnetic interactions with values of the magnetic coupling (<i>J</i>) of +4.60 (<b>1</b>) and +7.82 cm^–1 (<b>2</b>) [the spin Hamiltonian being defined as <i>Ĥ</i> = −<i>J</i>Σ_{<i>i</i> = 1}^<i>n</i>–1<i>Ŝ</i>_<i>i</i><i>Ŝ</i>_<i>i</i>+1]