Study of the Counter Cation Effects on the Supramolecular Structure and Electronic Properties of a Dianionic Oxamate-Based {NiII2} Helicate.

Herein, we describe the synthesis, crystal structure, and electronic properties of {[K2(dmso)(H2O)5][Ni2(H2mpba)3]·dmso·2H2O}n (1) and [Ni(H2O)6][Ni2(H2mpba)3]·3CH3OH·4H2O (2) [dmso = dimethyl sulfoxide; CH3OH = methanol; and H4mpba = 1,3-phenylenebis(oxamic acid)] bearing the [Ni2(H2mpba)3]2- helicate, hereafter referred to as {NiII2}. SHAPE software calculations indicate that the coordination geometry of all the NiII atoms in 1 and 2 is a distorted octahedron (Oh) whereas the coordination environments for K1 and K2 atoms in 1 are Snub disphenoid J84 (D2d) and distorted octahedron (Oh), respectively. The {NiII2} helicate in 1 is connected by K+ counter cations yielding a 2D coordination network with sql topology. In contrast to 1, the electroneutrality of the triple-stranded [Ni2(H2mpba)3] 2- dinuclear motif in 2 is achieved by a [Ni(H2O)6]2+ complex cation, where the three neighboring {NiII2} units interact in a supramolecular fashion through four R22(10) homosynthons yielding a 2D array. Voltammetric measurements reveal that both compounds are redox active (with the NiII/NiI pair being mediated by OH- ions) but with differences in formal potentials that reflect changes in the energy levels of molecular orbitals. The NiII ions from the helicate and the counter-ion (complex cation) in 2 can be reversibly reduced, resulting in the highest faradaic current intensities. The redox reactions in 1 also occur in an alkaline medium but at higher formal potentials. The connection of the helicate with the K+ counter cation has an impact on the energy levels of the molecular orbitals; this experimental behavior was further supported by X-ray absorption near-edge spectroscopy (XANES) experiments and computational calculations.

Building-up host-guest helicate motifs and chains: a magneto-structural study of new field-induced cobalt-based single-ion magnets.

In this work, we present the synthetic pathway, a refined structural description, complete solid-state characterization and the magnetic properties of four new cobalt(ii) compounds of formulas [Co(H2O)6][Co2(H2mpba)3]·2H2O·0.5dmso (1), [Co(H2O)6][Co2(H2mpba)3]·3H2O·0.5dpss (2), [Co2(H2mpba)2(H2O)4]n·4nH2O (3), and [Co2(H2mpba)2(CH3OH)2(H2O)2]n·0.5nH2O·2ndpss (4) [dpss = 2,2'-dipyridyldisulfide and H4mpba = 1,3-phenylenebis(oxamic) acid], where 2 and 4 were obtained from [Co(dpss)Cl2] (Pre-I) as the source of cobalt(ii). All four compounds are air-stable and were prepared under ambient conditions. 1 and 2 were obtained from a slow diffusion method [cobalt(ii) : H2mpba2- molar ratio used 1 : 1] and their structures are made up of [Co2(H2mpba)3]2- anionic helicate units and [Co(H2O)6]2+ cations, exhibiting supramolecular three-dimensional structures. Interestingly, a supramolecular honeycomb network between the helicate units interacting with each other through R22(10) type hydrogen bonds occurs in 2 hosting one co-crystallized dpss molecule. On the other hand, for the first time, linear (3) and zigzag (4) cobalt(ii) chains were isolated by slow evaporation of stirred solutions of mixed solvents with cobalt(ii) : H2mpba2- in 1 : 2 molar ratio at room temperature. Magnetic measurements of Pre-I revealed a quasi magnetically isolated S = 3/2 spin state with a significant second-order spin-orbit contribution as expected for tetrahedrally coordinated cobalt(ii) ions. The analysis of the variable temperature static (dc) magnetic susceptibility data through first- (1 and 3) and second-order spin-orbit coupling models (2 and 4) reveals the presence of magnetically non-interacting high-spin cobalt(ii) ions with easy-axis (1 and 4)/easy-plane magnetic anisotropies (2 and 4) with low rhombic distortions. Dynamic (ac) magnetic measurements for Pre-I and 1-4 below 8.0 K show that they are examples of field-induced Single-Ion Magnets (SIMs).

