Halogen-bonded (XB) complexes between halide anions and a cyclopropenylium-based anionic XB donor were characterized in solution for the first time. Spontaneous formation of such complexes confirms that halogen bonding is sufficiently strong to overcome electrostatic repulsion between two anions. The formation constants of such “anti-electrostatic” associations are comparable to those formed by halides with neutral halogenated electrophiles. However, while the latter usually show charge-transfer absorption bands, the UV-Vis spectra of the anion–anion complexes examined herein are determined by the electronic excitations within the XB donor. The identification of XB anion–anion complexes substantially extends the range of the feasible XB systems, and it provides vital information for the discussion of the nature of this interaction.Spontaneous formation of “anti-electrostatic” complexes in solution demonstrates that halogen bonding can be sufficiently strong to overcome anion–anion repulsion when the latter is attenuated by the polar medium.Halogen bonding (XB) is an attractive interaction between a Lewis base (LB) and a halogenated compound, exhibiting an electrophilic region on the halogen atom.1 It is most commonly related to electrostatic interaction between an electron-rich species (XB acceptor) and an area of positive electrostatic potential (σ-holes) on the surface of the halogen substituent in the electrophilic molecule (XB donor).2 Provided that mutual polarization of the interacting species is taken into account, the σ-hole model explains geometric features and the variation of stabilities of XB associations, especially in the series of relatively weak complexes.3 Based on the definition of halogen bonding and its electrostatic interpretation, this interaction is expected to involve either cationic or neutral XB donors. Electrostatic interaction of anionic halogenated species with electron-rich XB acceptors, however, seems to be repulsive, especially if the latter are also anionic. Yet, computational analyses predicted that halogen bonding between ions of like charges, called “anti-electrostatic” halogen bonding (AEXB),4 can possibly be formed5–12 and the first examples of AEXB complexes formed by different anions, i.e. halide anions and the anionic iodinated bis(dicyanomethylene)cyclopropanide derivatives 1 (see Scheme 1) or the anionic tetraiodo-p-benzoquinone radical, were characterized recently in the solid state.13,14 The identification of such complexes substantially extends the range of feasible XB systems, and it provides vital information for the discussion of the nature of this interaction. Computational results, however, significantly depend on the used methods and applied media (gas phase vs. polar environment and solvation models) and the solid state arrangements of the XB species might be affected by crystal forces and/or counterions. Unambiguous confirmation of the stability of the halogen-bonded anion–anion complexes and verification of their thermodynamic characteristics thus requires experimental characterization of the spontaneous formation of such associations in solution. Still, while the solution-phase complexes formed by hydrogen bonding between two anionic species were reported previously,15–17 there is currently no example of “anti-electrostatic” XB in solution.Open in a separate windowScheme 1Structures of the XB donor 1 and its hydrogen-substituted analogue 2.To examine halogen bonding between two anions in solution, we turn to the interaction between halides and 1,2-bis(dicyanomethylene)-3-iodo-cyclopropanide 1 (Scheme 1).‡ Even though this compound features a cationic cyclopropenylium core, it is overall anionic, and calculations have demonstrated that its electrostatic potential is universally negative across its entire surface.13 The solution of 1 (with tris(dimethylamino)cyclopropenium (TDA) as counterion) in acetonitrile is characterized by an absorption band at 288 nm with ε = 2.3 × 104 M−1 cm−1 (Fig. 1). As LB, we first applied iodide anions taken as a salt with n-tetrabutylammonium counter-ion, Bu4NI. This salt does not show absorption bands above 290 nm, but its addition to a solution of 1 led to a rise of absorption in the 290–350 nm range (Fig. 1). Subtraction of the absorption of the individual components from that of their mixture produced a differential spectrum which shows a maximum at about 301 nm (insert in Fig. 1). At constant concentration of the XB donor (1) and constant ionic strength, the intensity of the absorption in the range of 280–300 nm (and hence differential absorbance, ΔAbs) rises with increasing iodide concentration (Fig. S1 in the ESI†). This suggests that the interaction of iodide with 1 results in the formation of the [1, I−]-complex which shows a higher absorptivity in this spectral range (eqn (1)):1 + X− ⇌ [1, X−]1Open in a separate windowFig. 1Spectra of acetonitrile solutions with constant concentration of 1 (0.60 mM) and various concentrations of Bu4NI (6.0, 13, 32, 49, 75, 115 and 250 mM, solid lines from the bottom to the top). The dashed lines show spectra of the individual solutions 1 (c = 0.60 mM, red line) and Bu4NI (c = 250 mM, blue line). The ionic strength was maintained using Bu4NPF6. Insert: Differential spectra of the solutions obtained by subtraction of the absorption of the individual components from the spectra of their corresponding mixtures.To clarify the mode of interaction between 1 and iodide in the complex, we also performed analogous measurements with the hydrogen-substituted compound 2 (see Scheme 1). The addition of iodide to a solution of 2 in acetonitrile did not increase the absorption in the 280–300 nm spectral range. Instead, some decrease of the absorption band intensity of 2 with the increase of concentration of I− anions was observed (Fig. S2 in the ESI†). Such changes are related to a blue shift of this band resulting from the hydrogen bonding between 2 and iodide (formation of hydrogen-bonded [2, I−] complex is corroborated by the observation of the small shift of the NMR signal of the proton of 2 to the higher ppm values in the presence of I− anions, see Fig. S3 in the ESI†).