Mercury selenocyanates

The formation of Hg(SeCN)4 is well established by the potentiometric work of Toropova [56TOR], while her experimental data pertaining to the formation and the formation constant of Hg(SeCN)3 only comprise a few points. In their polarographic work Murayama and Takayanagi [72MUR/TAK] studied the anodic mercury wave in the presence of 0.001 to 0.003 M SeCN . The electrode process was assumed to comprise the charge transfer Hg(l) Hg + 2e combined with the formation of Hg(SeCN)2(aq) and Hg(SeCN)3. No primary data are provided and the evaluation procedure is rather involved, which makes the assessment difficult. The results are mixed equilibrium constants, since an activity coefficient correction was applied to the Hg ion. The following complexes are thus proposed to prevail in the Hg -SeCN system  

Recalculation and extrapolation of the data in the table to standard conditions by SIT with As from [97BAH/PAR] in Appendix A resulted in the accepted values  

The uncertainties assigned by this review to the first two constants are based on the discrepancy between the two reported values of log, A °((V.104), 298.15 K). The uncertainty limits of the final complex is based on the difference (0.2 logarithmic units) between the extrapolated values from 0.3 and 0.8 M NaNOs, respectively. 

Method Ionic medium t(°C) login pi login pi login Pi Reference 

Kullberg [74KUL2] determined the enthalpy change of Reaction (V.105) at 7=0.3 and 1 M from measurements presented in Appendix A to be -(191.9+1.5) kJ-mol. This value compares favourably with the value, (194 + 3) kJ-mol, derived from the temperature dependence of the equilibrium constant in [56TOR] at 7 = 0.3 M. 

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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... 

Finely divided free selenium reacts with mercury vapor to produce black mercury selenide. Suitable reagent paper is prepared by soaking filter paper in a solution of potassium selenocyanate (KCNSe), draining, and exposing to an atmosphere of hydrogen chloride (hood ). The potassium selenocyanate solution is readily prepared by vigorously shaking potassium cyanide solution with an excess of pure selenium powder in a stoppered flask. 

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