Copper(II) complexes of inverted porphyrin and its methylated derivatives

The inverted porphyrins 2-aza-5,10,15,20-tetraphenyl-21-carbaporphyrin (CTPPH2) and its methylated derivatives 2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrin (2-NCH3CTPPH) and 2-aza-2-methyl-5,10,15,20-tetraphenyl-21-methyl-21-carbaporphyrin (2-NCH3-21-CH3CTPPH) stabilize the rare organocopper(II) complexes (CTPP)CuII (1), (2-NCH3CTPP)CuII (2), (CTPPH)CuIIX (3-X), (2-NCH3CTPPH)CuIIX (4-X) (X = Cl-, TFA), and (2-NCH3-21-CH3CTPP)CuIICl (5). The EPR spectra recorded for 1, 2, 4, and 5 revealed typical features diagnostic of the copper(II) electronic structure. The superhyperfine coupling pattern indicates a presence of three nitrogen donors in the first coordination sphere. An addition of HX acid to 1 and 2 to yield the species 3-X and 4-X. The reaction mechanism includes protonation of the inner C(21) carbon accompanied by an axial coordination of anion. Methylation of (2-NCH3CTPP)CuII (2) with methyl iodide resulted in formation of (2-NCH3-21-CH3CTPP)CuIICl (5) which implies an existence of a sigma-carbanion-copper(II) bond in 2. The 2H NMR investigations carried out for the pyrrole deuterated derivatives (CTPP-d7)CuII, (2-NCH3-21-CH3CTTP-d7)CuIICl, and the methyl deuterated (2-NCH3-21-CD3CTPP)CuIICl one confirmed independently the copper(II) electronic structure with the considerable dx2-y2 metal orbital contribution to the SOMO. The redox properties of copper(II) inverted porphyrins were studied by the cyclic and differential pulse voltammetry. The halfwave potentials indicate a metal-centered oxidation of 1 (390 mV) and 2 (343 mV). The dimethylated homologue 5 reveals the reduction process at -224 mV attributed to the CuII/CuI transformation.     

Reductive approach to mixed valency (n = 1-) in the pyrazine ligand-bridged [(acac)2Ru(μ-L(2-))Ru(acac)2](n) (L(2-) = 2,5-pyrazine-dicarboxylate) through experiment and theory

The diruthenium(III) complex [(acac)(2)Ru(μ-L(2-))Ru(acac)(2)] (1) with acac(-) = acetylacetonato = 2,4-pentanedionato and a 2,5-pyrazine-dicarboxylato bridge, L(2-), has been obtained and structurally characterized as the rac (ΔΔ,ΛΛ) diastereomer. The Ru(III)Ru(III) configuration in 1 (d(Ru-Ru) = 6.799 ?) results in a triplet ground state (μ = 2.82 μ(B) at 300 K) with a density functional theory (DFT) calculated triplet-singlet gap of 10840 cm(-1) and the metal ions as the primary spin-bearing centers (Mulliken spin densities: Ru, 1.711; L, 0.105; acac, 0.184). The paramagnetic 1 exhibits broad, upfield shifted (1)H NMR signals with δ values ranging from -10 to -65 ppm and an anisotropic electron paramagnetic resonance (EPR) spectrum (g = 2.133, g(1) - g(3) = Δg = 0.512), accompanied by a weak half-field signal at g = 4.420 in glassy frozen acetonitrile at 4 K. Compound 1 displays two closely spaced oxidation steps to yield labile cations. In contrast, two well separated reversible reduction steps of 1 signify appreciable electrochemical metal-metal interaction in the Ru(II)Ru(III) mixed-valent state 1(-) (K(c) ≈ 10(7)). The intermediate 1(-) shows a weak, broad Ru(II)→Ru(III) intervalence charge transfer (IVCT) band at about 1040 nm (ε = 380 M(-1) cm(-1)); the DFT approach for 1(-) yielded Mulliken spin densities of 0.460 and 0.685 for the two metal centers. The monitoring of the ν(C═O) frequencies of the uncoordinated C═O groups of L(2-) in 1(n) by IR spectroelectrochemistry suggests valence averaging (Ru(2.5)Ru(2.5)) in 1(-) on the vibrational time scale. The mixed-valent 1(-) displays a rhombic EPR signal (g = 2.239 and Δg = 0.32) which reveals non-negligible contributions from the bridging ligand, reflecting a partial hole-transfer mechanism and being confirmed by the DFT-calculated spin distribution (Mulliken spin density of -0.241 for L in 1(-)). The major low energy electronic transitions in 1(n) (n = 0,-,2-) have been assigned as charge transfer processes with the support of TD-DFT analysis.     

