Carbon nitride’s properties can be tuned through the coordination of metal atoms, which can lead to enhanced catalytic activity. However, to date, there are few reported examples of inner-sphere coordination of metal complex fragments to carbon nitride. Therefore, the effects of coordination of metal complex fragments to carbon nitride haves been investigated.
Reaction of the rhenium carbonyl complex, [ReCl(CO)5] with the surface of urea-derived carbon nitride (UCN) results in [ReCl(CO)3(UCN)], with a rhenium concentration of 0.39 mmol g-1. The synthesis of the manganese analogue resulted in manganese oxidation leading to [Mn(UCN)] ([Mn] = 0.24 mmol g-1). Infrared spectroscopy, along with crystal structures of molecular analogues, [MCl(CO)3(DMNA-κ2N, N’)] (M = Re, Mn) was used to gain insight into the coordination of metals complex fragments to carbon nitride.
Two morphologies of carbon nitride, unstructured urea-derived carbon nitride (UCN) and porous cyanamide derived carbon nitride (CCN), were then decorated with [Ru(bpy)2]2+ fragments. The carbon nitride structure affected metal loading, as [Ru(bpy)2(UCN)](PF6)2 ([Ru] = 0.016 mmol g-1) showed lower metal loading compared to [Ru(bpy)2(CCN)](PF6)2 ([Ru] = 0.076 mmol g-1). [Ru(bpy)2(DMNA-κ2N, N’)](PF6)2 was synthesised as a molecular analogue to gain insight into the coordination mode. The photocatalytic activities of [Ru(bpy)2(UCN)](PF6)2 and [Ru(bpy)2(UCN)](PF6)2 were completely inhibited compared to the undecorated materials. EPR and photoluminescence suggested the presence of rapid, efficient quenching of excited states in ruthenium decorated carbon nitride.
[IrCl2Cp*(UCN)] ([Ir] = 0.069 mmol g-1) was synthesised to design a novel, recyclable hydrogenation catalyst. Direct hydrogenation reactions were carried out using hexane as a solvent, and despite low activity, [IrCl2Cp*(UCN)] showed good selectivity toward terminal alkenes and over 80% of catalytic activity was retained after 5 catalytic runs.
Direct coordination of metal complex fragments to carbon nitride is shown to be a viable route to tuning the properties of carbon nitride and developing recyclable novel catalysts.
