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1.
ACS Omega ; 4(2): 4000-4011, 2019 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-31459609

RESUMO

Metal-organic frameworks (MOFs) are promising gas adsorbents. Knowledge of the behavior of gas molecules adsorbed inside MOFs is crucial for advancing MOFs as gas capture materials. However, their behavior is not always well understood. In this work, carbon dioxide (CO2) adsorption in the microporous α-Zn3(HCOO)6 MOF was investigated. The behavior of the CO2 molecules inside the MOF was comprehensively studied by a combination of single-crystal X-ray diffraction (SCXRD) and multinuclear solid-state magnetic resonance spectroscopy. The locations of CO2 molecules adsorbed inside the channels of the framework were accurately determined using SCXRD, and the framework hydrogens from the formate linkers were found to act as adsorption sites. 67Zn solid-state NMR (SSNMR) results suggest that CO2 adsorption does not significantly affect the metal center environment. Variable-temperature 13C SSNMR experiments were performed to quantitatively examine guest dynamics. The results indicate that CO2 molecules adsorbed inside the MOF channel undergo two types of anisotropic motions: a localized rotation (or wobbling) upon the adsorption site and a twofold hopping between adjacent sites located along the MOF channel. Interestingly, 13C SSNMR spectroscopy targeting adsorbed CO2 reveals negative thermal expansion (NTE) of the framework as the temperature rose past ca. 293 K. A comparative study shows that carbon monoxide (CO) adsorption does not induce framework shrinkage at high temperatures, suggesting that the NTE effect is guest-specific.

2.
Dalton Trans ; 48(14): 4514-4519, 2019 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-30865752

RESUMO

A new paramagnetic ligand, betaDTDA, and its coordination complex with Fe(hfac)2 are reported (betaDTDA = 4-(benzothiazol-2'-yl)-1,2,3,5-dithiadiazolyl; hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). The neutral radical betaDTDA is the first dithiadiazolyl ligand designed to include an electropositive sulphur moiety outside the thiazyl heterocycle, increasing the capacity for supramolecular, structure-directing electrostatic contacts and enabling new pathways for magnetic exchange. The Fe(hfac)2(betaDTDA) complex is composed of a hs-Fe(ii) center with the three bidentate ligands arranged about the ion in a distorted octahedral 6-coordinate environment. The magnetic properties of crystalline Fe(hfac)2(betaDTDA) are consistent with strong antiferromagnetic (AF) coupling between the metal and ligand moments, giving rise to a well-defined Stotal = 3/2 ground state that is the only thermally populated state below 40 K. Below 4 K, this complex exhibits slow relaxation of the magnetization detected by ac susceptibility measurements consistent with a single-molecule magnet (SMM) behaviour.

3.
Chemistry ; 24(31): 7866-7881, 2018 Jun 04.
Artigo em Inglês | MEDLINE | ID: mdl-29575184

RESUMO

Methane is a promising clean and inexpensive energy alternative to traditional fossil fuels, however, its low volumetric energy density at ambient conditions has made devising viable, efficient methane storage systems very challenging. Metal-organic frameworks (MOFs) are promising candidates for methane storage. In order to improve the methane storage capacity of MOFs, a better understanding of the methane adsorption, mobility, and host-guest interactions within MOFs must be realized. In this study, methane adsorption within α-Mg3 (HCO2 )6 , α-Zn3 (HCO2 )6 , SIFSIX-3-Zn, and M-MOF-74 (M=Mg, Zn, Ni, Co) has been comprehensively examined. Single-crystal X-ray diffraction (SCXRD) experiments and DFT calculations of the methane adsorption locations were performed for α-Mg3 (HCO2 )6 , α-Zn3 (HCO2 )6 , and SIFSIX-3-Zn. The SCXRD thermal ellipsoids indicate that methane possesses significant mobility at the adsorption sites in each system. 2 H solid-state NMR (SSNMR) experiments targeting deuterated CH3 D guests in α-Mg3 (HCO2 )6 , α-Zn3 (HCO2 )6 , SIFSIX-3-Zn, and MOF-74 yield an interesting finding: the 2 H SSNMR spectra of methane adsorbed in these MOFs are significantly influenced by the chemical shielding anisotropy in addition to the quadrupolar interaction. The chemical shielding anisotropy contribution is likely due mainly to the nuclear independent chemical shift effect on the MOF surfaces. In addition, the 2 H SSNMR results and DFT calculations strongly indicate that the methane adsorption strength is linked to the MOF pore size and that dispersive forces are responsible for the methane adsorption in these systems. This work lays a very promising foundation for future studies of methane adsorption locations and dynamics within adsorbent MOF materials.

