Spacer-Length-Dependent Nuclearity and Cuprophilic Modulation in Copper(I) Complexes with Multidentate β-Thioketiminate Ligands

This study explores the impact of alkyl spacer length in multidentate β-thioketiminate ligands (H₂²<b>L</b>-H₂⁴<b>L</b>, H₂⁶<b>L</b>, and H₂⁸<b>L</b>) on the nuclearity and structural properties of copper(I) complexes. Ligands, synthesized thiation of β-ketoiminate precursors, were characterized by ¹H, ¹³C NMR, FT-IR, UV-vis spectroscopy, and ESI-MS. Reaction with CuO^<i>t</i>Bu led to the formation of tetranuclear ([<b>L</b>Cu₂]₂, C2-C4 spacers) and bis-trinuclear ([<b>L</b>Cu₂]₃, C6 and C8 spacers) complexes, analyzed by ¹H, ¹³C NMR, FT-IR, UV-vis, Raman, and single-crystal X-ray diffraction. Each Cu(I) center adopts a distorted trigonal planar geometry, coordinated by one nitrogen and two sulfur atoms through chelating and bridging modes. Shorter spacers favor tetranuclear clusters with stronger cuprophilic interactions (Cu···Cu: 2.58-3.43 Å), while longer spacers promote bis-trinuclear clusters, including a previously unreported triple-helicate with asymmetric Cu···Cu distances (2.76-2.87 Å). Importantly, coordination of 2,4,6-trimethylphenyl isocyanide induces fragmentation of these clusters into dinuclear [<b>L</b>(Cu-CNR)₂] complexes, as confirmed by single-crystal X-ray diffraction and FT-IR (νC≡N blue shift), revealing a spacer-dependent susceptibility to isocyanide-driven S-Cu bridge cleavage. These findings demonstrate spacer length as a key modulator of Cu(I) cluster nuclearity and metal-metal interactions, advancing bioinspired metallosupramolecular design.