Pressure versus Temperature Effects on Intramolecular Electron Transfer in Mixed‐Valence Complexes

Mixed‐valence trinuclear carboxylates, [M₃O(O₂CR)₆L₃] (M=metal, L=terminal ligand), have small differences in potential energy between the configurations M^IIM^IIIM^III?? M^IIIM^IIM^III??M^IIIM^IIIM^II, which means that small external changes can have large structural effects, owing to the differences in coordination geometry between M²⁺ and M³⁺ sites (e.g., about 0.2 Å for Fe? O bond lengths). It is well‐established that the electron transfer (ET) between the metal sites in these mixed‐valence molecules is strongly dependent on temperature and on the specific crystal environment; however, herein, for the first time, we examine the effect of pressure on the electron transfer. Based on single‐crystal X‐ray diffraction data that were measured at 15, 90, 100, 110, 130, 160, and 298 K on three different crystals, we first unexpectedly found that our batch of Fe₃O (O₂CC(CH₃)₃)₆(C₅H₅N)₃ ( 1 ) exhibited a different temperature dependence of the ET process than previous studies of compound 1 have shown. We observed a phase transition at around 130 K that was related to complete valence trapping and Hirshfeld surface analysis revealed that this phase transition was governed by a subtle competition between C? H???π and π???π intermolecular interactions. Subsequent high‐pressure single‐crystal X‐ray diffraction at pressures of 0.15, 0.35, 0.45, 0.74, and 0.96 GPa revealed that it was not possible to trigger the phase transition (i.e., valence trapping) by a reduction of the unit‐cell volume, owing to this external pressure. We conclude that modulation of the ET process requires anisotropic changes in the intermolecular interactions, which occur when various directional chemical bonds are affected differently by changes in temperature, but not by the application of pressure.     

Synthesis and Structure of Melamium Bromide C6N11H10Br and Melamium Iodide C6N11H10I

Melamium bromide and melamium iodide were synthesized from dicyandiamide in the presence of ammonium halides in evacuated Duran glass ampoules at temperatures of 450 °C. The crystal structures of both compounds were obtained from single‐crystal X‐ray diffraction. Melamium bromide C₆N₁₁H₁₀Br crystallizes in space group P2₁/n [no. 14, a = 7.0500(5), b = 28.7096(18), c = 10.8783(8) Å, β = 96.060(2)°, Z = 8, wR₂ = 0.2231] and exhibits a layer‐like arrangement of melamium ions, wherein both planar as well as twisted molecular structures of the cations occur. Melamium iodide C₆N₁₁H₁₀I crystallizes in space group P2₁/c [no. 14, a = 6.8569(3), b = 11.9949(6), c = 14.0932(6) Å, β = 97.613(2)°, Z = 4, wR₂ = 0.0654], however in a structure completely different from the one of melamium bromide. The melamium iodide structure is comprised of stacks of planar melamium ions that form complex, hydrogen‐bonded network layers with iodide ions within the layers. Both compounds were further characterized by FTIR spectroscopy, mass spectrometry, and elemental analyses. Melamium bromide and melamium iodide could be obtained as air stable and colorless crystals. Samples are crystallographically phase pure as shown by Rietveld refinement.     

The stuffed framework structure of SrP2N4: challenges to synthesis and crystal structure determination

SrP2N4 was obtained by high-pressure high-temperature synthesis utilizing the multianvil technique (5 GPa, 1400 degrees C) starting from mixtures of phosphorus(V) nitride and strontium azide. SrP2N4 turned out to be isotypic with BaGa(2)O(4) and is closely related to KGeAlO(4). The crystal structure (SrP2N4, a=17.1029(8), c=8.10318(5) A, space group P6(3) (no. 173), V=2052.70(2) A3, Z=24, R(F2)=0.0633) was solved from synchrotron powder diffraction data by applying a combination of direct methods, Patterson syntheses, and difference Fourier maps adding the unit cell information derived from electron diffraction and symmetry information obtained from 31P solid-state NMR spectroscopy. The structure of SrP2N4 was refined by the Rietveld method by utilizing both neutron and synchrotron X-ray powder diffraction data, and has been corroborated additionally by 31P solid-state NMR spectroscopy by employing through-bond connectivities and distance relations.     

