Selenocyanates structure

In recent years research in the field of transition-metal thiocyanates and selenocyanates received a new impetus, because of the partly interesting physical properties of such crystalline species. A review on Cd and Hg thiocyanate systems collects and sorts results of this endeavor.371 The nonlinear optical (NLO) properties of Cd thiocyanate and selenocyanate systems and criteria for the design of NLO crystals (crystal engineering), especially, have been discussed afterwards.372 Further contributions to the field have also been described.37, 374 The structure of mercury chlorothiocyanate has been re-determined.375... 

A number of selenocyanate compounds formulated as the adducts In(NCSe)3L have been reported5,92 with L = py n = 4), DMF (n - 3.5), Pr3PO (n = 3) and diantipyrylmethane (n — 2), but no structural details are available. The compounds In(NCSe)3L3 (L = bipy, phen) may well be salts of InL3+ and NCSe-, while the anionic complexes [In(NCSe)fi]3- are reported to involve an N-bonded ligand and six-coordinate indium.93,94... 

Magnesium Selenocyanate, Mg(CNSe)2, has been prepared by dissolving magnesium oxide in selenocyanic acid. On evaporation the salt is obtained as a gummy mass, apparently devoid of crystalline structure.2... 

The thiocyanate ion is sometimes regarded as a resonance hybrid of the two structures S—CsN and S—C=N Although organic compounds presumably related to each of the forms (of types R—S—(>s=N and R—N=C S) are known, the Raman spectra of solutions of ionic thiocyanates have been interpreted to show the presence of a feN link and the absence of a 0=S link, thus favoring the triple-bonded structure. Except for the ammonium salt, best made by heating ammonium dithio-carbamate (p. 236), ionic thiocyanates are best prepared by treatment of sulfur with the appropriate cyanide, either in solution or in fused state. (Selenocyanates may be prepared from selenium and ionic cyanides in the same way.)... 

The compounds (Et4N)4[M(NSCe)a] (M = Pa, U) have been characterized by comparing their spectral and crystallographic properties with the corresponding thiocyanate complexes (26). Some thorium(IV) complexes have been prepared containing DMF and N-bonded seleno-cyanate groups (326). Although various uranyl selenocyanate complexes have been reported, no structural data are available (686). 

Table XLI summarizes the structures of known, homogeneous, anionic selenocyanate complexes. Although fewer examples exist than for the corresponding thiocyanate complexes, it is apparent that a similar pattern exists for the two sets of complexes. Class a metals are coordinated by the nitrogen atom, whereas selenium is the donor for the class b metals. In mixed metal complexes containing bridging seleno-oyanate groups the nitrogen atom coordinates to the harder or class a metal, and the selenium atom bonds to the softer or class b metal, as was observed with the corresponding thiocyanate complexes.

---