Remarkable paramagnetically shifted (1)H and (2)H NMR spectra of iron(II) complexes of 2-aza-21-carbaporphyrin: an evidence for agostic interaction

Iron(II) 2-aza-21-carbaporphyrins have been characterized by paramagnetically shifted (1)H and (2)H NMR spectra. The high-spin iron(II) complex (HCTPPH)Fe(II)Br displays the beta-H resonances which reflect the combination sigma and pi routes of spin density delocalization. The uniquely large isotropic shift of the inner H(21) hydrogen (812 ppm, 298 K) indicates an Fe(II)-[C(21)-H] agostic interaction.     

Synthesis, structure, and redox properties of N-confused bis(porphyrinatonickel(II)) linked by o-xylene

In a reaction of 5,10,15,20-tetraaryl-2-aza-21-carbaporphyrinato nickel(II) 2 with alpha,alpha'-dibromo-o-xylene, three different complexes containing a xylene moiety were obtained in the presence of a proton scavenger. The products were characterized by mass spectrometry, UV-vis, NMR, and, in the case of the dimeric complex 3, X-ray crystallographic analysis (space group P, a =16.455(3) A, b = 16.776(3) A, c = 18.400(4) A, alpha = 77.43(3) degrees , beta = 75.31(3) degrees , gamma = 66.20(3) degrees , V = 4457.1(19) A3, Z = 2). The monomeric species, diamagnetic 4 and paramagnetic 5, contain one and two bromoxylene residues, respectively, while in 3, the xylene bridge links two macrocyclic subunits, involving their internal carbons (C21) coordinated to diamagnetic nickel(II). Cyclovoltammetric measurements for o-xylene-linked bis(carbaporphyrinoid) 3 indicate cooperative effects resulting from an interaction between the subunits despite the isolation of their aromatic pi-bond systems. An EPR-controlled titration of 3 with bromine allows consecutive detection of the mono- and bis-oxidized species (3Br, 3Br2). The spectral patterns and spin-Hamiltonian parameters indicate metal-centered oxidation in 3Br (gx = 2.358, gy = 2.150, gz = 2.062, A(Br)x = 15, A(Br)y = 35, A(Br)z = 129 G) and interaction of two electron spins of nickel(III) ions in 3Br2 (gx = 2.328, gy = 2.195, gz = 2.065, D = 0.0173 cm(-)1, E = -0.0018 cm(-1), A(Br)z = 63 G). A product of the chemical reduction of a protonated form of the dimer was also detected by means of EPR (g1 = 2.298, g2 = 2.218, g3 = 2.192), although no interaction between the nickel(I) centers can be observed for the reduced species.     

Iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin

The iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin (OTPP)H have been investigated. Insertion of iron(II) followed by one-electron oxidation yielded a high-spin, six-coordinate (OTPP)Fe(III)Cl(2) complex. The reduction of (OTPP)Fe(III)Cl(2) has been accomplished by means of moderate reducing reagents producing high-spin five-coordinate (OTPP)Fe(II)Cl. The molecular structure of (OTPP)Fe(III)Cl(2) has been determined by X-ray diffraction. The iron(III) 21-oxaporphyrin skeleton is essentially planar. The furan ring coordinates in the eta(1) fashion through the oxygen atom, which acquires trigonal geometry. The iron(III) apically coordinates two chloride ligands. Addition of potassium cyanide to a solution of (OTPP)Fe(III)Cl(2) in methanol-d(4) results in its conversion to a six-coordinate, low-spin complex [OTPP)Fe(III)(CN)(2)] which is spontaneously reduced to [OTPP)Fe(II)(CN)(2)](-) by excess cyanide. The spectroscopic features of [OTPP)Fe(III)(CN)(2)] correspond to the common low-spin iron(III) porphyrin (d(xy))(2)(d(xz)d(yz))(3) electronic configuration. Titration of (OTPP)Fe(III)Cl(2) or (OTPP)Fe(II)Cl with n-BuLi (toluene-d(8), 205 K) resulted in the formation of (OTPP)Fe(II)(CH(2)CH(2)CH(2)CH(3)). (OTPP)Fe(II)(n-Bu) decomposes via homolytic cleavage of the iron-carbon bond to produce (OTPP)Fe(I). The EPR spectrum (toluene-d(8), 77 K) is consistent with a (d(xy))(2)(d(xz))(2)(d(yz))(2)(d(z)(2)(1)(d[(x)(2)-(y)(2)])(0) ground electronic state of iron(I) oxaporphyrin (g(1) = 2.234, g(2) = 2.032, g(3) = 1.990). The (1)H NMR spectra of (OTPP)Fe(III)Cl(2), (OTPP)Fe(III)(CN)(2), ([(OTPP)Fe(III))](2)O)(2+), and (OTPP)Fe(II)Cl have been analyzed. There are considerable similarities in (1)H NMR properties within each iron(n) oxaporphyrin-iron(n) regular porphyrin or N-methylporphyrin pair (n = 2, 3). Contrary to this observation, the pattern of downfield positions of pyrrole resonances at 156.2, 126.5, 76.3 ppm and furan resonance at 161.4 ppm (273 K) detected for the two-electron reduction product of (OTPP)Fe(III)Cl(2) is unprecedented in the group of iron(I) porphyrins.     