§ Furthermore, since H-compound 2 should be at least as suitable as XB donor 1 to form anion–π complexes with the halide, this finding (as well as solid-state and computational data¶) rules out that any increase in absorption in this region observed with the I-compound 1 may be due to this alternative interaction.Likewise, the addition of NBu4I to a solution of TDA cations taken as a salt with Cl− anions did not result in an increase in the relevant region. Hence, we could also rule out anion–π interactions with the TDA counter-ions as source of the observed changes, which is in line with previous reports on the electron-rich nature of TDA.18All these observations (supported by the computational analysis, vide infra) indicate that the [1, I−] complex (eqn (1)) is formed via halogen bonding of I− with iodine substituents in 1. The changes in the intensities of the differential absorption ΔAbs as a function of the iodide concentration (with constant concentration of XB donor (1) as well as constant ionic strength) are well-modelled by the 1 : 1 binding isotherm (Fig. S1 in the ESI†). The fit of the absorption data produced a formation constant of K = 15 M−1 for the [1, I−] complex (Table 1).|| The overlap with the absorption of the individual XB donor hindered the accurate evaluation of the position and intensity of the absorption band of the corresponding complex which is formed upon LB-addition to 1. As such, the values of Δλmax shown in Table 1 represent a wavelength of the largest difference in the absorptivity of the [1, I−] complex and individual anion 1, and Δε reflects the difference of their absorptivity at this point (see the ESI† for the details of calculations).Equilibrium constants and spectral characteristics of the complexes of 1 with halide anions X−
Complexa
K [M−1]
Δλmaxc [nm]
10−3Δεd [M−1 cm−1]
1·I−
15 ± 2
302
9.0
1·I−b
8 ± 2
303
8.0
1·Br−
17 ± 2
302
3.7
1·Cl−
40 ± 8
302
3.0
Open in a separate windowaAll measurements performed in CH3CN at 22 °C, unless stated otherwise.bIn CH2Cl2.cWavelength of the maximum of the differential spectra.dDifferences in extinction coefficients of XB [1, I−] complex and individual 1 at Δλmax.Since earlier computational studies demonstrated substantial dependence of formation of the AEXB complexes on polarity of the medium,6–12 interaction between 1 and I− anions was also examined in dichloromethane. The spectral changes in this moderately-polar solvent were analogous to that in acetonitrile (Fig. S4 in the ESI†). * The values for the formation constants of the [1, I−] complex and Δε (obtained from the fitting of the ΔAbs vs. [I−] dependence) in CH2Cl2 are lower than those in acetonitrile (Table 1). This finding is in line with the computational studies,6–12 predicting stronger binding in more polar solvents.The addition of bromide or chloride salts to an acetonitrile solution of 1 caused changes in the UV-Vis range which were generally similar to that observed upon addition of iodide. The variations of the magnitude of the differential absorption intensities with the increase in the bromide or chloride concentrations are less pronounced than that observed upon addition of iodide (in agreement with the results of the DFT computations of the UV-Vis spectra of the complexes, vide infra). Yet, they could also be fitted using 1 : 1 binding isotherms (see Fig. S5 and S6 in the ESI†). The formation constants of the corresponding [1, Br−] and [1, Cl−] complexes resulted from the fitting of these dependencies are listed in Table 1. The values of K (which correspond to the free energy changes of complex formation in a range of −6 to −8 kJ mol−1) are comparable to those reported for complexes of neutral monodentate bromo- or iodosubstituted aliphatic or aromatic electrophiles with halides.19–22 Thus, despite the “anti-electrostatic” nature of XB complexes between two anions, the stabilities of such associations are similar to that observed with the most common neutral XB donors.In contrast to the similarity in thermodynamic characteristics, the UV-Vis spectral properties of the complexes of the anionic XB donor 1 with halides are substantially different from that reported for the analogous associations with the neutral XB donors. Specifically, a number of earlier studies revealed that intermolecular (XB or anion–π) complexes of halide anions are characterized by distinct absorption bands, which could be clearly segregated from the absorption of the interacting species.21–23 If the same neutral XB donor was used, the absorption bands of the corresponding complexes with chloride were blue shifted, and absorption bands of the complexes with iodide as LB were red shifted as compared to the bands of complexes with bromide. For example, XB complexes of CFBr3 with Cl−, Br− or I− show absorption band maxima at 247 nm, 269 nm and 312 nm, respectively (individual CFBr3 is characterized by an absorption band at 233 nm).21 Within a framework of the Mulliken charge-transfer theory of molecular complexes,24 such an order is related to a rise in the energy of the corresponding HOMO (and electron-donor strength) from Cl− to Br− and to I− anions. In the complexes with the same electron acceptor, this is accompanied by a decrease of the HOMO–LUMO gap, and thus, a red shift of the absorption band. The data in Table 1 shows, however, that the maxima of differential absorption spectra for these systems are observed at roughly the same wavelength. To clarify the reason for this observation, we carried out computational analysis of the associations between 1 and halide anions.The DFT optimization†† at M06-2X/def2-tzvpp level with acetonitrile as a medium (using PCM solvation model)25 produced thermodynamically stable XB complexes between 1 and I−, Br− or Cl− anions (they were similar to the complexes which were obtained earlier via M06-2X/def2-tzvp computations with SMD solvation model13). The calculated structure of the [1, I−] complex is shown in Fig. 2 and similar structures for the [1, Br−] and [1, Cl−] are shown in Fig. S7 in the ESI.†Open in a separate windowFig. 