Understanding the adsorption process in ZIF-8 using high pressure crystallography and computational modelling.

Some porous crystalline solids change their structure upon guest inclusion. Unlocking the potential of these solids for a wide variety of applications requires full characterisation of the response to adsorption and the underlying framework-guest interactions. Here, we introduce an approach to understanding gas uptake in porous metal-organic frameworks (MOFs) by loading liquefied gases at GPa pressures inside the Zn-based framework ZIF-8. An integrated experimental and computational study using high-pressure crystallography, grand canonical Monte Carlo (GCMC) and periodic DFT simulations has revealed six symmetry-independent adsorption sites within the framework and a transition to a high-pressure phase. The cryogenic high-pressure loading method offers a different approach to obtaining atomistic detail on guest molecules. The GCMC simulations provide information on interaction energies of the adsorption sites allowing to classify the sites by energy. DFT calculations reveal the energy barrier of the transition to the high-pressure phase. This combination of techniques provides a holistic approach to understanding both structural and energetic changes upon adsorption in MOFs.

Probing the origin of the giant magnetic anisotropy in trigonal bipyramidal Ni(ii) under high pressure.

Understanding and controlling magnetic anisotropy at the level of a single metal ion is vital if the miniaturisation of data storage is to continue to evolve into transformative technologies. Magnetic anisotropy is essential for a molecule-based magnetic memory as it pins the magnetic moment of a metal ion along the easy axis. Devices will require deposition of magnetic molecules on surfaces, where changes in molecular structure can significantly alter magnetic properties. Furthermore, if we are to use coordination complexes with high magnetic anisotropy as building blocks for larger systems we need to know how magnetic anisotropy is affected by structural distortions. Here we study a trigonal bipyramidal nickel(ii) complex where a giant magnetic anisotropy of several hundred wavenumbers can be engineered. By using high pressure, we show how the magnetic anisotropy is strongly influenced by small structural distortions. Using a combination of high pressure X-ray diffraction, ab initio methods and high pressure magnetic measurements, we find that hydrostatic pressure lowers both the trigonal symmetry and axial anisotropy, while increasing the rhombic anisotropy. The ligand-metal-ligand angles in the equatorial plane are found to play a crucial role in tuning the energy separation between the d x2-y2 and d xy orbitals, which is the determining factor that controls the magnitude of the axial anisotropy. These results demonstrate that the combination of high pressure techniques with ab initio studies is a powerful tool that gives a unique insight into the design of systems that show giant magnetic anisotropy.

Pressure induced enhancement of the magnetic ordering temperature in rhenium(IV) monomers.

Materials that demonstrate long-range magnetic order are synonymous with information storage and the electronics industry, with the phenomenon commonly associated with metals, metal alloys or metal oxides and sulfides. A lesser known family of magnetically ordered complexes are the monometallic compounds of highly anisotropic d-block transition metals; the 'transformation' from isolated zero-dimensional molecule to ordered, spin-canted, three-dimensional lattice being the result of through-space interactions arising from the combination of large magnetic anisotropy and spin-delocalization from metal to ligand which induces important intermolecular contacts. Here we report the effect of pressure on two such mononuclear rhenium(IV) compounds that exhibit long-range magnetic order under ambient conditions via a spin canting mechanism, with Tc controlled by the strength of the intermolecular interactions. As these are determined by intermolecular distance, 'squeezing' the molecules closer together generates remarkable enhancements in ordering temperatures, with a linear dependence of Tc with pressure.

Aminophobanes: hydrolytic stability, tautomerism and application in Cr-catalysed ethene oligomerisation.

9-Amino-9-phosphabicyclo[3.3.1]nonanes, (PhobPNHR'; R = Me or (i)Pr) are readily prepared by aminolysis of PhobPCl and are significantly less susceptible to hydrolysis than the acyclic analogues Cy2PNHR'. Treatment of Cy2PNHMe with Cy2PCl readily gave Cy2PNMePCy2. By contrast, treatment of PhobPCl with PhobPNHMe in the presence of Et3N does not afford PhobPNMePPhob but instead the salt [PhobP(= NMeH)PPhob]Cl is formed which, upon addition of [PtCl2(NC(t)Bu)2] gives the zwitterionic complex [PtCl3(PhobP(= NMeH)PPhob)]. The neutral PhobP(= NMe)PPhob is accessible from PhobNMeLi and is converted to the chelate [PdCl2(PhobPNMePPhob)] by addition of [PdCl2(cod)]. The anomalous preference of the PhobP group for the formation of PPN products is discussed. The unsymmetrical diphos ligands PhobPNMePAr2 (Ar = Ph, o-Tol) are prepared, converted to [Cr(CO)4(PhobPNMePAr2)] and shown to form Cr-catalysts for ethene oligomerisation, producing a pattern of higher alkenes that corresponds to a Schulz-Flory distribution overlaid on selective tri/tetramerisation.

