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【正文】 把它們稱為擬鹵素。 (CN)2 (SCN)2 (OCN)2 氰(cyanogen) 硫氰(thiocyanogen) 氧氰(o xycyanogen) (SeCN)2 (SCSN3)2 硒氰(selenocyanogen) (azidocarbondisulphide)CN－(cyanide) SCN－(thiocyanate) OCN－(cyanate) There are certain inorganic radicals which have the properties of existing either as monomeric anions or as neutral dimmers. 1．A list of some of the properties of the halogens which are mimicked by the pseudohalogens is as follows:(1) They form dimeric molecules, X－X , which are usually guite volatile. (2) They react with many metals to give salts。 the Ag(I)、Hg(I)、Pb(II) salts are insoluble in water.(3) They form acids with hydrogen, HX , which are highly dissociated in aqueous solution except HCN.(4) They form plexes with various metal ions.(5) They take disproportionation reactions in alkali and aqueous solution.(6) They are oxidized to dimeric moleculars. 2．Typical examples: (1) Formation by the oxidation of X－ ions: (2) Disproportionation of the free pseudohalogen by a basic: (3) Precipitation by certain metal ions: ↓ ↓(4) Formation of plex ions: (5) The capacity of oxidizing power : = +， = +， = +， = +。 2+ I2(SCSN3)2 + 2I－ 2I－ + (SCN)2I2 + 2SCN－Practice exercises： 1．Suggest probable structures for and give reasons why the two are probably not isostructural? 2．Predict the molecular structure of the following species encountered in this chapter: 3．Why are the halogen cations and best isolated as salts of , and similar anions? 3．氰和氰化物 ( cyanogens and cyanide ) (1) (CN)2結(jié)構(gòu)式：無色氣體，有苦杏仁臭味，極毒。 (2) preparation：可由加熱AgCN或Hg(CN)2與HgCl2共熱獲得： 2AgCN2Ag + (CN)2 Hg(CN)2 + HgCl2Hg2Cl2 + (CN)2 (3) reactivity： 所有氰化物劇毒，mg量級的KCN或NaCN就可使人致死。氰化物可以通過下列反應(yīng)，變成無毒物種。 2CN－ + O2(空氣) 2CNO－ ， CN－ + SCNS－ CN－ + O3CNO－ + O2 2CNO－ + 3+ 2OH－2+ N2 + 3O2 + H2O氰化物可以用C(IV)化合物與碳反應(yīng)制得： CaC2 + N2 CaCN2 + C CN－極易與過渡金屬離子Zn2+、Ag+、Cd2+形成穩(wěn)定的離子，難溶的重金屬氰化物在NaCN或KCN溶液中由于生成氰配離子而變得可溶。 Zn(CN)2 + 2 CN－ 4．硫氰和硫氰酸鹽 ( thiocyanogen and thiocyanate ) (1) preparation： a．(SCN)2：在乙醚中懸浮的AgSCN與碘或溴作用： 2AgSCN + Br22AgBr + (SCN)2 b．SCN－：KCN + SKSCN c．工業(yè)上：4NH3 + CS2NH4SCN + (NH4)2S (2) properties：常溫下(SCN)2是黃色液體。(SCN)2不穩(wěn)定，可逐漸聚合為難溶的棕紅色固體(SCN)x。 (SCN)2具有氧化性，它能把氧化。 (SCN)2 + H2S2H+ + 2 SCN－ + S ， 大多數(shù)硫氰酸鹽溶于水，而重金屬鹽如AgSCN、Hg(SCN)2難溶于水，SCN－是良好的配位體（ligand），F(xiàn)e(III) 離子可與其配位，得到深紅色的硫氰酸根配離子。 歡迎下載
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