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.

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.

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.

Selective, robust and cost-effective chemical sensors for detecting small volatile-organic compounds (VOCs) have widespread applications in industry, healthcare and environmental monitoring. Here we design a Pt(II) pincer-type material with selective absorptive and emissive responses to methanol and water. The yellow anhydrous form converts reversibly on a subsecond timescale to a red hydrate in the presence of parts-per-thousand levels of atmospheric water vapour. Exposure to methanol induces a similarly-rapid and reversible colour change to a blue methanol solvate. Stable smart coatings on glass demonstrate robust switching over 104 cycles, and flexible microporous polymer membranes incorporating microcrystals of the complex show identical vapochromic behaviour. The rapid vapochromic response can be rationalised from the crystal structure, and in combination with quantum-chemical modelling, we provide a complete microscopic picture of the switching mechanism. We discuss how this multiscale design approach can be used to obtain new compounds with tailored VOC selectivity and spectral responses.

Photocrystallography is a rapidly developing technique that enables the full three-dimensional structure of a molecule in a metastable or excited state to be elucidated when a single crystal of the complex is photoactivated by visible or UV light.[1] Pioneering work in the areas of both molecular and macromolecular photocrystallography has allowed the crystallographic characterization of species with microsecond and sub-microsecond lifetimes. [2, 3] Of equal importance are the detailed studies on the identification and stabilization of metastable species [4,5] because of potential photorefractive applications, including data storage and optical switching. [6] This area has been pioneered by Coppens et al., and they, and others, have now successfully determined the structures of a number of metastable species including several transitionmetal-nitrosyl, -nitro, and -SO 2 complexes. [7][8][9] A major limitation in the study of these systems has been the relatively low level of conversion from the ground state to the metastable state that can be achieved in the single crystal. Controlled, complete reversible interconversion is desirable if these materials are to find real applications as optical switches or in data-storage devices. Examples of high conversions into metastable species are rare; however, notable studies include the first example of a reversible 100 % conversion of the nickel(II)-nitro complex [Ni(dppe)(h 1 -NO 2 )Cl] (dppe = 1,2-bis(diphenylphosphino)ethane) into the nitrito isomer [Ni-(dppe)(h 1 -ONO)Cl] when irradiated with UV light-emitting diodes (LEDs) [10] at temperatures below 160 K. A 92 % lightinduced conversion from the h 1 -NO isomer to the h 1 -ON