Lan Wang, Zhen Qin, Shu-Fang Li, Xin-Ran Hao, Chu Chu, Bingbing Zhang, Dong Yan
We address this via a "multi-coordination-site-induced" strategy in metal complexes, employing d10 Cd2+ to induce second-order Jahn-Teller distortions alongside linear SCN- and planar π-conjugated ligands (pyrazole vs 1,2,4-triazolate).
Second-order nonlinear optical crystals are essential to photonics but face the challenge of combining large nonlinearity, high laser damage threshold, and suitable birefringence. We address this via a "multi-coordination-site-induced" strategy in metal complexes, employing d10 Cd2+ to induce second-order Jahn-Teller distortions alongside linear SCN- and planar π-conjugated ligands (pyrazole vs 1,2,4-triazolate). The centrosymmetric Cd(C3H4N2)2(SCN)2 (1) shows a wide bandgap (4.80 eV, Δn = 0.23), while the non-centrosymmetric Cd3(C2H2N3)4(SCN)2 (2) with distorted [CdN5S] octahedra achieves second-harmonic generation response [2.6 × KH2PO4], wide bandgap (4.60 eV), and moderate birefringence (0.18 at 546 nm), suitable for phase matching. Theoretical analysis attributes these properties to cooperative contributions of planar organic units and SCN- anions, confirming the effectiveness of this strategy.