Electron exchange between [Co(terpy)2]3+ and [Co(terpy)2]2+ can be monitored by 1H NMR exchange spectroscopy and allows the cobalt(II) spectra to be fully assigned.

The formation of sufficiently large three‐dimensional nano/macroporosity in bone scaffolds remains a challenge despite the numerous fabrication methods reported in literature. The presence of such porosity is required for tissue ingrowth and for the concurrent degradation of implanted structure. A new technique of combining the slip casting and polymer sponge methods using the slips with different powders was introduced in the study to prepare hydroxyapatite scaffolds with bimodal pore sizes. This technique provided better control over the microstructures of scaffolds and enhanced their mechanical properties compared to traditional methods. With this technique, we were able to produce scaffolds with mechanical and structural properties that could not be attained by the polymer sponge or slip‐casting method alone. The scaffolds were prepared with an open, uniform, and interconnected porous structure with a bimodal pore size of 100–300 μm. The bimodal porous hydroxyapatite scaffold sintered at 1200°C had a large flexural strength of 73.3 MPa and a porosity of 52.5 vol%. These bioscaffolds hold promise for applications in hard tissue engineering.

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A new polymorph of bis(2-aminopyridinium) fumarate-fumaric acid (1/1), 2C₅H₇N₂⁺∙C₄H₂O₄²⁻-·C₄H₄O₄, was obtained and its crystal structure determined by powder X-ray diffraction. The new polymorph (form II) crystallizes in the triclinic system (space group P-1), while the previous reported polymorph [form I; Ballabh, Trivedi, Dastidar & Suresh (2002). CrystEngComm, 4, 135-142; Büyükgüngör, Odabaşoğlu, Albayrak & Lönnecke (2004). Acta Cryst. C60, o470-o472] is monoclinic (space group P2₁/c). In both forms I and II, the asymmetric unit consists of one 2-aminopyridinium cation, half a fumaric acid molecule and half a fumarate dianion. The fumarate dianion is involved in hydrogen bonding with two neighbouring 2-aminopyridinium cations to form a hydrogen-bonded trimer in both forms. In form II, the hydrogen-bonded trimers are interlinked across centres of inversion via pairs of N-H∙∙∙O hydrogen bonds, whereas such trimers are joined via single N-H∙∙∙O hydrogen bonds in form I, leading to different packing modes for forms I and II. The results demonstrate the relevance and application of the powder diffraction method in the study of polymorphism of organic molecular materials.