α- and β-Carboxylic Groups as Primary Ligating Groups in Promoting Amide Deprotonation. Solid-State Behavior of N-Tosylalaninate-Copper(II) Complexes: Crystal and Molecular Structures of Bis(N-tosyl-β-alaninato)bis(imidazole)copper(II), Polymeric (N-Tosyl-α-alaninato)diaquacopper...

Article abstract of DOI:10.1021/ja00291a043

The interaction between N-tosyl-α- and N-tosyl-β-alanine and the copper(II) ion in aqueous solution at different pH gives rise to the formation of two types of compounds differing from each other by virtue of the presence on the amino acid of neutral (type 1) or deprotonated (type 2) NH group.Type 1 complexes are simple green complexes of formula Cu(Tsala)₂(Tsala^- = N-tosylalaninate anion), which show physical properties indicating dimeric or polymeric structure like copper(II) acetates and their amine adducts of formula Cu(Tsala)₂B₂ (B = imidazole (ImH), N-methylimidazole (MeImH), piperidine (PipdH), and morpholine (MorfH), and Tsala^- = N-tosyl-β-alaninate anion; B = ImH and MeImH, and Tsala^- = N-tosyl-α-alaninate anion), which present physical properties similar to those of Cu(Ts-β-ala)2(ImH)2, the crystal structure of which has also been determined.The Cu(Ts-β-ala)2(ImH)2 complex crystallizes in monoclinic P2₁/n space group with a = 14.287 (2) Angstroem, b = 7.169 (1) Angstroem, c = 16.363 (2) Angstroem, β = 110.6 (1) deg, Z = 2.Coordination around the copper, lying on the center of symmetry, is square planar and involves two centrosymmetric carboxylic oxygens of two amino acids and two imidazole molecules.Type 2 complexes contain only compounds of N-tosyl-α-alanine which present a coordinative behavior, strictly dependent on the pH of the solution, separating at pH >/=5 a blue compound of formula Cu(Ts-α-H_-1ala)*3H2O (Ts-α-H_-1ala^2- = N-tosyl-α-alaninate dianion; the NH group is also deprotonated) and at pH > 7 compounds of formula A2-1ala)2> (A = K⁺, piperidinium (PipdH2⁺), morpholinium (MorfH2⁺) cations).The crystals of -1ala)(H2O)2>*H2O are orthorhombic, space group Pbca with a = 27.198 (3) Angstroem, b = 9.001 (1) Angstroem, c = 11.908 (1) Angstroem, and Z = 8.The structure consists of polymeric -1ala)(H2O)2>n units, in which each copper atom is five-coordinated in a distorted square pyramid involving, at the base, the deprotonated amide nitrogen, one carboxylic oxygen, and two water molecules.The apex of the pyramid is occupied by a second carboxylate oxygen belonging to an adjacent amino acid molecule.The 2-1ala)2>*H2O complex crystallizes in monoclinic C2/c space group with a = 19.407 (2) Angstroem, b = 9.950 (1) Angstroem, c = 18.930 (2) Angstroem, β = 99.35 (1) deg, and Z = 4.The structure consists of piperidinium cations and -1ala)2>^2- anions.Coordination around the copper involves two centrosymmetric amino acid molecules coordinating via deprotonated sulfonamide nitrogen and one carboxylate oxygen in a square-planar arrangement.Magnetic and spectroscopic (EPR, IR, and vis) properties of all the complexes are reported.The ability of α- and β-carboxylic groups to behave as primary ligating groups is discussed.