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Thiocyanate [6] is known to be an important part in the biosynthesis of hypothiocyanite by a lactoperoxidase. [7] [8] [9] Thus the complete absence of thiocyanate or reduced thiocyanate [10] in the human body, (e.g., cystic fibrosis) is damaging to the human host defense system.
HSAB is an acronym for "hard and soft (Lewis) acids and bases".HSAB is widely used in chemistry for explaining the stability of compounds, reaction mechanisms and pathways. It assigns the terms 'hard' or 'soft', and 'acid' or 'base' to chemical species.
Hard metal cations, as classified by HSAB theory, tend to form N-bonded complexes (isothiocyanates), whereas class B or soft metal cations tend to form S-bonded thiocyanate complexes.
For example, the complex [Ni(dien) 2)] 2+ is more stable than the complex [Ni(en) 3)] 2+; both complexes are octahedral with six nitrogen atoms around the nickel ion, but dien (diethylenetriamine, 1,4,7-triazaheptane) is a tridentate ligand and en is bidentate. The number of chelate rings is one less than the number of donor atoms in the ligand.
An example is thiocyanate, SCN −, which can attach at either the sulfur atom or the nitrogen atom. Such compounds give rise to linkage isomerism . Polydentate and ambidentate are therefore two different types of polyfunctional ligands (ligands with more than one functional group ) which can bond to a metal center through different ligand ...
Ammonium thiocyanate is stable in air; however, upon heating it isomerizes to thiourea: The equilibrium mixtures at 150 °C and 180 °C contain 30.3% and 25.3% (by weight) thiourea, respectively. When heated at 200 °C, the dry powder decomposes to ammonia, hydrogen sulfide, and carbon disulfide, leaving a residue of guanidinium thiocyanate.
The esters of thiocyanic acid have the general structure R−S−C≡N, where R stands for an organyl group. Isothiocyanic acid, HNCS, is a Lewis acid whose free energy, enthalpy and entropy changes for its 1:1 association with a variety of Lewis bases in carbon tetrachloride solution at 25 °C have been reported.
Nickel chloride NiCl 2 is yellow, crystallising in the cadmium chloride structure. It can form a hexahydrate, NiCl 2 ·6H 2 O, a tetrahydrate NiCl 2 ·4H 2 O over 29 °C and a dihydrate, NiCl 2 ·2H 2 O over 64 °C. [3] Ammine complexes like hexaamminenickel chloride also exist. Nickel bromide NiBr 2 is