In reading inorganic teaching materials I've noticed an opposing orbital overlap trend. In the context of covalent solid state materials in the carbon column (all diamond-like structure), as you go down the column orbital overlap is said to decrease due to larger and larger atom size, thus leading to weaker bonding interactions and smaller band gaps. (Carbon is an insulator, silicon and germanium are semiconductors, alpha-tin is a metal.)
However, fast forward a few weeks in my syllabus and we are next looking at ligand field splitting parameters (the "delta" parameter) in the context of predicting high spin and low spin complexes. The parameter is said to increase from the 1st to 2nd to 3rd row of the transition metals specifically because overlap between metal and ligand orbitals is improving down the column, leading to stronger bonds and raising the eg antibonding orbitals in energy.
When the trend is applied to the halogens, their bond energies are said to decrease down the column due to poorer overlap and longer bonds. (F-F is the notable exception to the trend due to lots of e- / e- repulsion.)
What to do? Which to believe? Is the 2nd/3rd row trend different only because it involves metal/ligand overlap and not homonuclear interactions?
Thanks for any clarification!