To modify its steric and electronic properties as a support for heterogeneous catalysts, electron withdrawing and electron-donating ligands, hexafluoroacetylacetonate (Facac(-)) and acetylacetonate (Acac(-)), were introduced to the metal-organic framework (MOF), NU-1000, via a process akin to atomic layer deposition (ALD). In the absence of Facac(-) or Acac(-), NU-1000-supported, AIM-installed Ni(II) sites yield a mixture of C4, C6, C8, and polymeric products in ethylene oligomerization. (AIM = (A) under bar LD-like deposition in (M) under bar OFs). In contrast, both Ni-Facac-AIM-NU-1000 and Ni-Acac-AIM-NU-1000 exhibit quantitative catalytic selectivity for C4 species. Experimental findings are supported by density functional theory calculations, which show increases in the activation barrier for the C-C coupling step, due mainly to rearrangement of the siting of Facac(-) or Acac(-) to partially ligate added nickel. The results illustrate the important role of structure tuning support modifiers in controlling the activity of MOF-sited heterogeneous catalysts and in engendering catalytic selectivity. The results also illustrate the ease with which crystallographically well-defined modifications of the catalyst support can be introduced when the node coordinating molecular modifier is delivered via the vapor phase.