[closo-B10H8-10-PhI-1-COOH]- Anion: An Intermediate for Functional Anionic Carboxylate Ligands.

A potentially general intermediate, [closo-B10H8-10-PhI-1-COOH]-, for a class of functional anionic carboxylic acids, [closo-B10H8-10-X-1-COOH]2-, was obtained in four steps and 26% overall yield from [closo-B10H10]2-. It was converted to the pyridinium derivative (X = C5H5N+) and subsequently to coordination complexes with (phen)2Cu2+ and (phen)2Zn2+ ions. Both the acid and Zn(II) complex exhibit a cage-to-pyridine charge-transfer band. The availability of such acids opens access to functional metal-ion complexes with compensated charges.

Dicyanometalates as Building Blocks for Multinuclear Iron(II) Spin-Crossover Complexes.

A synthetic strategy featuring dicyanometalates [M(CN)2]- (M = Ag, Au) as N-coordinating ditopic linkers connecting partially blocked FeII centers has been employed to produce heterometallic hexanuclear complexes, which exhibit spin-crossover (SCO) behavior at the FeII sites. The reaction between tris(2-pyridylmethyl)amine (tpma)-capped FeII ions and [Ag(CN)2]- proceeded with partial decomposition of the dicyanoargentate and led to the formation of {[Fe(tpma)]4(µ-CN)2[µ-Ag(CN)2]2}(ClO4)4·3H2O (1), in which both [Ag(CN)2]- and CN- act as bridging ligands, and the opposite [Ag(CN)2]- bridges are engaged in a pronounced argentophilic d10-d10 interaction. In an analogous synthesis, the more stable [Au(CN)2]- species remained intact and furnished the complex {[Fe(tpma)]2[µ-Au2(CN)4]2} (2), which features two FeII centers bridged by two [Au2(CN)4]2- dimers. The use of S,S'-bis(2-pyridylmethyl)-1,2-thioethane (bpte) as a mixed-donor, N2S2-coordinating capping ligand yielded {[Fe(bpte)]2[µ-Au2(CN)4]2} (3), with a structure analogous to that of 2. Variable-temperature magnetic susceptibility measurements revealed that complexes 1-3 exhibit an onset of SCO above 350 K. Measurements above 400 K further confirmed the occurrence of a gradual spin-state conversion for complex 2.

Effect of Stacking Interactions on the Translation of Structurally Related Bis(thiosemicarbazonato)nickel(II) HER Catalysts to Modified Electrode Surfaces.

A series of crystalline nickel(II) complexes (1-3) based on inexpensive bis(thiosemicarbazone) ligands diacetylbis(4-methyl-3-thiosemicarbazone) (H2ATSM), diacetylbis(4,4-dimethyl-3-thiosemicarbazone) (H2ATSDM), and diacetylbis[4-(2,2,2-trifluoroethyl)-3-thiosemicarbazone] (H2ATSM-F6) were synthesized and characterized by single-crystal X-ray diffraction and NMR, UV-visible, and Fourier transform infrared spectroscopies. Modified electrodes GC-1-GC-3 were prepared with films of 1-3 deposited on glassy carbon and evaluated as potential hydrogen evolution reaction (HER) catalysts. HER studies in 0.5 M aqueous H2SO4 (10 mA cm-2) revealed dramatic shifts in the overpotential from 0.740 to 0.450 V after extended cycling for 1 and 2. The charge-transfer resistances for GC-1-GC-3 were determined to be 270, 160, and 630 Ω, respectively. Characterization of the modified surfaces for GC-1 and GC-2 by scanning electron microscopy and Raman spectroscopy revealed similar crystalline coatings before HER that changed to surface-modified crystallites after conditioning. The surface of GC-3 had an initial glasslike appearance before HER that delaminated after HER. The differences in the surface morphology and the effect of conditioning are correlated with crystal-packing effects. Complexes 1 and 2 pack as columns of interacting complexes in the crystallographic a direction with short interplanar spacings between 3.37 and 3.54 Å. Complex 3 packs as columns of isolated molecules in the crystallographic b direction with long-range interplanar spacings of 9.40 Å.

Spin Crossover in Fe(II) Complexes with N4S2 Coordination.

