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Structure and spectra of murexide and of alkali purpurates: Crystal structure of lithium purpurate dihydrate
Author(s) -
Bürgi H. B.,
Djurić S.,
Dobler M.,
Dunitz J. D.
Publication year - 1972
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19720550537
Subject(s) - chemistry , triclinic crystal system , lithium (medication) , ion , alkali metal , crystallography , molecule , ionic radius , ionic bonding , crystal structure , atom (system on chip) , crystal (programming language) , lithium atom , inorganic chemistry , ionization , medicine , organic chemistry , computer science , embedded system , endocrinology , programming language
Crystals of lithium purpurate dihydrate are triclinic, a = 6.715, b = 6.822, c = 14.038 Å, α = 96.85, β = 100.94, γ = 67.41°, space group P 1 , Z = 2. From the results of a detailed three‐dimensional analysis the lithium ion is found to be bonded to three atoms (two oxygen plus central nitrogen) of one purpurate anion, and also to an oxygen atom of a second purpurate anion and to a water molecule to complete a roughly square‐pyramidal 5‐coordination. The purpurate anion is markedly nonplanar, the two six‐membered rings being twisted by 22° around the central CN bonds. A molecular mechanics calculation, based on reasonable interatomic potential functions, reproduces the observed geometry of the lithium complex and indicates that with larger cations the degree of out‐of‐plane twisting should increase. The observed dependence of the characteristic long‐wave absorption of purpurate complexes on ionic radius is explained qualitatively on the basis of simple HMO‐theory.