4.
Chemistry ; 24(3): 743-749, 2018 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-29106762

RESUMO

The phosphorus-sulfur heterocycles 1,2-thiaphosphetenes and phosphirene sulfides have been prepared, and represent the first structurally characterized derivatives for either class of compound. These strained P-S ring systems are formed by the reaction of a phosphinidene sulfide and alkyne. Using an internal alkyne, only the 3-membered PV , phosphirene sulfide was produced, whereas a terminal alkyne yielded a mixture of phosphirene sulfide and 1,2-thiaphosphetene (PIII ). Detailed computational analysis revealed that for numerous derivatives of alkynes, the corresponding 4-membered rings are always more stable than the 3-membered isomers. The electronic nature of "free" phosphinidene sulfides (R-P=S) is discussed based on computational results.

5.
Inorg Chem ; 56(21): 13500-13509, 2017 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-29027797

RESUMO

The reactivity of 4-membered (RPCh)2 rings (Ch = S, Se) that contain phosphorus in the +3 oxidation state is reported. These compounds undergo ring expansion to (RPCh)3 with the addition of a Lewis base. The 6-membered rings were found to be more stable than the 4-membered precursors, and the mechanism of their formation was investigated experimentally and by density functional theory calculations. The computational work identified two plausible mechanisms involving a phosphinidene chalcogenide intermediate, either as a free species or stabilized by a suitable base. Both the 4- and 6-membered rings were found to react with coinage metals, giving the same products: (RPCh)3 rings bound to the metal center from the phosphorus atom in tripodal fashion.

6.
Dalton Trans ; 46(26): 8405-8414, 2017 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-28621358

RESUMO

Several platinum(ii) complexes with ligands containing azo groups have been prepared and structurally characterised, and their photoswitching between trans and cis azo group isomers has been studied. The azo groups in the cationic complexes [PtMe(bipy)(4-NC5H4-N[double bond, length as m-dash]N-4-C6H4X)][PF6], X = H, OH or NMe2, and in the dicationic complex [Pt(bipy)(4-H2NC6H4-N[double bond, length as m-dash]N-C6H5)2][OTf]2 undergo trans to cis photoswitching on irradiation at 365 nm. The complex [PtMe(bipy)(4-NC5H4-N[double bond, length as m-dash]N-4-C6H4NMe)2][PF6] also exhibits a reversible halochromic effect on protonation to give the dicationic complex [PtMe(bipy)(4-NC5H4-NH[double bond, length as m-dash]N-4-C6H4NMe2]2+. The nature of the frontier orbitals in the platinum(ii) complexes depends on the charge on the complex and on the degree of metal-ligand π-bonding.

7.
Dalton Trans ; 46(14): 4609-4616, 2017 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-28322396

RESUMO

A series of novel cationic Re(iii) complexes [(DAAm)Re(CO)(NCCH3)2][X] [DAAm = N,N-bis(2-arylaminoethyl)methylamine; aryl = C6F5 (a), Mes (b)] [X = OTf (2), BArF4 [BArF4 = tetrakis[3,5-(trifluoromethyl)phenyl]borate] (3), BF4 (4), PF6 (5)], and their analogue [(DAmA)Re(CO)(Cl)2] [DAmA = N,N-bis(2-arylamineethyl)methylamino; aryl = C6F5] (6) were synthesized. The catalytic efficiency for the hydrosilylation reaction of aldehydes using 4a (0.03 mol%) has been demonstrated to be significantly more active than rhenium catalysts previously reported in the literature. The data suggest that electron-withdrawing substituents at the diamido amine ligand increase the catalytic efficiency of the complexes. Excellent yields were achieved at ambient temperature under neat conditions using dimethylphenylsilane. The reaction affords TONs of up to 9200 and a TOF of up to 126 h-1. Kinetic and mechanistic studies were performed, and the data suggest that the reaction is via a non-hydride ionic hydrosilylation mechanism.

