11 Synthesis, Structures, and Bonding in Certain Sulfur and Selenium Chlorides and Organochlorides KENNETH J. WYNNE Downloaded by CORNELL UNIV on October 19, 2016 | http://pubs.acs.org Publication Date: December 1, 1972 | doi: 10.1021/ba-1972-0110.ch011
University of Georgia, Athens, Ga. 30601
Sulfur and selenium chlorides and organochlorides display a wide range of structural types and frequently phase dependent structural variations. Valence bond theory is the commonly utilized qualitative approach to bonding in these compounds. An alternative view based on qualitative three-center, four electron molecular orbital theory and differential orbital utilization has been developed in this paper. This approach is useful in rationalizing the solid state structure and acceptor behavior of sulfur(IV) and selenium(IV) chlorides and organochlorides. Divalent and tetravalent sulfur and selenium chlorides and organochlorides are prepared generally in a similar fashion but displaycontrasting stability and Lewis acid behavior. The SeCl molecule, previously known only in the gas phase, is stabilized in the crystalline tetramethylthiourea adduct SeCl (tmtu). 2
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r^his paper deals with synthesis, structure, and bonding in tetravalent sulfur and selenium chlorides and organochlorides and sulfur and selenium dichloride. The similarities and differences which exist between the sulfur compounds and their selenium analogs are discussed. Tetravalent sulfur and selenium chlorides and organochlorides are covered first while SC1 and SeCl are covered later. 2
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Sulfur and Selenium Tetrachlorides and their Organo Derivatives Synthesis and General Properties. Sulfur tetrachloride, a pale yellow crystalline solid, is prepared best by chlorination of sulfur dichloride at —78° (J). Selenium tetrachloride also pale yellow is available com150
Miller and Wiewiorowski; Sulfur Research Trends Advances in Chemistry; American Chemical Society: Washington, DC, 1972.
11.
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Synthesis, Structure, and Bonding
WYNNE
mercially but may be prepared by the direct chlorination of the element (2,3,4,5). Organosulfur trichlorides may be prepared ( β ) by the reac tion of disulfides either with chlorine (Equation 1) R S + 3C1 ->2RSC1
Downloaded by CORNELL UNIV on October 19, 2016 | http://pubs.acs.org Publication Date: December 1, 1972 | doi: 10.1021/ba-1972-0110.ch011
2
2
2
(1)
3
or more conveniently with sulfuryl chloride. Organoselenium trichlorides may be prepared similarly by chlorination of diselenides (7) or by treat ment of alkyl- or arylseleninic acids with concentrated HC1 (8). Diorganosulfur and -selenium dichlorides are prepared by the reaction of an appropriate diorganochalconide with chlorine (9,10,11) while triorganosulfonium and -selenonium salts may be prepared by the conventional methods used to produce ammonium salts (JO, 12). Since their stability does not depend on the oxidizing ability of chlorine, triorganosulfonium and -selenonium chlorides are stable as are salts containing many other anions. However sulfur tetrachloride and its mono- and diorgano derivatives are less stable thermally than their sele nium analogs (Table I). For this reason few organo- and diorganosulfur(IV) chlorides have been isolated, but these compounds have been postulated frequently as reaction intermediates (13, 14). Important in formation concerning the structure and bonding in these reactive sulfur intermediates is inferred from a study of their selenium counterparts, which may be studied at temperatures where the sulfur analogs are unstable. Although SeCl and its organo derivatives are more stable thermally than the corresponding sulfur compounds, they share with the latter a general sensitivity toward moisture and are decomposed completely upon dissolution in water. In addition certain selenium compounds, particularly dialkylselenium dihalides are light sensitive. Structure. Most of the compounds discussed here are only stable or are most stable as solids. It is, therefore, important to know the nature of the interactions which lead to the enhanced stability in the solid state. One way of viewing the structures of chalcogen halides and their organo derivatives in the solid state starts with a consideration of the coordination number (C.N.) of the central atom. This raises immediately a serious question concerning what constitutes bonded or coordinated atoms because varying chalcogen-halogen interactions at less than the 4
Table I.
Decomposition Points in the Solid State ( ° C )
SC1 (1) CH3SCI3 (β) C H SC1 (6) ( >-Cl-C H ) SCl (9) 4
6
7
5
3
e
4
2
2
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