The synthesis of [Cu(PteN^˄N)(P^˄P)][BF₄] complexes with pterin-fused phenanthroline (PteN^˄N) derivatives and bisphosphine (P^˄P) co-ligands was achieved through a mechanochemical approach. Due to the extremely poor solubility of PteN^˄N ligands, traditional solution methods are ineffective, whereas solid-state mechanochemistry reliably yielded the targeted heteroleptic—rather than homoleptic—complexes with considerable stability even in solution. The transformation from ligand to complex increased the solubility dramatically. The ligands and complexes were comprehensively characterised with a mixture of routine spectroscopic and spectrometric methods, the applicability of which depended to some extent on the compounds’ solubility, e.g., in the case of NMR spectroscopy. The photophysical properties of the complexes, which were not as exciting as anticipated, were assessed by absorption and emission spectroscopic methods, showing that further improvements are needed in complex design if these species are to be developed towards photocatalysis in the future.

Among the many structural model complexes for the molybdenum and tungsten dependent oxidoreductases, none are specifically highlighted as being water stable and water soluble, and only very few may have such potential. Herein, complex salts with potassium cations and bisdithiolene oxido molybdate or tungstate anions are described, which were designed to be water‐tolerant and soluble in purely aqueous medium. Four different routes to water‐soluble complexes of the type K ₂ [MOx(dt) ₂ ] (M = Mo, W; dt = ene‐1,2‐dithiolate, x  = 1, 2) are presented, the applicability of which depends on the varied, distinct ligand precursors. The crystal structures of the salts are examined in detail, with particular attention to cation–anion interactions, alongside an analysis of the corresponding infrared spectra to support structural interpretations and interaction characteristics.