Selenocyanate Explained

A selenocyanate is an ion or chemical compound that contains the -SeCN group, which could be in the form of an anion, SeCN⁻. Organic selenocyanates also exist.

Some complex ions with transition metals such as silver and mercury (mercuriselenocyanates) are known. Mercuriselenocyanate salts also include K, Fe, Co, Ni, Cu, Zn, and Cd.^[1] Complex ions include Fe(NCSe)₆³⁻, Fe(NCSe)₆⁴⁻, Fe(NCSe)₄²⁻, Co(NCSe)₆⁴⁻, Co(NCSe)₄²⁻, Ni(NCSe)₆⁴⁻, Zn(NCSe)₆⁴⁻, Rh(NCSe)₆⁴⁻, Pd(NCSe)₄²⁻, Ag(SeCN)₂⁻, Cd(NCSe)₄²⁻, Cd(NCSe)₆⁴⁻, Dy(NCSe)₆³⁻, Ho(NCSe)₆³⁻, Er(NCSe)₆³⁻, Pt(NCSe)₆²⁻, Au(NCSe)₄⁻, and Hg(NCSe)₄²⁻.^[2]

For hard metals, the negative charge is on the nitrogen atom which coordinates with the metal atom. Examples include Ti(NCSe)₆²⁻, V(NCSe)₆³⁻, VO(NCSe)₄²⁻, Cr(NCSe)₆³⁻, Mn(NCSe)₄²⁻, Mn(NCSe)₄²⁻, Y(NCSe)₆³⁻, Zr(NCSe)₆²⁻, Mo(NCSe)₆³⁻, Pr(NCSe)₆³⁻, Nd(NCSe)₆³⁻, Sm(NCSe)₆³⁻, Hf(NCSe)₆²⁻, Re₂(NCSe)₈²⁻, Pa(NCSe)₈⁴⁻ and U(NCSe)₈⁴⁻.^[3]

Production

Selenocyanate can be produced in the reaction of selenium, selenide, selenite or selenate with cyanide ions.^[4]

Se²⁻ + CN⁻ + 0.5 O₂ → SeCN⁻ + 2OH⁻

SeO₃²⁻ + 3CN⁻ → 2OCN⁻ + SeCN⁻ + 2OH⁻

SeO₄²⁻ + 4CN⁻ → 3OCN⁻ + SeCN⁻ + 2OH⁻

Reactions

Selenocyanate is oxidised to selenium and cyanate by bis (trifluoroacetoxy) iodobenzene.^[5]

Application

Selenocyanate is component of pollution from oil refineries and mine drainage water. Remediation methods have been investigated to extract selenocyanate from water. Methods considered include precipitation by metal salts, or extraction by plants. Indian mustard converts some selenocyanate to selenocystine and selenomethionine, and volatiles dimethylselenide and methylselenocyanate.^[6]

List

formula	crystal form	space group	Å	volume	density	comment	reference
[NH<sub>4</sub>][SeCN]	monoclinic	P21/c	a=4.3443 b=7.3615 c=12.9858 β=99.152° Z=4	416.99		pink due to contamination from red selenium	^[7]
KSeCN	monoclinic	P21/c	a=4.59 b=7.64 c=11.89 β=101.13°				^[8]
Ag[SeCN]	monoclinic	C2/c	a=8.8300 b=8.2471 c=8.4303 β=93.027° Z=8^[9]	613.05		solubility at 18°: 2.0×10^−8 Mol/litre
[NH<sub>4</sub>][Ag(SeCN)<sub>2</sub>]	orthorhombic	Pbca	a=7.15549 b=20.0671 c=10.4776 Z=8	1504.49
[NH<sub>4</sub>]3[Ag(SeCN)<sub>4</sub>]	tetragonal	I41/acd	a=14.0013 c=31.4678 Z=16	6168.8
[NH<sub>4</sub>]0.7K0.3[SeCN]
K2Hg(CNSe)4
[Cu(IPr)(NCSe)]2 IPr = 1,3- bis(2,6-diisopropylphenyl)imidazol-2-ylidene	triclinic	P	a=9.389 b=10.9745 c=14.0542 101.181 90.311 105.620 Z=1	1365.7		@100K	^[10]
ZnHg(CNSe)4
CdHg(CNSe)4

Notes and References

1. Benedetti-Pichler . A. A. . Spikes . W. F. . December 1934 . The use of potassium mercuri-selenocyanate as a reagent in qualitative microanalysis . Mikrochemie . en . 15 . 1 . 271–287 . 10.1007/BF02789376 . 0369-0261.
2. Book: Advances in Inorganic Chemistry and Radiochemistry . 2 May 1975 . Academic Press . 978-0-08-057866-8 . 355 . en.
3. Book: Advances in Inorganic Chemistry and Radiochemistry . 2 May 1975 . Academic Press . 978-0-08-057866-8 . 354 . en.
4. Book: Hullebusch . Eric D. van . Bioremediation of Selenium Contaminated Wastewater . 2 September 2017 . Springer . 978-3-319-57831-6 . 110–111 . en.
5. Papadoyannis . I. N. . Stratis . J. A. . Anthemidis . A. N. . January 1984 . Simultaneous Determination of Selenocyanate and Thiocyanate Ions in the Presence of Cyanide by Oxidation with bis (Trifluoroacetoxy) iodobenzene . Analytical Letters . en . 17 . 13 . 1511–1517 . 10.1080/00032718408065325 . 0003-2719.
6. de Souza . Mark P. . Pickering . Ingrid J. . Walla . Michael . Terry . Norman . Selenium Assimilation and Volatilization from Selenocyanate-Treated Indian Mustard and Muskgrass . Plant Physiology . 1 February 2002 . 128 . 2 . 625–633 . 10.1104/pp.010686. 11842165 . 148924 .
7. Shlyaykher . Alena . Tambornino . Frank . Synthesis and Stability of Ammonium Selenocyanate [NH 4 ][SeCN] and Its Reactivity toward Ag[SeCN] . Inorganic Chemistry . 15 July 2023 . 62 . 30 . 11943–11953 . 10.1021/acs.inorgchem.3c01345. 37453070 . 259924312 .
8. Swank . Duane D. . Willett . Roger D. . April 1965 . The Crystal Structure of Potassium Selenocyanate . Inorganic Chemistry . en . 4 . 4 . 499–501 . 10.1021/ic50026a013 . 0020-1669.
9. Book: Salomon . Mark . Salomon . M. . Ohtaki . H. . Silver Azide, Cyanide, Cyanamides, Cyanate, Selenocyanate and Thiocyanate: Solubilities of Solids . 3 September 2013 . Elsevier . 978-1-4831-5492-3 . 92 . en.
10. Dodds . Christopher A. . Kennedy . Alan R. . Thompson . Ross . 2019-08-25 . Taming Copper(I) Cyanate and Selenocyanate with N-Heterocyclic Carbenes . European Journal of Inorganic Chemistry . en . 2019 . 31 . 3581–3587 . 10.1002/ejic.201900515 . 202034228 . 1434-1948.