Observation of a re-entrant phase transition in the molecular complex tris(µ2-3,5-diiso-propyl-1,2,4-triazolato-κ2N1:N2)trigold(I) under high pressure.

We report a molecular crystal that exhibits four successive phase transitions under hydro-static pressure, driven by aurophilic interactions, with the ground-state structure re-emerging at high pressure. The effect of pressure on two polytypes of tris(µ2-3,5-diiso-propyl-1,2,4-triazolato-κ2N1:N2)trigold(I) (denoted Form-I and Form-II) has been analysed using luminescence spectroscopy, single-crystal X-ray diffraction and first-principles computation. A unique phase behaviour was observed in Form-I, with a complex sequence of phase transitions between 1 and 3.5 GPa. The ambient C2/c mother cell transforms to a P21/n phase above 1 GPa, followed by a P21/a phase above 2 GPa and a large-volume C2/c supercell at 2.70 GPa, with the previously observed P21/n phase then reappearing at higher pressure. The observation of crystallographically identical low- and high-pressure P21/n phases makes this a rare example of a re-entrant phase transformation. The phase behaviour has been characterized using detailed crystallographic theory and modelling, and rationalized in terms of molecular structural distortions. The dramatic changes in conformation are correlated with shifts of the luminescence maxima, from a band maximum at 14040 cm-1 at 2.40 GPa, decreasing steeply to 13550 cm-1 at 3 GPa. A similar study of Form-II displays more conventional crystallographic behaviour, indicating that the complex behaviour observed in Form-I is likely to be a direct consequence of the differences in crystal packing between the two polytypes.

B-Methylated Amine-Boranes: Substituent Redistribution, Catalytic Dehydrogenation, and Facile Metal-Free Hydrogen Transfer Reactions.

Although the dehydrogenation chemistry of amine-boranes substituted at nitrogen has attracted considerable attention, much less is known about the reactivity of their B-substituted analogues. When the B-methylated amine-borane adducts, RR'NH·BH2Me (1a: R = R' = H; 1b: R = Me, R' = H; 1c: R = R' = Me; 1d: R = R' = iPr), were heated to 70 °C in solution (THF or toluene), redistribution reactions were observed involving the apparent scrambling of the methyl and hydrogen substituents on boron to afford a mixture of the species RR'NH·BH3-xMex (x = 0-3). These reactions were postulated to arise via amine-borane dissociation followed by the reversible formation of diborane intermediates and adduct reformation. Dehydrocoupling of 1a-1d with Rh(I), Ir(III), and Ni(0) precatalysts in THF at 20 °C resulted in an array of products, including aminoborane RR'N═BHMe, cyclic diborazane [RR'N-BHMe]2, and borazine [RN-BMe]3 based on analysis by in situ (11)B NMR spectroscopy, with peak assignments further supported by density functional theory (DFT) calculations. Significantly, very rapid, metal-free hydrogen transfer between 1a and the monomeric aminoborane, iPr2N═BH2, to yield iPr2NH·BH3 (together with dehydrogenation products derived from 1a) was complete within only 10 min at 20 °C in THF, substantially faster than for the N-substituted analogue MeNH2·BH3. DFT calculations revealed that the hydrogen transfer proceeded via a concerted mechanism through a cyclic six-membered transition state analogous to that previously reported for the reaction of the N-dimethyl species Me2NH·BH3 and iPr2N═BH2. However, as a result of the presence of an electron donating methyl substituent on boron rather than on nitrogen, the process was more thermodynamically favorable and the activation energy barrier was reduced.

A high-pressure crystallographic and magnetic study of Na5[Mn(l-tart)2]·12H2O (l-tart = l-tartrate).

