A fluorescent EXAFS study on the structure of the solvated cobalt(II) ion and chlorocobalt(II) complexes in hexamethylphosphoric triamide

✍ Scribed by Kazuhiko Ozutsumi; Kazuyuki Tohji; Yasuo Udagawa; Yuriko Abe; Shin-ichi Ishiguro

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 568 KB
• Volume: 191
• Category: Article
• ISSN: 0020-1693
• DOI: 10.1016/s0020-1693(00)93459-5

✦ Synopsis

The coordination structure of the cobalt(I1) ion and its chloro complexes of low concentration (-20 mmol dme3) in hexamethylphosphoric triamide (HMPA) has been explored by laboratory EXAFS (extended X-ray absorption fine structure) modified for fluorescence detection. The cobalt(I1) ion is four-coordinated in HMPA, unlike other oxygen-donor solvents such as water and N,N-dimethylformamide (DMF). The Co-0 (HMPA) bond lengths within complexes are revealed to be 194(l), 195(l), 194(l) and 202(2) pm for [Co(hmpa),]*+, [CoCl(hmpa),]+, [CW&(hmpa),] and [CYoCl,(hmpa)]-, respectively. The Co-O bond length is significantly shorter than that within six-coordinate [Co(H,O),]'+ (208 pm) or [Co(dmf),]*' (206 pm), and remains practically unchanged upon formation of mono-and dichloro complexes. On the other hand, the Ck+Cl bond length is 224(l), 227(l) and 229(l) pm within [CoCl(hmpa)3]', [CoC12(hmpa)2] and [CoCl,(hmpa)]-, respectively, all of which are appreciably shorter than that within the six-coordinate [cOCl(H20),]+ (235 pm). The origin of the different thermodynamic behavior of chloro complexation of cobalt(I1) in HMPA from that in DMF will be discussed on the basis of these structural data.