• • ISOC and ISOB exhibit SHG intensities greater than 6× KDP and band gaps exceeding 4.0 eV, a combination unique among inorganic selenites, enabling high-power UV laser applications.
• • The InO6Br polyhedra show the highest polarization anisotropy and hyperpolarizability among all reported indium oxy-chloride and oxy-bromide groups, indicating superior NLO efficiency.
• • The synthesis of InO6X (X = Cl, Br) polyhedra marks the first seven-coordinated indium oxyhalide polyhedra, expanding the structural diversity of metal-centered NLO motifs.
• • The use of SeO3 groups for chelation and structure direction successfully yielded non-centrosymmetric structures, a critical requirement for SHG activity.