Selenocyanate ions

Pseudohalides of Se in which the role of halogen is played by cyanide, thiocyanate or selenocyanate are known and, in the case of Se are much more stable with respect to disproportionation than are the halides themselves. Examples are Se(CN)2, Se2(CN)2, Se(SeCN)2, Se(SCN)2, Se2(SCN)2. The selenocyanate ion SeCN is ambidentate like the thiocyanate ion, etc., p. 325), being capable of ligating to metal centres via either N or Se, as in the osmium(IV) complexes [OsCl5(NCSe)], [OsCl5(SeCN)], and trans-[OsCU(NCSe)(SeCN)]2-.920) Tellurium and polonium pseudohalogen analogues include Te(CN)2 and Po(CN)4 but have been much... 

Coordination chemistry of cyanate, thiocyanate and selenocyanate ions. A. H. Norbury, Adv. Inorg. Chem. Radiochem., 1975,17,232-386 (825). 

Coordination Chemistry of the Cyanate, Thiocyanate, and Selenocyanate Ions A. H. Norbury... 

Therefore, if an acceptor coordinates thiocyanate and selenocyanate ions via their S and Se donor atoms, respectively, the selenocyanate complexes should be considerably stronger than the thiocyanate complexes, and moreover formed in considerably more exothermic reactions. If, on the other hand, an acceptor prefers to coordinate these ligands via their harder donor atom N, the bonds formed will be less covalent and the reactions much less exothermic than in the case of S or Se coordination. The strength of the bonds will be little influenced by an exchange of S for Se and much the same value of AH°n may therefore be expected for thiocyanate and selenocyanate complexes. 

Selenocyanate complexes, 17 354, 356 homogeneous anionic, 17 354, 355 infrared spectra, 17 255 mixed-ligand, 17 354, 356 electronic effects, 17 355 steric effects, 17 354, 355 Selenocyanate ions, see also Chalcogeno cya-nates... 

The selenocyanate ion is much less stable than the thiocyanate ion. However, silver selenocyanate complexes are in general more stable than the corresponding thiocyanates.148 Complex species of the type [Ag(SeCN) ]1 rt and [Ag SeCN)]"-1 (n = 1-4) have been predicted from potentiometric and solubility studies in aqueous solution. 

The thiocyanate and selenocyanate ions (SCN- and SeCN-) react with RhCl3 3H20 to form [RhXfi]3" anions.1170"1172 Both the SCN- and the SeCN- are chalcogen-bonded, consistent with the soft character of the Rh111 in many complexes. 

COORDINATION CHEMISTRY OF THE CYANATE, THIOCYANATE, AND SELENOCYANATE IONS... 

Ab initio calculations of the nuclear quadrupole coupling constant suggest that the cyanate nitrogen atom is more ionic than that of the thiocyanate ion (118), but measurements show the latter to be more ionic than that in the selenocyanate ion (397). 

The selenocyanate ion, SeCN", is an ambidentate ion which may coordinate to metal ions via either the nitrogen atom (to hard metal ions) or the selenium atom (to soft metal ions) [74AHR/AVS], [75NOR], [79KAR/CRE]. Its potassium salt can be pre-... 

Kullberg [74KUL] found it impossible to study the aqueous Cu -SeCN system since a brown precipitate was immediately formed upon addition of selenocyanate ions to a copper(ll) solution. Toropova [56TOR] prepared CuSeCN(s) by adding KSeCN to a solution of copper(l) sulphite or thiosulphate complexes, and tried to study the complex formation by measuring the solubility of CuSeCN in selenocyanate solutions. The experiment failed since the complexes initially formed were found to decompose into elementary selenium and copper(l) cyanide compounds. 

Ion interaction coefficients, for the selenocyanate ion and its metal ion complexes are not available. Data for the thiocyanate ion have therefore been used as an approximation for extrapolation by SIT of selenocyanate equilibrium constants to standard conditions. 

Hamada, S., Decomposition equilibrium of selenocyanate ion, Nippon Kagaku Kaishi (J. Chem. Soc. Japan), 82, (1961), 1327-1330, in Japanese, English translation in [62HAM]. Cited on pages 207, 459. 

---