Tetrakis(ferrocenylethynyl)ethene: Synthesis, (Spectro)electrochemical and quantum chemical characterisation

Light Activated Release of Nitrile Ligands from trans-Ru(L)(PPh3)2(nitrile) Complexes

A series of trans-RuL(PPh3)2(nitrile) and {RuL(PPh3)2}.2-μ-(nitrile)-based complexes [where L = 2,2'-(3,4-diphenyl-pyrrole-2,5-diyl)dipyridine (dpp), di(pyridin-2-yl)isoindoline-1,3-diimine (bpi), or 4-(4-methoxyphenyl)-6-phenyl-2,2'-bipyridine (Pbpy); and nitrile = 1,4-dibenzontirile, 4-ethynylbenzonitrile, or dicyanamide] were synthesized and characterized, and their electrochemical and photochemical behaviors were investigated. Those complexes that contained a significant nitrile contribution to their 3MLLCT show a release of their nitrile ligand (when L = dpp or Pbpy and the nitrile ligand = 4-dibenzontirile, or 4-ethynylbenzonitrile) with dissociation constants up to 8.09 × 10-4 s-1.

Optical and Infrared Spectroelectrochemical Studies of CN-Substituted Bipyridyl Complexes of Ruthenium(II)

Ruthenium(II) polypyridyl complexes [Ru(CN-Me-bpy)_x(bpy)_3-x]²⁺ (CN-Me-bpy = 4,4'-dicyano-5,5'-dimethyl-2,2'-bipyridine, bpy = 2,2'-bipyridine, and x = 1-3, abbreviated as 1²⁺, 2²⁺, and 3²⁺) undergo four (1²⁺) or five (2²⁺ and 3²⁺) successive one-electron reduction steps between -1.3 and -2.75 V versus ferrocenium/ferrocene (Fc⁺/Fc) in tetrahydrofuran. The CN-Me-bpy ligands are reduced first, with successive one-electron reductions in 2²⁺ and 3²⁺ being separated by 150-210 mV; reduction of the unsubstituted bpy ligand in 1²⁺ and 2²⁺ occurs only when all CN-Me-bpy ligands have been converted to their radical anions. Absorption spectra of the first three reduction products of each complex were measured across the UV, visible, near-IR (NIR), and mid-IR regions and interpreted with the help of density functional theory calculations. Reduction of the CN-Me-bpy ligand shifts the ν(C≡N) IR band by ca. -45 cm^-1, enhances its intensity ∼35 times, and splits the symmetrical and antisymmetrical modes. Semireduced complexes containing two and three CN-derivatized ligands 2⁺, 3⁺, and 3⁰ show distinct ν(C≡N) features due to the presence of both CN-Me-bpy and CN-Me-bpy^•-, confirming that each reduction is localized on a single ligand. NIR spectra of 1⁰, 1^-, and 2^- exhibit a prominent band attributable to the CN-Me-bpy^•- moiety between 6000 and 7500 cm^-1, whereas bpy^•--based absorption occurs between 4500 and 6000 cm^-1; complexes 2⁺, 3⁺, and 3⁰ also exhibit a band at ca. 3300 cm^-1 due to a CN-Me-bpy^•- → CN-Me-bpy interligand charge-transfer transition. In the UV-vis region, the decrease of π → π* intraligand bands of the neutral ligands and the emergence of the corresponding bands of the radical anions are most diagnostic. The first reduction product of 1²⁺ is spectroscopically similar to the lowest triplet metal-to-ligand charge-transfer excited state, which shows pronounced NIR absorption, and its ν(C≡N) IR band is shifted by -38 cm^-1 and 5-7-fold-enhanced relative to the ground state.

Zwitterionic Mixed-Valence Species for the Design of Neutral Clocked Molecular Quantum-Dot Cellular Automata

Mixed-valence compounds can be used for the design of molecular quantum-dot cellular automata (QCA). Here, we investigate the QCA properties of a three-dot "Y"-shaped functionalized zwitterionic neutral closo-carborane model 1-(3,5-{Cp(dHpe)Fe-C≡C-}₂(C₆H₃))-10-Cp(dHpe)Fe-C≡C-closo-1-CB₉H₈ (1) (Cp = cyclopentadienyl (η⁵-C₅H₅) and dHpe = 1,2-bis(phosphino)ethane (H₂PCH₂CH₂PH₂)) as a neutral clocked molecular half-cell. DFT results clearly demonstrate that 1 can display simultaneously the two most basic properties necessary for clocked QCA operation, i.e., bistable switching behavior and clocked control. This is possible due to the three stable states (two active and one null) of 1, corresponding to occupation of each of the three iron-ethynyl groups by the positive charge. In addition, the proximal electronic bias effects can be overcome by the zwitterionic nature of 1, which could be imposed by external counterions, rendering these effects more predictable.

Tetraiodoallene, I2C=C=CI2 – the missing link between I2C=CI2 and I2C=C=C=CI2 – and the oxidation product, 2,2-diiodoacrylicacid, I2C=CH(CO2H)

The X-ray structure of tetraiodoallene is reported. On standing, atmospheric hydrolysis converts this compound into 2,2-diiodoacrylic acid, for which a structure has also been determined. Energy framework diagrams have been constructed for the two compounds.

Sandwich and half-sandwich metal complexes derived from cross-conjugated 3-methylene-penta-1,4-diynes

Mono-, di- and trimetallic derivatives of the cross-conjugated 3-methylene-penta-1,4-diyne moiety have been prepared, and studied by (spectro)electrochemical methods.