Reaction of hexaaquacopper(II) perchlorate with n-methyl-2-hydroxypyridine generated a family of (n-methyl-2-pyridone)xCu(ClO4)2 complexes: (3-methyl-2-pyridone)6Cu(ClO4)2 (1), (4-methyl-2-pyridone)6Cu(ClO4)2 (2), (5-methyl-2-pyridone)6Cu(ClO4)2 (3), (5-methyl-2-pyridone)4(H2O)2Cu(ClO4)2.2(5-methyl-2-pyridone) (4), and (6-methyl-2-pyridone)4Cu(ClO4)2 (5). Variable temperature X-ray structural analysis reveals a mixture of elongation and compression Jahn-Teller or Jahn-Teller-like distortions. Compound 1 undergoes a temperature dependent phase transition from a Jahn-Teller elongated structure to a Jahn-Teller compressed structure.
Dickie et al. (Fri,) studied this question.