Mononuclear, dinuclear, and pentanuclear [[N,S(thiolate)]iron(II)] complexes: nuclearity control, incorporation of hydroxide bridging ligands, and magnetic behavior

The mixed N3S(thiolate) ligand 1-[bis[2-(pyridin-2-yl)ethyl]amino]-2-methylpropane-2-thiol (Py2SH) was used in the synthesis of four iron(II) complexes: [(Py2S)FeCl] (1), [(Py2S)FeBr] (2), [(Py2S)4Fe5II(mu-OH)2](BF4)4 (3), and [(Py2S)2Fe2II(mu-OH)]BF4 (4). The X-ray structures of 1 and 2 revealed monomeric iron(II)-alkylthiolate complexes with distorted trigonal-bipyramidal geometries. The paramagnetic 1H NMR spectra of 1 and 2 display resonances from delta = -25 ppm to +100 ppm, consistent with a high-spin iron(II) ion (S = 2). Spectral assignments were made on the basis of chemical shift information and T1 measurements and show the monomeric structures are intact in solution. To provide entry into hydroxide-containing complexes, a novel synthetic method was developed involving strict aprotic conditions and limiting amounts of H2O. Reaction of Py2SH with NaH and Fe(BF4)2.6 H2O under aprotic conditions led to the isolation of the pentanuclear, mu-OH complex 3, which has a novel dimer-of-dimers type structure connected by a central iron atom. Conductivity data on 3 show this structure is retained in CH2Cl2. Rational modification of the ligand-to-metal ratio allows control over the nuclearity of the product, yielding the dinuclear complex 4. The X-ray structure of 4 reveals an unprecedented face-sharing, biooctahedral complex with an [S2O] bridging arrangement. The magnetic properties of 3 and 4 in the range 1.9-300 K were successfully modeled. Dinuclear 4 is antiferromagnetically coupled [J = -18.8(2) cm(-1)]. Pentanuclear 3 exhibits ferrimagnetic behavior, with a high-spin ground state of S(T) = 6, and was best modeled with three different exchange parameters [J = -15.3(2), J' = -24.7(3), and J' = -5.36(7) cm(-1)]. DFT calculations provided good support for the interpretation of the magnetic properties.     

Magnetic susceptibility and ground-state zero-field splitting in high-spin mononuclear manganese(III) of inverted N-methylated porphyrin complexes: Mn(2-NCH3NCTPP)Br

The crystal structures of diamagnetic dichloro(2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N',N')-tin(IV) methanol solvate [Sn(2-NCH 3NCTPP)Cl 2.2(0.2MeOH); 6.2(0.2MeOH)] and paramagnetic bromo(2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N',N')-manganese(III) [Mn(2-NCH 3NCTPP)Br; 5] were determined. The coordination sphere around Sn (4+) in 6.2(0.2MeOH) is described as six-coordinate octahedron ( OC-6) in which the apical site is occupied by two transoid Cl (-) ligands, whereas for the Mn (3+) ion in 5, it is a five-coordinate square pyramid ( SPY-5) in which the unidentate Br (-) ligand occupies the axial site. The g value of 9.19 (or 10.4) measured from the parallel polarization (or perpendicular polarization) of X-band EPR spectra at 4 K is consistent with a high spin mononuclear manganese(III) ( S = 2) in 5. The magnitude of axial ( D) and rhombic ( E) zero-field splitting (ZFS) for the mononuclear Mn(III) in 5 were determined approximately as -2.4 cm (-1) and -0.0013 cm (-1), respectively, by paramagnetic susceptibility measurements and conventional EPR spectroscopy. Owing to weak C(45)-H(45A)...Br(1) hydrogen bonds, the mononuclear Mn(III) neutral molecules of 5 are arranged in a one-dimensional network. A weak Mn(III)...Mn(III) ferromagnetic interaction ( J = 0.56 cm (-1)) operates via a [Mn(1)-C(2)-C(1)-N(4)-C(45)-H(45A)...Br(1)-Mn(1)] superexchange pathway in complex 5.     