Reactions of Fe(II) precursors with the tetradentate ligand S,S'-bis(2-pyridylmethyl)-1,2-thioethane (bpte) and monodentate NCE(-) coligands afforded mononuclear complexes [Fe(bpte)(NCE)2] (1, E = S; 2, E = Se; 3, E = BH3) that exhibit temperature-induced spin crossover (SCO). As the ligand field strength increases from NCS(-) to NCSe(-) to NCBH3(-), the SCO shifts to higher temperatures. Complex 1 exhibits only a partial (15%) conversion from the high-spin (HS) to the low-spin (LS) state, with an onset around 100 K. Complex 3 exhibits a complete SCO with T1/2 = 243 K. While the γ-2 polymorph also shows the complete SCO with T1/2 = 192 K, the α-2 polymorph exhibits a two-step SCO with the first step leading to a 50% HS → LS conversion with T1/2 = 120 K and the second step proceeding incompletely in the 80-50 K range. The amount of residual HS fraction of α-2 that remains below 60 K depends on the cooling rate. Fast flash-cooling allows trapping of as much as 45% of the HS fraction, while slow cooling leads to a 14% residual HS fraction. The slowly cooled sample of α-2 was subjected to irradiation in the magnetometer cavity resulting in a light-induced excited spin state trapping (LIESST) effect. As demonstrated by Mössbauer spectroscopy, an HS fraction of up to 85% could be achieved by irradiation at 4.2 K.

Spin crossover in tetranuclear Fe(II) complexes, {[(tpma)Fe(µ-CN)]4}X4 (X = ClO4(-), BF4(-)).

Two Fe(II) complexes, {[(tpma)Fe(µ-CN)]4}X4 (X = ClO4(-) (1a), BF4(-) (1b); tpma = tris(2-pyridylmethyl)amine), were prepared by reacting the {Fe(tpma)}(2+) building block with (Bu4N)CN. The crystal structures of 1a and 1b feature a tetranuclear cation composed of cyanide-bridged Fe(II) ions, each capped with a tetradentate tpma ligand. The Fe4(µ-CN)4 core of the complex is strongly distorted, assuming a butterfly-like geometry. Both complexes exhibit gradual temperature-driven spin crossover (SCO) associated with the high-spin (HS) ↔ low-spin (LS) transition at two out of four metal centers. The evolution of HS and LS Fe(II) ions with temperature was followed by a combination of X-ray crystallography, magnetic measurements, and Mössbauer spectroscopy. Only the Fe(II) ions surrounded by six N atoms undergo the SCO. A comparison of the temperature-dependent SCO curves for the samples stored under solvent and the dried samples shows that the former exhibit a much more abrupt SCO. This finding was interpreted in terms of the increased structural disorder and decreased crystallinity caused by the loss of the interstitial solvent molecules in the dried samples.

Production of low-sulfur fuels from catalytic pyrolysis of waste tires using formulated red mud catalyst.

Waste tires (WT) are produced in millions of tons per annum and their safe disposal is always a major environmental challenge because of fire hazards and the increasing cost of landfills. WT has high organic matter content that can be converted into fuels and chemicals if suitable technologies can be developed. Herein we report the in situ catalytic pyrolysis of WT using formulated red mud catalyst to produce low sulfur fuel that can be fractionated or can be used without fractionation. The in situ catalytic pyrolysis was conducted at 450-550 °C using formulated red mud catalyst. The yield of pyrolysis liquids ranged from 35 to 40 wt%. The liquid was very rich in limonene and long chain aliphatic hydrocarbons. The catalyst was effective in removing the sulfur compounds in the oil through reactive adsorption desulfurization mechanism. The sulfur species reacted with hematite, calcite, sodium hydroxide, and zinc oxide to form sulfides and were retained in the catalyst. The minimum sulfur content of the catalytic pyrolysis oil was 0.38 wt%. After catalyst regeneration in air through combustion, the catalyst activity was restored, and the catalyst was reused.

Building a two-dimensional network from mixed-valence copper units held together by acetone bridges.

