Effect of basic site substituents on concerted proton-electron transfer in hydrogen-bonded pyridyl-phenols.

Separated concerted proton-electron transfer (sCPET) reactions of two series of phenols with pendent substituted pyridyl moieties are described. The pyridine is either attached directly to the phenol (HOAr-pyX) or connected through a methylene linker (HOArCH(2)pyX) (X = 4-NO(2), 5-CF(3), 4-CH(3), and 4-NMe(2)). Electron-donating and -withdrawing substituents have a substantial effect on the chemical environment of the transferring proton, as indicated by IR and (1)H NMR spectra, X-ray structures, and computational studies. One-electron oxidation of the phenols occurs concomitantly with proton transfer from the phenolic oxygen to the pyridyl nitrogen. The oxidation potentials vary linearly with the pK(a) of the free pyridine (pyX), with slopes slightly below the Nerstian value of 59 mV/pK(a). For the HOArCH(2)pyX series, the rate constants k(sCPET) for oxidation by NAr(3)(•+) or [Fe(diimine)(3)](3+) vary primarily with the thermodynamic driving force (ΔG°(sCPET)), whether ΔG° is changed by varying the potential of the oxidant or the substituent on the pyridine, indicating a constant intrinsic barrier λ. In contrast, the substituents in the HOAr-pyX series affect λ as well as ΔG°(sCPET), and compounds with electron-withdrawing substituents have significantly lower reactivity. The relationship between the structural and spectroscopic properties of the phenols and their CPET reactivity is discussed.

Synthesis, protonation, and reduction of ruthenium-peroxo complexes with pendent nitrogen bases.

Cyclopentadienyl and pentamethylcyclopentadienyl ruthenium(II) complexes have been synthesized with cyclic (RPCH(2)NR'CH(2))(2) ligands, with the goal of using these [Cp(R'')Ru(P(R)(2)N(R')(2))](+) complexes for catalytic O(2) reduction to H(2)O (R = t-butyl, phenyl; R' = benzyl, phenyl; R" = methyl, H). In each compound, the Ru is coordinated to the two phosphines, positioning the amines of the ligand in the second coordination sphere where they may act as proton relays to a bound dioxygen ligand. The phosphine, amine, and cyclopentadienyl substituents have been systematically varied in order to understand the effects of each of these parameters on the properties of the complexes. These Cp(R")Ru(P(R)(2)N(R')(2))(+) complexes react with O(2) to form η(2)-peroxo complexes, which have been characterized by NMR, IR, and X-ray crystallography. The peak reduction potentials of the O(2) ligated complexes have been shown by cyclic voltammetry to vary as much as 0.1 V upon varying the phosphine and amine. In the presence of acid, protonation of these complexes occurs at the pendent amine, forming a hydrogen bond between the protonated amine and the bound O(2). The ruthenium-peroxo complexes decompose upon reduction, precluding catalytic O(2) reduction. The irreversible reduction potentials of the protonated O(2) complexes depend on the basicity of the pendent amine, giving insight into the role of the proton relay in facilitating reduction.

Copper(I) cyanide networks: synthesis, structure, and luminescence behavior. Part 2. Piperazine ligands and hexamethylenetetramine.

A variety of photoluminescent, and in some cases thermochromic, metal-organic networks of CuCN were self-assembled in aqueous reactions with amine ligands: (CuCN) 2(Pip) ( 1a), (CuCN) 20(Pip) 7 ( 1b), (CuCN) 7(MePip) 2 ( 2), (CuCN) 2(Me 2Pip) ( 3a), (CuCN) 4(Me 2Pip) ( 3b), (CuCN) 7(EtPip) 2 ( 4), (CuCN) 4(Et 2Pip) ( 5), (CuCN) 3(BzPip) 2 ( 6a), (CuCN) 5(BzPip) 2 ( 6b), (CuCN) 7(BzPip) 2 ( 6c), (CuCN) 4(BzPip) ( 6d), (CuCN) 2(Bz 2Pip) ( 7), (CuCN)(Ph 2CHPip) ( 8a), (CuCN) 2(Ph 2CHPip) ( 8b), (CuCN) 3(HMTA) 2 ( 9a), (CuCN) 5(HMTA) 2 ( 9b), and (CuCN) 5(HMTA) ( 9c) (Pip = piperazine, MePip = N-methylpiperazine, Me 2Pip = N, N'-dimethylpiperazine, EtPip = N-ethylpiperazine, Et 2Pip = N, N'-diethylpiperazine, BzPip = N-benzylpiperazine, Bz 2Pip = N, N'-dibenzylpiperazine, Ph 2CHPip = N-(diphenylmethyl)piperazine, and HMTA = hexamethylenetetramine). New X-ray structures are reported for 1b, 2, 3b, 4, 5, 6a, 6d, 7, 8b, 9b, and 9c. An important structural theme is the formation of (6,3) (CuCN) 2(piperazine) sheets with or without threading of independent CuCN chains. Strong luminescence at ambient temperature is observed for all but complexes 6 and 7. All luminescent compounds show a broad emission band in the blue region at about 450 nm attributable to metal-to-ligand charge transfer behavior based on the large Stokes shift between excitation and emission maxima. 3, 8, and 9 are thermochromic due to an additional lower energy emission band, which is absent at 77 K.

