Selenosalicylate; a little-studied heavy-element analogue of the versatile thiosalicylate ligand

Selenosalicylic acid (ortho-HSeC₆H₄CO₂H), the heavy element congener of the widely studied thiosalicylic acid, was prepared by reaction of 2-carboxybenzenediazonium chloride (HO₂CC₆H₄N₂⁺Cl^-) with Na₂Se₂, followed by reduction of the resulting diselenide (SeC₆H₄CO₂H)₂ with zinc and acetic acid. The coordination chemistry of the selenosalicylate ligand towards a variety of platinum(ii), palladium(ii), nickel(ii), gold(iii), gold(i), rhodium(iii), iridium(iii) and ruthenium(ii) centres was explored. X-ray crystal structure determinations were carried out on the complexes [Pt(SeC₆H₄CO₂)(PPh₃)₂], [{(p-cym)Ru(SeC₆H₄CO₂)}₂] (p-cym = η⁶-p-cymene, CH₃C₆H₄CH(CH₃)₂), [{Cp*Rh(SeC₆H₄CO₂)}₂] (Cp* = η⁵-C₅Me₅) and [Cp*Ir(SeC₆H₄CO₂)(PPh₃)], and comparisons are made with corresponding thiosalicylate complexes. The complexes were characterised by NMR spectroscopy as well as ESI mass spectrometry, which indicated a greater propensity for fragmentation including by selenium loss, compared to the thiosalicylate analogues. Hirshfeld surface analysis to visualise and quantify intermolecular interactions revealed the dominance of H⋯H contacts in [{(p-cym)Ru(SeC₆H₄CO₂)}₂] and [Cp*Ir(SeC₆H₄CO₂)(PPh₃)].