Thermodynamics and hydration of the europium complexes of a nitrogen heterocycle methane-1,1-diphosphonic acid

Abstract

The enthalpies for formation of five Eu 3ϩ complexes with N-piperidinomethane-1,1-diphosphonic acid (H 4 pmdp) have been determined by titration calorimetry in 2 M (Na,H)ClO 4 media at 25 ЊC. Both protonation enthalpies and entropies, and the structure of H 4 pmdp in the solid state indicate protonation of the piperidine nitrogen to give a zwitterion in the free ligand. Luminescent lifetime measurements show that the formation of the 1 : 1 and 1 : 2 Eu : L complexes of a variety of methane-1,1-diphosphonic acids liberates an average of 3.3 ± 0.1 water molecules per ligand from the Eu inner hydration sphere. The number of water molecules in the inner coordination sphere and the thermodynamic parameters of the complexes suggest that the structure of the Eu 3ϩ -pmdp complexes and the strength of the Eu 3ϩ -pmdp bonds are similar to those of other methane-1,1-diphosphonic acids despite the presence of the piperidine ring. However, the complexation entropies argue for weaker solvation of the Eu-pmdp complexes probably due to the hydrophobic character of the piperidine ring.

Synthesis and Characterization of 1‐, 2‐, and 3‐Dimensional Bimetallic UO22+/Zn2+ Phosphonoacetates

“…[1][2][3] In spite of this relevance to separations and nuclear fuel stewardship, our knowledge of the structural chemistry of actinide phosphonates has largely been limited to those uranyl phenylphosphonates reported by Clearfield et al, [4][5][6][7][8][9][10][11][12] as well as a handful of other compounds. [13][14][15][16][17][18] More recently, in an effort to probe the structural chemistry of uranyl phosphonate compounds and extend the known catalog of these materials beyond monophosphonates, the interaction of UO 2 2+ with polyphosphonate [19][20][21][22][23][24] and carboxyphosphonate ligands [25][26][27] has been explored.…”

“…[32,33] With respect to the latter, the interactions of biological species with uranium are influenced by the functionality of cellular components that include hydroxy, amino, phosphoryl, and carboxyl groups. [29,34] Carboxyphosphonate compounds contain functionalites analogous to those found in bacteria and other microorganisms, namely both phosphonate (-PO 3 ) and carboxylate (-CO 2 ) groups, and thus provide a suitable model for understanding the complexation behavior of actinides in bio-systems. [35] Whereas a number of UO 2 2+ -carboxylate structures have been synthesized, [36][37][38][39][40][41][42][43][44][45][46][47][48][49] far fewer examples of solid-state UO 2 2+ -carboxyphosphonate architectures have been reported.…”

Crystal Structure, Solid‐State NMR Spectroscopic and Photoluminescence Studies of Organic‐Inorganic Hybrid Materials (HL)6[Ge6(OH)6(hedp)6]·2(L)·nH2O, L = hqn or phen

“…[1][2][3][4][5][6][7][8][9][10][11][12] The organic components of these hybrid materials, until recently based mainly on carboxylic acid functional groups, are at present being replaced by phosphonic acid moieties because of their higher chelating versatility and ability to direct interesting structural topologies. [9,13,14] Examples of these organic chelating molecules include N-(phosphonomethyl)iminodiacetic acid (H 4 pmida) [15] and 1-hydroxyethane-1,1-diphosphonic acid (H 4 HEDP). [16][17][18] ing of 8-hydroxyquinoline and the relative orientation of adjacent such molecules.…”

Actinides in Solution: Complexation and Kinetics

“…23.23), although the stability constants indicate that a range of AnH n edtmp nÀ5 complexes exist in 1 M NaOH for a concentration of 1 Â 10 À4 M edtmp (Shalinets, 1972b). Inter-ligand hydrogen bonding between the amines and the phosphonates (Jensen et al, 2000b) and steric constraints (Shalinets, 1972c) apparently resist the formation of complexes in these aminomethylenephosphonates.…”

“…Partially protonated complexes are believed to be a key factor in the strength of these diphosphonate complexes, stabilizing the 1:2 actinide:phosphonate complexes through inter-ligand, intracomplex hydrogen bonding (Nash et al, 1995). The larger anionic charge of the fully deprotonated phosphonic acids, the presence of inter-ligand hydrogen bonding, and the enhanced dehydration of the metal cations on complexation (Jensen et al, 2000b), contribute to the stability of actinide-diphosphonate complexes, as does the strength of the An-O¼P bond. Complexation of An(IV) cations by neutral, fully protonated methanediphosphonic acid, CH 2 (PO 3 H 2 ) 2 , persist in 2 M nitric acid at ligand concentrations as low as 0.05 M (Nash, 1991b).…”