8.
Angew Chem Int Ed Engl ; 56(22): 6236-6240, 2017 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-28071846

RESUMO

Four-membered rings with a P2 Ch2 core (Ch=S, Se) and phosphorus in the +3 oxidation state have been synthesized. The utility of these rings as a source of monomeric phosphinidene chalcogenides was probed by the addition of an N-heterocyclic carbene, resulting in a base-stabilized phosphinidene sulfide. Similarly, persistence of the phosphinidene selenide in solution was shown through cycloaddition chemistry with 2,3-dimethylbutadiene at elevated temperatures. The observed reactivity was explained by detailed computational work that established the conditions upon which the P2 Ch2 rings can liberate phosphinidene chalcogenides.

9.
J Am Chem Soc ; 139(3): 1129-1144, 2017 01 25.
Artigo em Inglês | MEDLINE | ID: mdl-28084731

RESUMO

Superstructures, combining nanoscopic constituents into micrometer-size assemblies, have a great potential for utilization of the size-dependent quantum-confinement properties in multifunctional electronic and optoelectronic devices. Two diverse superstructures of nanoscopic CdSe were prepared using solvothermal conversion of the same cadmium selenophenolate precursor (Me4N)2[Cd(SePh)4]: the first is a superlattice of monodisperse [Cd54Se32(SePh)48(dmf)4]4- nanoclusters; the second is a unique porous CdSe crystal. Nanoclusters were crystallized as cubic crystals (≤0.5 mm in size) after solvothermal treatment at 200 °C in DMF. UV-vis absorption and PLE spectra of the reported nanoclusters are consistent with previously established trends for the known families of tetrahedral CdSe frameworks. In contrast to these, results of PL spectra are rather unexpected, as distinct room temperature emission is observed both in solution and in the solid state. The porous CdSe crystals were isolated as red hexagonal prisms (≤70 µm in size) via solvothermal treatment under similar conditions but with the addition of an alkylammonium salt. The presence of a three-dimensional CdSe network having a coherent crystalline structure inside hexagonal prisms was concluded based on powder X-ray diffraction, selected area electron diffraction and electron microscopy imaging. Self-assembly via oriented attachment of crystalline nanoparticles is discussed as the most probable mechanism of formation.

10.
Dalton Trans ; 45(48): 19485-19490, 2016 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-27891539

RESUMO

The combination of a palladium(ii) precursor with a diimine-phenol ligand and an oxidant (H2O2 or O2) under different conditions has, serendipitously, given both a molecular square and a molecular tetrahedron by self-assembly of building blocks comprising palladium(ii) centres coordinated to the oxidised forms of the ligand.

11.
Dalton Trans ; 45(17): 7226-30, 2016 04 25.
Artigo em Inglês | MEDLINE | ID: mdl-27064526

RESUMO

The addition of an alkynyl cyclopropyl mechanistic probe to a digermyne did not lead to any ring-opened rearrangement products indicating that the reaction pathway does not involve any vinylic radicals or cations and providing experimental insight into the addition of alkynes to digermynes.

12.
Chem Commun (Camb) ; 51(51): 10334-6, 2015 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-26027959

RESUMO

The complex [PtMe2({κ(2)-N,N-RN[double bond, length as m-dash]CH-2-C5H4N})] reacts with oxygen in acetone solution to give the platinum(iv) complex [Pt(OH)Me2{κ(3)-N,N,O-RNH-CH(2-C5H4N)(CH[double bond, length as m-dash]CMeO)}], when R = 2-C6H4OH, but not when R = Ph. It has been suggested that the phenol substituent plays two key biomimetic roles; firstly, in proton coupled electron transfer reactions in the activation of oxygen and hydroperoxide groups and, secondly, in proton relay from a methyl group of the coordinated acetone.


Assuntos
Compostos Organoplatínicos/síntese química , Oxigênio/química , Fenóis/química , Biomimética , Ligantes , Compostos Organoplatínicos/química , Oxirredução , Espectroscopia de Prótons por Ressonância Magnética
13.
Chemistry ; 21(27): 9790-6, 2015 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-26037242

RESUMO

The synthesis and characterization of two bimetallic, cationic low-valent gallium-cryptand[2.2.2] complexes is reported. The reaction of cryptand[2.2.2] with Ga2Cl4 gave two different cations, [Ga3Cl4 (crypt-222)](+) (1) or [Ga2Cl2 (crypt-222)](2+) (2), depending on whether or not trimethylsilyl triflate (Me3SiOTf) was added as a co-reagent. Complexes 1 and 2 are the first examples of bimetallic cryptand[2.2.2] complexes, as well as the first low-valent gallium-cryptand[2.2.2] complexes. Computational methods were used to evaluate the bonding in the gallium cores.

