Correlation between Solution and the Solid State: The pH Dependent Composition in the Ternary System [Co(H₂O)₆]²⁺ or [Ni(H₂O)₆]²⁺/Piperazine/Phosphate

Abstract

The protolytic equilibria of piperazine (C4H10N2) 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 [M2+(H2O)5(C4H11N2+)]3+ and [M2+(H2O)5(C4H10N2)]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(H2O)6]2+(C4H12N22+)(HPO42—)2 at pH 3.5 and 6.2 (M = Co, Ni), and Co3(PO4)2·8H2O 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(H2O)6](C4H12N2)(HPO4)2 with M = Co and Ni is based on an extended hydrogen bonded network between the three ionic building blocks.

Mixed-valence phosphato–hydrogenphosphato–iron network compounds1∞{[C4N2H11.6]1.5[FeIIFeIII(PO4)(H0.8PO4)2]·H2O} and3∞[FeII5FeIII2(PO4)2(H0.5PO4)4]: structure elucidation with the help of Mössbauer spectroscopy and a caveat on X-ray diffraction

“…40 ) 2 (M = Co(), Ni()) which could be grown regardless of the solution pH values between 3.5 and 6.2. 29 The structures stabilize the coexistence of [C 4 N 2 H 12 ] 2ϩ and HPO 4 2Ϫ in a ratio which could not be found in aqueous solution (see Fig. 2).…”

“…Compound 1 ∞ {[C 4 N 2 H 11.6 ] 1.5 [Fe II Fe III (PO 4 )(H 0.8 PO 4 ) 2 ]ؒH 2 O}, 1 Hydrothermal treatment of piperazinedium hydrogenphosphate monohydrate 29 with iron() chloride in the presence of triethylamine in tetrahydrofuran at 180 ЊC yielded darkblue crystals (turning green upon grinding) which have been analyzed as 1 ∞ {[C 4 N 2 H 11.6 ] 1.5 [Fe II Fe III (PO 4 )(H 0.8 PO 4 ) 2 ]ؒH 2 O} (1) (eqn. ( 1)) from single-crystal X-ray diffraction and Mössbauer spectroscopy.…”

Concentration dependent tautomerism in green [Cu(HL1)(L2)] and brown [Cu(L1)(HL2)] with H2L1 = (E)-N′-(2-hydroxy-3-methoxybenzylidene)benzoylhydrazone and HL2 = pyridine-4-carboxylic (isonicotinic) acid

“…Also, the solidstate composition, discussed below, is primarily influenced by the solubility and not necessarily by the solution composition. 27 The hydrazone H 2 L 1 shows IR bands assigned to n (OH) (3563 cm -1 ), n (NH) (3377 and 3215 cm - where either the mono-anion (HL 1 )or di-anion (L 1 ) 2of the Schiff base functions as a ligand (Scheme 1 and 3). The ratio of 1 to 2 in the crystalline solid depends on the solution concentration from which they are crystallized.…”

Hydrophilic interior between hydrophobic regions in inverse bilayer structures of cation–1,1′-binaphthalene-2,2′-diyl phosphate salts

“…Hydrogen bonding to phosphate occurs essentially only to the terminal P-O (À) bonds, with each oxygen atom typically accepting 2-3, and rarely 4, hydrogen bonds. 15 The only exception is the isonicotinium acid structure 2, where, in the absence of solvent molecules of crystallization, there is only one hydrogen bond to each terminal oxygen atom.…”

“…8 Coordination polyhedron of [Cu(H 2 O) 2 (CH 3 OH) 4 ] 21 in 5. Selected bond lengths (A ˚) and angles (1): Cu-O5 1.937(4), Cu-O6 2.112(4), Cu-O7 2.167(4); O5-Cu-O6 91.97(16), O5-Cu-O6 5 88.03(16), O5-Cu-O7 86.97(17), O5-Cu-O7 5 93.03(17), O6-Cu-O7 87.58(15), O6-Cu-O7 5 92.42(15). Vibrational ellipsoids are drawn at the 50% level; symmetry transformation 5 = Àx, Ày, Àz.…”