pH-Dependent Assembly and Conversions of Six Cadmium(II)-Based Coordination Complexes

摘要

Six cadmium(II) complexes containing the N(2)O(2) donor tetradentate asymmetrical Schiff base ligand 2-{[2-(dimethylamino)ethylimino]methyl}-6-methoxyphenol (HL(5)), namely, [(Cd(3)L(2)(5)O(4))(2)]center dot CH(3)OH center dot H(2)O (I), [Cd(L(5))Cl](2)center dot CH(3)OH (2), [Cd(2)(HL(5))Cl(4)](n) (3), {[Cd(3)(H(2)L(5))(2)Cl(8)]center dot 2H(2)O} (4), [(H(2)L(5))(2)](2+)center dot[Cd(3)Cl(4)](2-)center dot H(2)O (5), and [(H(2)L(5))(2)](2+)center dot[CdCl(4)](2-) (6), have been synthesized using cadmium(II) chloride and the asymmetrical Schiff base ligand H L5 under different pH conditions at room temperature. The diverse structures show the marked sensitivity of the structural chemistry of the tetradentate asymmetrical Schiff base ligand HL(5). Complex 1 formed at pH = 10 exhibits a rare zero-dimensional structure of trinuclear cadmium(11). At pH = 8-9, a dinuclear cadmium(11) complex 2 is formed. The reaction at pH = 5-7 leads to two one-dimensional structures of 3 and 4. A further decrease of the pH to 3-5 results in a zero-dimensional structure 5. Owing to the departure of lattice water molecules in the crystal, complex 5 at room temperature can gradually undergo single-crystal-to-single-crystal transformation to result in complex 6. The results further show that conversions of complex 1-5 can also be achieved by adjusting the pH value of the reaction solution, 1 --> 2(pH) (= 8) --> 5(pH = 3) and 5. Comparing these experimental results, it is clear that the pH plays a crucial role in the formation of the resulting structures, which simultaneously provides very effective strategies for constructing the Cd(II) compounds with N(2)O(2) donor tetradentate asymmetrical Schiff base ligand. The strong fluorescent emissions of the six compounds (1-6) make them potentially useful photoactive materials. Furthermore, six Schiff base cadmium complexes (1-6), with 2,2-diphenyl-1-picrylhydrazyl (DPPH) as a co-oxidant exhibited the stronger scavenging activity.

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