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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Synthetic, structural, and luminescence study of uranyl coordination polymers containing chelating terpyridine and trispyridyltriazine ligands

In this work, seven uranyl coordination polymers [(UO 2 )(BrC 8 H 3 O 4 )(C 15 H 11 N 3 )] ( 1 ), [(UO 2 )(ClC 8 H 3 O 4 )(C 15 H 11 N 3 )] ( 2 ), [(UO 2 )(BrC 8 H 3 O 4 )(C 18 H 12 N 6 )]·H 2 O ( 3 ), [(UO 2 )(ClC 8 H 3 O 4 )(C 18 H 12 N 6 )]·2H 2 O ( 4 ), [(UO 2 )(C 8 H 3 IO 4 )(C 18 H 12 N 6 )]·2C 3 H 7 O ( 5 ), [(UO 2 )(C 9 H 6 O 4 )(C 18 H 12 N 6 )]·H 2 O ( 6 ), and [(UO 2 )(C 6 H 2 O 4 S)(C 18 H 12 N 6 )]·2H 2 O ( 7 ) containing N-donor ligands 2,2':6',2''-terpyridine (TPY) and 2,4,6-tripyridyl s-triazine (TPTZ); and O-donor linkers thiophene 2,5-dicarboxylic acid (TDC) and X-1,4-benzene dicarboxylic acid (X-BDC, where X = Me, Cl, Br, I) were synthesized and characterized using single crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD), and fluorescence spectroscopy. Each compound crystallizes as binuclear pseudo dimers containing a UO 2 2+ pentagonal bipyramidal primary building unit. Fluorescence spectra of 1–4 , and 6–7 show characteristic UO 2 2+ emission whereas 5 is non-emissive. Red shifts within the emission of 1–4 are noted as a function of N-donor ligands TPY and TPTZ whereas emission shifts are not observed in TPTZ bearing compounds ( 3 , 4 , 6 , 7 ) containing different O-donor linkers. Luminescent lifetimes of 1–7 were obtained and fitted with either bi-exponential or tri-exponential components.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Highly Active Electrolytes for Rechargeable Mg Batteries Based on [Mg2(μ-Cl)2]2+ Cation Complex in Dimethoxyethane

Highly active electrolytes based on a novel [Mg2(μ-Cl)2]2+ cation complex for reversible Mg deposition were developed and analyzed in this work. These electrolytes were formulated in dimethoxyethane through dehalodimerization of non-nucleophilic MgCl2 by reacting with either Mg salts (such as Mg(TFSI)2, TFSI= bis(trifluoromethane)sulfonylimide) or Lewis acid salts (such as AlEtCl2 or AlCl3). The cation complex was identified for the first time as [Mg2(μ-Cl)2(DME)4]2+ (DME=dimethoxyethane) and its molecular structure was characterized by single crystal X-ray diffraction, Raman spectroscopy and NMR. The electrolyte synthesis process was studied and rational approaches for formulating highly active electrolytes were proposed. Through control of the anions, electrolytes with efficiency close to 100%, wide electrochemical window (up to 3.5V) and high ionic conductivity (> 6 mS/cm) were obtained. The electrolyte synthesis and understandings developed in this work could bring significant opportunities for rational formulation of electrolytes with the general formula [Mg2(μ-Cl)2(DME)4][anion]x for practical Mg batteries.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

