A scale that attempts to quantify the weakly coordinating character of a variety of solvents and anions is presented. For each group (solvent or anion), a coordinating ability index has been calculated, based on the probability of it being coordinated in the presence of a transition metal atom, compared to the probability of finding it as a solvation molecule or as non-coordinating counterion in a crystal structure. The corresponding index is also defined for the same groups in the presence of lanthanides, and the similarities and differences are discussed.
Graphene electrodes are promising candidates to improve reproducibility and stability in molecular electronics through new electrode-molecule anchoring strategies. Here we report sequential electron transport in few-layer graphene transistors containing individual curcuminoidbased molecules anchored to the electrodes via π − π orbital bonding. We show the coexistence of inelastic co-tunneling excitations with single-electron transport physics owing to an intermediate molecule-electrode coupling; we argue that an intermediate electron-phonon coupling is the origin of these vibrational-assisted excitations. These experimental observations are complemented with density functional theory calculations to model electron transport and the interaction between electrons and vibrational modes of the curcuminoid molecule. We find
Two related single-molecule magnets, [Co(9Accm)2(py)2] and [Co(9Accm)2(2,2′-bpy)], with cis and trans disposition of the CCMoid ligands were studied in solution, in the solid state and by deposition on different surfaces.
A family of iron(III) spin crossover complexes with different counteranions, [Fe(qsal-F) − 5, or NCS − 6) have been prepared. All compounds are isostructural and crystallize (triclinic P1̅ space group) with two independent iron(III) centers (Fe1 and Fe2) in the asymmetric unit. No solvent molecules are found in the crystal lattice, allowing us to directly probe the relative influence of anion variation on the spin crossover characteristics. The crystal packing is governed by three types of π−π interactions (type A, type B, and type C), which form undulating 1D chains. Additional interactions (π−F, C−H•••O/F, and P4AE) connect the neighboring chains to form a complex supramolecular network. Hirshfeld surface analysis supports these findings. The anions are located between the cationic [Fe(qsal-F) 2 ] + chains; hence, similar interchain distances (d chain ) are observed irrespective of the anion. However, the interplane distances (d plane ) are influenced by the crystal packing and increase proportionally with the anion size. Magnetic studies reveal that smaller anions tend to stabilize the low-spin state (NO 3 − 3, ClO 4 − 4, and BF 4 − 5), while larger anions (PF 6 − 1 and OTf − 2) exhibit lower transition temperatures (T onset for 1 = 200 K and T for 2 = 190 K) and gradual spin crossovers. The anomaly is 6, where, despite having the smallest anion, it exhibits the lowest transition temperature with magnetic hysteresis in the first step (T 1/2 ↑ = 170 K and T 1/2 ↓ = 157 K). This suggests the size, shape, and supramolecular connectivity of the anion all influence the magnetic properties.
We studied the electronic and conductance properties of two thiophene-curcuminoid molecules, 2-thphCCM (1) and 3-thphCCM (2), where the only structural difference is the position of the sulfur atoms in the thiophene terminal groups. We used electrochemical techniques as well as UV-vis absorption studies to obtain the values of the HOMO-LUMO band gap energies, showing that molecule 1 has lower values than 2. Theoretical calculations show the same trend. Self-assembled monolayers (SAMs) of these molecules were studied using electrochemistry, showing that the interaction with gold reduces drastically the HOMO-LUMO gap in both molecules to almost the same value. Single-molecule conductance measurements show that molecule 2 has two different conductance values, whereas molecule 1 exhibits only one. Based on theoretical calculations we conclude that the lowest conductance value, similar in both molecules, corresponds to a van der waals interaction between the thiophene ring and the electrodes. The one order of magnitud higher conductance value for molecule 2 corresponds to a covalent interaction between the sulfur atoms and the gold electrodes.
The influence of the halogen substituent on crystal packing and redox properties is investigated in a series of heteroleptic complexes [Fe(qsal-X)(dipic)]·MeOH (qsal-X = 4-halogen-2-[(8-quinolylimino)methyl]phenolate; dipic = 2,6-pyridinedicarboxylate; X = F...
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