The crystal structure and magnetic properties of the compound Na5[Mn(l-tart)2]·12H2O (1, l-tart = l-tartrate) have been investigated over the pressure range 0.34-3.49 GPa. The bulk modulus of 1 has been determined as 23.9(6) GPa, with a compression of the coordination spheres around the Na(+) ions observed. 1 is therefore relatively incompressible, helping it to retain its magnetic anisotropy under pressure.

Locating Gases in Porous Materials: Cryogenic Loading of Fuel-Related Gases Into a Sc-based Metal-Organic Framework under Extreme Pressures.

An alternative approach to loading metal organic frameworks with gas molecules at high (kbar) pressures is reported. The technique, which uses liquefied gases as pressure transmitting media within a diamond anvil cell along with a single-crystal of a porous metal-organic framework, is demonstrated to have considerable advantages over other gas-loading methods when investigating host-guest interactions. Specifically, loading the metal-organic framework Sc2BDC3 with liquefied CO2 at 2 kbar reveals the presence of three adsorption sites, one previously unreported, and resolves previous inconsistencies between structural data and adsorption isotherms. A further study with supercritical CH4 at 3-25 kbar demonstrates hyperfilling of the Sc2 BDC3 and two high-pressure displacive and reversible phase transitions are induced as the filled MOF adapts to reduce the volume of the system.

Tunable trimers: using temperature and pressure to control luminescent emission in gold(I) pyrazolate-based trimers.

A systematic investigation into the relationship between the solid-state luminescence and the intermolecular Au⋅⋅⋅Au interactions in a series of pyrazolate-based gold(I) trimers; tris(µ2 -pyrazolato-N,N')-tri-gold(I) (1), tris(µ2 -3,4,5- trimethylpyrazolato-N,N')-tri-gold(I) (2), tris(µ2 -3-methyl-5-phenylpyrazolato-N,N')-tri-gold(I) (3) and tris(µ2 -3,5-diphenylpyrazolato-N,N')-tri-gold(I) (4) has been carried out using variable temperature and high pressure X-ray crystallography, solid-state emission spectroscopy, Raman spectroscopy and computational techniques. Single-crystal X-ray studies show that there is a significant reduction in the intertrimer Au⋅⋅⋅Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular Au⋅⋅⋅Au contacts of between 0.04 and 0.08 Å. The solid-state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red-shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Au⋅⋅⋅Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm(-1) per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in Au⋅⋅⋅Au distance observed by diffraction.

Generation of aminoborane monomers RR'N=BH2 from amine-boronium cations [RR'NH-BH2L](+): metal catalyst-free formation of polyaminoboranes at ambient temperature.

Protonation of MeRNH·BH3 (R = Me or H) with HX (X = B(C6F5)4, OTf, or Cl), followed by immediate, spontaneous H2 elimination, yielded the amine-boronium cation salt [MeRNH·BH2(OEt2)][B(C6F5)4] and related polar covalent analogs, MeRNH·BH2X (X = OTf or Cl). These species can be deprotonated to conveniently generate reactive aminoborane monomers MeRN=BH2 which oligomerize or polymerize; in the case of MeNH2·BH3, the two step process gave poly(N-methylaminoborane), [MeNH-BH2]n.

New di-ferrocenyl-ethynylpyridinyl triphenylphosphine copper halide complexes and related di-ferricenyl electro-crystallized materials.

Three new neutral di-ferrocenyl-ethynylpyridinyl copper complexes, [L2(CuCl)2(PPh3)2] (), [L2(CuBr)2(PPh3)2] (), and [L2(CuI)2(PPh3)2] () were synthesized from the ferrocenyl-ethynylpyridine ligand (L) (), the appropriate copper halide CuX (with X = Cl(-), Br(-), I(-)) and triphenylphosphine. These neutral complexes were fully characterized by spectroscopic methods and by single crystal X-ray crystallography. Cyclic voltammetry in dichloroethane revealed chemically reversible ferrocenyl oxidation signals followed by characteristic "stripping reduction peaks" showing evidence for oxidation-product electro-crystallization. Scanning electron microscopy confirmed spontaneous formation of crystalline oxidation products with three distinct morphologies for X = Cl(-), Br(-), I(-). Energy dispersive X-ray elemental analysis data show Fe : P ratios of 1 : 2.0, 1 : 2.1 and 1 : 2.1 for electro-crystallization products of complexes , , and , respectively, indicating the presence of two [PF6](-) anions in the vicinity of the dioxidized complexes, and suggesting product formulae [](2+)[PF6](-)2, [](2+)[PF6](-)2 and [](2+)[PF6](-)2.

