We present a systematic study of the evolution of structural parameters and electronic correlations as a function of 3d band filling in a single crystal series of BaT2As2 (T = Cr-Cu). The structure trends are discussed in relation to the orbital occupation of the corresponding d elements supported by calculations of the charge density and electron localization function. Analysis of our specific heat data yields the mass enhancement (m*/m(b)) throughout the series. By combining the structural data with the mass enhancement values, we find that the decrease in m*/m(b) for n > 5 follows an increase of the crystal field splitting, determined by the progressive distortion of the As -T-As angle from the ideal tetrahedral environment. This study finds a strong interplay between crystal structure, bonding behavior, band filling, and electronic properties.