Bonding effects and the crystal structures of (NH4)2

Area of Science:

• Crystal structure analysis
• Coordination chemistry
• Solid-state physics

Background:

• Tutton salts, specifically diammonium hexaaquacopper disulfate, exhibit Jahn-Teller distortions in their octahedral copper complexes.
• Previous studies indicated structural differences upon deuteration, with a shift in the longest copper-oxygen bond.
• The role of water ligand mass versus hydrogen bonding in these structural changes remained unclear.

Purpose of the Study:

• To determine the crystal structures of Tutton salts using normal water and isotopically substituted H2(18)O.
• To compare the structural effects of isotopic substitution with those of deuteration.
• To elucidate the primary cause of structural differences: hydrogen bonding or ligand mass.

Main Methods:

• X-ray diffraction at low temperature (9.5 K).
• Crystallographic analysis of diammonium hexaaquacopper disulfate with H2O and H2(18)O.
• Comparison of bond lengths and hydrogen bonding interactions.

Main Results:

• Crystal structures of the Tutton salts with normal water and H2(18)O were found to be very similar.
• Cu-O(7) was identified as the longest copper-oxygen bond in both structures.
• The observed structural differences upon deuteration are attributed to hydrogen bonding effects, not increased water ligand mass.

Conclusions:

• Hydrogen bonding plays a significant role in the structural variations observed in Tutton salts, particularly concerning Jahn-Teller distortions.
• The mass of water ligands is less critical than hydrogen bonding in influencing the Jahn-Teller coupling and resulting crystal structures.
• Comparative analysis with other Tutton salts under varying conditions provides broader insights into these interactions.