14.
Inorg Chem ; 54(9): 4466-74, 2015 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-25880717

RESUMO

The synthesis and characterization of an Fe(III) catecholate-nitronylnitroxide (CAT-NN) complex (1-NN) that undergoes Fe(III) spin-crossover is described. Our aim is to determine whether the intraligand exchange coupling of the semiquinone-nitronylnitroxide Fe(II)(SQ-NN) excited state resulting from irradiation of the CAT → Fe(III) LMCT band would affect either the intrinsic photophysics or the iron spin-crossover event when compared to the complex lacking the nitronylnitroxide radical (1). X-ray crystallographic analysis provides bond lengths consistent with a ferric catecholate charge distribution. Mössbauer spectroscopy clearly demonstrates Fe(III) spin-crossover, hyperfine couplings, and a weak ferromagnetic Fe(III)-CAT-NN exchange, and spin-crossover is corroborated by variable-temperature magnetic susceptibility and electronic absorption studies. To explore the effect of the NN radical on photophysical processes, we conducted room-temperature transient absorption experiments. Upon excitation of the ligand-to-metal charge transfer band, an Fe(II)SQ state is populated and most likely undergoes fast intersystem crossing to the ligand field manifold, where it rapidly decays into a metastable low-spin Fe(III)CAT state, followed by repopulation of the high-spin Fe(III)CAT ground state. The decay components of 1-NN are slightly faster than those obtained for 1, perhaps due to the higher number of microstates present within the LMCT and LF manifolds for 1-NN. Although the effects of the NN radical are manifest in neither the spin-crossover nor the photophysics, our results lay the groundwork for future studies.

15.
J Phys Chem B ; 118(47): 13601-8, 2014 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-25345716

RESUMO

A Raman spectroscopic evaluation of numerous crystalline solvates with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI or LiN(SO2CF3)2) has been conducted over a wide temperature range. Four new crystalline solvate structures-(PHEN)3:LiTFSI, (2,9-DMPHEN)2:LiTFSI, (G3)1:LiTFSI and (2,6-DMPy)1/2:LiTFSI with phenanthroline, 2,9-dimethyl[1,10]phenanthroline, triglyme, and 2,6-dimethylpyridine, respectively-have been determined to aid in this study. The spectroscopic data have been correlated with varying modes of TFSI(-)···Li(+) cation coordination within the solvate structures to create an electrolyte characterization tool to facilitate the Raman band deconvolution assignments for the determination of ionic association interactions within electrolytes containing LiTFSI. It is found, however, that significant difficulties may be encountered when identifying the distributions of specific forms of TFSI(-) anion coordination present in liquid electrolyte mixtures due to the wide range of TFSI(-)···Li(+) cation interactions possible and the overlap of the corresponding spectroscopic data signatures.

16.
Acta Crystallogr Sect E Struct Rep Online ; 70(Pt 5): o556-7, 2014 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-24860364

RESUMO

In the title compound, C18H23N5O4·CH2Cl2, the di-chloro-methane solvent mol-ecule is disordered over two sets of sites in a 0.630 (13):0.370 (13) ratio. The dihedral angle between the uracil and phenyl rings is 30.2 (1)°. In the crystal, the principal inter-actions are N-H⋯O hydrogen bonds, which link uracil units across centres of symmetry, forming eight-membered rings with an R (2) 2(8) graph-set motif. The structure also displays C-H⋯O and C-H⋯Cl hydrogen bonds. Intra-molecular C-H⋯O short contacts are also observed.

17.
Acta Crystallogr Sect E Struct Rep Online ; 70(Pt 12): o1223-4, 2014 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-25553012

RESUMO

The absolute configuration of the title mol-ecular salt, C15H18N(+)·C8H6ClO3 (-), has been confirmed by resonant scattering. In the (R)-N-benzyl-1-phenyl-ethyl-ammonium cation, the phenyl rings are inclined to one another by 44.65 (7)°. In the crystal, the (R)-4-chloro-mandelate anions are linked via O-H⋯O hydrogen bonds and bridged by N-H⋯O hydrogen bonds involving the cations, forming chains along [010]. There are C-H⋯O hydrogen bonds present within the chains, which are linked via C-H⋯π inter-actions and a short Cl⋯Cl inter-action [3.193 (1) Å] forming a three-dimensional framework. The structure was refined as a two-component inversion twin giving a Flack parameter of 0.05 (4).