Electrical conductivity in two mixed-valence liquids

In this work, two different room-temperature liquid systems were investigated, both of which conduct a DC electrical current without decomposition or net chemical transformation. DC electrical conductivity is possible in both cases because of the presence of two different oxidation states of a redox-active species. One system is a 1:1 molar mixture of n -butylferrocene (BuFc) and its cation bis(trifluoromethane)sulfonimide salt, [BuFc + ][NTf 2 - ], while the other is a 1:1 molar mixture of TEMPO and its cation bis(trifluoromethane)sulfonimide salt, [TEMPO + ][NTf 2 - ]. The TEMPO–[TEMPO + ][NTf 2 - ] system is notable in that it is an electrically conducting liquid in which the conductivity originates from an organic molecule in two different oxidation states, with no metals present. Single-crystal X-ray diffraction of [TEMPO + ][NTf 2 - ] revealed a complex structure with structurally different cation–anion interactions for cis - and trans [NTf 2 - ] conformers. The electron transfer self-exchange rate constant for BuFc/BuFc + in CD 3 CN was determined by 1 H NMR spectroscopy to be 5.4 × 10 6 M -1 s -1 . The rate constant allowed calculation of an estimated electrical conductivity of 7.6 × 10 -5 Ω -1 cm -1 for BuFc–[BuFc + ][NTf 2 - ], twice the measured value of 3.8 × 10 -5 Ω -1 cm -1 . Similarly, a previously reported self-exchange rate constant for TEMPO/TEMPO + in CH 3 CN led to an estimated conductivity of 1.3 × 10 -4 Ω -1 cm -1 for TEMPO–[TEMPO + ][NTf 2 - ], a factor of about 3 higher than the measured value of 4.3 × 10 -5 Ω -1 cm -1 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Organogold oligomers: Exploiting iClick and aurophilic cluster formation to prepare solution stable Au 4 repeating units

A novel synthetic method to create gold based metallo–oligomers/polymers via the combination of inorganic click (iClick) with intermolecular aurophilic interactions is demonstrated. Complexes [PEt 3 Au] 4 (μ-N 3 C 2 C 6 H 5 ) (1) and [PPhMe 2 Au] 4 3 C 2 C 6 H 5 ) (2) and {[PEt 3 Au] 4 [(μ-N 3 C 2 ) 2 -9,9-dihexyl-9H-fluorene]} n (8) have been synthesized via iClick. The tetranuclear structures of 1 and 2, induced by aurophilic bonding, are confirmed in the solid state through single crystal X-ray diffraction experiments and in solution via variable temperature NMR spectroscopy. The extended 1D structure of 8 is constructed by aurophilic induced self-assembly. 1 H DOSY NMR analysis reveals that the aurophilic bonds in 1, 2, and 8 are retained in the solution phase. The degree of polymerization within complex 8 is temperature and concentration dependent, as determined by 1 H DOSY NMR. The complex 8 is a rare example of a solution stable higher ordered structure linked by aurophilic interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A divergent route to core- and peripherally functionalized diazacoronenes that act as colorimetric and fluorescence proton sensors

Combining core annulation and peripheral group modification, we have demonstrated a divergent synthesis of a family of highly functionalized coronene derivatives from a readily accessible dichlorodiazaperylene intermediate. Various reactions, such as aromatic nucleophilic substitution, Kumada coupling and Suzuki coupling proceed effectively on α-positions of the pyridine sites, giving rise to alkoxy, thioalkyl, alkyl or aryl substituted polycyclic aromatic hydrocarbons. In addition to peripheral group modulation, the aromatic core structures can be altered by annulation with thiophene or benzene ring systems. Corresponding single crystal X-ray diffraction and optical studies indicate that the heteroatom linkages not only impact the solid state packing, but also significantly influence the optoelectronic properties. Furthermore, these azacoronene derivatives display significant acid-induced spectroscopic changes, suggesting their great potential as colorimetric and fluorescence proton sensors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Direct structural evidence of commensurate-to-incommensurate transition of hydrocarbon adsorption in a microporous metal organic framework

Here, the efficiency of physisorption-based separation of gas-mixtures depends on the selectivity of adsorbent which is directly linked to size, shape, polarizability and other physical properties of adsorbed molecules. Commensurate adsorption is an interesting and important adsorption phenomenon, where the adsorbed amount, location, and orientation of an adsorbate are commensurate with the crystal symmetry of the adsorbent. Understanding this phenomenon is important and beneficial as it can provide vital information about adsorbate–adsorbent interaction and adsorption–desorption mechanism. So far, only sporadic examples of commensurate adsorption have been reported in porous materials such as zeolites and metal organic frameworks (MOFs). In this work we show for the first time direct structural evidence of commensurate-to-incommensurate transition of linear hydrocarbon molecules (C 2 –C7) in a microporous MOF, by employing a number of analytical techniques including single crystal X-ray diffraction (SCXRD), in situ powder X-ray diffraction coupled with differential scanning calorimetry (PXRD-DSC), gas adsorption and molecular simulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

