In situ studies of reversible solid-gas reactions of ethylene responsive silver pyrazolates.

Solid-gas reactions and in situ powder X-ray diffraction investigations of trinuclear silver complexes {[3,4,5-(CF3)3Pz]Ag}3 and {[4-Br-3,5-(CF3)2Pz]Ag}3 supported by highly fluorinated pyrazolates reveal that they undergo intricate ethylene-triggered structural transformations in the solid-state producing dinuclear silver-ethylene adducts. Despite the complexity, the chemistry is reversible producing precursor trimers with the loss of ethylene. Less reactive {[3,5-(CF3)2Pz]Ag}3 under ethylene pressure and low-temperature conditions stops at an unusual silver-ethylene complex in the trinuclear state, which could serve as a model for intermediates likely present in more common trimer-dimer reorganizations described above. Complete structural data of three novel silver-ethylene complexes are presented together with a thorough computational analysis of the mechanism.

Chemical Bonding in Homoleptic Carbonyl Cations [M{Fe(CO)5 }2 ]+ (M=Cu, Ag, Au).

Syntheses of the copper and gold complexes [Cu{Fe(CO)5 }2 ][SbF6 ] and [Au{Fe(CO)5 }2 ][HOB{3,5-(CF3 )2 C6 H3 }3 ] containing the homoleptic carbonyl cations [M{Fe(CO)5 }2 ]+ (M=Cu, Au) are reported. Structural data of the rare, trimetallic Cu2 Fe, Ag2 Fe and Au2 Fe complexes [Cu{Fe(CO)5 }2 ][SbF6 ], [Ag{Fe(CO)5 }2 ][SbF6 ] and [Au{Fe(CO)5 }2 ][HOB{3,5-(CF3 )2 C6 H3 }3 ] are also given. The silver and gold cations [M{Fe(CO)5 }2 ]+ (M=Ag, Au) possess a nearly linear Fe-M-Fe' moiety but the Fe-Cu-Fe' in [Cu{Fe(CO)5 }2 ][SbF6 ] exhibits a significant bending angle of 147° due to the strong interaction with the [SbF6 ]- anion. The Fe(CO)5 ligands adopt a distorted square-pyramidal geometry in the cations [M{Fe(CO)5 }2 ]+ , with the basal CO groups inclined towards M. The geometry optimization with DFT methods of the cations [M{Fe(CO)5 }2 ]+ (M=Cu, Ag, Au) gives equilibrium structures with linear Fe-M-Fe' fragments and D2 symmetry for the copper and silver cations and D4d symmetry for the gold cation. There is nearly free rotation of the Fe(CO)5 ligands around the Fe-M-Fe' axis. The calculated bond dissociation energies for the loss of both Fe(CO)5 ligands from the cations [M{Fe(CO)5 }2 ]+ show the order M=Au (De =137.2 kcal mol-1 )>Cu (De =109.0 kcal mol-1 )>Ag (De =92.4 kcal mol-1 ). The QTAIM analysis shows bond paths and bond critical points for the M-Fe linkage but not between M and the CO ligands. The EDA-NOCV calculations suggest that the [Fe(CO)5 ]→M+ ←[Fe(CO)5 ] donation is significantly stronger than the [Fe(CO)5 ]←M+ →[Fe(CO)5 ] backdonation. Inspection of the pairwise orbital interactions identifies four contributions for the charge donation of the Fe(CO)5 ligands into the vacant (n)s and (n)p AOs of M+ and five components for the backdonation from the occupied (n-1)d AOs of M+ into vacant ligand orbitals.

Isolable 1-Butene Copper(I) Complexes and 1-Butene/Butane Separation Using Structurally Adaptable Copper Pyrazolates.

Non-porous small molecule adsorbents such as {[3,5-(CF3 )2 Pz]Cu}3 (where Pz=pyrazolate) are an emerging class of materials that display attractive features for ethene-ethane separation. This work examines the chemistry of fluorinated copper(I) pyrazolates {[3,5-(CF3 )2 Pz]Cu}3 and {[4-Br-3,5-(CF3 )2 Pz]Cu}3 with much larger 1-butene in both solution and solid state, and reports the isolation of rare 1-butene complexes of copper(I), {[3,5-(CF3 )2 Pz]Cu(H2 C=CHC2 H5 )}2 and {[4-Br-3,5-(CF3 )2 Pz]Cu(H2 C=CHC2 H5 )}2 and their structural, spectroscopic, and computational data. The copper-butene adduct formation in solution involves olefin-induced structural transformation of trinuclear copper(I) pyrazolates to dinuclear mixed-ligand systems. Remarkably, larger 1-butene is able to penetrate the dense solid material and to coordinate with copper(I) ions at high molar occupancy. A comparison to analogous ethene and propene complexes of copper(I) is also provided.

