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The reaction of 1,10-diaza-18-crown-6 (= aza-crown) with an excess of carbon disulfide in the presence and absence of a base (MOH or NEt3 with M = Li, Na, K, Rb and Cs) gave eight bis-dithiocarbamate (bisdtc) salts of compositions [Li2(aza-crown-bisdtc)]·5H2O (1), [Na2(aza-crown-bisdtc)]·3H2O (2), [K2(aza-crown-bisdtc)(MeOH)3] (3), [Rb2(aza-crown-bisdtc)(MeOH)2] (4), [Cs2(aza-crown-bisdtc)(MeOH)2] (5), [Rb2(aza-crown-bisdtc)(aza-crown)] (6), [(HNEt3)2(aza-crown-bisdtc)] (7), and [(H2aza-crown)(aza-crown-bisdtc)]·2H2O (8), which were characterized as far as possible by spectroscopic methods, mass spectrometry and single-crystal X-ray diffraction (SCXRD) analysis. The SCXRD studies of the alkali metal salts 3–6 revealed five different coordination modes of the dtc ligands towards the metal center, which are generally coordinated to at least one metal atom in the anisobidentate mode and involved in di-, tri- or tetranuclear M–S–M bridging. The coordination numbers for the metal ions vary from seven to ten with the participation of oxygen atoms from the crown ether and from solvent molecules (MeOH), the sulfur atoms or all atoms of the dtc groups and in one case a nitrogen atom from a neutral aza-crown. The coordination geometries are significantly distorted from ideal regular polyhedra, which is attributed to the presence of extensive bridging through the metal-coordinated oxygen and sulfur atoms as well as the small bite angle of the dtc groups. The supramolecular analysis of the alkali metal salts showed the formation of either a tetranuclear metal cluster or a 1D strand through M–OMeOH–M, M–Ocrown-ether–M and M–Sdtc–M bridging, which in three of the four salts resulted in 2D or 3D coordination polymers due to further linkage by the aza-crown ligands. In the crystal structure of the alkali metal salt 3 and the ammonium salts 7 and 8, hydrogen bond formation is observed involving strong charge-assisted O–H⋯−Sdtc, N+–H⋯O and N+–H⋯−Sdtc interactions as well as weaker Ow–H⋯O and C–H⋯O/S interactions. The thermogravimetric analysis of the alkaline derivatives 3–5 showed good thermal stability, with a decomposition point of around 250 °C.

The dianionic aza crown ether-dtc N,N'-bis(dithiocarbamate)-1,10-diaza-18-crown-6 (L2-) is a versatile ligand capable of yielding binuclear complexes with group 10 elements, also known as Ni-triade, [μ-(κ2-S,-S'-L)M2(PPh3)4]Cl2 (M = Pd (1), Pt (2)), [μ-(κ2-S,-S'-L)M2(PPh3)4](BPh4)2 (M = Pd (3), Pt (4)), and μ-(κ-S,-S'-L)Ni2(PPh3)2Cl2 (5), and has proven to be an excellent option to the design of metal-based drugs able to provide multiple response to cell resistance. Palladium and platinum complexes, 1 and 2, were tested for cytotoxicity in the human cervix carcinoma cell line HeLa-229, the human ovarian carcinoma cell line A2780, and the cisplatin-resistant mutant A2780cis, finding significant activity toward all three cancer cell lines, with low micromolar IC50 values, comparable to cisplatin. Markedly, against the cisplatin resistant cell line A2780cis, compound 2 exhibits better cytotoxic activity than the clinical drug (IC50 = 2.3 ± 0.2 μM for 2 versus 3.6 ± 0.5 μM for cisplatin). Moreover, an enhancement of the antitumor response is achieved when adding an equimolar amount of alkali metal chloride (NaCl or KCl) to the medium, for instance, testing compound 1 against the cisplatin-resistant A2780cis cells, the IC50 decreases from 9.3 ± 0.4 to 7.4 ± 0.3 and 5.4 ± 0.1 μM, respectively, after addition of the salt solution. For the platinum derivative 2, the IC50 improves by ca. 40% reaching 1.3 ± 0.1 μM when potassium chloride is added. Likewise, the resistant factor found for 2 (RF = 1) confirms that this complex circumvents cisplatin-resistance in A2780cis and is improved with the addition of potassium chloride (RF = 0.65). The presence of the aza crown ether moiety as linker in the systems studied herein is a key point since, in addition to allowing and facilitating interaction with alkali metal ions, this unit is flexible enough to adapt to a variety of environments, as confirmed by the X-ray crystal structures described, where different conformations and ways to fold in are found. In order to gain insight into the electronic and structural facts involved in the interaction of complex 2 with the alkali metal ions, a DFT study was performed, and the description of the molecular electrostatic potentials (MEPs) is also presented.

The 1 : 1 adduct formation between crown ether (1,10-diaza-18-crown-6) and PdCl2 was observed as an inclusion compound and the molecular structure of complex PdLCl2 (L = 1,10-diaza-18-crown-6) was analyzed using a single crystal X-ray diffraction technique. Two different isomers were isolated upon changing the crystallization solvent system, i.e. CH2Cl2 afforded isomer PdLCl2(a) and a 1 : 1 CH2Cl2 : MeOH solvent system produced isomer PdLCl2(b); both structures were compared with a previously reported isomer PdLCl2(c) that exhibited a different structural arrangement. The three crystalline structures showed trans/syn, trans/anti and cis/syn relationships in relation to the Cl–Pd–Cl angle and the hydrogen atoms at the HN–Pd–NH moieties, respectively. In addition, DFT computational studies revealed the trans/syn isomer to be the most stable conformation by 5.8 kcal mol−1 and allowed the proposal of a potential mechanism for the conversion of this isomer into the trans/anti and cis/syn isomers. Along the same line, the related lead complex PbLCl2(d) was recrystallized from CH2Cl2 and analyzed using a single crystal X-ray diffraction technique, which showed to be structurally different to another previously reported structure of this complex PbLCl2(e), due to the inert pair effect. The analysis was expanded by comparing both series of structures with other relevant analogous complexes of different transition metals.

Twelve boronic esters (1a-1l) synthesized from 4-halo- substituted arylboronic acids (halo = F, Cl, Br, I and CF3) with 2-amino-2- alkyl (H, Me) -1,3-propanediol in presence of (3- or 4)-pyridine carboxaldehyde are described. A solvent mixture toluene/methanol 1:4 ratio was used. All compounds include both donor/acceptor functional groups, which are the necessary elements to self-assembly of the molecular species. Several secondary interactions as I⋯N, Br⋯Br, Br⋯B, F⋯B, C H⋯N, C H⋯O, Br⋯π and C H⋯π support the 1D and 2D polymeric frameworks in solid state. The coordination of the nitrogen atom from the pyridine moiety with the boron atom was not observed in either solution or solid state.