2Optimized geometries of the [1, I−] complex with (3, −1) bond critical points (yellow spheres) and the bond path (green line) from the QTAIM analysis. The blue–green disc indicates intermolecular attractive interactions resulting from the NCI treatments (s = 0.4 a.u. isosurfaces, color scale: −0.035 (blue) < ρ < 0.02 (red) a.u.).QTAIM analysis26 of these structures revealed the presence of the bond paths (shown as the green line) and (3, −1) bond critical points (BCPs) indicating bonding interaction between iodine substituent of 1 and halide anions. Characteristics of these BCPs (electron density of about 0.015 a.u., Laplacians of electron density of about 0.05 a.u. and energy density of about 0.0004 a.u., see Table S1 in the ESI†) are typical for the moderately strong supramolecular halogen bonds.27 The Non-Covalent Interaction (NCI) Indexes treatment28 produced characteristic green–blue discs at the critical points'' positions, confirming bonding interaction in all these complexes.Binding energies, ΔE, for the [1, X−] complexes are listed in Table 2. They are negative and their variations are consistent with the changes in experimental formation constants measured with three halide anions in Table 1. The ΔE value for [1, I−] calculated in dichloromethane is also negative. Its magnitude is lower than that in acetonitrile, in agreement with the smaller formation constant of [1, I−] in less polar dichloromethane.Calculated characteristics of the [1, X−] complexesa
Complex
ΔE, kJ mol−1
λmax,c nm
10−4ε,c M−1 cm−1
Δλmax,d M−1 cm−1
10−3Δε,d M−1 cm−1
1·I−
−14.2
252
5.70
255
14
1·I−b
−4.7
253
6.07
—
—
1·Br−
−14.8
252
5.02
253
7.4
1·Cl−
−16.2
251
4.78
249
5.3
Open in a separate windowaIn CH3CN, if not noted otherwise.bIn CH2Cl2.cExtinction coefficient for the lowest-energy absorption band of the complex.dPosition and extinction coefficient of the differential absorption (see Fig. 3).The TD DFT calculations of the individual XB donor 1 and its complexes with halides (which were carried at the same level as the optimizations) produced strong absorption bands in the UV range (Fig. 3). The calculated spectrum of the individual anion 1 (λmax = 252 nm and ε = 4.27 × 104 M−1 cm−1) is characterized by somewhat higher energy and intensity of the absorption band than the experimental one, but the differences of about 0.6 eV in energy and about 0.3 in log ε are common for the TD DFT calculations.Open in a separate windowFig. 3Calculated spectra of 1 and its complexes (as indicated). The dashed lines show differential absorption obtained by subtraction of absorption of 1 from the absorption of the corresponding complex.The TD DFT calculations of the XB complexes with all three anions produced absorption bands at essentially the same wavelength as that of the individual XB donor 1, but their intensities were higher (in contrast, the hydrogen-bonded complex of 2 with iodide showed absorption band with slightly lower intensity than that of individual 2). The differential spectra obtained by subtraction of the spectra of individual anion 1 from the spectra of the complexes are shown in Fig. 3, and their characteristics are listed in Table 2. Similarly to the experimental data in Table 1, the calculated values of Δλmax are very close in complexes with different halides, and values of Δε are increasing in the order 1·Cl− < 1·Br− < 1·I−.An analysis of the calculated spectra of the complexes revealed that the distinction in spectral characteristics of the XB complexes of anionic and neutral XB donors with halides are related to the differences in the molecular orbital energies of the interacting species. Specifically, the energy of the highest occupied molecular orbital (HOMO) of the anionic XB donor 1 is higher than the energies of the HOMOs of I−, Br− and Cl−, and the energy of the lowest unoccupied molecular orbital (LUMO) of 1 is lower than those of the halides (Table S2 in the ESI†). As such, the lowest-energy electron excitations (with the substantial oscillator strength) in the AEXB complexes involve molecular orbitals localized mostly on the XB donor (see Fig. S8 in the ESI†). Accordingly, the energy of the absorption bands is essentially independent on the halide. Still, due to the molecular orbital interactions between the halides and 1, the small segments of the HOMOs of the complexes are localized on the halides, which affected the intensity of the transitions.‡‡ In contrast, in the XB complexes with the neutral halogenated electrophiles, the energies of the HOMOs and LUMOs of the halides are higher than the energies of the corresponding orbitals of the XB donors. As such, the HOMO of such complexes (as well as the other common molecular complexes) is localized mostly on the XB acceptors (electron donor), and the LUMO on the XB donor (electron acceptor). Accordingly, their lowest energy absorption bands represent in essence charge-transfer transition, and its energy vary with the energies of the HOMO of halides (the TD DFT calculations suggest that similar charge-transfer transitions in complexes of halides with 1 occur at higher energies, and they are overshadowed by the absorption of components).In summary, combined experimental (UV-Vis spectral) and computational studies of the interaction between halides and 1 demonstrated spontaneous formation of the anion–anion XB complexes in moderately-polar and polar solvents (which attenuate the electrostatic anion–anion repulsion and facilitate close approach of the interacting species§§). To the best of our knowledge, this constitutes the first experimental observation of AEXBs in solution. Stabilities of such “anti-electrostatic” associations are comparable to that formed by halide anions with the common neutral bromo- and iodo-substituted aliphatic or aromatic XB donors. These findings confirm that halogen bonding between our anionic XB donor 1 and halides is sufficiently strong to overcome electrostatic repulsion between two anions. It also supports earlier conclusions29 that besides electrostatics, molecular-orbital (weakly-covalent interaction) play an important role in the formation of XB complexes. Since the HOMO of 1 is higher in energy than those of the halides, the lowest-energy absorption bands in the anion–anion complexes is related mostly to the transition between the XB-donor localized MOs (in contrast to the charge transfer transition in the analogous complexes with neutral XB donors). Therefore, the energies of these transitions are similar in all complexes and the interaction with halides only slightly increase their intensities. 相似文献
