Variable Coordination Mode of Chloranilic Acid. Synthesis, Structure, and Electrochemical Properties of Some Osmium Complexes
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- 作者：Parna Gupta ; Anindya Das ; Falguni Basuli ; Alfonso Castineiras ; William S. Sheldrick ; Heike Mayer-Figge ; and Samaresh Bhattacharya
- 刊名：Inorganic Chemistry
- 出版年：2005
- 出版时间：March 21, 2005
- 年：2005
- 卷：44
- 期：6
- 页码：2081 - 2088
- 全文大小：176K
- 年卷期：v.44,no.6(March 21, 2005)
- ISSN：1520-510X
文摘
Reaction of chloranilic acid (H2ca) with [Os(bpy)2Br2] (bpy = 2,2'-bipyridine) affords a dinuclear complex of type[{Os(bpy)2}2(ca)]2+, isolated as the perchlorate salt. A similar reaction of H2ca with [Os(PPh3)2(pap)Br2] (pap =2-(phenylazo)pyridine) affords a dinuclear complex of type [{Os(PPh3)2(pap)}2(ca)]2+ (isolated as the perchloratesalt) and a mononuclear complex of type [Os(PPh3)2(pap)(ca)]. Reaction of H2ca with [Os(PPh3)2(CO)2(HCOO)2]gives a dinuclear complex of type [{Os(PPh3)2(CO)2}2(r-ca)], where r-ca is the two electron reduced form of thechloranilate ligand. The structures of the [{Os(PPh3)2(pap)}2(ca)](ClO4)2, [Os(PPh3)2(pap)(ca)], and [{Os(PPh3)2(CO)2}2(r-ca)] complexes have been determined by X-ray crystallography. In the [{Os(bpy)2}2(ca)]2+ and [{Os(PPh3)2(pap)}2(ca)]2+ complexes, the chloranilate dianion is serving as a tetradentate bridging ligand. In the[Os(PPh3)2(pap)(ca)] complex, the chloranilate dianion is serving as a bidentate chelating ligand. In the [{Os(PPh3)2(CO)2}2(r-ca)] complex, the reduced form of the chloranilate ligand (r-ca4-) is serving as a tetradentatebridging ligand. All the four complexes are diamagnetic and show intense metal-to-ligand charge-transfer transitionsin the visible region. The [Os(PPh3)2(pap)(ca)] complex shows an Os(II)-Os(III) oxidation, followed by an Os(III)-Os(IV) oxidation on the positive side of a standard calomel electrode. The three dinuclear complexes show twosuccessive oxidations on the positive side of SCE. The mixed-valent OsII-OsIII species have been generated in thecase of the two chloranilate-bridged complexes by coulometric oxidation of the homovalent OsII-OsII species. Themixed-valent OsII-OsIII species show intense intervalence charge-transfer transitions in the near-IR region.