Room Temperature Bulk Synthesis of Silver Nanocables Wrapped with Polypyrrole

Wet chemical synthesis of silver cables wrapped with polypyrrole is reported in aqueous media without use of any surfactant/capping agent and/or template. The method employs direct polymerization of pyrrole in an aqueous solution with AgNO₃ as an oxidizing agent. The four probe conductivity results for the as‐synthesized silver nanocables of polypyrrole films were found to be 3, 5, 5, and 9 S · cm⁻¹ for a 1: 2, 1: 1, 1: 0.5, and 1: 0.1 silver‐to‐pyrrole ratio, respectively. This approach can be extended to other monomers such as aniline and N‐methylaniline (NMA) to prepare different morphologies of silver nanostructures. Aniline monomer polymerization occurred at room temperature to produce a coating of a silver mirror on the side walls of the glass vial, as in the case of Tollen's process of making silver mirrors. The silver mirror coating strategy was extended to a poly(ethylene terephthalate) (PET) surface and the resistivity of the polyaniline‐coated Ag nanocomposites were measured and found to be semiconducting.

     

High Pressure Behavior of Mercury Cyanamide HgCN2

Using the diamond anvil cell technique, angle‐dispersive X‐ray diffraction and Raman spectroscopy were employed to study the high pressure behavior of mercury cyanamide. Its decomposition under pressure starts at 1.9 GPa and is not completed even up to 10 GPa. The decomposition product α‐Hg transforms to β‐Hg during 7–10 GPa, while the C/N residual is not detectable by X‐ray diffraction. The zero pressure bulk modulus of mercury cyanamide is estimated as 38.5 GPa.     

High‐Pressure Synthesis and Structural Investigation of H3P8O8N9: A New Phosphorus(V) Oxonitride Imide with an Interrupted Framework Structure

The first crystalline phosphorus oxonitride imide H₃P₈O₈N₉ (=P₈O₈N₆(NH)₃) has been synthesized under high‐pressure and high‐temperature conditions. To this end, a new, highly reactive phosphorus oxonitride imide precursor compound was prepared and treated at 12 GPa and 750 °C by using a multianvil assembly. H₃P₈O₈N₉ was obtained as a colorless, microcrystalline solid. The crystal structure of H₃P₈O₈N₉ was solved ab initio by powder X‐ray diffraction analysis, applying the charge‐flipping algorithm, and refined by the Rietveld method (C2/c (no. 15), a=1352.11(7), b=479.83(3), c=1820.42(9) pm, β=96.955(4)°, Z=4). H₃P₈O₈N₉ exhibits a highly condensed (κ=0.47), 3D, but interrupted network that is composed of all‐side vertex‐sharing (Q⁴) and only threefold‐linking (Q³) P(O,N)₄ tetrahedra in a Q⁴/Q³ ratio of 3:1. The structure, which includes 4‐ring assemblies as the smallest ring size, can be subdivided into alternating open‐branched zweier double layers {oB,${2{{2\hfill \atop \infty \hfill}}}$ }[²P₃(O,N)₇] and layers containing pairwise‐linked Q³ tetrahedra parallel (001). Information on the hydrogen atoms in H₃P₈O₈N₉ was obtained by 1D ¹H MAS, 2D homo‐ and heteronuclear (together with ³¹P) correlation NMR spectroscopy, and a ¹H spin‐diffusion experiment with a hard‐pulse sequence designed for selective excitation of a single peak. Two hydrogen sites with a multiplicity ratio of 2:1 were identified and thus the formula of H₃P₈O₈N₉ was unambiguously determined. The protons were assigned to Wyckoff positions 8f and 4e, the latter located within the Q³ tetrahedra layers.     