18.
Dalton Trans ; 43(1): 240-50, 2014 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-24096386

RESUMO

Two dimeric boron complexes of potentially tetradentate and trianionic ß-diketiminate ligands bearing phenol substituents were prepared and characterized. The synthetic routes employed were designed to circumvent the undesirable formation of ß-ketimines and 2-methylbenzoxazoles observed when traditional synthetic routes toward the target ß-diketiminate ligands were attempted. The title complexes were isolated via demethylation of ß-diketimine ligands and boron difluoride complexes bearing 2-anisole N-aryl substituents using boron tribromide. The resulting complexes were found to contain a unique hydrogen-bond-supported boron-oxygen-boron bridge, as confirmed by X-ray crystallography. The stability of the resulting dimeric structures relative to the corresponding monomeric, tetradentate boron complexes was studied computationally, and theory confirmed that the dimeric structures were strongly favored. The absorption spectra of the dimers were red-shifted relative to the parent ß-diketimine ligands. The complexes were irreversibly oxidized and reduced electrochemically and were weakly emissive at low concentrations (Stokes shifts between 23 and 31 nm), showing little solvent dependence.

19.
J Am Chem Soc ; 135(45): 17144-54, 2013 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-24187945

RESUMO

The preparation and characterization of three new donor-bridge-acceptor biradical complexes are described. Using variable-temperature magnetic susceptibility, EPR hyperfine coupling constants, and the results of X-ray crystal structures, we evaluate both exchange and electronic couplings as a function of bridge length for two quintessential molecular bridges: oligo(para-phenylene), ß = 0.39 Å(-1) and oligo(2,5-thiophene), ß = 0.22 Å(-1). This report represents the first direct comparison of exchange/electronic couplings and distance attenuation parameters (ß) for these bridges. The work provides a direct measurement of superexchange contributions to ß, with no contribution from incoherent hopping. The different ß values determined for oligo(para-phenylene) and oligo(2,5-thiophene) are due primarily to the D-B energy gap, Δ, rather than bridge-bridge electronic couplings, H(BB). This is supported by the fact that the H(BB) values extracted from the experimental data for oligo(para-phenylene) (H(BB) = 11,400 cm(-1)) and oligo(2,5-thiophene) (12,300 cm(-1)) differ by <10%. The results presented here offer unique insight into the intrinsic molecular factors that govern H(DA) and ß, which are important for understanding the electronic origin of electron transfer and electron transport mediated by molecular bridges.

20.
J Am Chem Soc ; 135(39): 14713-25, 2013 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-24060285

RESUMO

A combination of variable-temperature EPR spectroscopy, electronic absorption spectroscopy, and magnetic susceptibility measurements have been performed on Tp(Cum,Me)Zn(SQ-m-Ph-NN) (1-meta) a donor-bridge-acceptor (D-B-A) biradical that possesses a cross-conjugated meta-phenylene (m-Ph) bridge and a spin singlet ground state. The experimental results have been interpreted in the context of detailed bonding and excited-state computations in order to understand the excited-state electronic structure of 1-meta. The results reveal important excited-state contributions to the ground-state singlet-triplet splitting in this cross-conjugated D-B-A biradical that contribute to our understanding of electronic coupling in cross-conjugated molecules and specifically to quantum interference effects. In contrast to the conjugated isomer, which is a D-B-A biradical possessing a para-phenylene bridge, admixture of a single low-lying singly excited D → A type configuration into the cross-conjugated D-B-A biradical ground state makes a negligible contribution to the ground-state magnetic exchange interaction. Instead, an excited state formed by a Ph-NN (HOMO) → Ph-NN (LUMO) one-electron promotion configurationally mixes into the ground state of the m-Ph bridged D-A biradical. This results in a double (dynamic) spin polarization mechanism as the dominant contributor to ground-state antiferromagnetic exchange coupling between the SQ and NN spins. Thus, the dominant exchange mechanism is one that activates the bridge moiety via the spin polarization of a doubly occupied orbital with phenylene bridge character. This mechanism is important, as it enhances the electronic and magnetic communication in cross-conjugated D-B-A molecules where, in the case of 1-meta, the magnetic exchange in the active electron approximation is expected to be J ~ 0 cm(-1). We hypothesize that similar superexchange mechanisms are common to all cross-conjugated D-B-A triads. Our results are compared to quantum interference effects on electron transfer/transport when cross-conjugated molecules are employed as the bridge or molecular wire component and suggest a mechanism by which electronic coupling (and therefore electron transfer/transport) can be modulated.

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