Synthesis and structure of (2-hydroxy-2' -carboxy-5-methylazobenzoate)potassium (I)

Abstract

The salt K(Hazc).1.5H₂O has been isolated by reacting H₂azc (where H₂azc=2-hydroxy-2'-carboxy- 5-methylazobenzene) with KOH. X-ray structure determination has revealed the presence of an infinite structure in which the potassium ions are bridged by carboxylic, phenolic and water oxygen atoms but not coordinated to the azo function. One water molecule is also hydrogen-bonded to a carboxyl oxygen function. The potassium ion has a coordination sphere KO₇ formed by carboxyl, aquo and phenolic oxygen atoms. Its geometry is irregular with three K - O bonds in the range 2.672(3)-2.762(3) Å and the remaining four in the range 2.921(3)-3.157(3) Å. The significant deviation in K-O bond distances (0.2 Å) is attributed to the hydrogen-bonding with some oxygen atoms. The bridging water molecules are of two types: one occupying a general position and the other sitting on a crystallographic two-fold axis. Crystal data are: crystal system, monoclinic; space group C2/c; a=35.423(11) Å, b=4.462(2) Å, c= 18.181(7) Å, <i>β=</i>95.48(3)<i>; </i>V=2861(2) ų <i>; </i> Z=8; R = 4.41%, R_w = 4.56%.