Synthesis,Structure, and Reactivity of RuII Complexes with Trimethylsilylethinylamidinate Ligands

The mononuclear amidinate complexes [(η⁶‐cymene)‐RuCl( 1a )] ( 2 ) and [(η⁶‐C₆H₆)RuCl( 1b )] ( 3 ), with the trimethylsilyl‐ethinylamidinate ligands [Me₃SiC≡CC(N‐c‐C₆H₁₁)₂]^– ( 1a^– ) and[Me₃SiC≡CC(N‐i‐C₃H₇)₂]^– ( 1b^– ) were synthesized in high yields by salt metathesis. In addition, the related phosphane complexes[(η⁵‐C₅H₅)Ru(PPh₃)( 1b )] ( 4a ) [(η⁵‐C₅Me₅)Ru(PPh₃)( 1b )] ( 4b ), and [(η⁶‐C₆H₆)Ru(PPh₃)( 1b )](BF₄) ( 5 ‐BF₄) were prepared by ligand exchange reactions. Investigations on the removal of the trimethyl‐silyl group using [Bu₄N]F resulted in the isolation of [(η⁶‐C₆H₆)Ru(PPh₃){(N‐i‐C₃H₇)₂CC≡CH}](BF₄) ( 6 ‐BF₄) bearing a terminal alkynyl hydrogen atom, while 2 and 3 revealed to yield intricate reaction mixtures. Compounds 1a / b to 6 ‐BF₄ were characterized by multinuclear NMR (¹H, ¹³C, ³¹P) and IR spectroscopy and elemental analyses, including X‐ray diffraction analysis of 1b , 2 , and 3 .     

Piezochromism in Nickel Salicylaldoximato Complexes: Tuning Crystal‐Field Splitting with High Pressure

The crystal structures of bis(3‐fluoro‐salicylaldoximato)nickel(II) and bis(3‐methoxy‐salicylaldoximato)nickel(II) have been determined at room temperature between ambient pressure and approximately 6 GPa. The principal effect of pressure is to reduce intermolecular contact distances. In the fluoro system molecules are stacked, and the Ni???Ni distance decreases from 3.19 Å at ambient pressure to 2.82 Å at 5.4 GPa. These data are similar to those observed in bis(dimethylglyoximato)nickel(II) over a similar pressure range, though contrary to that system, and in spite of their structural similarity, the salicyloximato does not become conducting at high pressure. Ni–ligand distances also shorten, on average by 0.017 and 0.011 Å for the fluoro and methoxy complexes, respectively. Bond compression is small if the bond in question is directed towards an interstitial void. A band at 620 nm, which occurs in the visible spectrum of each derivative, can be assigned to a transition to an antibonding molecular orbital based on the metal 3d(x²?y²) orbital. Time‐dependent density functional theory calculations show that the energy of this orbital is sensitive to pressure, increasing in energy as the Ni–ligand distances are compressed, and consequently increasing the energy of the transition. The resulting blueshift of the UV‐visible band leads to piezochromism, and crystals of both complexes, which are green at ambient pressure, become red at 5 GPa.     

Cobaltocenium Carboxylate Transition Metal Complexes: Synthesis,Structure, Reactivity,and Cytotoxicity

Cobaltocenium carboxylate is an unusual betaine that functions as a formally neutral carboxylate ligand with late transition metal centers comprising Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Rh⁺. Structurally, a rich coordination chemistry is observed – from simple monomeric homoleptic complexes to heteroleptic dimeric, trimeric, and polymeric compounds, as shown by X‐ray diffraction of 11 compounds. Chemically, thermal decarboxylation was investigated aiming at the formation of cobaltocenium‐carbene transition metal complexes, in analogy to such chemistry of imidazolium carboxylate betaines. Cytotoxicity studies of cobaltocenium carboxylate transition metal complexes were performed to evaluate the medicinal bioorganometallic potential of these compounds. While cobaltocenium carboxylate was inactive, its complexes with Ag⁺, Cd²⁺, and Hg²⁺ triggered significant cytotoxic effects.     