[Ni III (OMe)]-mediated reductive activation of CO 2 affording a Ni(κ 1 -OCO) complex

Here, carbon dioxide is expected to be employed as an inexpensive and potential feedstock of C 1 sources for the mass production of valuable chemicals and fuel. Versatile chemical transformations of CO 2 , i.e. insertion of CO 2 producing bicarbonate/acetate/formate, cleavage of CO 2 yielding μ-CO/μ-oxo transition-metal complexes, and electrocatalytic reduction of CO 2 affording CO/HCOOH/CH 3 OH/CH 4 /C 2 H 4 /oxalate were well documented. Herein, we report a novel pathway for the reductive activation of CO 2 by the [Ni III (OMe)(P(C 6 H 3 -3-SiMe 3 -2-S) 3 )] – complex, yielding the [Ni III (κ 1 -OCO˙ – )(P(C 6 H 3 -3-SiMe 3 -2-S) 3 )] – complex. The formation of this unusual Ni III (κ 1 -OCO ˙– ) complex was characterized by single-crystal X-ray diffraction, EPR, IR, SQUID, Ni/S K-edge X-ray absorption spectroscopy, and Ni valence-to-core X-ray emission spectroscopy. The inertness of the analogous complexes [Ni III (SPh)], [Ni II (CO)], and [Ni II (N 2 H 4 )] toward CO 2 , in contrast, demonstrates that the ionic [Ni III (OMe)] core attracts the binding of weak σ-donor CO 2 and triggers the subsequent reduction of CO 2 by the nucleophilic [OMe] – in the immediate vicinity. This metal–ligand cooperative activation of CO 2 may open a novel pathway promoting the subsequent incorporation of CO 2 in the buildup of functionalized products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Gold-rich R 3 Au 7 Sn 3 : Establishing the interdependence between electronic features and physical properties

Two new polar intermetallic compounds Y 3 Au 7 Sn 3 (I) and Gd 3 Au 7 Sn 3 (II) have been synthesized and their structures have been determined by single crystal X-ray diffraction (P6 3/m ; Z = 2, a = 8.148(1)/8.185(3), and c = 9.394(2)/9.415(3) for I/II, respectively). They can formally be assigned to the Cu 10 Sn 3 type and consist of parallel slabs of Sn centered, edge-sharing trigonal Au 6 antiprisms connected through R 3 (R = Y, Gd) triangles. Additional Au atoms reside in the centres of trigonal Au 6 prisms forming Au@Au 6 clusters with Au–Au distances of 2.906–2.960 Å, while the R–R contacts in the R 3 groups are considerably larger than the sums of their metallic radii. These exclusive structural arrangements provide alluring systems to study the synergism between strongly correlated systems, particularly, those in the structure of (II), and extensive polar intermetallic contacts, which has been inspected by measurements of the magnetic properties, heat capacities and electrical conductivities of both compounds. Gd 3 Au 7 Sn 3 shows an antiferromagnetic ordering at 13 K, while Y 3 Au 7 Sn 3 is a Pauli paramagnet and a downward curvature in its electrical resistivity at about 1.9 K points to a superconducting transition. DFT-based band structure calculations on R 3 Au 7 Sn 3 (R = Y, Gd) account for the results of the conductivity measurements and different spin ordering models of (II) provide conclusive hints about its magnetic structure. As a result, chemical bonding analyses of both compounds indicate that the vast majority of bonding originates from the heteroatomic Au–Gd and Au–Sn interactions, while homoatomic Au–Au bonding is evident within the Au@Au 6 clusters.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Gd 3 Ni 2 and Gd 3 Co x Ni 2-x : magnetism and unexpected Co/Ni crystallographic ordering