Solid-state interconversions: unique 100 % reversible transformations between the ground and metastable states in single-crystals of a series of nickel(II) nitro complexes.

The solid-state, low-temperature linkage isomerism in a series of five square planar group 10 phosphino nitro complexes have been investigated by a combination of photocrystallographic experiments, Raman spectroscopy and computer modelling. The factors influencing the reversible solid-state interconversion between the nitro and nitrito structural isomers have also been investigated, providing insight into the dynamics of this process. The cis-[Ni(dcpe)(NO2)2] (1) and cis-[Ni(dppe)(NO2)2] (2) complexes show reversible 100 % interconversion between the η(1)-NO2 nitro isomer and the η(1)-ONO nitrito form when single-crystals are irradiated with 400 nm light at 100 K. Variable temperature photocrystallographic studies for these complexes established that the metastable nitrito isomer reverted to the ground-state nitro isomer at temperatures above 180 K. By comparison, the related trans complex [Ni(PCy3)2(NO2)2] (3) showed 82 % conversion under the same experimental conditions at 100 K. The level of conversion to the metastable nitrito isomers is further reduced when the nickel centre is replaced by palladium or platinum. Prolonged irradiation of the trans-[Pd(PCy3)2(NO2)2] (4) and trans-[Pt(PCy3)2(NO2)2] (5) with 400 nm light gives reversible conversions of 44 and 27 %, respectively, consistent with the slower kinetics associated with the heavier members of group 10. The mechanism of the interconversion has been investigated by theoretical calculations based on the model complex [Ni(dmpe)Cl(NO2)].

Steady-state and pseudo-steady-state photocrystallographic studies on linkage isomers of [Ni(Et4dien)(η2-O,ON)(η1-NO2)]: identification of a new linkage isomer.

At temperatures below 150 K, the photoactivated metastable endo-nitrito linkage isomer [Ni(Et4 dien)(η(2)-O,ON)(η(1)-ONO)] (Et4 dien=N,N,N',N'-tetraethyldiethylenetriamine) can be generated with 100 % conversion from the ground state nitro-(η(1)-NO2) isomer on irradiation with 500 nm light, in the single crystal by steady-state photocrystallographic techniques. Kinetic studies show the system is no longer metastable above 150 K, decaying back to the ground state nitro-(η(1)-NO2) arrangement over several hours at 150 K. Variable-temperature kinetic measurements in the range of 150-160 K show that the rate of endo-nitrito decay is highly dependent on temperature, and an activation energy of Eact =+48.6(4) kJ mol(-1) is calculated for the decay process. Pseudo-steady-state experiments, where the crystal is continually pumped by the light source for the duration of the X-ray experiment, show the production of a previously unobserved, exo-nitrito-(η(1)-ONO) linkage isomer only at temperatures close to the metastable limit (ca. 140-190 K). This exo isomer is considered to be a transient excited-state species, as it is only observed in data collected by pseudo-steady-state methods.

TMEDA in iron-catalyzed Kumada coupling: amine adduct versus homoleptic "ate" complex formation.

The reactions of iron chlorides with mesityl Grignard reagents and tetramethylethylenediamine (TMEDA) under catalytically relevant conditions tend to yield the homoleptic "ate" complex [Fe(mes)3 ](-) (mes=mesityl) rather than adducts of the diamine, and it is this ate complex that accounts for the catalytic activity. Both [Fe(mes)3 ](-) and the related complex [Fe(Bn)3 ](-) (Bn=benzyl) react faster with representative electrophiles than the equivalent neutral [FeR2 (TMEDA)] complexes. Fe(I) species are observed under catalytically relevant conditions with both benzyl and smaller aryl Grignard reagents. The X-ray structures of [Fe(Bn)3 ](-) and [Fe(Bn)4 ](-) were determined; [Fe(Bn)4 ](-) is the first homoleptic σ-hydrocarbyl Fe(III) complex that has been structurally characterized.

