Characterization of Tetracyanopyridine (TCNPy)-Based Magnets: V[TCNPy]2 ⋠z (CH2 Cl2 ) (Tc =111†K) and V[TCNPy]3 ⋠z (CH2 Cl2 ) (Tc =90†K).

The reaction of 2,3,5,6-tetracyanopyridine (TCNPy) with V(CO)6 in CH2 Cl2 forms new organic-based magnets of V[TCNPy]x ⋅z (CH2 Cl2 ) (x=2, 3) composition. Analysis of the IR spectra suggests that the TCNPy is reduced and coordinated to V(II) sites through the nitriles. V[TCNPy]x order as ferrimagnets with 111 and 90 K Tc values for V[TCNPy]2 and V[TCNPy]3 , respectively. Their respective remanent magnetizations and coercive fields are 1260 and 250 emuOe mol(-1) and 9 and 6 Oe at 5 K, and they exhibit some spin-glass behavior.

The Tetracyanopyridinide Dimer Dianion, σ-[TCNPy]2 (2.).

The reaction of 2,3,5,6-tetracyanopyridine (TCNPy) and Cr(C6 H6 )2 forms diamagnetic σ-[TCNPy]2 (2-) possessing a 1.572(3) Šintrafragment sp(3) -sp(3) bond. This is in contrast to the structurally related 1,2,4,5-tetracyanobenzene and 1,2,4,5-tetracyanopyrazine that form π-dimer dianions possessing long, multicenter bonds.

Photocatalytic reduction of artificial and natural nucleotide co-factors with a chlorophyll-like tin-dihydroporphyrin sensitizer.

An efficient photocatalytic two-electron reduction and protonation of nicotine amide adenine dinucleotide (NAD(+)), as well as the synthetic nucleotide co-factor analogue N-benzyl-3-carbamoyl-pyridinium (BNAD(+)), powered by photons in the long-wavelength region of visible light (λirr > 610 nm), is demonstrated for the first time. This functional artificial photosynthetic counterpart of the complete energy-trapping and solar-to-fuel conversion primary processes occurring in natural photosystem I (PS I) is achieved with a robust water-soluble tin(IV) complex of meso-tetrakis(N-methylpyridinium)-chlorin acting as the light-harvesting sensitizer (threshold wavelength of λthr = 660 nm). In buffered aqueous solution, this chlorophyll-like compound photocatalytically recycles a rhodium hydride complex of the type [Cp*Rh(bpy)H](+), which is able to mediate regioselective hydride transfer processes. Different one- and two-electron donors are tested for the reductive quenching of the irradiated tin complex to initiate the secondary dark reactions leading to nucleotide co-factor reduction. Very promising conversion efficiencies, quantum yields, and excellent photosensitizer stabilities are observed. As an example of a catalytic dark reaction utilizing the reduction equivalents of accumulated NADH, an enzymatic process for the selective transformation of aldehydes with alcohol dehydrogenase (ADH) coupled to the primary photoreactions of the system is also demonstrated. A tentative reaction mechanism for the transfer of two electrons and one proton from the reductively quenched tin chlorin sensitizer to the rhodium co-catalyst, acting as a reversible hydride carrier, is proposed.

Synthesis and characterization of redox-active charge-transfer complexes with 2,3,5,6-tetracyanopyridine (TCNPy) for the photogeneration of pyridinium radicals.

The heteroaromatic polynitrile compound tetracyanopyridine (TCNPy) is introduced as a new electron acceptor for the formation of deeply colored charge-transfer complexes. In MeCN, TCNPy is characterized by a quasireversible one-electron-reduction process at -0.51 V (versus SCE). The tetracyanopyridine radical anion undergoes a secondary chemical reaction, which is assigned to a protonation step. TCNPy has been demonstrated to generate 1:1 complexes with various electron donors, including tetrathiafulvalene (TTF) and dihydroxybenzene derivatives, such as p-hydroquinone and catechol. Visible- or NIR-light-induced excitation of the intense charge-transfer bands of these compounds leads to a direct optical electron-transfer process for the formation of the corresponding radical-ion pairs. The presence of available electron donors that contain protic groups in close proximity to the TCNPy acceptor site opens up a new strategy for the photocontrolled generation of pyridinium radicals in a stepwise proton-coupled electron-transfer (PCET) sequence.