Conformational flexibility of the di(1,3-diaminopropane)-copper(II) cation: Part 2 1. Structure determination for aqua-di(1,3-diaminopropane-N,N′)-copper(II) dichloride and chlorodi(1,3-diaminopropane-N,N′)-copper(II) chloride methanol solvate and DFT calculations for aqua-di(1,3-diaminopropane-N,N′)copper(II) cation

Article abstract of DOI:10.1016/0020-1693(95)04796-4

The structures of aqua-di(1,3-diaminopropane-N,N′)copper(II) dichloride (1) and chloro-di(1,3-diaminopropane-N,N′)copper(II) chloride methanol solvate (2) were determined by single crystal X-ray methods. [Cu(tn)₂H₂O]Cl₂ (1) (tn = 1,3-diaminopropane), C₆H₂₂Cl₂CuN₄O,M_r = 300.72, tetragonal, space group P4₂nm (No. 102), a = 9.3146(5), c = 7.591(1) A, V = 658.63(9) A³,Z = 2,D_c = 1.516 g cm^-3. [Cu(tn)₂Cl]Cl·MeOH (2), C₇H₂₄Cl₂CuN₄O,M_r = 314.74, monoclinic, space group P2₁/c (No. 14), a = 8.598(2), b = 16.176(2), c = 10.418(4) A, β = 107.11(3)°, V = 1384.7(7) A³, Z = 4, D_c = 1.510 g cm^-3. Compound 1 is formed in aqueous solution, whereas 2 was obtained in methanol. The coordination polyhedron in 1 is square pyramid with exceptionally high site symmetry of 4mm (C_4v) around the copper(II) cation. The distances from the central copper(II) cation to the two nearest chloride ions are different in 2, 2.736(2) and 3.322(2) A. If the remote chloride is not taken into consideration, the coordination polyhedron could be described as distorted square pyramid. In both compounds the chelate rings display chair conformation. In 1 the two tn ligands are coordinated to copper in syn-like fashion, whereas in 2 the rings are in normal anti-like conformation. The rare syn-like conformation is a stable conformation, since the overall geometry was not changed during optimization carried out at the LDA/DNP level of theory. The optimized syn-like conformation is favoured by 16.38 kJ mol^-1 over the optimized anti-like conformation of the [Cu(tn)₂(H₂O)]²⁺ cation.