Poly(organo)phosphazenes are a family of inorganic molecular hybrid polymers with very diverse properties due to the vast array of organic substituents possible. This tutorial review aims to introduce the basics of the synthetic chemistry of polyphosphazenes, detailing for readers outside the field the essential knowledge required to design and prepare polyphosphazenes with desired properties. A particular focus is given to some of the recent advances in their chemical synthesis which allows not only the preparation of polyphosphazenes with controlled molecular weights and polydispersities, but also novel branched architectures and block copolymers. We also discuss the preparation of supramolecular structures, bioconjugates and in situ forming gels from this diverse family of functional materials. This tutorial review aims to equip the reader to prepare defined polyphosphazenes with unique property combinations and in doing so we hope to stimulate further research and yet more innovative applications for these highly interesting multifaceted materials.

The pharmacologically active [Ru(CO)₃Cl(glycinate)] is shown to be in equilibrium with [Ru(CO)₂(CO₂H)Cl(glycinate)]⁻ (isomers) at around pH 3.1 which then at physiological pH reacts with more base to give [Ru(CO)₂(CO₂)Cl(glycinate)]²⁻ (isomers) or [Ru(CO)₂(CO₂H)(OH)(glycinate)]⁻ (isomers). The ease with which [Ru(CO)₃Cl(glycinate)] reacts with hydroxide results in it producing a solution in water with a pH of around 2 to 2.5 depending on concentration and making its solutions more acidic than those of acetic acid at comparable concentrations. Acidification of [Ru(CO)₃Cl(glycinate)] with HCl gives [Ru(CO)₃Cl₂(NH₂CH₂CO₂H)]. The crystal structures of [Ru(CO)₃Cl(glycinate)] and [Ru(CO)₃Cl₂(NH₂CH₂CO₂Me)] are reported.

Poly[(organo)phosphazenes] are a unique class of extremely versatile polymers with a range of applications including tissue engineering and drug delivery, as hydrogels, shape memory polymers and as stimuli responsive materials. This review aims to divulge the basic principles of designing polyphosphazenes for drug and gene delivery and portray the huge potential of these extremely versatile materials for such applications. Polyphosphazenes offer a number of distinct advantages as carriers for bioconjugates; alongside their completely degradable backbone, to non-toxic degradation products, they possess an inherently and uniquely high functionality and, thanks to recent advances in their polymer chemistry, can be prepared with controlled molecular weights and narrow polydispersities, as well as self-assembled supra-molecular structures. Importantly, the rate of degradation/hydrolysis of the polymers can be carefully tuned to suit the desired application. In this review we detail the recent developments in the chemistry of polyphosphazenes, relevant to drug and gene delivery and describe recent investigations into their application in this field.