The crystal structure, composition and physical properties of Gd 3 Ni 2 , which was earlier reported to exist in the Gd–Ni system without any details of its structure and properties, have been determined. This rare earth binary compound is a high-temperature phase: it forms via a peritectic reaction at 988 K (715 °C) and decomposes below ≈923 K (650 °C). The compound can be retained at room temperature as a metastable phase by quenching after high temperature annealing. Gd 3 Ni 2 crystallizes in the monoclinic Dy 3 Ni 2 structure type [mS20, C2/m (No. 12), Z = 4; with lattice parameters a = 13.418(3) Å, b = 3.720(1) Å, c = 9.640(2) Å, β = 106.250(3)°]. Ni can be substituted by Co up to 50% (i.e. up to and including Gd 3 CoNi) with no change in the structural prototype; the substitution of Co for Ni stabilizes the R 3 Co x Ni 2-x phases down to room temperature. The crystal structure, magnetic properties and magnetocaloric effect (MCE) have been investigated for both Gd 3 Ni 2 and the related Gd 3 Co x Ni 2-x solid solution alloys (0 ≤ x ≤ 1). The crystal structure of the Gd 3 CoNi is a ternary ordered derivative of the monoclinic Dy 3 Ni 2 -type, where Co fully occupies only one of the two 4i Wyckoff sites available for the transition metal. To the best of our knowledge, this is the first example of an intermetallic phase showing ordered site occupations by the chemically quite similar elements Co and Ni. All compounds show long range ferromagnetic ordering, with T C progressively increasing from 147 K (for Gd 3 Ni 2 ) to 176 K (for Gd 3 CoNi) as a cubic function of the Co content. Evidence of Co contributing to the magnetic interactions in these compounds has been found. First-principles total energy calculations predicted the ordered occupation of Co and Ni at the crystallographic sites of Gd3CoNi, which was later confirmed by single crystal X-ray diffraction. The increased conduction electronic state (3d) exchange splitting at the Fermi level supports the experimentally observed enhanced Curie temperature in Gd 3 CoNi compared to Gd 3 Ni 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Controlling superstructural ordering in the clathrate-I Ba 8 M 16 P 30 (M = Cu, Zn) through the formation of metal–metal bonds

Order–disorder–order phase transitions in the clathrate-I Ba 8 Cu 16 P 30 were induced and controlled by aliovalent substitutions of Zn into the framework. Unaltered Ba 8 Cu 16 P 30 crystallizes in an ordered orthorhombic ( Pbcn ) clathrate-I superstructure that maintains complete segregation of metal and phosphorus atoms over 23 different crystallographic positions in the clathrate framework. The driving force for the formation of this Pbcn superstructure is the avoidance of Cu–Cu bonds. This superstructure is preserved upon aliovalent substitution of Zn for Cu in Ba 8 Cu 16– x Zn x P 30 with 0 < x < 1.6 (10% Zn/M total ), but vanishes at greater substitution concentrations. Higher Zn concentrations (up to 35% Zn/M total ) resulted in the additional substitution of Zn for P in Ba 8 M 16+ y P 30– y (M = Cu, Zn) with 0 ≤ y ≤ 1. This causes the formation of Cu–Zn bonds in the framework, leading to a collapse of the orthorhombic superstructure into the more common cubic subcell of clathrate-I ( Pm n ). In the resulting cubic phases, each clathrate framework position is jointly occupied by three different elements: Cu, Zn, and P. Detailed structural characterization of the Ba–Cu–Zn–P clathrates-I via single crystal X-ray diffraction, joint synchrotron X-ray and neutron powder diffractions, pair distribution function analysis, electron diffraction and high-resolution electron microscopy, along with elemental analysis, indicates that local ordering is present in the cubic clathrate framework, suggesting the evolution of Cu–Zn bonds. For the compounds with the highest Zn content, a disorder–order transformation is detected due to the formation of another superstructure with trigonal symmetry and Cu–Zn bonds in the clathrate-I framework. It is shown that small changes in the composition, synthesis, and crystal structure have significant impacts on the structural and transport properties of Zn-substituted Ba 8 Cu 16 P 30 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Schiff-base coordination complexes with plutonium( iv ) and cerium( iv )