Five-coordinate iron(III) porphycenes: (1)H NMR, magnetic, and structural studies

Five-coordinate iron(III) 2,7,12,17-tetrapropylporphycene (TPrPc)Fe(III)X (X = C(6)H(5)O(-), Cl(-), Br(-), I(-), ClO(4)(-)) complexes have been investigated. The (1)H NMR spectra demonstrate downfield shifts for pyrrole resonances [(TPrPc)Fe(III)(C(6)H(5)O), 65.3 ppm; (TPrPc)Fe(III)Cl, 28.5 ppm] but large upfield ones for (TPrPc)Fe(III)Br (-7.8 ppm), (TPrPc)Fe(III)I (-49.4 ppm), and (TPrPc)Fe(III)ClO(4) (-77.1 ppm) (294 K, CD(2)Cl(2)). The pyrrole chemical shifts span the remarkable +70 to -80 ppm range. The variable-temperature (1)H NMR spectra of (TPrPc)Fe(III)X demonstrate anti-Curie behavior with a sign reversal for (TPrPc)Fe(III)Cl. These behaviors are consistent with the admixed S = 3/2, 5/2 ground electronic state with a dominating contribution of the S = 3/2 one. In terms of the chemical shift, (TPrPc)Fe(III)(ClO(4)) can be considered as an example of the purest S = 3/2 state in the investigated series. The extent of the S = 5/2 contribution in the admixed S = 3/2, 5/2 ground electronic state, as gradated solely the basis of the pyrrole proton paramagnetic shifts, is controlled by the strength of the axial ligand, following the magnetochemical series (Evans, D. R.; Reed, C. A. J. Am. Chem. Soc. 2000, 122, 4660). Significantly iron(III) 2,7,12,17-tetrapropylporphycene, soluble in typical organic solvents, can be considered as a universal framework to classify the ligand strength in a magnetochemical series, consistently using the beta-H pyrrole paramagnetic shifts as a fundamental criterion. The structure of (TPrPc)Fe(III)Cl has been determined by X-ray crystallography. The iron is five-coordinate with bonds of nearly equal length to the four pyrrole nitrogen atoms (Fe-N in the range 1.983(5)-2.006(6) A). The iron lies 0.583(1) A out of the mean plane of the macrocycle and 0.502(5) A out of the mean N(4) plane. In the solid, pairs of molecules are positioned about the center of symmetry so there is face-to-face pi-pi contact. The mean plane separation is 3.38 A, and the lateral shift of the porphycene center along the Fe-N bond is 4.490 A. The distance from one porphycene center to the other is 5.62 A, and the iron-iron separation is 6.304(2) A.     

Low-temperature UV-visible and NMR spectroscopic investigations of O(2) binding to ((6)L)Fe(II), a ferrous heme bearing covalently tethered axial pyridine ligands

In this report, we describe the reversible dioxygen reactivity of ((6)L)Fe(II) (1) [(6)L = partially fluorinated tetraphenylporphyrin with covalently appended TMPA moiety; TMPA = tris(2-pyridylmethyl)amine] using a combination of low-temperature UV-vis and multinuclear ((1)H and (2)H) NMR spectroscopies. Complex 1, or its pyrrole-deuterated analogue ((6)L-d(8))Fe(II) (1-d(8)), exhibits downfield shifted pyrrole resonances (delta 28-60 ppm) in all solvents utilized [CH(2)Cl(2), (CH(3))(2)C(O), CH(3)CN, THF], indicative of a five-coordinate high-spin ferrous heme, even when there is no exogenous axial solvent ligand present (i.e., in methylene chloride). Furthermore, ((6)L)Fe(II) (1) exhibits non-pyrrolic upfield and downfield shifted peaks in CH(2)Cl(2), (CH(3))(2)C(O), and CH(3)CN solvents, which we ascribed to resonances arising from the intra- or intermolecular binding of a TMPA-pyridyl arm to the ferrous heme. Upon exposure to dioxygen at 193 K in methylene chloride, ((6)L)Fe(II) (1) [UV-vis: lambda(max) = 433 (Soret), 529 (sh), 559 nm] reversibly forms a dioxygen adduct [UV-vis: lambda(max) = 422 (Soret), 542 nm], formulated as the six-coordinate low-spin [delta(pyrrole) 9.3 ppm, 193 K] heme-superoxo complex ((6)L)Fe(III)-(O(2)(-)) (2). The coordination of the tethered pyridyl arm to the heme-superoxo complex as axial base ligand is suggested. In coordinating solvents such as THF, reversible oxygenation (193 K) of ((6)L)Fe(II) (1) [UV-vis: lambda(max) = 424 (Soret), 542 nm] also occurs to give a similar adduct ((6)L)Fe(III)-(O(2)(-)) (2) [UV-vis: lambda(max) = 418 (Soret), 537 nm. (2)H NMR: delta(pyrrole) 8.9 ppm, 193 K]. Here, we are unable to distinguish between a bound solvent ligand or tethered pyridyl arm as axial base ligand. In all solvents, the dioxygen adducts decompose (thermally) to the ferric-hydroxy complex ((6)L)Fe(III)-OH (3) [UV-vis: lambda(max) = 412-414 (Soret), 566-575 nm; approximately delta(pyrrole) 120 ppm at 193 K]. This study on the O(2)-binding chemistry of the heme-only homonuclear ((6)L)Fe(II) (1) system lays the foundation for a more complete understanding of the dioxygen reactivity of heterobinuclear heme-Cu complexes, such as [((6)L)Fe(II)Cu(I)](+), which are models for cytochrome c oxidase.     

