Synthesis and solution behaviour of stable mono-, di- and trinuclear Pd(II) complexes of 2,5-pyridinedihydroxamic acid: X-ray crystal structure of a novel Pd(II) hydroxamato complex

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• 作者：Darren M. Griffith^a ; ^{dgriffith@rcsi.ie} ; Linda Bí ; r&oacute ; ^b ; James A. Platts^c ; Helge Mü ; ller-Bunz^d ; Etelka Farkas^b ; Pé ; ter Bugly&oacute ; ^b
• 关键词：Palladium complex ; Hydroxamic acid ; Scavenger ; Density functional theory ; Solution equilibrium ; Stability constant
• 刊名：Inorganica Chimica Acta
• 出版年：2012
• 出版时间：15 January, 2012
• 年：2012
• 卷：380
• 期：Complete
• 页码：291-300
• 全文大小：658 K

文摘

Mono-, di- and trinuclear Pd(II) complexes of 2,5-pyridinedihydroxamic acid (2,5-pyha) are reported. The X-ray crystal structure of the mononuclear complex, [Pd(en)(2,5-pyha_-1H)]Cl (en = ethylenediamine), was determined exhibiting an (N_py,N) binding mode of 2,5-pyha where (N_py,N) is through a pyridine N and deprotonated hydroxamate N. Such a coordination mode has never previously been observed for a Pd(II) hydroxamato complex. The first examples of di- and trinuclear Pd(II) complexes of a hydroxamic acid are described where one 2,5-pyha ligand acts as a bridge for two and three Pd(en) moieties, respectively. The stability of potential binding modes of 2,5-pyha for a proposed dinuclear complex were investigated by density functional theory at the RI-BP86/def2-TZVP level, in the Turbomole package. It was found that (N_py,N), (O,O?² gave the more stable complex where (N_py,N? is through a pyridine N and deprotonated hydroximate N and (O,O?² is via the carbonyl oxygen atom and the deprotonated hydroxyl group of the hydroxamic acid at the 2-position on the pyridine ring. A trinuclear complex, [{Pd(en)}₃(2,5-pyha_-4H)](PF₆)₂ was isolated and fully characterised. Spectroscopic studies indicate that the coordination modes are (N_py,N), (O,O?² and (O,O?⁵ where (N_py,N? is through a pyridine N and deprotonated hydroximate N and (O,O? is via doubly deprotonated hydroximate groups at positions 2 and 5 on the pyridine ring. Stability constants for the mono-, di- and trinuclear [Pd(en)]²⁺ complexes of 2,5-pyridinedihydroxamic acid are also reported. In solution at equimolar concentrations, 2,5-pyha effectively binds one equivalent of Pd(II) to give a mononuclear Pd(II) 2,5-pyha complex and under strongly acidic conditions. In addition formation of stable trinuclear Pd(II) 2,5-pyha complexes are favoured at an excess of Pd(II).