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首页> 外文期刊>Chemistry: A European journal >The Formation of the Sulfur Halides SX_4 from SX_2 and X_2: Reaction Enthalpies, Transition States, and Activation Energies for X=F and Cl
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The Formation of the Sulfur Halides SX_4 from SX_2 and X_2: Reaction Enthalpies, Transition States, and Activation Energies for X=F and Cl

机译：由SX_2和X_2形成卤化硫SX_4：X = F和Cl的反应焓，过渡态和活化能

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High-level ab initio MO calculations by different methods demonstrate that the reaction of SF_2 with F_2 to form SF_4 is strongly exothermic and exergonic [CCSD(T)/6-311 + G(2df)//MP2/6-311 + G~*: #DELTA#H_(298)~0 = -445 kJ mol~(-1), #DELTA#G_(298)~0 = -398 kJ mol~(-1)] and proceeds via a very weakly bonded intermediate 2 with C_s symmetry. The structure of 2 corresponds to a donor-acceptor complex F_2S -> F_2 with a considerable transfer of charge (0.69e). The transition state (TS1) between 2 and SF_4 has a similar structure to 2 but with C_1 symmetry. The energy of the adduct and of TS1 is almost the same as the combined energy of the separate molecules SF_2 and F_2. Therefore, the overall activation energy for the reaction of SF_2 with F_2 to form SF_4 is practically negligible (6 kJ mol~(-1) at 298 K). The analogous reaction of SCl_2 with Cl_2 to form the hypothetical molecule SCl_4 is endothermic and endergonic (#DELTA#H_(298)~o = +32 kJ mol~(-1), (#DELTA#H_(298)~o = +74 kJ mol~(-1)). The ground-state geometry of SCl_4 has C_(2v) symmetry at the MP2/6-311 + G~* level and the coordination geometry at sulfur is pseudo-trigonal-bipyramidal. The transition state (TS2) of this reaction is ionic ([SCl_3~+]Cl~-) and has C_1 symmetry. The activation energy at 0 K for the chlorination of SCl_2 amounts to 203 kJ mol~(-1) at the CCSD (T)/6-311 + G(2df) level; it is 43 kJ mol~(-1) lower than the experimental bond dissociation energy of Cl_2. The proposed formation of the analogous tetrathiasulfuranes S(SR)_4 from (RS)_2S and RSSR is discussed in connection with the various interconversion reactions of polysulfur compounds.
机译：通过不同方法进行的从头算起的高MO从头计算，表明SF_2与F_2形成SF_4的反应强烈放热且是强能[CCSD（T）/ 6-311 + G（2df）// MP2 / 6-311 + G〜 *：＃DELTA＃H_（298）〜0 = -445 kJ mol〜（-1），＃DELTA＃G_（298）〜0 = -398 kJ mol〜（-1）]，并通过键合非常弱的中间体进行2具有C_s对称性。 2的结构对应于供体-受体复合体F_2S-> F_2，具有相当大的电荷转移（0.69e）。 2和SF_4之间的过渡状态（TS1）具有与2相似的结构，但具有C_1对称性。加合物和TS1的能量与分离的分子SF_2和F_2的组合能量几乎相同。因此，SF_2与F_2反应形成SF_4的总活化能实际上可以忽略不计（在298 K时为6 kJ mol〜（-1））。 SCl_2与Cl_2形成假想分子SCl_4的类似反应是吸热的和正电子的（＃DELTA＃H_（298）〜o = +32 kJ mol〜（-1），（＃DELTA＃H_（298）〜o = + 74 kJ mol〜（-1））。SCl_4的基态几何在MP2 / 6-311 + G〜*能级具有C_（2v）对称性，硫的配位几何是准三角双锥体。该反应的状态（TS2）为离子型（[SCl_3〜+] Cl〜-），具有C_1对称性，在CCSD下，0 K时氯化SCl_2的活化能为203 kJ mol〜（-1）（T ）/ 6-311 + G（2df）的水平;比Cl_2的实验键解离能低43 kJ mol〜（-1）;拟由（RS）_2S和结合多硫化合物的各种相互转化反应讨论了RSSR。

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