Influence of particle size on solid solution formation and phase interfaces in Li0.5FePO4 revealed by 31P and 7Li solid state NMR spectroscopy

Here we report the observation of electron delocalization in nano-dimension xLiFePO(4):(1 - x)FePO(4) (x = 0.5) using high temperature, static, (31)P solid state NMR. The (31)P paramagnetic shift in this material shows extreme sensitivity to the oxidation state of the Fe center. At room temperature two distinct (31)P resonances arising from FePO(4) and LiFePO(4) are observed at 5800 ppm and 3800 ppm, respectively. At temperatures near 400 °C these resonances coalesce into a single narrowed peak centered around 3200 ppm caused by the averaging of the electronic environments at the phosphate centers, resulting from the delocalization of the electrons among the iron centers. (7)Li MAS NMR spectra of nanometre sized xLiFePO(4):(1 - x)FePO(4) (x = 0.5) particles at ambient temperature reveal evidence of Li residing at the phase interface between the LiFePO(4) and FePO(4) domains. Moreover, a new broad resonance is resolved at 65 ppm, and is attributed to Li adjacent to the anti-site Fe defect. This information is considered in light of the (7)Li MAS spectrum of LiMnPO(4), which despite being iso-structural with LiFePO(4) yields a remarkably different (7)Li MAS spectrum due to the different electronic states of the paramagnetic centers. For LiMnPO(4) the higher (7)Li MAS paramagnetic shift (65 ppm) and narrowed isotropic resonance (FWHM ≈ 500 Hz) is attributed to an additional unpaired electron in the t(2g) orbital as compared to LiFePO(4) which has δ(iso) = -11 ppm and a FWHM = 9500 Hz. Only the delithiated phase FePO(4) is iso-electronic and iso-structural with LiMnPO(4). This similarity is readily observed in the (7)Li MAS spectrum of xLiFePO(4):(1 - x)FePO(4) (x = 0.5) where Li sitting near Fe in the 3+ oxidation state takes on spectral features reminiscent of LiMnPO(4). Overall, these spectral features allow for better understanding of the chemical and electrochemical (de)lithiation mechanisms of LiFePO(4) and the Li-environments generated upon cycling.     

SYNTHESES,CRYSTAL STRUCTURES AND UREASE INHIBITORY ACTIVITIES OF ZnII AND NiII COMPLEXES DERIVED FROM 4,4′-DIMETHOXY-2,2′-(PROPANE-1,3- DIYLDIIMINODIMETHYLENE)DIPHENOL

Journal of Structural Chemistry - Two new zinc(II) and nickel(II) complexes, [Zn2L(μ2-η1:η1-CH3COO)(μ2-η1:η2-CH3COO)]n (1) and...     

Synthesis, characterization and ethylene reactivity of 2-diphenylphosphanylbenzamido nickel complexes

