This study reports the structural analysis and antitumor properties of a new dinuclear heteroleptic discrete Cd(II) complex, [Cd2(H2L)(NO3)3(H2O)3]NO3 (1), synthesized through the reaction of Cd(NO3)2·4H2O with bis(1-(pyridin-2-yl)-methylidene)carbazide (H2L). The asymmetric unit of 1 comprises two dinuclear heteroleptic [Cd2(H2L)(NO3)3(H2O)3]+ cations and two NO3− anions. Each [Cd2(H2L)(NO3)3(H2O)3]+ cation features two distinct coordination polyhedra: [Cd(N^N′^O)(NO3)2(H2O)] and [Cd(N^N′^O)(NO3)(H2O)2]+ (N^N′^O = one chelating pendant arm of H2L). Notably, the coordinated NO3− anions exhibit either bidentate or anisobidentate coordination modes. The crystal structure of 1 is stabilized by a range of intermolecular interactions, including O–H⋯O, N–H⋯O, and π⋯π interactions. Additionally, antiparallel NO⋯NO interactions involving the coordinated nitrato ligands were identified and confirmed using NCIplot and QTAIM computational tools. The cytotoxic and antiproliferative effects of 1, as well as its inhibition of colonization and metastasis in the MCF-7, Huh7, HCT-116, and A549 cell lines, were investigated. While H2L exhibited no cytotoxicity, complex 1 demonstrated cell-killing activity, with IC50 values of 17.05 µM for MCF-7, 14.02 µM for Huh7, and 27.27 µM for HCT-116 cells. In addition, 1 increased the expression of the DNA damage response protein p21 in HCT-116 cells. A549 cells showed lower sensitivity to 1 compared to the other cell lines examined in this study.