Overcoming Fundamental Limitations in Adsorbent Design: Alkene Adsorption by Non-porous Copper(I) Complexes.

Purifying alkenes from alkanes requires cryogenic distillation. This consumes energy equivalent to countries of ca. 5 million people. Replacing distillation with adsorption processes would significantly increase energy efficiency. Trade-offs between kinetics, selectivity, capacity, and heat of adsorption have prevented production of an optimal adsorbent. We report adsorbents that overcome these trade-offs. [Cu-Br]3 and [Cu-H]3 are air-stable trinuclear complexes that undergo reversible solid-state inter-molecular rearrangements to produce dinuclear [Cu-Br⋅(alkene)]2 and [Cu-H⋅(alkene)]2 . The reversible solid-state rearrangement, confirmed in situ using powder X-ray diffraction, allows adsorbent design trade-offs to be overcome, coupling low heat of adsorption (-10 to -17 kJ mol-1alkene ), high alkene:alkane selectivity (47; 29), and uptake capacity (>2.5 molalkene mol-1Cu3 ). Most remarkably, [Cu-H]3 displays fast uptake and regenerates capacity within 10 minutes.

An experimental and computational NMR study of organometallic nine-membered rings: Trinuclear silver(I) complexes of pyrazolate ligands.

This work reports the calculation of the nuclear magnetic resonance (NMR) chemical shifts of eight trinuclear Ag(I) complexes of pyrazolate ligands using the relativistic program ZORA. The data from the literature concern exclusively 1 H, 13 C, and 19 F nuclei. For this reason, one of the complexes that is derived from 3,5-bis-trifluoromethyl-1H-pyrazole has been studied anew, and the 15 N and 109 Ag chemical shifts determined for the first time in solution. Solid-state NMR data of this compound have been obtained for some nuclei (1 H, 13 C, and 19 F) but not for others (14 N, 15 N, and 109 Ag).

Brightly phosphorescent tetranuclear copper(i) pyrazolates.

Described herein is the synthesis and photophysics of two tetranuclear copper complexes, {[3,5-(Pri)2,4-(Br)Pz]Cu}4 and {[3-(CF3),5-(But)Pz]Cu}4 tailor-designed by manipulating the pyrazolyl ring substituents. Unlike their trinuclear analogues, the luminescence of the tetranuclear species is molecular (not supramolecular) in nature with extremely high solid-state quantum yields of ∼80% at room temperature.

Acetylene and terminal alkyne complexes of copper(i) supported by fluorinated pyrazolates: syntheses, structures, and transformations.

Trinuclear {µ-[3,5-(CF3)2Pz]Cu}3 reacts with acetylene to produce the 2 : 1 copper(i) acetylene complex, Cu4(µ-[3,5-(CF3)2Pz])4(µ-HC[triple bond, length as m-dash]CH)2. Related Cu4(µ-[4-Br-3,5-(CF3)2Pz])4(µ-HC[triple bond, length as m-dash]CH)2 and Cu4(µ-[4-Cl-3,5-(CF3)2Pz])4(µ-HC[triple bond, length as m-dash]CH)2 have also been isolated using the corresponding copper(i) pyrazolate and acetylene. The 1 : 1 adducts Cu2(µ-[3,5-(CF3)2Pz])2(HC[triple bond, length as m-dash]CH)2 and Cu2(µ-[4-Br-3,5-(CF3)2Pz])2(HC[triple bond, length as m-dash]CH)2 are significantly less stable to the acetylene loss and can be observed in solution at low temperatures under excess acetylene. The X-ray crystal structures of 2 : 1 and 1 : 1 complexes, Cu4(µ-[3,5-(CF3)2Pz])4(µ-HC[triple bond, length as m-dash]CH)2 and Cu2(µ-[4-Br-3,5-(CF3)2Pz])2(HC[triple bond, length as m-dash]CH)2 are reported. Raman data show a reduction in [small nu, Greek, macron]C[triple bond, length as m-dash]C stretching frequency by about ∼340 and ∼163 cm-1 in the 2 : 1 and 1 : 1 Cu(i)/acetylene complexes, respectively, from that of the free acetylene. Copper(i) pyrazolate complexes of the terminal alkynes, phenylacetylene, 1,8-nonadiyne, and 1,7-octadiyne are also reported. They form adducts involving one copper atom on each alkyne moiety. The {µ-[3,5-(CF3)2Pz]Cu}3 is also a very versatile and competent catalyst for alkyne transformations as evident from its ability to catalyze the alkyne C(sp)-H bond carboxylation chemistry with CO2, azide-alkyne cycloadditions leading to 1,2,3-triazoles including the use of acetylene itself as a substrate, and thiol addition to phenylacetylene affording vinyl sulfides.