PuL 2 and CeL 2 (L = N,N'-bis[(4,4'-diethylamino)salicylidene]-1,2-phenylenediamine) have been synthesized, and characterized by single crystal X-ray diffraction, UV/vis/NIR spectroscopy, and cyclic voltammetry. Furthermore, these studies reveal the enhanced stabilization of Pu(IV) versus Ce(IV) with this Schiff base, and quasi-reversible redox behavior only with the plutonium complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Streams, cascades, and pools: various water cluster motifs in structurally similar Ni(ii) complexes

Hydrogen bonding (HB) interactions are well known to impact the properties of water in the bulk and within hydrated materials. A series of Ni(II) complexes based on chelates containing N-(2-aminoethyl)-1-methylimidazole-2-carboxamide have been synthesized and fully characterized by single crystal X-ray diffraction, spectroscopic methods, and thermal analysis. The complexes reveal a variety of water cluster motifs dependent on the packing arrangement in the solid state. A key feature is the orientation of the carboxamide moiety, which leads to the formation of void spaces that accommodate water through HB interactions. The water motifs contain 1D water chains (streams), 2D tapes of infused rings (cascades), and isolated water dimers (pools). The HB motifs in the hydrated structures vary as a function of the crystal packing of the host molecules. Thermal analyses show a correlation between the HB motif in the hydrated crystals and the temperature range of the dehydration process. The conductivity of the hydrated crystals varies as a function of the crystal packing interactions between metal complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A series of dithiocarbamates for americium, curium, and californium

Characterizing how actinide properties change across the f-element series is critical for improving predictive capabilities and solving many nuclear problems facing our society. Unfortunately, it is difficult to make direct comparisons across the 5f-element series because so little is known about trans-plutonium elements. Results described in this paper help to address this issue through isolation of An(S 2 CNEt 2 ) 3 (N 2 C 12 H 8 ) (Am, Cm, and Cf). These findings included the first single crystal X-ray diffraction measurements of Cm–S (mean of 2.86 ± 0.04 Å) and Cf–S (mean of 2.84 ± 0.04 Å) bond distances. Furthermore, they highlight the potential of An(S 2 CNEt 2 ) 3 (N 2 C 12 H 8 ) for providing a test bed for comparative analyses of actinide versus lanthanide bonding interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Exploring crown-ether functionalization on the stabilization of hexavalent neptunium

Crown-ether molecules are used in radiochemical separations due to their high selectivity for a range of metal cations. Previous investigations regarding the interactions of 18-crown-6 (18C6) with 237 Np suggested the formation of a Np(V) inclusion complex, but also reported rapid reduction of Np(VI) to Np(V) in the presence of the ether molecule. Herein, we investigate the impact of crown ether functionalization by exploring the Np(V) and Np(VI) dicyclohexano-18-crown-6 (DCH-18C6) systems. Two [X(DCH-18C6)] 2 [Np(VI)O 2 Cl 4 ] compounds (X = K (1) and Na (2)) were crystallized and characterized by single crystal X-ray diffraction and Raman spectroscopy. Additional studies of Np(VI), Np(V), and Np(V)/Np(VI) in solution indicated redox stability in the presence of functionalized crowns and preferential crystallization of Np(VI) DCH-18C6 solids. Furthermore, these results indicate that functionalization of the crown can lead to higher resistance to radiolysis and increased stability of the Np(VI) oxidation state in solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Single crystal structure and photocatalytic behavior of grafted uranyl on the Zr-node of a pyrene-based metal–organic framework

Accurately characterizing actinide oxides bound to metal–organic frameworks (MOFs) is important for designing MOFs as radioactive waste sorbents and catalytic supports. Here, the zirconium MOF NU-1000 was post-synthetically modified through solvothermal deposition to include the uranyl (UO 2 2+ ) ion and characterized via single-crystal X-ray diffraction. Additonally, bond lengths derived from the diffraction pattern and Raman spectroscopy indicate that UO 2 2+ maintains its chemical properties upon deposition, while alcohol oxidation photocatalysis reveals photo-interactions between the pyrene linkers and the UO 2 2+ ion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Hydrothermal synthesis and structural characterization of several complex rare earth tantalates: Ln 2 TaO 5 (OH) (Ln = La, Pr) and Ln 3 Ta 2 O 9 (OH) (Ln = Pr, Nd)

