in which member of the following pairs of complexes would 10Dqoct. be the langer and why?
Cr(H2O)62+ and Cr(H2O)63+,
CrF63- and Cr(NH3)63-
MnF62- and ReF62-
be the langer
I think this is supposed to say "1.0 Delta(greek sign) oct be the larger and why"
oct means octahedral
This looked familiar (I was an organometallic chemist a long time ago) and I'm pretty sure has to do with crystal field theory and crystal field stabilization energy (google this or find its Wiki)
Certain ligands cause the d orbitals of the transition metal to split in their energies (so they are not all the same) and some are higher than others. If its octahedral and the ligands are pointing on the xyz axes, the dxy, dyz and dxz orbitals (called "t2g" orbitals) are lower in energy because they point in between the axes, the dx2-y2 and dz2 (called "eg" orbitals) are raised in energy because they point directly at the ligand. The ligands themselves will determine how large this gap in energies between the t2g and eg orbital sets. Weak field ligands like Br- will cause a small splitting and strong field ligands like CN- and CO will cause a larger gap.
The oxidation number like +2 or +3 will determine how many electrons are in those d orbitals and the ligands will determine if those electrons will be low spin (paired up on the lower energy orbitals) or high spin (unpaired, some will go into the higher level orbitals)
Wow, that really took me back but this is really classical coordination chemistry.(Basolo and Johnson, wrote a great little book called "Coordination chem") - you might also find this topic in advanced inorganic text
To answer the question you need to determine if the ligands in the pair are strong or weak and what the CFSE would be for each, as well as how many electrons would be in the d orbitals