The mixed-valence supramolecular product di-µ2-acetone-di-µ3-trifluoroacetato-deca-µ2-trifluoroacetato-octacopper(I)dicopper(II), [Cu10(C2F3O2)12(C3H6O)2] or {[Cu(I)4(O2CCF3)4]2-{µ2-OC(CH3)2}2-[Cu(II)2(O2CCF3)4]}, was prepared by co-deposition of two building units, namely a bis-acetone adduct of [Cu(II)2(O2CCF3)4] and a very electrophilic tetranuclear [Cu(I)4(O2CCF3)4] complex. The asymmetric unit contains one molecule of the compound with a total of ten independent Cu atoms. Acetone molecules serve as bridges between the [Cu(II)2(O2CCF3)4] and [Cu(I)4(O2CCF3)4] units. Additionally, the tetracopper(I) trifluoroacetate units are involved in intermolecular Cu···O interactions, forming a layered two-dimensional network in the extended structure.

Tetra-ethyl-ammonium dicyanido(5,10,15,20-tetra-phenyl-porphyrinato)ferrate(III) di-chloro-methane monosolvate.

The title compound, (C8H20N)[Fe(C44H28N4)(CN)2]·CH2Cl2 or (Et4N)[Fe(TPP)(CN)2], was recrystallized from di-chloro-methane-diethyl ether. The compound crystallizes with the two unique halves of the Fe(III) porphyrinato complex, one tetra-ethyl-ammonium cation and one inter-stitial di-chloro-methane mol-ecule within the asymmetric unit. Both anionic Fe(III) complexes exhibit inversion symmetry. Both the cation and the solvent mol-ecules show positional disorder. The cation is disordered over two sets of sites with an occupancy ratio of 0.710 (3):0.290 (3); the solvent mol-ecule is disordered over three positions with a 0.584 (6):0.208 (3):0.202 (5) ratio. The crystal packing features columns of [Fe(TPP)(CN)2](-) anions that propagate along [001]. The columns further pack into layers that are parallel to (011) and also include the Et4N(+) cations. The inter-stitial CH2Cl2 mol-ecules appear in the inter-layer space. This complex may serve as a useful precursor for the assembly of multinuclear and extended CN-bridged complexes for the design of single-mol-ecule and single-chain magnets, respectively.

Physical structure of constitutional isomers influences antiproliferation activity of thiosemicarbazone-alkylthiocarbamate copper complexes.

A series of hybrid thiosemicarbazone-alkylthiocarbamate copper complexes with similar electronic environments but distinct physical structures have been prepared, characterized, and evaluated for antiproliferation activity. The complexes include the constitutional isomers (1-phenylpropane-1-imine-(O-ethylthiocarbamato)-2-one-(N-methylthiosemicarbazonato))copper(II) (CuL1) and (1-phenylpropane-1-one-(N-methylthiosemicarbazonato)-2-imine-(O-ethylthiocarbamato))copper(II) (CuL2) along with (1-propane-1-imine-(O-ethylthiocarbamato)-2-one-(N-methylthiosemicarbazonato))copper(II) (CuL3). Complexes CuL1 and CuL2 differ in the positions of the pendent thiosemicarbazone (TSC) and alkylthiocarbamate (ATC) moieties on the 1-phenylpropane backbone. Complex CuL3 employs a propane backbone with the TSC in the 2-position as in CuL1. The isomer pair CuL1 and CuL2 have equivalent electronic environments with indistinguishable CuII/I potentials (E1/2 = -0.86 V vs. ferrocenium/ferrocene) and electron paramagnetic resonance (EPR) spectra (g∥ = 2.26, g⊥ = 2.08). The electronic structure of CuL3 has a similar E1/2 of -0.84 V and identical EPR parameters to CuL1, 2. Single crystal X-ray diffraction studies confirm a consistent donor environment with no substantial variation in the CuN or CuS bond distances and angles between the complexes. The antiproliferation activities of the CuL1-3 were evaluated against the lung adenocarcinoma cell line (A549) and nonmalignant lung fibroblast cell line (IMR-90) using the MTT assay. CuL1 had the highest A549 activity (A549EC50 = 0.065 µM) and selectivity (IMR-90EC50/A549EC50 = 20). The constitutional isomer CuL2 displayed decreased A549 activity (0.18 µM) and selectivity (10.6). The complex CuL3 displayed activity (0.009 µM) similar to CuL1 but with a lack of selectivity (1.0). Cellular copper loading determined by ICP-MS was consistent with the activity and selectivity trends. The complexes CuL1-3 did not induce reactive oxygen species (ROS) generation.

[closo-B10H8-1,10-(COOH)2]2-: a building block for functional materials?