Exploring the structural landscape of 2-(thiophen-2-yl)-1,3-benzothiazole: high-Z' packing polymorphism and cocrystallization with calix[4]tube.

We report here for the first time a cocrystal of the so-called neutral calix[4]tube, which is two tail-to-tail-arranged and partially deprotonated tetrakis(carboxymethoxy)calix[4]arenes, including three sodium ions, with 2-(thiophen-2-yl)-1,3-benzothiazole, namely trisodium bis(carboxymethoxy)bis(carboxylatomethoxy)calix[4]arene tris(carboxymethoxy)(carboxylatomethoxy)calix[4]arene-2-(thiophen-2-yl)-1,3-benzothiazole-dimethyl sulfoxide-water (1/1/2/2), 3Na+·C36H30O122-·C36H31O12-·C11H7NS2·2C2H6OS·2H2O, which provides a new approach into the host-guest chemistry of inclusion complexes. Three packing polymorphs of the same benzothiazole with high Z' (one with Z' = 8 and two with Z' = 4) were also discovered in the course of our desired cocrystallization. The inspection of these polymorphs and a previously known polymorph with Z' = 2 revealed that Z' increases as the strength of intermolecular contacts decreases. Also, these results expand the frontier of invoking calixarenes as a host for nonsolvent small molecules, besides providing knowledge on the rare formation of high-Z' packing polymorphs of simple molecules, such as the target benzothiazole.

ss-NMR and single-crystal X-ray diffraction in the elucidation of a new polymorph of bischalcone (1E,4E)-1,5-bis(4-fluorophenyl)penta-1,4-dien-3-one.

We report a new polymorph of (1E,4E)-1,5-bis(4-fluorophenyl)penta-1,4-dien-3-one, C17H12F2O. Contrary to the precedent literature polymorph with Z' = 3, our polymorph has one half molecule in the asymmetric unit disordered over two 50% occupancy sites. Each site corresponds to one conformation around the single bond vicinal to the carbonyl group (so-called anti or syn). The other half of the bischalcone is generated by twofold rotation symmetry, giving rise to two half-occupied and overlapping molecules presenting both anti and syn conformations in their open chain. Such a disorder allows for distinct patterns of intermolecular C-H...O contacts involving the carbonyl and anti-oriented ß-C-H groups, which is reflected in three 13C NMR chemical shifts for the carbonyl C atom. Here, we have also assessed the cytotoxicity of three symmetric bischalcones through their in vitro antitumour potential against three cancer cell lines. Cytotoxicity assays revealed that this biological property increases as halogen electronegativity increases.

Semisynthesis and absolute configuration of a novel rearranged 19,20-δ-lactone (9ßH)-pimarane diterpene.

Annonalide (3ß,20-epoxy-3α,16-dihydroxy-15-oxo-7-pimaren-19,6ß-olide, C20H26O6, 1) is the major (9ßH)-pimarane diterpene isolated from tubers of Cassimirella ampla, and it exhibits cytotoxic properties upon interaction with ctDNA. We have prepared new derivatives of 1 by modification of the (9ßH)-pimarane backbone and report here the semisynthesis and absolute configuration of a novel rearranged 19,20-δ-lactone (9ßH)-pimarane. Our approach was the reduction of the carbonyl groups of 1 with sodium borohydride, at positions C15 (no stereoselectivity) and C3 (stereoselective reduction), followed by rearrangement of the 6,19-γ-lactone ring into the six-membered 19,20-δ-lactone ring in 4a (3ß,6ß,16-trihydroxy-7-pimaren-19,20ß-olide monohydrate, C20H30O6·H2O). The absolute structure of the new compound, 4a, was determined unambiguously with a Flack parameter x of -0.01 (11), supporting the stereochemistry assignment of 1 redetermined here. Besides the changes in the pattern of covalent bonds caused by reduction and lactone rearrangement, the conformation of one of the three fused cyclohexane rings is profoundly different in 4a, adopting a chair conformation instead of the boat shape found in 1. Furthermore, the intramolecular hydrogen bond present in 1 is lost in new compound 4a, due to hydrogen bonding between the 3-OH group and the solvent water molecule.