Synthesis,Crystal Structure,Bonding, and Properties of (Ba6O)(OsN3)2

The new barium nitridoosmate oxide (Ba₆O)(OsN₃)₂ was prepared by reacting elemental barium and osmium (3:1) in nitrogen at 815–830 °C. The crystal structure of (Ba₆O)(OsN₃)₂ as determined by laboratory powder X‐ray diffraction ( , No 148: a=b=8.112(1) Å, c=17.390(1) Å, V=991.0(1) ų, Z=3), consists of sheets of trigonal OsN₃ units and trigonal‐antiprismatic Ba₆O groups, and is structurally related to the “313 nitrides” AE₃MN₃ (AE=Ca, Sr, Ba, M=V–Co, Ga). Density functional calculations, using a hybrid functional, likewise indicate the existence of oxygen in the Ba₆ polyhedra. The oxidation state 4+ of osmium is confirmed, both by the calculations and by XPS measurements. The bonding properties of the OsN₃^5? units are analyzed and compared to the Raman spectrum. The compound is paramagnetic from room temperature down to T=10 K. Between room temperature and 100 K it obeys the Curie–Weiss law (μ=1.68 μ_B). (Ba₆O)(OsN₃)₂ is semiconducting with a good electronic conductivity at room temperature (8.74×10^?2 Ω^?1 cm^?1). Below 142 K the temperature dependence of the conductivity resembles that of a variable‐range hopping mechanism.     

High‐Pressure Synthesis,Crystal Structure,and Properties of GdS2 with Thermodynamic Investigations in the Phase Diagram Gd–S

Gadolinium disulfide was prepared by high‐pressure synthesis at 8 GPa and 1173 K. It crystallizes in the monoclinic space group P12₁/a1 (No. 14) with lattice parameters a = 7.879(1) Å; b = 3.936(1) Å, c = 7.926(1) Å and β = 90.08(1)°. The crystal structure is a twofold superstructure of the aristotype ZrSSi and consists of puckered cationic [GdS]⁺ double slabs that are sandwiched by planar sulfur sheets containing S₂^2– dumbbells. The thermal decomposition of GdS₂ proceeds via the sulfur‐deficient polysulfides GdS_1.9, GdS_1.85 and GdS_1.77 and eventually results in the sesquisulfide Gd₂S₃. GdS₂ is a paramagnetic semiconductor which orders antiferromagnetically at T_N = 7.7(1) K. A metamagnetic transition is observed in the magnetically ordered state.     

Influence of Tourmaline on Negative Air Ion Emitting Property of Poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) fibers containing 2 wt% tourmaline powder were found to emit an average 5100 particles/cc negative air ions under frictional conditions, much higher than that of pure poly(ethylene terephthalate) fibers which emitted an average 200 particles/cc negative air ions, but the emitted negative air ions were reduced to 4400 particles/cc when poly(ethylene terephthalate) fibers contained 4 wt% tourmaline powder. In order to understand the influence of tourmaline powder on the negative air ion emitting property of the poly(ethylene terephthalate) fibers, scanning electron microscopy (SEM) morphology, energy dispersive X‐rays (EDX) and wide angle X‐ray diffraction (WAXD) analysis of the PET/tourmaline fiber specimens were performed. Possible reasons are proposed to account for the interesting negative air ion emitting property of the PET/tourmaline fiber specimens. Aggregates of tourmaline powder occurred in the PET matrix, which caused a reduction of the breaking tenacity of the PET/tourmaline fibers.     

Synthesis of stable silicon heterocycles by reaction of organic substrates with a chlorosilylene [PhC(NtBu)2SiCl

Heteroleptic chlorosilylene (PhC(NtBu)(2)SiCl) (1) reacts with unsaturated organic compounds under oxidative addition. Reactions of 1 with cyclooctatetraene (COT) and a diimine afford [1+4]-cycloaddition products 3 and 6, respectively. In the case of COT, one Si-N bond of the amidinato ligand is cleaved, resulting in tetracoordinate silicon, whereas with a diimine a pentacoordinate silicon is formed. Treatment of 1 with ArN=C=NAr (Ar=2,6-iPr(2)C(6)H(3)) yields silaimine complex 4 with cleavage of one of the C=N bonds. The facile isolation of silaimine complexes is probably due to the kinetic protection afforded by the bulky Ar moiety. When 1 is treated with tert-butyl isocyanate, cleavage of the C=O bond is observed, which leads to formation of the four-membered Si(2)O(2) cycle 5. The same product is formed when 1 is allowed to react with trimethylamine N-oxide. When 1 is treated with diphenyl disulfide, cleavage of the S-S bond occurs to form 7. All products have been characterized by multinuclear NMR spectroscopy, EI mass spectrometry, and elemental analysis. In addition, the molecular structures of 3-6 have been determined by single-crystal X-ray diffraction studies. Collectively, these results suggest that owing to the presence of the lone pair of electrons, the propensity of 1 to undergo oxidative addition is very high.     