Addition of primary amines to N-[2-(diphenylphosphanyl)benzoyloxy]succinimide affords 2-diphenylphosphanylbenzamides, Ph2PC6H4C(O)NHR (R = C(CH3)3, 3; R = H, 4; R = CH2CH2CH3, 5; R = CH(CH3)2, 6). Addition of NiCl(eta3-CH2C6H5)(PMe3) to the deprotonated potassium salts of the amides and subsequent treatment of two equivalents of B(C6F5)3 to the resulting products furnishes eta3-benzyl zwitterionic nickel(II) complexes, [Ph2PC6H4C(O)NR-kappa2N,P]Ni(eta3-CH2C6H5) (R = C6H5, 9; R = C(CH3)3, 10; R = H, 11; R = CH2CH2CH3, 12; R = CH(CH3)2, 13). Solid structures of 9, 11, 13 and the intermediate eta1-benzyl nickel(II) complexes, [Ph2PC6H4C(O)NR-kappa2N,P]Ni(eta1-CH2C6H5)(PMe3) (R = C6H5, 7; R = C(CH3)3, 8) were determined by X-ray crystallography. When ethylene is added to the eta3-benzyl zwitterionic nickel(II) complexes, butene is obtained by the complexes 9-12 but complex 13 provides very high molecular-weight branched polyethylene (Mw, approximately 1300000) with excellent activity (up to 5200 kg mol-1 h-1 at 100 psi gauge).     

Nickel(II) complexes of 21-C-alkylated inverted porphyrins: synthesis,protonation, and redox properties

Reaction of the nickel(II) complex of an inverted porphyrin, (5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrinato)nickel(II) (1), with haloalkanes in the presence of proton scavengers yields 21-C-alkylated complexes. The products are separated and characterized spectroscopically. Chirality of the formed substituted metalloporphyrins is discussed on the basis of the (1)H NMR spectra. Diastereomers are observed for the complexes containing chiral substituents. Protonation of the external nitrogen of the inverted pyrrole is combined with coordination of the apical ligand that leads to paramagnetic nickel(II) complexes. Very strong differentiation of the isotropic shift for diastereotopic methylene protons is observed in (1)H NMR spectra of the protonated paramagnetic species. For the systems containing benzyl, allyl, and ethoxymethyl substituents a mild dealkylation in solution of protonated complexes is observed in the presence of oxygen. Redox properties of the alkylated complexes are studied by means of cyclic voltammetry. Oxidation of the nickel center in 21-alkylated systems takes place at the potentials comparable to that of unsubstituted complex 1. Protonation introduces small changes to the potential of the Ni(II)/Ni(III) redox couple, but it stabilizes nickel(I) species. Products of chemical oxidation and reduction of the alkylated complexes are detected by means of the EPR spectroscopy indicating in both cases metal-centered redox processes.     

Hydrothermal synthesis,crystal structure,and solid-state NMR spectroscopy of a new indium silicate: K2In(OH)(Si4O10)

A new indium(III) silicate, K(2)In(OH)(Si(4)O(10)), has been synthesized by a high-temperature, high-pressure hydrothermal method. It crystallizes in the monoclinic space group P2(1)/m (No. 11) with a = 11.410(1) A, b = 8.373(1) A, c = 11.611(1) A, beta = 112.201(2) degrees, and Z = 4. The structure, which is analogous to that of K(2)CuSi(4)O(10), consists of unbranched vierer 4-fold chains of corner-sharing SiO(4) tetrahedra running along the b axis linked together via corner sharing by chains of trans-corner-sharing InO(4)(OH)(2) octahedra to form a 3-D framework which delimits 8-ring and 6-ring channels to accommodate K(+) cations. The presence of hydroxyl groups is confirmed by IR spectroscopy. The (29)Si MAS NMR exhibits four resonances at -88.6, -90.1, -97.4, and -98.2 ppm corresponding to four distinct crystallographic Si sites. A (1)H --> (29)Si CP/MAS NMR experiment was performed to assign the four resonances.     

Cadmium(II) and zinc(II) complexes of pyrrole-appended oxacarbaporphyrin: a side-on coordination mode of O-confused carbaporphyrin

