Transition Metal Complexes with Reactive Trimethylsilylchalcogenolate Ligands: Precursors for the Preparation of Ternary Nanoclusters

The Co2+ and Mn2+ complexes (N,N´-tmeda)Co(ESiMe3)2 (E = S, 1a; E = Se, 1b), (3,5-Me2C5H3N)2Co(ESiMe3)2 (E = S, 2a; E = Se, 2b), [Li(N,N´-tmeda)]2[(N,N´-tmeda)Mn5(μ-ESiMe3)2(ESiMe3)4(μ4-E)(μ3-E)2] (E = S, 3a; E = Se, 3b), [Li(N,N´-tmeda)]2[Mn(SSiMe3)4] (4), [Li(N,N´-tmeda)]4[Mn4(SeSiMe3)4(μ3-Se)4] (5), and [Li(N,N´-tmeda)]4[Mn(Se4)3] (6) have been isolated from reactions of Li[ESiMe3] and the chloride salts of these metals. The treatment of (N,N´-tmeda)CoCl2 with two equivalents of Li[ESiMe3] (E = S, Se) yields 1a and 1b, respectively, whereas similar reactions with MnCl2 yield the polynuclear complexes 3a (E = S) and 3b (E = Se). The selective preparation of the mononuclear complex 4 is achieved by increasing the reaction ratios of Li[SSiMe3] to MnCl2 to 4:1. Single crystal X-ray analysis of complexes 1−5, confirms the presence of potentially reactive trimethylsilylchalcogenolate moieties and distorted tetrahedral geometry around the metal centers in each of these complexes. These compounds could potentially be utilized as a convenient source of paramagnetic ions into a semiconductor matrix for the synthesis of ternary clusters. The ternary clusters (N,N´-tmeda)6Zn14-xMnxS13Cl2 (7a-d) and (N,N´-tmeda)6Zn14-xMnxSe13Cl2 (8a-d) and the binary clusters (N,N´-tmeda)6Zn14E13Cl2 (E= S, 9a; Se, 9b) have been synthesized by reacting (N,N´-tmeda)Zn(ESiMe3)2 with Mn2+ and Zn2+ salts. Single crystal X-ray analysis of the complexes confirms the presence of the six ‘(N,N´-tmeda)ZnE2’ units as capping ligands that stabilize the clusters, and distorted tetrahedral geometry around the metal centers. Mn2+ is incorporated into the ZnE matrix by substitution of Zn2+ ions in the cluster core. Complexes 7a, 8a and 8d represent the first examples of ‘Mn/ZnE’ clusters with structural characterization and indications of the local chemical environment of the Mn2+ ions. DFT calculations indicate that replacement of Zn with Mn is perfectly feasible and at least partly allows for the identification of some sites preferred by the Mn2+ metals. These calculations, combined with luminescence studies suggest a distribution of the Mn2+ in the clusters. The room temperature emission spectra of clusters 7c-d display a significant red shift relative to the all zinc cluster 9a, with a peak maximum centered at 730 nm. Clusters 8c-d have a peak maximum at 640 nm in their emission spectra. The chalcogenolate complexes 3a and 4 have been utilized as molecular precursors for the isolation of ternary nanoclusters, with approximate formulae [Mn35/36Ag118/116S94(PnPr3)30], 10 and [Mn19/20Ag150/148S94(PnPr3)30], 11 respectively. Mn2+ is incorporated into the Ag2S matrix by substitution of two Ag+ ions in the cluster core

Zinc Chalcogenolate Complexes as Precursors to ZnE and Mn/ZnE (E = S, Se) Clusters

The ternary clusters (tmeda)₆Zn_{14–<i>x</i>}Mn_<i>x</i>S₁₃Cl₂ (<b>1a</b>–<b>d</b>) and (tmeda)₆Zn_{14–<i>x</i>}Mn_<i>x</i>Se₁₃Cl₂ (<b>2a</b>–<b>d</b>), (tmeda = <i>N,N,N′,N′</i>-tetramethylethylenediamine; <i>x</i> ≈ 2–8) and the binary clusters (tmeda)₆Zn₁₄E₁₃Cl₂ (E = S, <b>3</b>; Se, <b>4</b>;) have been isolated by reacting (tmeda)­Zn­(ESiMe₃)₂ with Mn­(II) and Zn­(II) salts. Single crystal X-ray analysis of the complexes confirms the presence of the six “(tmeda)­ZnE₂” units as capping ligands that stabilize the clusters, and distorted tetrahedral geometry around the metal centers. Mn­(II) is incorporated into the ZnE framework by substitution of Zn­(II) ions in the cluster. The polynuclear complexes (tmeda)₆Zn_12.3Mn_1.7S₁₃Cl₂ <b>1a</b>, (tmeda)₆Zn_12.0Mn_2.0Se₁₃Cl₂ <b>2a</b>, and (tmeda)₆Zn_8.4Mn_5.6Se₁₃Cl₂ <b>2d</b> represent the first examples of “Mn/ZnE” clusters with structural characterization and indications of the local chemical environment of the Mn­(II) ions. The incorporation of higher amounts of Mn into <b>1d</b> and <b>2d</b> has been confirmed by elemental analysis. Density functional theory (DFT) calculations indicate that replacement of Zn with Mn is perfectly feasible and at least partly allows for the identification of some sites preferred by the Mn­(II) metals. These calculations, combined with luminescence studies, suggest a distribution of the Mn­(II) in the clusters. The room temperature emission spectra of clusters <b>1c</b>–<b>d</b> display a significant red shift relative to the all zinc cluster <b>3</b>, with a peak maximum centered at 730 nm. Clusters <b>2c</b>–<b>d</b> display a peak maximum at 640 nm in their emission spectra