Periodic trends in metal–metal interactions in edge-shared [M2Cl10]4− systems, involving the transition metals from groups 4 through 8 and electronic configurations ranging from d1d1 through d5d5, have been investigated by calculating metal–metal bonding and spin-polarization (exchange) effects using density functional theory. The trends found in this study are compared with those for the analogous face-shared [M2Cl9]3− systems reported in earlier work. Strong linear correlations between the metal–metal bonding and spin-polarization terms have been obtained for all groups considered. In general, spin polarization and electron localization are predominant in 3d–3d species whereas electron delocalization and metal–metal bonding are favoured in 5d–5d species, with more variable results observed for 4d–4d systems. As previously found for face-shared [M2Cl9]3− systems, the strong correlations between the metal–metal bonding and spin polarization energy terms can be related to the fact that both properties appear to be similarly affected by the changes in the metal orbital properties and electron density occurring within the dndn groups. A significant difference between the face-shared and edge-shared systems is that while the 4d metals in the former show a strong tendency for delocalized metal–metal bonded structures, the edge-shared counterparts display much greater variation with both metal–metal bonded and weakly coupled complexes observed. The tendency for weaker metal–metal interactions can be traced to the inability of the edge-shared bridging structure to accommodate the smaller metal–metal distances required for strong metal–metal bonding. 相似文献
Electronic interactions can radically enhance the performance of supported metal catalysts and are critical for fundamentally understanding the nature of catalysts. However, at the microscopic level, the details of such interactions tuning the electronic properties of the sites on the metal particle''s surface and metal–support interface remain obscure. Herein, we found polarized electronic metal–support interaction (pEMSI) in oxide-supported Pd nanoparticles (NPs) describing the enhanced accumulation of electrons at the surface of NPs (superficial Pdδ−) with positive Pd atoms distributed on the interface (interfacial Pdδ+). More superficial Pdδ− species mean stronger pEMSI resulting from the synergistic effect of moderate Pd–oxide interaction, high structural fluxionality and electron transport activity of Pd NPs. The surface Pdδ− species are responsible for improved catalytic performance for H2 evolution from metal hydrides and formates. These extensive insights into the nature of supported-metal NPs may open new avenues for regulating a metal particle''s electronic structure precisely and exploiting high-performance catalysts.A new type of electronic effect, polarized metal-support interaction (pEMSI), in oxide-supported Pd nanoparticles describing the enhanced accumulation of electrons at the superficial surface is responsible for improved catalytic H2 evolution.相似文献
Functional nanoporous materials are widely explored for CO2 separation, in particular, small-pore aluminosilicate zeolites having a “trapdoor” effect. Such an effect allows the specific adsorbate to push away the sited cations inside the window followed by exclusive admission to the zeolite pores, which is more advantageous for highly selective CO2 separation. Herein, we demonstrated that the protonated organic structure-directing agent in the small-pore silicoaluminophosphate (SAPO) RHO zeolite can be directly exchanged with Na+, K+, or Cs+ and that the Na+ form of SAPO-RHO exhibited unprecedented separation for CO2/CH4, superior to all of the nanoporous materials reported to date. Rietveld refinement revealed that Na+ is sited in the center of the single eight-membered ring (s8r), while K+ and Cs+ are sited in the center of the double 8-rings (d8rs). Theoretical calculations showed that the interaction between Na+ and the s8r in SAPO-RHO was stronger than that in aluminosilicate RHO, giving an enhanced “trapdoor” effect and record high selectivity for CO2 with the separation factor of 2196 for CO2/CH4 (0.02/0.98 bar). The separation factor of Na-SAPO-RHO for CO2/N2 was 196, which was the top level among zeolitic materials. This work opens a new avenue for gas separation by using diverse silicoaluminophosphate zeolites in terms of the cation-tailored “trapdoor” effect.The sodium form of silicoaluminophosphate RHO zeolite exhibits a pronounced cation-tailored “trapdoor” effect, showing an unprecedented selectivity adsorption separation performance for CO2/CH4 and CO2/N2.相似文献
The reaction between basic [(PCP)Pd(H)] (PCP = 2,6-(CH2P(t-C4H9)2)2C6H4) and acidic [LWH(CO)3] (L = Cp (1a), Tp (1b); Cp = η5-cyclopentadienyl, Tp = κ3-hydridotris(pyrazolyl)borate) leads to the formation of bimolecular complexes [LW(CO)2(μ-CO)⋯Pd(PCP)] (4a, 4b), which catalyze amine-borane (Me2NHBH3, tBuNH2BH3) dehydrogenation. The combination of variable-temperature (1H, 31P{1H}, 11B NMR and IR) spectroscopies and computational (ωB97XD/def2-TZVP) studies reveal the formation of an η1-borane complex [(PCP)Pd(Me2NHBH3)]+[LW(CO3)]− (5) in the first step, where a BH bond strongly binds palladium and an amine group is hydrogen-bonded to tungsten. The subsequent intracomplex proton transfer is the rate-determining step, followed by an almost barrierless hydride transfer. Bimetallic species 4 are easily regenerated through hydrogen evolution in the reaction between two hydrides.Bimetallic complexes [LW(CO)2(μ-CO)⋯Pd(PCP)] cooperatively activate amine-boranes for their dehydrogenation via N–H proton tunneling at RDS and H2 evolution from two neutral hydrides.相似文献
