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Abstract: Efforts to delineate the interactions of neurotoxic Al(III) with low molecular mass substrates relevant to neurodegenerative processes, led to the investigation of the pH-specific synthetic chemistry of the binary Al(III)-[N-(phosphonomethyl) iminodiacetic acid] (Al-NTAP), Al(III)-[nitrilo-tris(methylene-phosphonic acid)] (Al-NTA3P), and Al(III)-[1-hydroxy ethylidene-1,1-diphosphonic acid] (Al-HEDP) systems, in correlation with solution speciation studies. Reaction of Al(NO3)3·9H2O with NTAP at pH 7.0 and 4.0 afforded the new species (CH6N3)4[Al2(C5H6NPO7)2(OH)2]·8H2O (1) and (NH4)2[Al2(C5H6NPO7)2(H2O)2]·4H2O (2), while reaction of Al(NO3)3·9H2O with NTA3P led to K8[Al2(C3H6NP3O9)2(OH)2]·20H2O (3). Complexes 1–3 were characterized by elemental analysis, FT-IR, 13C, 31P, 1H NMR (for 1–2 solid state and solution NMR where feasible), and X-ray crystallography. The structures of 1–3 reveal the presence of uniquely defined dinuclear complexes of octahedral Al(III) bound to fully deprotonated phosphonate ligands, water and hydroxo moieties. The aqueous solution speciation studies on the aforementioned binary systems project a clear picture of the binary Al(III)–(carboxy)phosphonate interactions and species under variable pH-conditions and specific Al(III):ligand stoichiometry. The concurrent solid state and solution work (a) exemplifies essential structural and chemical attributes of soluble aqueous species, reflecting well-defined interactions of Al(III) with phosphosubstrates and (b) strengthens the potential linkage of neurotoxic Al(III) chemical reactivity toward O,N-containing (carboxy)phosphate-rich cellular targets. [Copyright &y& Elsevier]

Synthetic efforts targeting soluble species of Co(II) with the low molecular mass physiological ligand citric acid led to the isolation of the first dinuclear complex [Co[sub 2](C[sub 6]H[sub 5]O[sub 7])[sub 2](H[sub 2]O)[sub 4]][sup 2-], at pH ∼5, in the form of its K[sup +] (1) and Na[sup +] (2) salts. Both 1 and 2 were characterized analytically, spectroscopically (FT-IR, UV/visible, EPR), and magnetically. Complex 1 crystallizes in the monoclinic space group P2[sub 1]/n, with a: 10.348(5) Å, b = 11.578(6) Å, c = 12.138(6) Å, β = 112.62(2)°, V- 1342(1) A, and Z = 2. Complex 2 crystallizes in the monoclinic space group P2[sub 1]/c, with a = 9.234(4) Å, b = 11.913(4) Å, c- 11.728(6) Å, β = 99.93(2)°, V-- 1271(1) ų, and Z =2. X-ray crystallography on 1 and 2 reveals the presence of two Co(II)ions, in a dinuclear assembly, octahedrally coordinated by two citrate ligands in a tridentate fashion. The octahedral environment around each Co(II)is complemented by another singly bonded citrate belonging to the adjacent Co(II) unit and two water molecules. Magnetic susceptibility and EPR studies on 1, in the solid state, corroborate the X-ray results, indicating a weak interaction between the two Co(II)ions. Moreover, EPR and UV/visible studies in solution suggest that 1 does not retain its dimeric structure, yielding a mononuclear octahedral Co(II)-citrate species. Detailed speciation studies suggest the presence of a number of species including the mononuclear complex [Co(C[sub 6]H[sub 5]O[sub 7])][sup -], optimally present around pH ∼5. in consonance with EPR and UV/visible spectroscopy, [Co(C[sub 6]H[sub 5]O[sub 7])]- is likely the scaffolding unit on the basis of which the dimer [CO[sub 2](C[sub 6]H[sub 5]O[sub 7])[sub 2](H[sub 2]O)[sub 4][sup 2-] is isolated from aqueous solutions. Collectively, this comprehensive study offers significant structural insight into the Co(II)-citrate speciation... [ABSTRACT FROM AUTHOR]