Carbonyl complexes of copper(i) stabilized by bridging fluorinated pyrazolates and halide ions.

Syntheses of neutral and anionic, di- and tetra-nuclear copper carbon monoxide complexes using binary copper(i) pyrazolate precursors are reported. The reaction of {[3,5-(CF3)2Pz]Cu}3 (2), {[4-Cl-3,5-(CF3)2Pz]Cu}3 (3) or {[3,4,5-(CF3)3Pz]Cu}3 (4) with CO in CH2Cl2 led to copper carbonyl complexes. They however, lose CO quite easily if not kept under a CO atmosphere. Compounds {[3,5-(CF3)2Pz]Cu(CO)}2 (5) and {[3,4,5-(CF3)3Pz]Cu(CO)}2 (7) were characterized by X-ray crystallography. They are dinuclear species with a Cu2N4 core. The reaction of {[3,5-(CF3)2Pz]Cu}3 with CO in the presence of [NEt4]Br or [NEt4][3,5-(CF3)2Pz] affords relatively more stable [NEt4][{[3,5-(CF3)2Pz]Cu(CO)}4(µ4-Br)] (8) and [NEt4]{[3,5-(CF3)2Pz]3Cu2(CO)2} (9). The related [NEt4][{[4-Cl-3,5-(CF3)2Pz]Cu(CO)}4(µ4-Br)] (10) and [NEt4][{[4-Cl-3,5-(CF3)2Pz]Cu(CO)}4(µ4-Cl)] (11) can be synthesized using {[4-Cl-3,5-(CF3)2Pz]Cu}3, CO and [NEt4]Br or [NEt4]Cl. The X-ray structures show that 8, 10 and 11 are tetranuclear species with terminal Cu-CO groups and quadruply bridging Cl- and Br- ions. Compound 9 features an anionic cage of nearly D3h symmetry formed by three bridging [3,5-(CF3)2Pz]- ions and two terminal Cu-CO moieties. Theoretical calculations show that bonding in these 16- and 18-electron copper complexes follows Dewar-Chatt-Duncanson (DCD) model, where the CO stretching frequencies correlate well to the orbital interaction energy ΔEorb. The major Cu-CO interaction however is electrostatic in nature. Further theoretical exploration of the role of the substituent at pyrazolyl ring 4-position between -H, -Cl, and -CF3, shows a slight decrease in covalent character of the Cu-CO interaction and diminished π-back bonding as pyrazolate groups become more weakly donating with added electron withdrawing substituents.

Low Heat of Adsorption of Ethylene Achieved by Major Solid-State Structural Rearrangement of a Discrete Copper(I) Complex.

The trinuclear copper(I) pyrazolate complex [Cu3 ] rearranges to the dinuclear analogue [Cu2 ⋅(C2 H4 )2 ] when exposed to ethylene gas. Remarkably, the [Cu3 ]↔[Cu2 ⋅(C2 H4 )2 ] rearrangement occurs reversibly in the solid state. Furthermore, this transformation emulates solution chemistry. The bond-making and breaking processes associated with the rearrangement in the solid-state result in an observed heat of adsorption (-13±1 kJ mol-1 per Cu-C2 H4 interaction) significantly lower than other Cu-C2 H4 interactions (≥-24 kJ mol-1 ). The low overall heat of adsorption, "step" isotherms, high ethylene capacity (2.76 mmol g-1 ; 7.6 wt % at 293 K), and high ethylene/ethane selectivity (136:1 at 293 K) make [Cu3 ] an interesting basis for the rational design of materials for low-energy ethylene/ethane separations.

Mesoporous magnetic secondary nanostructures as versatile adsorbent for efficient scavenging of heavy metals.

Porous magnetic secondary nanostructures exhibit high surface area because of the presence of plentiful interparticle spaces or pores. Mesoporous Fe3O4 secondary nanostructures (MFSNs) have been studied here as versatile adsorbent for heavy metal scavenging. The porosity combined with magnetic functionality of the secondary nanostructures has facilitated efficient heavy metal (As, Cu and Cd) remediation from water solution within a short period of contact time. It is because of the larger surface area of MFSNs due to the porous network in addition to primary nanostructures which provides abundant adsorption sites facilitating high adsorption of the heavy metal ions. The brilliance of adsorption property of MFSNs has been realized through comprehensive adsorption studies and detailed kinetics. Due to their larger dimension, MFSNs help in overcoming the Brownian motion which facilitates easy separation of the metal ion sorbed secondary nanostructures and also do not get drained out during filtration, thus providing pure water.