We report here porphodilactol derivatives and their corresponding metal complexes. These systems show promise as “all-in-one” phototheranostics and are predicated on a design strategy that involves controlling the relationship between intersystem crossing (ISC) and photothermal conversion efficiency following photoexcitation. The requisite balance was achieved by tuning the aromaticity of these porphyrinoid derivatives and forming complexes with one of two lanthanide cations, namely Gd3+ and Lu3+. The net result led to a metalloporphodilactol system, Gd-trans-2, with seemingly optimal ISC efficiency, photothermal conversion efficiency and fluorescence properties, as well as good chemical stability. Encapsulation of Gd-trans-2 within mesoporous silica nanoparticles (MSN) allowed its evaluation for tumour diagnosis and therapy. It was found to be effective as an “all-in-one” phototheranostic that allowed for NIR fluorescence/photoacoustic dual-modal imaging while providing an excellent combined PTT/PDT therapeutic efficacy in vitro and in vivo in 4T1-tumour-bearing mice.We report here porphodilactol derivatives and their corresponding metal complexes as “all-in-one” phototheranostics by controlling the relationship between intersystem crossing (ISC) and photothermal conversion efficiency following photoexcitation.相似文献
The first C3‐symmetric 44‐core‐valence‐electron triangular palladium clusters, [{(SAr′)(PAr3)Pd}3]+, have been synthesized by activation of the C? S bond of isothioureas. Owing to delocalized metal–metal bonding, these stable complexes are the first noble‐metal analogues of the π‐aromatic cyclopropenyl cation [C3H3]+, with their all‐metal aromaticity involving d‐type atomic orbitals. 相似文献
The conformational energy landscape and the associated electronic structure and spectroscopic properties (UV/Vis/near‐infrared (NIR) and IR) of three formally d5/d6 mixed‐valence diruthenium complex cations, [{Ru(dppe)Cp*}2(μ‐C≡CC6H4C≡C)]+, [ 1 ]+, [trans‐{RuCl(dppe)2}2(μ‐C≡CC6H4C≡C)]+, [ 2 ]+, and the Creutz–Taube ion, [{Ru(NH3)5}2(μ‐pz)]5+, [ 3 ]5+ (Cp=cyclopentadienyl; dppe=1,2‐bis(diphenylphosphino)ethane; pz=pyrazine), have been studied using a nonstandard hybrid density functional BLYP35 with 35 % exact exchange and continuum solvent models. For the closely related monocations [ 1 ]+ and [ 2 ]+, the calculations indicated that the lowest‐energy conformers exhibited delocalized electronic structures (or class III mixed‐valence character). However, these minima alone explained neither the presence of shoulder(s) in the NIR absorption envelope nor the presence of features in the observed vibrational spectra characteristic of both delocalized and valence‐trapped electronic structures. A series of computational models have been used to demonstrate that the mutual conformation of the metal fragments—and even more importantly the orientation of the bridging ligand relative to those metal centers—influences the electronic coupling sufficiently to afford valence‐trapped conformations, which are of sufficiently low energy to be thermally populated. Areas in the conformational phase space with variable degrees of symmetry breaking of structures and spin‐density distributions are shown to be responsible for the characteristic spectroscopic features of these two complexes. The Creutz–Taube ion [ 3 ]5+ also exhibits low‐lying valence‐trapped conformational areas, but the electronic transitions that characterize these conformations with valence‐localized electronic structures have low intensities and do not influence the observed spectroscopic characteristics to any notable extent. 相似文献
An efficient strategy for designing charge-transfer complexes using coinage metal cyclic trinuclear complexes (CTCs) is described herein. Due to opposite quadrupolar electrostatic contributions from metal ions and ligand substituents, [Au(μ-Pz-(i-C3H7)2)]3·[Ag(μ-Tz-(n-C3F7)2)]3 (Pz = pyrazolate, Tz = triazolate) has been obtained and its structure verified by single crystal X-ray diffraction – representing the 1st crystallographically-verified stacked adduct of monovalent coinage metal CTCs. Abundant supramolecular interactions with aggregate covalent bonding strength arise from a combination of M–M′ (Au → Ag), metal–π, π–π interactions and hydrogen bonding in this charge-transfer complex, according to density functional theory analyses, yielding a computed binding energy of 66 kcal mol−1 between the two trimer moieties – a large value for intermolecular interactions between adjacent d10 centres (nearly doubling the value for a recently-claimed Au(i) → Cu(i) polar-covalent bond: Proc. Natl. Acad. Sci. U.S.A., 2017, 114, E5042) – which becomes 87 kcal mol−1 with benzene stacking. Surprisingly, DFT analysis suggests that: (a) some other literature precedents should have attained a stacked product akin to the one herein, with similar or even higher binding energy; and (b) a high overall intertrimer bonding energy by inferior electrostatic assistance, underscoring genuine orbital overlap between M and M′ frontier molecular orbitals in such polar-covalent M–M′ bonds in this family of molecules. The Au → Ag bonding is reminiscent of classical Werner-type coordinate-covalent bonds such as H3N: → Ag in [Ag(NH3)2]+, as demonstrated herein quantitatively. Solid-state and molecular modeling illustrate electron flow from the π-basic gold trimer to the π-acidic silver trimer with augmented contributions from ligand-to-ligand’ (LL′CT) and metal-to-ligand (MLCT) charge transfer.A stacked Ag3–Au3 bonded (66 kcal mol−1) complex obtained crystallographically exhibits charge-transfer characteristics arising from multiple cooperative supramolecular interactions.相似文献
The back cover picture shows Steely alien is invading a lilac garden . A synthetic all‐metal cluster compound is shown computationally to possess five‐fold (π and σ) aromaticity, including d‐orbital aromaticity. The bottleable [Pd3Sn8Bi6]4 cluster features a core‐shell shape akin to an unidentified flying object (UFO), in which a triangular Pd3 core is largely floating inside a Sn8Bi6 shell. Electron clouds in the system are delocalized over the Pd3 core, trigonal pyramid Sn4 caps, peripheral Bi6 ring, and roof‐like Sn2Bi2 walls, whose electron‐counting follows the (4n + 2) Hückel rule. The finding is beyond imagination and should help appease debate on the nature of aromaticity in the community. More details are discussed in the article by Zhai et al. on page 126–130.
