Thermodynamic and Steady-State Fluorescence Emission Studies on Metal Complexes of Receptors Containing Benzene Subunits

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• 作者：M. Alexandra Bernardo ; Fernando Pina ; Enrique Garc&iacute ; a-Españ ; a ; Julio Latorre ; Santiago V. Luis ; José ; M. Llinares ; José ; A. Ram&iacute ; rez ; and Conxa Soriano
• 刊名：Inorganic Chemistry
• 出版年：1998
• 出版时间：August 10, 1998
• 年：1998
• 卷：37
• 期：16
• 页码：3935 - 3942
• 全文大小：599K
• 年卷期：v.37,no.16(August 10, 1998)
• ISSN：1520-510X

文摘

The thermodynamic properties of the Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺ complexes of a family of N,N'-dibenzylated open-chain polyamines are described. For comparison, similar studies are reported for polyazacyclophane macrocyclic receptors containing an aromatic subunit linking the ends of a polyamine bridge. Themetal complexes of the dibenzylated ligands show lower stability constants than those reported for relatednonbenzylated open-chain polyamines. On the other hand, the stability constants of these complexes are clearlyhigher than those found for complexes of polyazacyclophane macrocycles containing a single para-substitutedbenzene spacer interrupting saturated polyamine bridges. All the studied complexes follow the Irving-Williamsstability order. The crystal structure of [Cu(L7)(H₂O)](ClO₄)₂ (L7 = 1-benzyl-1,5,8,12-tetrazadodecane) showsa very strongly axially distorted square planar coordination geometry for Cu²⁺. Crystals of [Cu(L7)(H₂O)](ClO₄)₂(C₁₅H₂₄Cl₂CuN₄O₉) are orthorhombic, space group P2₁2₁2₁, with a = 7.586(1) Å, b = 10.715(3) Å, andc = 28.13(2) Å, Z = 4, R₁ = 0.0572, and wR₂ = 0.1570. Steady-state fluorescence emission studies performedon the Cu²⁺ and Zn²⁺ complexes show that, while none of the Cu²⁺ complexes is emissive (CHEQ effect),fluorescence emission is observed for those Zn²⁺ complexes with all the nitrogen donors either protonated orcoordinated to the metal ions (CHEF effect). The composition of the frontier molecular orbitals of the free-ligands and of the Cu²⁺ and Zn²⁺ complexes supports this behavior. The use of these water-soluble ligands aschemosensors by means of enhancement or quenching of the fluorescence emission is also discussed.