A New Ammine Dual‐Cation (Li,Mg) Borohydride: Synthesis,Structure, and Dehydrogenation Enhancement

A new ammine dual‐cation borohydride, LiMg(BH₄)₃(NH₃)₂, has been successfully synthesized simply by ball‐milling of Mg(BH₄)₂ and LiBH₄ ? NH₃. Structure analysis of the synthesized LiMg(BH₄)₃(NH₃)₂ revealed that it crystallized in the space group P6₃ (no. 173) with lattice parameters of a=b=8.0002(1) Å, c=8.4276(1) Å, α=β=90°, and γ=120° at 50 °C. A three‐dimensional architecture is built up through corner‐connecting BH₄ units. Strong N? H???H? B dihydrogen bonds exist between the NH₃ and BH₄ units, enabling LiMg(BH₄)₃(NH₃)₂ to undergo dehydrogenation at a much lower temperature. Dehydrogenation studies have revealed that the LiMg(BH₄)₃(NH₃)₂/LiBH₄ composite is able to release over 8 wt % hydrogen below 200 °C, which is comparable to that released by Mg(BH₄)₃(NH₃)₂. More importantly, it was found that release of the byproduct NH₃ in this system can be completely suppressed by adjusting the ratio of Mg(BH₄)₂ and LiBH₄ ? NH₃. This chemical control route highlights a potential method for modifying the dehydrogenation properties of other ammine borohydride systems.     

Synthesis,Structures and Reactivity of Lanthanoid(II) Formamidinates of Varying Steric Bulk

New reactive, divalent lanthanoid formamidinates [Yb(Form)₂(thf)₂] (Form=[RNCHNR]; R=o‐MeC₆H₄ (o‐TolForm; 1 ), 2,6‐Me₂C₆H₃ (XylForm; 2 ), 2,4,6‐Me₃C₆H₂ (MesForm; 3 ), 2,6‐Et₂C₆H₃ (EtForm; 4 ), o‐PhC₆H₄ (o‐PhPhForm; 5 ), 2,6‐iPr₂C₆H₃ (DippForm; 6 ), o‐HC₆F₄ (TFForm; 7 )) and [Eu(DippForm)₂(thf)₂] ( 8 ) have been prepared by redox transmetallation/protolysis reactions between an excess of a lanthanoid metal, Hg(C₆F₅)₂ and the corresponding formamidine (HForm). X‐ray crystal structures of 2 – 6 and 8 show them to be monomeric with six‐coordinate lanthanoid atoms, chelating N,N′‐Form ligands and cis‐thf donors. However, [Yb(TFForm)₂(thf)₂] ( 7 ) crystallizes from THF as [Yb(TFForm)₂(thf)₃] ( 7 a ), in which ytterbium is seven coordinate and the thf ligands are “pseudo‐meridional”. Representative complexes undergo C? X (X=F, Cl, Br) activation reactions with perfluorodecalin, hexachloroethane or 1,2‐dichloroethane, and 1‐bromo‐2,3,4,5‐tetrafluorobenzene, giving [Yb(EtForm)₂F]₂ ( 9) , [Yb(o‐PhPhForm)₂F]₂ ( 10) , [Yb(o‐PhPhForm)₂Cl(thf)₂] ( 11) , [Yb(DippForm)₂Cl(thf)] ( 12) and [Yb(DippForm)₂Br(thf)] ( 16) . X‐ray crystallography has shown 9 to be a six‐coordinate, fluoride‐bridged dimer, 12 and 16 to be six‐coordinate monomers with the halide and thf ligands cis to each other, and 11 to have a seven‐coordinate Yb atom with “pseudo‐meridional” unidentate ligands and thf donors cis to each other. The analogous terbium compound [Tb(DippForm)₂Cl(thf)₂] ( 13 ), prepared by metathesis, has a similar structure to 11 . C? Br activation also accompanies the redox transmetallation/protolysis reactions between La, Nd or Yb metals, Hg(2‐BrC₆F₄)₂, and HDippForm, yielding [Ln(DippForm)₂Br(thf)] complexes (Ln=La ( 14 ), Nd ( 15 ), Yb ( 16 )).