Metal complexes of some asymmetric diaminodiamide ligands—III1,2: Rates of conversion from octahedral to square planar complexes of Ni(II)

Dissociation of the two amide protons from complexes of asymmetric diaminodiamides with Ni(II) in aqueous solution occurs under moderately basic conditions. The loss of the protons is accompanied by a conversion of the complex from octahedral to square planar. The rates of conversion for complexes NiL²⁺ were measured spectrophotometrically and were found to depend linearly on [OH^?]. The diaminodiamide ligands used were S, R, S- and S, S, S-N, N′-dialanylpropylenediamine (DAPN), S, S-N, N′-dialanylethylenediamine (DAEN), R-N, N′-diglycylpropylenediamine (DGPN), and N, N′-diglycylethylenediamine (DGEN). The rates varied in the order SS-DAEN > DGEN > SRS-DAPN > R-DGPN ≈ SSS-DAPN.     

New synthesis and X-ray diffraction study of a polymeric form of Ag(I) dithio-o-toluato, [Ag4(S2C-o-C6H4CH3)4]n

The title compound was synthesized by CS₂ insertion in the C-M bonds of the corresponding AgLi ate organomental compound. It contains flattened tetrahedral Ag₄ units, connected in polymeric chains by intermolecular Ag...S interactions. Two Ag atoms and three S atoms are in a distorted square pyramidal arrangement around each silver atom. The crystals are tetragonal, space group 14₁/a witha=23.706(2) andc=12.934(2) Å. The structure was refined toR=0.032 for 889 reflections.     

Rigid dendritic donor-acceptor ensembles: control over energy and electron transduction

Several generations of phenylenevinylene dendrons, covalently attached to a C(60) core, have been developed as synthetic model systems with hierarchical, fine-tuned architectures. End-capping of these dendritic spacers with dibutylaniline or dodecyloxynaphthalene, as antennas/electron donors, yielded new donor-bridge-acceptor ensembles in which one, two, or four donors are allocated at the peripheral positions of the well-defined dendrons, while the electron accepting fullerene is placed at the focal point of the dendron. On the basis of our cyclic voltammetry experiments, which disclose a single anodic oxidation and several cathodic reduction processes, we rule out significant, long-range couplings between the fullerene core and the end-standing donors in their ground-state configuration. Photophysical investigations, on the other hand, show that upon photoexcitation an efficient and rapid transfer of singlet excited-state energy (6 x 10(10) to 2.5 x 10(12) s(-1)) controls the reactivity of the initially excited antenna portion. Spectroscopic and kinetic evidence suggests that yet a second contribution, that is, an intramolecular electron-transfer, exists, affording C(60)(.-) -dendron(.+) with quantum yields (Phi) as high as 0.76 and lifetimes (tau) that are on the order of hundreds of nanoseconds (220-725 ns). Variation of the energy gap modulates the interplay of these two pathways (i.e., competition or sequence between energy and electron transfer).     

Topological effects of a rigid chiral spacer on the electronic interactions in donor-acceptor ensembles

Two triads (donor-spacer-acceptor), exTTF-BN-C60 (6) and ZnP-BN-C60 (7), in which electron donors (i.e., exTTF or ZnP) are covalently linked to C60 through a chiral binaphthyl bridge (BN), have been prepared in a multistep synthetic procedure starting from a highly soluble enantiomerically pure binaphthyl building block (1). Unlike other oligomeric bridges, with binaphthyl bridges, the conjugation between the donor and the acceptor units is broken and geometric conformational changes are facilitated. Consequently, distances and electronic interactions between the donor and C60 are drastically changed. Both donor-spacer-acceptor (D-s-A) systems (i.e., 6 and 7) exhibit redox processes that correspond to all three constituent electroactive units, namely, donor, BN, and C60. Appreciable differences were, however, observed when comparing triad 6, in which no significant exTTF-C60 interactions were noted, with D-s-A 7, whose geometry favors donor-acceptor and pi-pi interactions that result in ZnP-C60 electronic communication. This through-space interaction is, for example, reflected in the redox potentials. Excited-state studies, carried out by fluorescence and transient absorption spectroscopy, also support through-space rather than through-bond interactions. Although both triads form the corresponding radical-ion pair, that is, exTTF*+-BN-C60*- and ZnP*+-BN-C60*-, dramatic differences were found in their lifetimes: 165 micros and 730 ns, respectively.     

First asymmetric synthesis of 3-alkoxycarbonyl-2-amino-4-aryl-4H-naphtho[1,2-b]pyrans

The first asymmetric synthesis of 3-alkoxycarbonyl-2-amino-4-aryl-4H-naphtho[1,2-b]pyrans, by Michael addition of 1-naphthol to chirally modified arylidenecyanoacetates 6 and 7 , is described. Good yields and low diastereomeric excesses have been obtained in the 1,4-conjugate additions. The absolute stereochemistry at C-4 in major isomers of pyrans 8 and 9 has been assigned as 5 by X-ray analysis of major pyran 8 .     

Diradical Organic One-Dimensional Polymers Synthesized on a Metallic Surface

We report on the synthesis and characterization of atomically precise one-dimensional diradical peripentacene polymers on a Au(111) surface. By means of high-resolution scanning probe microscopy complemented by theoretical simulations, we provide evidence of their magnetic properties, which arise from the presence of two unpaired spins at their termini. Additionally, we probe a transition of their magnetic properties related to the length of the polymer. Peripentacene dimers exhibit an antiferromagnetic (S=0) singlet ground state. They are characterized by singlet–triplet spin-flip inelastic excitations with an effective exchange coupling (J_eff) of 2.5 meV, whereas trimers and longer peripentacene polymers reveal a paramagnetic nature and feature Kondo fingerprints at each terminus due to the unpaired spin. Our work provides access to the precise fabrication of polymers featuring diradical character which are potentially useful in carbon-based optoelectronics and spintronics.     

Chemical Functionalization of 2D Materials

This Special Issue of Chemistry–A European Journal is dedicated to the Chemical Functionalization of 2D Materials, and features some great contributions from experts in the field of 2D materials. This issue was originally assembled to support the Symposium G “Chemical Functionalization of 2D Materials” at the European Materials Research Society (E-MRS) 2020 Spring Meeting, which was originally scheduled to be held in Strasbourg, France, from May 25th to 29th, 2020. Although the E-MRS 2020 Spring Meeting has been cancelled due to the COVID-19 outbreak, the publication of this Special Issue has proceeded and has become even more important as the contributors discuss diverse and timely research themes related to 2D materials. In this Editorial, a brief overview of the different types of 2D materials is given, together with the chemical functionalization schemes that can be applied to them to achieve new properties as well as enable improved performance in applications. Some of the articles featured in this Special Issue are also highlighted, with the hope that they will inspire readers and further advance the field.