The precise modulation of the spatial orientations and connection modes of primitives is vital for certain critically important optical functions for nonlinear optical (NLO) materials (specifically, second-harmonic generation (SHG) and optical bandgap); however, we are yet to achieve a sufficient level of control for the designed construction of efficient broadband NLO materials. Exploiting the changes in microscopic polarization that may result from dimensional increase, we propose herein a zero-dimensional (0D)-to-three-dimensional (3D) dimensionality-increase strategy to realize strong broadband SHG responses for the first time. The novel 3D pseudo diamond-like Zn(SCN)2 has been synthesized by removing SHG-inactive [NH4]+ counter cations and H2O molecules that are located between the adjacent discrete [Zn(SCN)4] building blocks within the 0D (NH4)2Zn(SCN)4·3H2O. The 0D-to-3D dimensionality engineering, proceeding from (NH4)2Zn(SCN)4·3H2O to Zn(SCN)2, results in significantly enhanced SHG responses and efficient broadband activity (8 × KH2PO4 @ 1064 nm, 4.18 eV bandgap for the former c.f. 2 × β-BaB2O4 @ 380 nm, 30 × KH2PO4 @ 1064 nm, 2 × KTiOPO4 @ 2100 nm, 4.78 eV bandgap for the latter) from the UV to the NIR regions (SHG@300-1050 nm). Theoretical calculations and crystal structure analyses reveal that the coordination-bond-connected [Zn(SCN)4] building blocks within the diamond-like structure of Zn(SCN)2 are responsible for its giant broadband SHG responses.