Complexes of the Lewis base-free cations (MeBDI)Mg+ and (tBuBDI)Mg+ with Ph–X ligands (X = F, Cl, Br, I) have been studied (MeBDI = HC[C(Me)N-DIPP]2 and tBuBDI = HC[C(tBu)N-DIPP]2; DIPP = 2,6-diisopropylphenyl). For the smaller β-diketiminate ligand (MeBDI) only complexes with PhF could be isolated. Heavier Ph–X ligands could not compete with bonding of Mg to the weakly coordinating anion B(C6F5)4−. For the cations with the bulkier tBuBDI ligand, the full series of halobenzene complexes was structurally characterized. Crystal structures show that the Mg⋯X–Ph angle strongly decreases with the size of X: F 139.1°, Cl 101.4°, Br 97.7°, I 95.1°. This trend, which is supported by DFT calculations, can be explained with the σ-hole which increases from F to I. Charge calculation and Atoms-In-Molecules analyses show that Mg⋯F–Ph bonding originates from electrostatic attraction between Mg2+ and the very polar Cδ+–Fδ− bond. For the heavier halobenzenes, polarization of the halogen atom becomes increasingly important (Cl < Br < I). Complexation with Mg leads in all cases to significant Ph–X bond activation and elongation. This unusual coordination of halogenated species to early main group metals is therefore relevant to C–X bond breaking.Complexes of a highly Lewis acidic Mg cation and the full series of Ph–X (X = F, Cl, Br, I) have been structurally characterized. The Mg⋯X–Ph angle decreases with halogen size on account of the growing halogen σ-hole.相似文献
Reaction of 1-(2′-pyridylazo)-2-naphthol (Hpan) with [Ru(dmso)4Cl2] (dmso = dimethylsulfoxide), [Ru(trpy)Cl3] (trpy = 2,2′,2″-terpyridine), [Ru(bpy)Cl3] (bpy = 2,2′-bipyridine) and [Ru(PPh3)3Cl2] in refluxing ethanol in the presence of a base (NEt3) affords, respectively, the [Ru(pan)2], [Ru(trpy)(pan)]+ (isolated as perchlorate salt), [Ru(bpy)(pan)Cl] and [Ru(PPh3)2(pan)Cl] complexes. Structures of these four complexes have been determined by X-ray crystallography. In each of these complexes, the pan ligand is coordinated to the metal center as a monoanionic tridentate N,N,O-donor. Reaction of the [Ru(bpy)(pan)Cl] complex with pyridine (py) and 4-picoline (pic) in the presence of silver ion has yielded the [Ru(bpy)(pan)(py)]+ and [Ru(bpy)(pan)(pic)]+ complexes (isolated as perchlorate salts), respectively. All the complexes are diamagnetic (low-spin d6, S = 0) and show characteristic 1H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a Ru(II)–Ru(III) oxidation on the positive side of SCE. Except in the [Ru(pan)2] complex, a second oxidative response has been observed in the other five complexes. Reductions of the coordinated ligands have also been observed on the negative side of SCE. The [Ru(trpy)(pan)]ClO4, [Ru(bpy)(pan)(py)]ClO4 and [Ru(bpy)(pan)(pic)]ClO4 complexes have been observed to bind to DNA, but they have not been able to cleave super-coiled DNA on UV irradiation. 相似文献
The redox chemistry of uranium is dominated by single electron transfer reactions while single metal four-electron transfers remain unknown in f-element chemistry. Here we show that the oxo bridged diuranium(iii) complex [K(2.2.2-cryptand)]2[{((Me3Si)2N)3U}2(μ-O)], 1, effects the two-electron reduction of diphenylacetylene and the four-electron reduction of azobenzene through a masked U(ii) intermediate affording a stable metallacyclopropene complex of uranium(iv), [K(2.2.2-cryptand)][U(η2-C2Ph2){N(SiMe3)2}3], 3, and a bis(imido)uranium(vi) complex [K(2.2.2-cryptand)][U(NPh)2{N(SiMe3)2}3], 4, respectively. The same reactivity is observed for the previously reported U(ii) complex [K(2.2.2-cryptand)][U{N(SiMe3)2}3], 2. Computational studies indicate that the four-electron reduction of azobenzene occurs at a single U(ii) centre via two consecutive two-electron transfers and involves the formation of a U(iv) hydrazide intermediate. The isolation of the cis-hydrazide intermediate [K(2.2.2-cryptand)][U(N2Ph2){N(SiMe3)2}3], 5, corroborated the mechanism proposed for the formation of the U(vi) bis(imido) complex. The reduction of azobenzene by U(ii) provided the first example of a “clear-cut” single metal four-electron transfer in f-element chemistry.Both a masked and the actual complex [U(ii){N(SiMe3)2}3]+ effect the reduction of azobenzene to yield a U(vi) bis-imido species providing the first example of a “clear-cut” metal centred four-electron reduction in f-element chemistry.相似文献
Reaction of [Ru(trpy)Cl3] with quinolin-8-ol (HQ) yields [Ru(trpy)(Q)Cl]. Treatment of [Ru(trpy)(Q)Cl] with Ag+ in Me2CO–H2O (3:1) and MeCN gives [Ru(trpy)- (Q)(H2O)]+ and [Ru(trpy)(Q)(MeCN)]+, respectively, which were isolated as their perchlorate salts. A similar reaction in EtOH, in the presence of NaN3, yields [Ru(trpy)(Q)(N3)]. All complexes are diamagnetic (low-spin, d6, S = 0) and show many intense m.l.c.t. transitions in the visible region. They display a reversible RuII-RuIII oxidation in the -0.13-0.48 V versus s.c.e. range, followed by an irreversible RuIII-RuIV oxidation in the 0.46–1.08V versus s.c.e. range and three trpy-based reductions on the negative side of s.c.e. Chemical oxidation of [RuII(trpy)(Q)Cl] by Ce4+ gives [Ru(trpy)-(Q)Cl]+ which shows intense l.m.c.t. transitions in the visible region together with a weak ligand field transition in the lower energy region. The complex is one-electron paramagnetic (low-spin, d5, S=1/2) and shows a rhombic e.s.r. spectrum in MeCN–PhMe (1:1) solution at 77K. Chemical oxidation of [Ru(trpy)(Q)-(H2O)]+ results in the formation of a -oxo dimer, [{Ru(trpy)(Q)}2O]2+. 相似文献