Reactions are reported of early rare earth oxides, RE 2 O 3 (RE = La, Pr, Nd) with Ta 2 O 5 under hydrothermal conditions (650 °C, 1.5 kbar) in concentrated aqueous hydroxide (20–30 M KOH) as a mineralizer. Under various stoichiometries several members of two new structure types were isolated, Ln 2 TaO 5 (OH) (Ln = La, Pr) and Ln 3 Ta 2 O 9 (OH) (Ln = Pr, Nd). The analogous niobate La 2 NbO 5 (OH) was also obtained. Both structure types were characterized by single crystal X-ray diffraction and contain pentavalent tantalatum oxide octahedra and complex rare earth oxide frameworks. The Ln 2 TaO 5 (OH) structure type contains Ln–O 8 and Ln–O 9 building blocks and TaO 6 octahedra in a 3-D framework. It contains a 3-D rare earth oxide framework formed by from zig-zag chains of rare earth oxides linking sheets of rare earth oxides. The tantalates form edge-shared Ta 2 O 10 dimers occupying gaps in the rare earth oxide frameworks. The structure of Ln 3 Ta 2 O 9 (OH) contains two types of 2-D rare earth oxide slabs built of seven and eight coordinate rare earth metals. The tantalate units form 2-D slabs through a multiple corner-sharing scheme of TaO 6 octahedra. The Ln 3 Ta 2 O 9 (OH) structure type has an interesting close structural relationship to the previously reported rare earth titanate La 5 Ti 4 O 15 (OH), which is discussed. The presence of hydroxide in the lattice is confirmed by IR spectroscopy and the H atom locations are assigned unambiguously using bond valence sums.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Flux crystal growth of uranium(v) containing oxyfluoride perovskites

The novel phases Rb 4 NaU 3 O 12-x F x (1), K 4 NaU 3 O 12-x F x (2), and Rb 2.1 K 1.9 KU 3 O 12-x F x (3) were synthesized by molten flux methods using mixed alkali fluoride melts. The oxyfluorides crystallize in the cubic space group Im[3 with combining macron]m with a lattice parameters of 8.7472(2) Å, 8.6264(2) Å, and 8.8390(3) Å, respectively. All three structures crystallize in a cubic perovskite structure, ABO 3 (A 4 BB' 3 O 12 ), where the A site is fully occupied by an alkali cation, and the B site is shared by the remaining smaller alkali cation and uranium in an ordered fashion such that the alkali cation on the B site is surrounded by square uranyl bipyramids. The structures were characterized by single crystal X-ray diffraction, energy dispersive spectroscopy, X-ray absorption near edge structure spectroscopy, X-ray photoelectron spectroscopy, magnetic susceptibility measurements, DFT calculations, thermogravimetric analysis, and UV-vis spectroscopy, all of which support the presence of U(V) in the three new materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

UO 2 2+ -mediated ring contraction of pyrihexaphyrin: synthesis of a contracted expanded porphyrin-uranyl complex

A new mixed hexaphyrin, pyrihexaphyrin (0.1.0.0.1.0) (1), was prepared via an acid catalyzed cyclization between 5,5'-(pyridine-2,6-diyl)bis(pyrrole-2-carbaldehyde) (2) and terpyrrole (3). This expanded porphyrin undergoes a ring contraction upon metallation with uranyl silylamide [UO 2 [N(SiMe 3 ) 2 ] 2 ] under anaerobic conditions followed by purification over basic aluminum oxide exposed to air. The uranyl-contracted pyrihexaphyrin (0.0.0.0.1.0) complex (4) produced as a result contains a unique structural architecture and possesses a formally 22 π-electron globally aromatic periphery, as inferred from NMR spectroscopy, single crystal X-ray diffraction, and computational analyses. Support for the proposed contraction mechanism came from experimental data and DFT calculations. Proton NMR and mass spectroscopic analysis provided the first insight into expanded porphyrin-mediated activation of the uranyl dication (UO 2 2+ ).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