This thesis presents a detailed study of crystal structure determination using single-crystal X-ray diffraction, applied to a ruthenium (II) complex. It outlines key crystallographic concepts, the theoretical principles of X-ray scattering, and data processing workflow using APEX and SHELXL. The experimental section describes crystal selection, data collection, integration, scaling, space-group determination and structure refinement. The results show how structural parameters of the ruthenium complex were solved, refined, and validated through refinement commands, quality indicators and standard crystallographic validation tools.