A pyrrole adduct of 5,20-diphenyl-10,15-di(p-tolyl)-2-oxa-21-carbaporphyrin [(H,pyr)OCPH]H(2) reacted with sodium ethanolate to yield 5,20-diphenyl-10,15-di(p-tolyl)-3-ethoxy-3-(2'-pyrrol)-2-oxa-21-carbaporphyrin [(EtO,pyr)OCPH]H(2). Subsequently, "true" O-confused oxaporphyrin with a pendant pyrrole ring [(pyr)OCPH]H was formed by the addition of acid to [(EtO,pyr)OCPH]H(2), which triggered an ethanol elimination. In the course of this process, the tetrahedral-trigonal rearrangements originated at the C(3) atom. Insertion of zinc(II), cadmium(II), and nickel(II) into [(pyr)OCPH]H yielded [(pyr)OCPH]Zn(II)Cl, [(pyr)OCPH]Cd(II)Cl, and [(pyr)OCP]Ni(II). The formation of [(pyr)OCP]Ni(II) was accompanied by the C(21)H dehydrogenation step. The nickel(II) ion of [(pyr)OCP]Ni(II), coordinated to a dianionic macrocyclic ligand, is bound by three pyrrolic nitrogens and a trigonally hybridized C(21) atom of the inverted furan. The pyrrole-appended O-confused carbaporphyrin acts as a monoanionic ligand toward zinc(II) and cadmium(II) cations. Three nitrogen atoms and the C(21)H fragment of the inverted furan occupy equatorial positions. In (1)H NMR spectra, the unique inner C(21)H resonances of the inverted furan ring are located at 0.15 ppm for [(pyr)OCPH]Zn(II)Cl, and at 0.21 ppm for [(pyr)OCPH]Cd(II)Cl. The proximity of the furan fragment to the metal ion induces direct scalar couplings between the spin-active nucleus of the metal ((111/113)Cd) and the adjacent (1)H nucleus. The interaction of the metal ion and C(21)H was also reflected by significant changes in carbon chemical shifts ([(pyr)OCPH]Zn(II)Cl, 78.3 ppm; [(pyr)OCPH]Cd(II)Cl, 81.4 ppm; the free base, 101.3 ppm). The density functional theory (DFT) has been applied to model the molecular structures of zinc(II) and cadmium(II) complexes of O-confused oxaporphyrin with an appended pyrrole ring. The Cd...C(21) distance in the optimized structure exceeds the typical Cd-C bond lengths, but is much shorter than the corresponding van der Waals contact.     

Spectroscopy and stereochemistry of the optically active copper(II), cobalt(II) and nickel(II) complexes with Schiff bases N,N′-(1R,2R)-(−)-1,2-cyclohexylenebis(3-methylbenzylideneiminato) and N,N′-(1R,2R)-(−)-1,2-cyclohexylenebis(5-methylbenzylideneiminato)

Schiff bases obtained from N,N′-(1R,2R)-1,2-cyclohexanediamine and 2-hydroxy-3-methylbenzaldehyde, 2-hydroxy-5-methylbenzaldehyde, have been used as ligands for copper(II), cobalt(II) and nickel(II). The complexes were characterized with UV–Vis, circular dichroism (CD), infrared, diamagnetic and paramagnetic ¹H NMR spectroscopy. CD spectra revealed exciton coupled π→π* transitions. Assignments of LMCT and d–d transitions in CD spectra of Ni(II), Co(II) and Cu(II) complexes is proposed. CD data are characteristic for central ion tetrahedral distortion from the planarity and λ conformation of the cyclohexane ring. ¹H NMR of Ni(II) complexes exhibited significant coordination shifts of CHN and ring protons which are in the closest proximity to Ni(II). The ¹H NMR paramagnetic spectra of Co(II) complexes revealed the most upfield shifted resonance at −60 ppm assigned to CHN and −28 ppm to hydrogen atom at C(5′) of the phenyl ring. Results of spectral analyses suggest central ions in a distorted square-planar geometry with N₂O₂ chromofore group.     

A new coordination mode of the photometric reagent glyoxalbis(2-hydroxyanil) (H2gbha): bis-bidentate bridging by gbha2- in the redox series [(mu-gbha)[Ru(acac)2]2]n (n = -2, -1, 0, +1, +2), including a radical-bridged diruthenium(III) and a Ru(III)/Ru(IV) intermediate

The bis-bidentate bridging function of gbha2- with N,O-/N,O- coordination was observed for the first time in the complex (mu-gbha)[Ru(III)(acac)2]2 (1). Density functional theory calculations of 1 yield a triplet ground state with a large (deltaE > 6000 cm(-1)) singlet-triplet gap. Intermolecular antiferromagnetic coupling was observed (J approximately -5.3 cm(-1)) for the solid. Complex 1 undergoes two one-electron reduction and two one-electron oxidation steps; the five redox forms [(mu-gbha)[Ru(acac)2]2]n (n = -2, -1, 0, +1, +2) were characterized by UV-vis-NIR spectroelectrochemistry (NIR = near infrared). The paramagnetic intermediates were also investigated by electron paramagnetic resonance (EPR) spectroscopy. The monoanion with a comproportionation constant K(c) of 2.7 x 10(8) does not exhibit an NIR band for a Ru(III)/Ru(II) mixed-valent situation; it is best described as a 1,4-diazabutadiene radical anion containing ligand gbha*3-, which binds two ruthenium(III) centers. A Ru(III)-type EPR spectrum with g1 = 2.27, g2 = 2.21, and g3 = 1.73 is observed as a result of antiferromagnetic coupling between one Ru(III) and the ligand radical. The EPR-active monocation (K(c) = 1.7 x 10(6)) exhibits a broad (deltanu(1/2) = 2600 cm(-1)) intervalence charge-transfer band at 1800 nm, indicating a valence-averaged (Ru3.5)2 formulation (class III) with a tendency toward class II (borderline situation).     