Poly[mu-2-aminopyrazine-kappa2N1:N4-mu-cyanido-copper(I)]: a three-dimensional network from laboratory powder diffraction data.

In the title compound, [Cu(CN)(C(4)H(5)N(3))](n) or [Cu(mu-CN)(mu-PyzNH(2))](n) (PyzNH(2) is 2-aminopyrazine), the Cu(I) center is tetrahedrally coordinated by two cyanide and two PyzNH(2) ligands. The Cu(I)-cyano links give rise to [Cu-CN](infinity) chains running along the c axis, which are bridged by bidentate PyzNH(2) ligands. The three-dimensional framework can be described as being formed by two interpenetrated three-dimensional honeycomb-like networks, both made of 26-membered rings of composition [Cu(6)(mu-CN)(2)(mu-PyzNH(2))(4)].

Threaded structure and blue luminescence of (CuCN)20(Piperazine)7.

The structurally unique and highly luminescent 20 : 7 complex of CuCN with piperazine (Pip) was formed under aqueous conditions; its structure reveals two interpenetrated 2D sub-networks in 6 : 1 ratio: (CuCN)2(Pip) and (CuCN)8(Pip), the latter consisting of Cu18(CN)16(Pip)2 macrocycles.

Copper(I) cyanide networks: synthesis, luminescence behavior and thermal analysis. Part 1. Diimine ligands.

Metal-organic networks of CuCN with diimines (L) = pyrazine (Pyz), 2-aminopyrazine (PyzNH(2)), quinoxaline (Qox), phenazine (Phz), 4,4'-bipyridyl (Bpy), pyrimidine (Pym), 2-aminopyrimidine (PymNH(2)), 2,4-diaminopyrimidine (Pym(NH(2))(2)), 2,4,6-triaminopyrimidine (Pym(NH(2))(3)), quinazoline (Qnz), pyridazine (Pdz), and phthalazine (Ptz) were studied. Open reflux reactions produced complexes (CuCN)(2)(L) for L = Qox, Phz, Bpy, PymNH(2), Pym(NH(2))(2), Qnz, and Pdz and (CuCN)(3)(L) complexes for L = Pyz, PyzNH(2), Qox, Bpy, Pym(NH(2))(3), and Pdz. Also produced were (CuCN)(3)(Pyz)(2), (CuCN)(PyzNH(2)), (CuCN)7(Pym)(2), (CuCN)(5)(Qnz)(2) and (CuCN)(5)(Ptz)(2). X-ray structures are presented for (CuCN)(2)(Pdz), (CuCN)(2)(PymNH(2)), and (CuCN)(7)(Pym)(2). Hydrothermal reactions yielded additional X-ray structures of (CuCN)(2)(PyzNH(2)), (CuCN)(3)(Pym(NH(2))(2)), (CuCN)(4)(Qnz), a second (CuCN)(2)(Pdz) phase, (CuCN)(5)(Pdz)2, (CuCN)(2)(Ptz), and (CuCN)(7)(Ptz)2. Structural trends, including cuprophilic interactions and cyano-bridged Cu(2)(CN)(2) dimer formation, are discussed. Particularly short Cu...Cu interactions are noted for the novel 4- and 5-coordinate Cu(2)(CN)(2) dimers. Thermal analyses show that most of the complexes decompose with loss of L around 160-180 degrees C. Luminescence behavior is relatively weak in the products.