Calorimetric and structural investigation of monomeric and dimeric copper(II)-N-protecetd aminoacidates

A calorimetric investigation of the dehydration of structurally-known binary copper(II)-N-protected aminoacidates is reported to compare their relative stability. In order to consider a series of strictly related compounds, the crystal and molecular structure of N-benzoyl-α-alaninate (bz-α-ala) complex is also determined. The compound crystallizes in the triclinic space group P1− with 1 formula unit in a cell of dimensions a = 9.425(3), b = 9.579(3), c = 12.644 Å, α = 74.10(2)°, β = 78.95(2)°, γ = 88.32(3)°. The structure was solved using the Patterson and Fourier methods and refined by least-squares calculations to a conventional R factor of 5.6% for 3134 counter data. It consists of centrosymmetric tetracarboxylato bridged binuclear molecules showing the copper(II) acetate structure.The calorimetric analysis shows higher dehydration Ea values for dimeric species with respect to blue ones which assign a peculiar stability to dimeric structures. The crystal size strongly influences kinetic parameters because the proportion between water molecules on the surface and in the bulk varies with the crystal dimensions.