Six new copper(II) complexes with 2,2′:6′,2′′-terpyridine (4′-Rⁿ-terpy) [1 (R¹ = furan-2-yl), 2 (R² = thiophen-2-yl), and 3 (R³ = 1-methyl-1H-pyrrol-2-yl)] and 2,6-di(thiazol-2-yl)pyridine derivatives (Rⁿ-dtpy) [4 (R¹), 5 (R²), and 6 (R³)] have been synthesized by a reaction between copper(II) chloride and the corresponding ligand. The complexes have been characterized by UV-vis and IR spectroscopy, and their structures have been determined by X-ray analysis. The antiproliferative potential of copper(II) complexes of 2,2′:6′,2′′-terpyridine and 2,6-di(thiazol-2-yl)pyridine derivatives towards human colorectal (HCT116) and ovarian (A2780) carcinoma as well as towards lung (A549) and breast adenocarcinoma (MCF7) cell lines was examined. Complex 1 and complex 6 were found to have the highest antiproliferative effect on A2780 ovarian carcinoma cells, particularly when compared with complex 2, 3 with no antiproliferative effect. The order of cytotoxicity in this cell line is 6 > 1 > 5 > 4 > 2 ≈ 3. Complex 2 seems to be much more specific towards colorectal carcinoma HCT116 and lung adenocarcinoma A549 cells. The viability loss induced by the complexes agrees with Hoechst 33258 staining and typical morphological apoptotic characteristics like chromatin condensation and nuclear fragmentation. The specificity towards different types of cell lines and the low cytotoxic activity towards healthy cells are of particular interest and are a positive feature for further developments. Complexes 1–6 were also tested in the oxidation of alkanes and alcohols with hydrogen peroxide and tert-butyl-hydroperoxide (TBHP). The most active catalyst 4 gave, after 120 min, 0.105 M of cyclohexanol + cyclohexanone after reduction with PPh₃. This concentration corresponds to a yield of 23% and TON = 210. Oxidation of cis-1,2-dimethylcyclohexane with m-CPBA catalyzed by 4 in the presence of HNO₃ gave a product of a stereoselective reaction (trans/cis = 0.47). Oxidation of secondary alcohols afforded the target ketones in yields up to 98% and TON = 630.

The 2D coordination polymer of dca-bridged cobalt( ii ), [Co(dca) ₂ (atz) ₂ ] _n , exhibits slow relaxation of the magnetization at low temperatures being thus a new example of single-ion magnet (SIM).

Three cobalt(II) complexes of formulae [Co(dca)₂(bim)₄] (1), [Co(dca)₂(bim)₂]_n (2) and [Co(dca)₂(bmim)₂]_n (3) [dca = dicyanamide, bim = 1-benzylimidazole and bmim = 1-benzyl-2-methylimidazole] were prepared and structurally analyzed by single-crystal X-ray crystallography. Compound 1 is a mononuclear species where the cobalt(II) ion is six-coordinate with four bim molecules in the equatorial positions [Co–N_bim = 2.1546(15) and 2.1489(15) Å] and two trans-positioned dca ligands [Co–N_dca = 2.1575(18) Å] in the axial sites of a somewhat distorted octahedral surrounding. The structures of 2 and 3 consist of two-dimensional grids of cobalt(II) ions where each metal atom is linked to the other four metal centres by single dca bridges exhibiting the μ_1,5-dca coordination mode [Co–N_dca = 2.190(3)–2.220(3) (2) and 2.127(3)–2.153(3) Å (3)]. Two trans-coordinated bim (2)/bmim (3) molecules achieve the six-coordination around each cobalt(II) ion [Co–N_bim = 2.128(3)–2.134(4) Å (2) and Co–N_bmim = 2.156(3)–2.163(39) Å (3)]. The values of the cobalt–cobalt separation through the single dca bridges are 8.927(2) and 8.968(2) Å in 2 and 8.7110(5) and 8.7158(5) Å in 3. Magnetic susceptibility measurements for 1–3 in the temperature range of 2.0–300 K reveal that these compounds behave as magnetically isolated high-spin cobalt(II) ions with a significant orbital contribution to the magnetic moment. Alternating current (ac) magnetic susceptibility measurements for 1–3 show a frequency dependence of out-of-phase susceptibility under static applied fields in the range of 500–2500 G, a feature which is characteristic of the single-ion magnet behaviour (SIM) of the Co(II) ion in them. The values of the energy barrier for the magnetic relaxation (E_a) are 5.45–7.74 (1), 4.53–9.24 (2) and 11.48–15.44 cm⁻¹ (3). They compare well with those previously reported for the analogous dca-bridged 2D compound [Co(dca)₂(atz)₂]_n (4) (E_a = 5.1 cm⁻¹ under an applied static field of 1000 G), which was the subject of a previous report.

Six new Re(I) complexes of the general formula [ReCl(CO)₃(4′-R-terpy-κ²N)] with 2,2′:6′,2′′-terpyridine-based ligands have been synthesized and characterized by IR, NMR (¹H and ¹³C), UV-Vis spectroscopy and single crystal X-ray analysis. The luminescent properties of [ReCl(CO)₃(4′-R-terpy-κ²N)] were studied in solution and solid state, at 298 and 77 K, respectively. To obtain detailed insight into the electronic structures and spectroscopic properties of [ReCl(CO)₃(4′-R-terpy-κ²N)], the density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed. Also, the suitability of this class of materials for being applied in organic light emitting diodes (OLEDs) has been preliminarily tested.