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Correlation between Solution and the Solid State: The pH Dependent Composition in the Ternary System [Co(H 2 O) 6 ] 2+ or [Ni(H 2 O) 6 ] 2+ /Piperazine/Phosphate
Author(s) -
Craven Emma,
AbuShandi Khalid,
Janiak Christoph
Publication year - 2003
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200390031
Subject(s) - potentiometric titration , chemistry , crystallization , titration , piperazine , nickel , cobalt , inorganic chemistry , ternary operation , ligand (biochemistry) , ionic strength , metal , crystallography , nuclear chemistry , ion , aqueous solution , organic chemistry , biochemistry , receptor , computer science , programming language
The protolytic equilibria of piperazine (C 4 H 10 N 2 ) and phosphate have been investigated in the presence of cobalt or nickel chloride or nitrate by potentiometric titrations between pH 2 and 8. Potentiometric titrations suggest the presence of [M 2+ (H 2 O) 5 (C 4 H 11 N 2 + )] 3+ and [M 2+ (H 2 O) 5 (C 4 H 10 N 2 )] 2+ in solution with stability constants logK of 3.1 and 3.8 for M = Co and 3.1 and 3.6 for M = Ni, respectively. Crystallization experiments were then conducted at selected pH values to isolate desired species from the known solution composition. Crystallization afforded [M(H 2 O) 6 ] 2+ (C 4 H 12 N 2 2+ )(HPO 4 2— ) 2 at pH 3.5 and 6.2 (M = Co, Ni), and Co 3 (PO 4 ) 2 ·8H 2 O at pH 10.5. No crystals with the dihydrogenphosphate anion or a metal‐bound piperazine ligand could be isolated under the reaction conditions. The solid‐state assembly in the isomorphous structures of [M(H 2 O) 6 ](C 4 H 12 N 2 )(HPO 4 ) 2 with M = Co and Ni is based on an extended hydrogen bonded network between the three ionic building blocks.