Tale of a twist: magnetic and optical switching in copper(II) semiquinone complexes

An intermediate (C) that is observed in both phenol hydroxylation and catechol oxidation with the side-on peroxide species [Cu(2)O(2)(DBED)(2)](2+) (DBED = N(1),N(2)-di-tert-butylethane-1,2-diamine) is identified as a copper(II) semiquinone species ([1](+)) through independent synthesis and characterization. The reaction of the redox-active 3,5-di-tert-butylquinone ligand with [(DBED)Cu(I)(MeCN)](+) yields a copper(II) semiquinone [1](+) complex with a singlet ground state and an intense purple chromophore (ε(580) ~ 3500 M(-1) cm(-1)). All other copper(II) semiquinone complexes characterized to date are paramagnetic and weakly colored (ε(800) ~ 500 M(-1) cm(-1)). Antiferromagnetic coupling between the Cu(II) center and the semiquinone radical in [1](+) is characterized by paramagnetic (1)H NMR and SQUID magnetometry. Comparative X-ray crystal structures along with density functional theory calculations correlate the geometric structures of copper(II) semiquinone complexes with their magnetic and optical properties. The unique observable properties of [1](+) originate from an increase in the overlap of the Cu 3d and semiquinone π orbitals resulting from a large rhombic distortion in the structure with a twist of 51°, attributable to the large isotropic demands of the tert-butyl substituents of the DBED ligand. Independent characterization of [1](+) allows the spectroscopic yields of intermediate C to be quantified in this intriguing hydroxylation reaction.     

Studies on the behaviour of beta-ethylthioethylenethioglycollate in aqueous Ni(II) and Cu(II) solutions

The stability constants of the 1:1 and 1:2 complexes of nickel and copper(II) with beta-ethylthioethylenethioglycollic acid have been determined at 25 degrees at ionic strength 1.0 (NaClO(4)). The values for the nickel complexes are K(1) = 1.11 +/- 0.06 x 10(2) (spectrophotometrically) or 1.25 +/- 0.11 x 10(2) (potentiometrically) and K(2) = 3.04 +/- 0.24 x 10(2) (potentiometrically). The corresponding values for the copper complexes are K(1) = 1.27 +/- 0.02 x 10(3) or 1.28 +/- 0.03 x 10(3) and K(2) = 7.29 +/- 0.30 x 10(2).     

Synthesis and characterization of transition metal complexes of dimeric N-confused porphyrin linked by an o-xylene fragment

Insertion of nickel(II), zinc, cadmium, or silver(III) into both macrocyclic crevices of 2,2'-o-xylene-bis(5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbaporphyrin) results in homometallic dimeric complexes which were isolated and characterized by NMR, UV-vis, mass spectrometry, and cyclic voltammetry. The 1H NMR study of these systems at low temperatures (203-233 K) allowed determination of most stable conformers with respect to a rotational freedom around the xylene bridge. An unfolded conformation for the dicationic bis(silver(III)) complex was determined on the basis of 2D nuclear Overhauser effect spectrometry experimentation. A mixture of nonequally populated diastereomers is observed for bis(zinc) and bis(cadmium) complexes due to a possibility of two different orientations of the apical anionic ligands with respect to the bridge. In a reaction of 5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbaporphyrinato nickel(II) with 2-(o-bromoxylene)-5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbaporphyrin in the presence of a proton scavenger, two isomeric bis(N-confused porphyrin) complexes with one subunit "empty" and the other metalated by nickel(II) were obtained. In the product 10, the o-xylene links external nitrogens of the subunits while product 11 consists of the xylene bridge between external nitrogen of the nonmetalated subunit and internal carbon of the fragment containing a nickel(II) ion. The products were characterized by mass spectrometry, UV-vis, NMR, and, in the case of complex 11, also by X-ray crystallographic analysis (space group P1, a =17.007(3), b = 18.130(3), c = 18.797(2) A, alpha = 105.856(13) degrees, beta = 107.447(13) degrees, gamma = 98.818(15) degrees, V = 5141.1(15) A3, Z = 2). Insertion of zinc or silver(III) into an empty crevice of 10 resulted in heterometallic zinc-nickel(II) or silver(III)-nickel(II) complexes 12 or 13, respectively, which were characterized by NMR, UV-vis, and cyclic voltammetry. The subunits in the bis(porphyrin) systems retain spectroscopic and redox properties typical for monomeric complexes.