Topology-Dependent Hydrogen-Bond Cooperativity and Many-Body Stabilization in HSCN Oligomers

Hydrogen-bond cooperativity plays a key role in determining the stability and properties of molecular aggregates, yet the influence of aggregation topology on its microscopic origin remains poorly understood for thiocyanic acid (HSCN). Here, the structural, energetic, electronic, and spectroscopic properties of HSCN oligomers (monomer–pentamer) with linear, ladder, and cyclic topologies were investigated using dispersion-corrected density functional theory. Interaction energy and many-body decomposition analyses show that aggregate stabilization is dominated by pairwise hydrogen-bond interactions, while cooperative many-body effects increase systematically with cluster size and are maximized in cyclic assemblies. Complementary QTAIM, NCI-RDG, and charge-density-difference analyses reveal progressive strengthening of the S–H···N hydrogen-bond network accompanied by enhanced intermolecular polarization, without altering its closed-shell character. These electronic signatures are consistently reflected in the vibrational spectra through systematic red shifts of the S–H stretching mode. Together, the energetic, real-space electronic, and spectroscopic results demonstrate that hydrogen-bond topology governs the emergence of cooperative stabilization in HSCN oligomers, with cyclic architectures providing the most effective framework for collective hydrogen-bond reinforcement.