The first families of alkaline-earth stannylides [Ae(SnPh3)2·(thf)x] (Ae = Ca, x = 3, 1; Sr, x = 3, 2; Ba, x = 4, 3) and [Ae{Sn(SiMe3)3}2·(thf)x] (Ae = Ca, x = 4, 4; Sr, x = 4, 5; Ba, x = 4, 6), where Ae is a large alkaline earth with direct Ae–Sn bonds, are presented. All complexes have been characterised by high-resolution solution NMR spectroscopy, including 119Sn NMR, and by X-ray diffraction crystallography. The molecular structures of [Ca(SnPh3)2·(thf)4] (1′), [Sr(SnPh3)2·(thf)4] (2′), [Ba(SnPh3)2·(thf)5] (3′), 4, 5 and [Ba{Sn(SiMe3)3}2·(thf)5] (6′), most of which crystallised as higher thf solvates than their parents 1–6, were established by XRD analysis; the experimentally determined Sn–Ae–Sn′ angles lie in the range 158.10(3)–179.33(4)°. In a given series, the 119Sn NMR chemical shifts are slightly deshielded upon descending group 2 from Ca to Ba, while the silyl-substituted stannyls are much more shielded than the phenyl ones (δ119Sn/ppm: 1′, −133.4; 2′, −123.6; 3′, −95.5; 4, −856.8; 5, −848.2; 6′, −792.7). The bonding and electronic properties of these complexes were also analysed by DFT calculations. The combined spectroscopic, crystallographic and computational analysis of these complexes provide some insight into the main features of these unique families of homoleptic complexes. A comprehensive DFT study (Wiberg bond index, QTAIM and energy decomposition analysis) points at a primarily ionic Ae–Sn bonding, with a small covalent contribution, in these series of complexes; the Sn–Ae–Sn′ angle is associated with a flat energy potential surface around its minimum, consistent with the broad range of values determined by experimental and computational methods.The complete series of heterobimetallic alkaline-earth distannyls [Ae{SnR3}2·(thf)x] (Ae = Ca, Sr, Ba) have been prepared for R = Ph and SiMe3, and their bonding and electronic properties have been comprehensively investigated.相似文献
A new family of ten dinuclear Ru(ii) complexes based on the bis[pyrrolyl Ru(ii)] triad scaffold, where two Ru(bpy)2 centers are separated by a variety of organic linkers, was prepared to evaluate the influence of the organic chromophore on the spectroscopic and in vitro photodynamic therapy (PDT) properties of the compounds. The bis[pyrrolyl Ru(ii)] triads absorbed strongly throughout the visible region, with several members having molar extinction coefficients (ε) ≥ 104 at 600–620 nm and longer. Phosphorescence quantum yields (Φp) were generally less than 0.1% and in some cases undetectable. The singlet oxygen quantum yields (ΦΔ) ranged from 5% to 77% and generally correlated with their photocytotoxicities toward human leukemia (HL-60) cells regardless of the wavelength of light used. Dark cytotoxicities varied ten-fold, with EC50 values in the range of 10–100 μM and phototherapeutic indices (PIs) as large as 5400 and 260 with broadband visible (28 J cm–2, 7.8 mW cm–2) and 625 nm red (100 J cm–2, 42 mW cm–2) light, respectively. The bis[pyrrolyl Ru(ii)] triad with a pyrenyl linker (5h) was especially potent, with an EC50 value of 1 nM and PI > 27 000 with visible light and subnanomolar activity with 625 nm light (100 J cm–2, 28 mW cm–2). The lead compound 5h was also tested in a tumor spheroid assay using the HL60 cell line and exhibited greater photocytotoxicity in this more resistant model (EC50 = 60 nM and PI > 1200 with 625 nm light) despite a lower dark cytotoxicity. The in vitro PDT effects of 5h extended to bacteria, where submicromolar EC50 values and PIs >300 against S. mutans and S. aureus were obtained with visible light. This activity was attenuated with 625 nm red light, but PIs were still near 50. The ligand-localized 3ππ* state contributed by the pyrenyl linker of 5h likely plays a key role in its phototoxic effects toward cancer cells and bacteria. 相似文献
Ru-complexes are widely studied because of their use in biological applications and photoconversion technologies. We reveal novel insights into the chemical bonding of a series of Ru(ii)- and Ru(iii)-complexes by leveraging recent advances in high-energy-resolution tender X-ray spectroscopy and theoretical calculations. We perform Ru 2p4d resonant inelastic X-ray scattering (RIXS) to probe the valence excitations in dilute solvated Ru-complexes. Combining these experiments with a newly developed theoretical approach based on time-dependent density functional theory, we assign the spectral features and quantify the metal–ligand bonding interactions. The valence-to-core RIXS features uniquely identify the metal-centered and charge transfer states and allow extracting the ligand-field splitting for all the complexes. The combined experimental and theoretical approach described here is shown to reliably characterize the ground and excited valence states of Ru complexes, and serve as a basis for future investigations of ruthenium, or other 4d metals active sites, in biological and chemical applications.Combined experimental and theoretical Ru 2p4d resonant inelastic X-ray scattering study probes the chemical bonding and the valence excited states of solvated Ru complexes.相似文献
