Advanced crystallisation methods for small organic molecules.

Molecular materials based on small organic molecules often require advanced structural analysis, beyond the capability of spectroscopic techniques, to fully characterise them. In such cases, diffraction methods such as single crystal X-ray diffraction (SCXRD), are one of the most powerful tools available to researchers, providing molecular and structural elucidation at atomic level resolution, including absolute stereochemistry. However SCXRD, and related diffraction methods, are heavily dependent on the availability of suitable, high-quality crystals, thus crystallisation often becomes the major bottleneck in preparing samples. Following a summary of classical methods for the crystallisation of small organic molecules, this review will focus on a number of recently developed advanced methods for crystalline material sample preparation for SCXRD. This review will cover two main areas of modern small organic molecule crystallisation, namely the inclusion of molecules within host complexes (e.g., "crystalline sponge" and tetraaryladamantane based inclusion chaperones) and the use of high-throughput crystallisation, employing "under-oil" approaches (e.g., microbatch under-oil and ENaCt). Representative examples have been included for each technique, together with a discussion of their relative advantages and limitations to aid the reader in selecting the most appropriate technique to overcome a specific analytical challenge.

Hydrogen peroxide assisted photorelease of an anthraquinone-based ligand from [Ru(2,2'-bipyridine)2(9,10-dioxo-9,10-dihydroanthracen-1-olate)]Cl in aqueous solution.

A new class of light-activated ruthenium(ii) complex was designed as a potential blocker of biological functioning, especially for targeting redox reactions within mitochondria under light activation. Based on our concepts the complex [Ru(bipy)2(1-hydroxyanthra-9,10 quinone)]Cl (RU1) was prepared and studied to understand the preliminary reaction mechanisms and its excited state behaviour through a series of stability tests, electrochemistry, UV-Visible kinetics and femtosecond transient absorption spectroscopy experiments. Under white light in the presence of H2O2 two different reactions (fast and slow) appear to take place. The complex loses the quinone-based ligand and a resulting Ru(iii) or Ru(v) species is produced. The complex RU1 shows potential to consume H2O2 from the one carbon metabolism in mitochondria, and hence may cut the energy cycle pathway of tumor cells.

Preparation and properties of a calcium(II)-based molecular chain decorated with manganese(II) butterfly-like complexes.

The room temperature reaction of [Mn2O2(bipy)4](ClO4)3 (bipy = 2,2'-bipyridine) with Ca(CHCl2COO)2 in methanol produced a yellow crystalline material. The X-ray determined structure comprises of a multiple calcium(II) carboxylate bridged chain-like structure which is decorated with [Mn(bipy)2(OH2)](2+) subunits. The redox behaviour for the complex in H2O and MeCN is reported. In the latter solvent the oxidation of the manganese ions appears to be facilitated by the presence of the calcium ions. Magnetic susceptibility and low temperature magnetization measurements show that the Mn moment is isotropic, with g = 1.99(1) and S = 5/2, confirming it is in the 2+ oxidation state. A very weak antiferromagnetic interaction is also detected. Frequency-dependent ac measurements evidence slow magnetic relaxation of the Mn(bipy)2 units. Two relaxation mechanisms are identified: a very slow direct process and a faster one caused by the Resonant Phonon Trapping mechanism. This is the first example of field-induced single ion magnet (SIM) behavior in a mononuclear Mn(II) complex.