New multi-ferrocenyl- and multi-ferricenyl- materials via coordination-driven self-assembly and via charge-driven electro-crystallization.

Three new tetra-ferrocenylethynylpyridinyl copper complexes, L4(CuI)4 (3), L4(CuBr)2 (4), and L4(CuCl)2 (5) have been prepared from the reaction of ferrocenylethynylpyridine (L)(2) with copper halides CuX (with X = I(-), Br(-), Cl(-)).The ligand 2 and the complexes 3-5 have been fully characterized by spectroscopic methods. The structures of 2-4 have been confirmed by single-crystal X-ray crystallography. 2 forms a dimer in the crystalline-state through C-H··N hydrogen bonds. 4 and 5 are dimers and 3 a tetramer, in all cases linked through Cu-X··Cu bridging interactions. Cyclic voltammetry in dichloroethane showed chemically reversible multiferrocenyl oxidation signals with evidence for product electro-crystallization. The oxidation products were isolated by electrodeposition onto a Pt disc electrode and investigated by scanning electron microscopy which confirmed the spontaneous formation of crystalline oxidation products with distinctive morphologies. Energy dispersive X-ray elemental analysis shows the presence of hexafluorophosphate (counterion) with the P:Fe ratio of 1:1, 0.5:1, and 1:1 for the electrocrystallized products 3, 4, and 5, respectively, suggesting the formulas [3](4+)(PF6(-))4, [4](2+)(PF6(-))2, and [5](4+)(PF6(-))4 for the electro-crystallized products.

Polyaminoborane main chain scission using N-heterocyclic carbenes; formation of donor-stabilised monomeric aminoboranes.

The reaction of N-heterocyclic carbenes with polyaminoboranes [MeNH-BH2]n or [NH2-BH2]n at 20 °C led to depolymerisation and the formation of labile, monomeric aminoborane-NHC adducts, RNH-BH2-NHC (R = Me or H); a similar NHC adduct of Ph2N=BCl2 was characterized by single crystal X-ray diffraction.

Long-range intramolecular electronic communication in bis(ferrocenylethynyl) complexes incorporating conjugated heterocyclic spacers: synthesis, crystallography, and electrochemistry.

A new series of bis(ferrocenylethynyl) complexes, 3-7, and a mono(ferrocenylethynyl) complex, 8, have been synthesized incorporating conjugated heterocyclic spacer groups, with the ethynyl group facilitating an effective long-range intramolecular interaction. The complexes were characterized by NMR, IR, and UV-vis spectroscopy as well as X-ray crystallography. The redox properties of these complexes were investigated using cyclic voltammetry and spectroelectrochemistry. Although there is a large separation of ∼14 Å between the two redox centers, ΔE(1/2) values in this series of complexes ranged from 50 to 110 mV. The appearance of intervalance charge-transfer bands in the UV-vis-near-IR region for the monocationic complexes further confirmed effective intramolecular electronic communication. Computational studies are presented that show the degree of delocalization across the Fc-C≡C-C≡C-Fc (Fc = C5H5FeC5H4) highest occupied molecular orbital.

Photoactivated linkage isomerism in single crystals of nickel, palladium and platinum di-nitro complexes--a photocrystallographic investigation.

Low temperature, single crystal photocrystallographic studies have been carried out on four square planar Group 10 complexes [Ni(PEt(3))(2)(NO(2))(2)] 1, [Pd(PPh(3))(2)(NO(2))(2)] 2, [Pd(AsPh(3))(2)(NO(2))(2)] 3 and [Pt(PPh(3))(2)(NO(2))(2)] 4, in which the two nitro groups adopt the trans configuration. Irradiation with UV light, at 100 K, of single crystals of complexes 1-3 photoisomerise from the η(1)-NO(2) nitro form to the η(1)-ONO nitrito form occurred. Complex 1 underwent 25% conversion to the nitrito form before crystal decomposition occurred. 2 and 3 underwent 46% and 39% conversion, respectively, to the nitrito form when a photostationary state was reached. While under the same experimental conditions 4 showed no isomerisation. The photocrystallographic results can be correlated with the results of DFT calculations and with the observed trends in the solution UV/visible absorption spectroscopy obtained for these complexes. The results suggest that while steric factors in the isomerization processes are important there may also be a kinetic effect relating to the lability of the metal involved.