Monomeric Hg(II) selenolate complexes derived from 2-phenylbenzamide ligands were prepared by oxidative addition of diselenides [{C₆H₄(CONR₂)Se}₂, R = Me, Et, ⁱPr] to elemental Hg and reductive cleavage of the Se–N bond of isoselenazolone derivatives [(NO₂)C₆H₃(CONSe)R, (R = allyl, ⁿbutyl)] followed by the treatment with HgCl₂. The complexes have been characterized by multinuclear NMR (¹H, ¹³C and ⁷⁷Se) spectroscopy and mass spectrometry which suggest the monomeric form of these in solution. The molecular structures of diselenides [C₆H₄(CONR₂)Se]₂ and mercury selenolates [Hg{(NO₂)C₆H₃(CONH-C₃H₅)Se}₂], [Hg{C₆H₄(CONⁱPr₂)Se}₂] and [Hg{C₆H₄(CONMe₂)Se}₂] were established by a single crystal X-ray diffraction study. Diselenides show strong intramolecular non-bonded Se⋯O interactions, which are influenced by the nature of C(O)N₂ and decrease with the sterically bulky alkyl substituent (Se⋯O = 2.823 Å for R = di-Me, 2.760 Å for R = allyl, and 3.157 Å for R = di-ⁱPr). Mercury complexes derived from less bulky 2-phenyl-N,N-dialkylbenzamide ligands associated with poor or no intramolecular non-bonded Hg⋯O interactions (4.91 Å for R = di-Me, 4.199 Å for R = allyl) and instead strong intermolecular Hg⋯O [2.792(3) and 2.820(4) Å] for di-Me and allyl and Hg⋯Se [3.3212(5) and 3.4076(8) Å] interactions were observed which lead to a dimeric form in the crystals. On the other hand, the mercury complex derived from the sterically bulky diisopropyl amide ligand shows a strong intramolecular non-bonded Hg⋯O (2.860 Å) interaction, adopts linear geometry and exists as a monomer. Thermogravimetric analysis (TGA) of the mercury selenolate complexes revealed two-step decomposition which leads to the formation of HgSe. The mercury selenolate complex 3c derived from the sterically bulky 2-phenyl-N,N-diisopropylbenzamide ligand decomposed to give HgSe in the range of 220–300 °C.