Nanocluster Isotope Distributions Measured by Electrospray Time-of-Flight Mass Spectrometry

Electrospray ionization (ESI) mass spectrometry (MS) is a widely used tool for the characterization of organometallic nanoclusters. By matching experimental mass spectra with calculated isotope distributions it is possible to determine the elemental composition of these analytes. In this work we conduct ESI-MS investigations on M₁₄E₁₃Cl₂(tmeda)₆ nanoclusters, where M is a transition metal, E represents a chalcogen, and tmeda is <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethyl-ethylenediamine. ESI mass spectra of these systems agree poorly with theoretical isotope distributions when data are acquired under standard conditions. This behavior is attributed to dead-time artifacts of the time-of-flight (TOF) analyzer used. It is well-known that excessively high TOF ion count rates lead to dead-time issues. Surprisingly, our data reveal that nanocluster spectra are affected by this problem even at moderate signal intensities that do not cause any problems for other types of analytes. This unexpected vulnerability is attributed to the extremely wide isotope distributions of the nanoclusters studied here. A good match between experimental and calculated nanocluster spectra is obtained only at ion count rates that are more than 1 order of magnitude below commonly used levels. Discrepancies between measured and theoretical isotope distributions have been observed in a number of previous ESI-MS nanocluster investigations. The dead-time issue identified here likely represents a contributing factor to the spectral distortions that were observed in those earlier studies. Using low-intensity ESI-MS conditions we demonstrate the feasibility of analyzing highly heterogeneous nanocluster samples that comprise subpopulations with a wide range of metal compositions

Suitability of habitats in Nepal for <i>Dactylorhiza hatagirea</i> now and under predicted future changes in climate

Dactylorhiza hatagirea is a terrestrial orchid listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and classified as threatened by International Union for Conservation of Nature (IUCN). It is endemic to the Hindu-Kush Himalayan region, distributed from Pakistan to China. The main threat to its existence is climate change and the associated change in the distribution of its suitable habitats to higher altitudes due to increasing temperature. It is therefore necessary to determine the habitats that are suitable for its survival and their expected distribution after the predicted changes in climate. To do this, we use Maxent modelling of the data for its 208 locations. We predict its distribution in 2050 and 2070 using four climate change models and two greenhouse gas concentration trajectories. This revealed severe losses of suitable habitat in Nepal, in which, under the worst scenario, there will be a 71–81% reduction the number of suitable locations for D. hatagirea by 2050 and 95–98% by 2070. Under the most favorable scenario, this reduction will be 65–85% by 2070. The intermediate greenhouse gas concentration trajectory surprisingly would result in a greater reduction by 2070 than the worst-case scenario. Our results provide important guidelines that local authorities interested in conserving this species could use to select areas that need to be protected now and in the future

Copper Chalcogenide Clusters Stabilized with Ferrocene-Based Diphosphine Ligands

The redox-active diphosphine ligand 1,1′-bis­(diphenylphosphino)­ferrocene (dppf) has been used to stabilize the copper­(I) chalcogenide clusters [Cu₁₂(μ₄-S)₆(μ-dppf)₄] (<b>1</b>), [Cu₈(μ₄-Se)₄(μ-dppf)₃] (<b>2</b>), [Cu₄(μ₄-Te)­(μ₄-η²-Te₂)­(μ-dppf)₂] (<b>3</b>), and [Cu₁₂(μ₅-Te)₄(μ₈-η²-Te₂)₂(μ-dppf)₄] (<b>4</b>), prepared by the reaction of the copper­(I) acetate coordination complex (dppf)­CuOAc (<b>5</b>) with 0.5 equiv of E­(SiMe₃)₂ (E = S, Se, Te). Single-crystal X-ray analyses of complexes <b>1</b>–<b>4</b> confirm the presence of {Cu_2<i>x</i>E_<i>x</i>} cores stabilized by dppf ligands on their surfaces, where the bidentate ligands adopt bridging coordination modes. The redox chemistry of cluster <b>1</b> was examined using cyclic voltammetry and compared to the electrochemistry of the free ligand dppf and the corresponding copper­(I) acetate coordination complex <b>5</b>. Cluster <b>1</b> shows the expected consecutive oxidations of the ferrocene moieties, Cu^I centers, and phosphine of the dppf ligand

Copper Chalcogenide Clusters Stabilized with Ferrocene-Based Diphosphine Ligands

The redox-active diphosphine ligand 1,1′-bis­(diphenylphosphino)­ferrocene (dppf) has been used to stabilize the copper­(I) chalcogenide clusters [Cu₁₂(μ₄-S)₆(μ-dppf)₄] (<b>1</b>), [Cu₈(μ₄-Se)₄(μ-dppf)₃] (<b>2</b>), [Cu₄(μ₄-Te)­(μ₄-η²-Te₂)­(μ-dppf)₂] (<b>3</b>), and [Cu₁₂(μ₅-Te)₄(μ₈-η²-Te₂)₂(μ-dppf)₄] (<b>4</b>), prepared by the reaction of the copper­(I) acetate coordination complex (dppf)­CuOAc (<b>5</b>) with 0.5 equiv of E­(SiMe₃)₂ (E = S, Se, Te). Single-crystal X-ray analyses of complexes <b>1</b>–<b>4</b> confirm the presence of {Cu_2<i>x</i>E_<i>x</i>} cores stabilized by dppf ligands on their surfaces, where the bidentate ligands adopt bridging coordination modes. The redox chemistry of cluster <b>1</b> was examined using cyclic voltammetry and compared to the electrochemistry of the free ligand dppf and the corresponding copper­(I) acetate coordination complex <b>5</b>. Cluster <b>1</b> shows the expected consecutive oxidations of the ferrocene moieties, Cu^I centers, and phosphine of the dppf ligand