[closo-B10H8-1,10-(COOH)2]2- was obtained in five steps and 40% overall yield from [closo-B10H10]2-. It can be converted to [closo-B10H8-1,10-(CO)2] and subsequently to carbonium ylides [closo-B10H8-1-COOH-10-(C(NRCH2)2)]. The diacid, its derivatives, and di-ylide [closo-B10H8-1,10-(C(NHMe)2)2] are characterized by spectroscopic and single crystal XRD methods augmented with DFT results.

Reversible Cu(4) <--> Cu(6) core interconversion and temperature induced single-crystal-to-single-crystal phase transition for copper(I) carboxylate.

The first example of a reversible [Cu(4)] <--> [Cu(6)] interconversion for polynuclear copper(I) complexes under controlled experimental settings is reported. It illustrates the key role of specific crystal growth conditions for accessing the target cluster nuclearity that consequently determines physical properties of the resulting solid state products. Thus, when copper(I) benzoate crystallizes from a 1,2-dichlorobenzene solution at room temperature, it forms [Cu(4)]-core based crystalline material, [Cu(4)(O(2)CC(6)H(5))(4)] (1). In contrast, crystal growth by deposition from the gas phase at elevated temperatures results in the exclusive formation of [Cu(6)(O(2)CC(6)H(5))(6)] (2). Complexes 1 and 2 have been isolated in pure form, fully characterized, and reversibly interconverted into each other. The effect of a core structure on the spectroscopic properties of 1 and 2, such as IR, Raman, and photoluminescence, has been investigated. Additionally, a combination of X-ray powder and single crystal diffraction methods has been used to discover the temperature induced phase transition in the hexanuclear copper(I) system. Two modifications of 2 exhibiting slightly different solid state packing of the [Cu(6)(O(2)CC(6)H(5))(6)] units have been identified at room and low temperature. Moreover, reversible single-crystal-to-single-crystal transitions between these polymorphic forms have been confirmed. The important role of weak intermolecular interactions between polynuclear copper(I) units in the solid state has also been revealed and discussed.

Photocatalytic hydrogen evolution on Si photocathodes modified with bis(thiosemicarbazonato)nickel(ii)/Nafion.

The molecular catalyst diacetyl-bis(N-4-methyl-3-thiosemi-carbazonato)nickel(ii) (NiATSM) was integrated with Si for light-driven hydrogen evolution from water. Compared to an equivalent loading of Ni metal, the NiATSM/p-Si electrode performed better. Durability of the surface-bound catalyst under operation in acid was achieved without covalent attachment by using Nafion binding.

Tetranuclear copper(I) clusters: impact of bridging carboxylate ligands on solid state structure and photoluminescence.

The X-ray crystallographic characterization and solid state photoluminescence (PL) study of three new tetranuclear copper(I) clusters, [Cu4(O2CR)4], R = (3-F)C6H4 (1), (2,3,4-F)3C6H2 (2), and CF3/C6F5 (3), revealed a dependence of PL on the structural type.

Fluorinated copper(I) carboxylates as advanced tunable p-dopants for organic light-emitting diodes.

Volatile copper(I) benzoates with variable degrees of fluorination are used for p-doping of organic hole-transport layers in single-carrier devices, charge-generation layers, and in organic light-emitting diodes. The charge-transport abilities of the doped materials correlate with the degree and position of the fluorination on the aromatic ring of the carboxylate groups.

Insulated copper(I) "wires": structural variations and photoluminescence.

An unprecedented "molecular wire" type of structure for the copper(I) carboxylate family has been synthesized by utilizing copper-copper interactions and controllable switch of copper-oxygen interactions. Several modifications of the same complex, copper(I) 2,4,6-triisopropylbenzoate, have been isolated to allow evaluation of the structural variation effects on photoluminescent behavior.

Tetranuclear copper(I) carboxylates: the effect of a stepwise increase in Lewis acidity on solid-state structures and photoluminescence.

X-Ray diffraction studies of three aliphatic copper(I) carboxylates revealed a tetranuclear core structure for [Cu(4)(O(2)CCH(2)CH(3))(4)] (1), [Cu(4)(O(2)CCF(3))(O(2)CCH(2)CH(3))(3)] (2), and [Cu(4)(O(2)CCF(2)CF(3))(4)] (3). The effect of a stepwise increase in electrophilicity on solid-state interactions of copper(I) tetramers as well as the implications of structural variations on photoluminescent properties of the above copper(I) propionates have been discussed.