Careful optimization of the reaction conditions provided access to the particularly small tetraruthenium macrocycle 2Ru2Ph-Croc, which is composed out of two redox-active divinylphenylene-bridged diruthenium entities {Ru}-1,4-CH=CH-C6H4-CH=CH-{Ru} (Ru2Ph; {Ru} = Ru(CO)Cl(PiPr3)2) and two likewise redox-active and potentially non-innocent croconate linkers. According to single X-ray diffraction analysis, the central cavity of 2Ru2Ph-Croc is shielded by the bulky PiPr3 ligands, which come into close contact. Cyclic voltammetry revealed two pairs of split anodic waves in the weakly ion pairing CH2Cl2/NBu4BArF24 (BArF24 = [B{C6H3(CF3)2-3,5}4]− electrolyte, while the third and fourth waves fall together in CH2Cl2/NBu4PF6. The various oxidized forms were electrogenerated and scrutinized by IR and UV/Vis/NIR spectroscopy. This allowed us to assign the individual oxidations to the metal-organic Ru2Ph entities within 2Ru2Ph-Croc, while the croconate ligands remain largely uninvolved. The lack of specific NIR bands that could be assigned to intervalence charge transfer (IVCT) in the mono- and trications indicates that these mixed-valent species are strictly charge-localized. 2Ru2Ph-Croc is hence an exemplary case, where stepwise IR band shifts and quite sizable redox splittings between consecutive one-electron oxidations would, on first sight, point to electronic coupling, but are exclusively due to electrostatic and inductive effects. This makes 2Ru2Ph-Croc a true “pretender”. 相似文献
Precisely locating extra-framework cations in anionic metal–organic framework compounds remains a long-standing, yet crucial, challenge for elucidating structure–performance relationships in functional materials. Single-crystal X-ray diffraction is one of the most powerful approaches for this task, but single crystals of frameworks often degrade when subjected to post-synthetic metalation or reduction. Here, we demonstrate the growth of sizable single crystals of the robust metal–organic framework Fe2(bdp)3 (bdp2− = benzene-1,4-dipyrazolate) and employ single-crystal-to-single-crystal chemical reductions to access the solvated framework materials A2Fe2(bdp)3·yTHF (A = Li+, Na+, K+). X-ray diffraction analysis of the sodium and potassium congeners reveals that the cations are located near the center of the triangular framework channels and are stabilized by weak cation–π interactions with the framework ligands. Freeze-drying with benzene enables isolation of activated single crystals of Na0.5Fe2(bdp)3 and Li2Fe2(bdp)3 and the first structural characterization of activated metal–organic frameworks wherein extra-framework alkali metal cations are also structurally located. Comparison of the solvated and activated sodium-containing structures reveals that the cation positions differ in the two materials, likely due to cation migration that occurs upon solvent removal to maximize stabilizing cation–π interactions. Hydrogen adsorption data indicate that these cation–framework interactions are sufficient to diminish the effective cationic charge, leading to little or no enhancement in gas uptake relative to Fe2(bdp)3. In contrast, Mg0.85Fe2(bdp)3 exhibits enhanced H2 affinity and capacity over the non-reduced parent material. This observation shows that increasing the charge density of the pore-residing cation serves to compensate for charge dampening effects resulting from cation–framework interactions and thereby promotes stronger cation–H2 interactions.Single-crystal X-ray diffraction reveals structural influences on gas adsorption properties in anionic metal–organic frameworks.相似文献
Gas‐phase clusters are deemed to be σ‐aromatic when they satisfy the 4n+2 rule of aromaticity for delocalized σ electrons and fulfill other requirements known for aromatic systems. While the range of n values was shown to be quite broad when applied to short‐lived clusters found in molecular‐beam experiments, stability of all‐metal cluster‐like fragments isolated in condensed phase was previously shown to be mainly ascribed to two electrons (n=0). In this work, the applicability of this concept is extended towards solid‐state compounds by demonstrating a unique example of a storable compound, which was isolated as a stable [K([2.2.2]crypt)]+ salt, featuring a [Au2Sb16]4? cluster core possessing two all‐metal aromatic AuSb4 fragments with six delocalized σ electrons each (n=1). This discovery pushes the boundaries of the original idea of Kekulé and firmly establishes the usefulness of the σ‐aromaticity concept as a general idea for both small clusters and solid‐state compounds. 相似文献
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