In general, if the atoms that make up the ring contain heteroatoms, such rings become heterocycles, and organic compounds containing heterocycles are called heterocyclic compounds. An article called New mode of ion size discrimination for Group 2 metals using poly(pyrazolyl)borate ligands. Control of stability and structure of chelate complexes by intraligand contact, published in 1993-05-19, which mentions a compound: 18583-60-3, Name is Potassiumtris(1-pyrazolyl)borohydride, Molecular C9H10BKN6, Safety of Potassiumtris(1-pyrazolyl)borohydride.
Selectivity of [HnB(pz)4-n]- (n = 0-2; pz = pyrazolyl ring) for Group 2 metal ions was studied by liquid-liquid extraction The dominant extracted species is [HnB(pz)4-4n]2M. Bidentate [H2B(pz)2]- is a weak extracting reagent for Be2+ and Mg2+. Hydrotris(pyrazolyl)borate extracts Be2+, Mg2+, and Ca2+ effectively, and Sr2+ to some extent. Although [B(pz)4]-, a potentially tridentate ligand similar to [HB(pz)3]-, extracts Be2+ and Mg2+, the extractability for Ca2+ drops drastically. The different selectivity of these ligands cannot be explained from basicity of the donor atoms. To explore the origin of the selectivity, x-ray crystal structures of the extracted species were determined Complexes of [HB(pz)3]2Mg (1), [HB(pz)3]2Ca (2), and [B(pz)4]2Mg(3) have distorted octahedral geometries with each ligand having tridentate coordination. In the complex [B(pz)4]2Be (4), the ligands are bidentate and the geometry about the Be atom is distorted tetrahedral. The extracted species of Be2+ with [HB(pz)3]- changes from [HB(pz)3]2Be to [(HB(pz)3)BdOH]3 (5) as the initial concentration of Be2+ increases at 10-4-10-2 M. Complex 5 consists of bidentate [HB(pz)3]- and a cyclic [BeOH]33+ moiety which is the dominant species of Be in aqueous solution (pH 5). The 1H NMR spectra show that solution structures of these complexes in CDCl3 are similar to the structure in solid state. Examination of the dimensions of the complexes revealed that the stability and structure of poly(pyrazolyl)borate complexes of Group 2 metals are controlled by intraligand contact between pyrazolyl rings bonded to the central B atom. This is a novel model of ion size discrimination by chelating ligands.
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Reference:
Piperazine – Wikipedia,
Piperazines – an overview | ScienceDirect Topics