A crystallographic and solid state spectroscopic study of the spin crossover behaviour of [Fe(abpt)2(NCS)2] (abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) polymorph A is reported. Structural features including crystallographic cell parameters, bond lengths and distortion parameters are monitored between 375 K and 30 K and crystal structures are reported at seven temperatures across the spin transition. In addition, the light induced excited spin state trapping (LIESST) metastable high spin structure, HS*, is reported at 30 K by continuous irradiation with a 670 nm, 5 mW CW laser during the data collection. Relaxation of the HS* state at 30 K with the laser switched off is found to occur within ∼4000 s in accordance with the literature. High pressure single crystal datasets are also reported to examine the effect of pressure on the spin transition. Single crystal variable temperature UV-Vis spectroscopy and resonant ultrasound spectroscopy support the crystallographic evidence relating to the spin crossover transition presented herein. Strain analysis of the lattice parameters yields the temperature dependence of the spin order parameter, indicating strong spin–lattice coupling to give a volume strain of up to ∼4% and a shear strain of up to ∼1.5%. These, in turn, are responsible for changes in elastic constants by up to ∼35%.

A number of hydrogen-bonded co-crystals, consisting of a cinnamic acid derivative and a pyridyl co-crystallizer, have been synthesized and their properties investigated by X-ray diffraction. Samples were prepared by recrystallization or solvent drop grinding of trans-cinnamic acid (1), 4-methylcinnamic acid (2), 4-methoxy cinnamic acid (3) or 3,4-methoxy cinnamic acid (4), with 4,4-dipyridyl (A), iso-nicotinamide (B) or nicotinamide (C). The X-ray single-crystal structures of seven novel co-crystals, obtained through recrystallization, are examined and the hydrogen-bonding interactions discussed. Consistent hydrogen-bonding motifs were observed for samples prepared when using 4,4-dipyridyl (A) or iso-nicotinamide (B) as the co-crystallizing agent. Powder X-ray diffraction analysis of the samples prepared by solvent drop grinding suggests the formation of ten co-crystals.

Halide abstraction from the ruthenium N-heterocyclic carbene complex Ru(IPr)2(CO)HCl (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with NaBAr4F (BAr4F = B{C6H3(3,5-CF3)2}4) gave the salt [Ru(IPr)2(CO)H]BAr4F (2), which was shown through a combined X-ray/neutron structure refinement and quantum theory of atoms in molecules (QTAIM) study to contain a bifurcated Ru···η3-H2C ξ-agostic interaction involving one iPr substituent of the IPr ligand. This system complements the previously reported [Ru(IMes)2(CO)H]+ cation (IMes =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), where a non-agostic form is favored. Treatment of 2 with CO, H2, and the amine–boranes H3B·NR2H (R = Me, H) gave [Ru(IPr)2(CO)3H]BAr4F (3), [Ru(IPr)2(CO)(η2-H2)H]BAr4F (4), and [Ru(IPr)2(CO)(κ2-H2BH·NR2H)H]BAr4F (R = Me, 5; R = H, 6), respectively. Heating 5 in the presence of Me3SiCH═CH2 led to alkene hydroboration and formation of the C–H activated product [Ru(IPr)(IPr)′(CO)]BAr4F (7). X-ray characterization of 3 and 5–7 was complemented by DFT calculations, and the mechanism of H2/H exchange in 4 was also elucidated. Treatment of 2 with HBcat resulted in Ru–H abstraction to form the boryl complex [Ru(IPr)2(CO)(Bcat)] BAr4F (8), which proved to be competent in the catalytic hydroboration of 1-hexene. In 8, a combined X-ray/neutron structure refinement and QTAIM analysis suggested the presence of a single Ru···η2-HC ξ-agostic interaction.