Phosphorus-31 nuclear magnetic resonance study of aluminium(III) ortho-phosphate complexes in aqueous solution

Previously, a model for aluminium(III) phosphate complexation in 3 M (Na)ClO4 aqueous solution at 25 degrees C has been proposed, on the basis of potentiometric titration data, in which there are eleven phosphorus-containing species. Support for this model is provided by the assignment to these species of eight peaks in P-31 NMR spectra obtained, under the same conditions of temperature and ionic strength, from a set of Al(ClO4)(3)-H3PO4 NaH2PO4 solutions. The assignment was made by correlating fractional NMR peak areas with fractional complex concentrations calculated using the potentiometric data model. The chemical shift in the range 0.3-0.91 ppm is assigned to H3PO4, H3PO4- H-6(PO4)(2)(-), H-5(PO4)(2)(-), and in part to Al3H-8(H3PO4)(5)(+) and Al3H-6(H(3)pO(4))(4)(3+), in fast proton exchange. The peaks at -6.8, -7.4 and -12.4 ppm are.assigned to isomers of Al(H2PO4)(2)(+). The signal at -7.4 is also due to AlH2PO42+. Polynuclear complexes have been assigned as follows. Al3H-5(H3PO4)(2)(4+) -11.5, Al3H-6(H3PO4)(4)(3+) -11.7, Al3H-8,(H3PO4)(5)(+) -12.3 and Al3H-6(H3PO4)(4)(3+) -16.8 ppm. A further four peaks were observed but could not be assigned. All chemical shifts are relative to 85% phosphoric acid as external reference

Complexation of beryllium(II) ion by phosphinate ligands in aqueous solution. Synthesis and XRPD structure determination of Be[(PhPO2)(2)CH2](H2O)(2)

Two bifunctional ligands, phenyl(carboxymethyl)phosphinate (ccp(2-)) and P,P'-diphenylmethylenediphosphinate (pcp(2-)), have been tested as chelating agents of beryllium(II). Both ligands have the same charge and a similar chelating structure, but whereas the 1:1 adduct of pcp(2-), Be(pcp)((HO)-O-2)(2), could be isolated as a white powder, no pure compound could be isolated from solutions containing beryllium(II) and ccp(2-). Instead, the solutions were examined by means of potentiometry and Be-9 NMR spectroscopy. Analysis of the potentiometric titration data with the program HYPERQUAD suggested the formation of the complex species BeL, [BeHL](+), [BeL2](2-), and [BeHL2](-) (L = ccp). The formation constants for these species were determined at 25 degreesC and / = 0.5 mol dm(-3) NaCIO4. The Be-9 NIVIR spectra are consistent with this model. The formation constants found for the ccp(2-) complexes are lower than those reported for related phosphonate ligands. However, the effective stability constant (which gives a better indication of the intrinsic coordinating capacity of the ligand at a particular pH) of the complex [Be(ccp)(2)](2-) at pH < 4 is greater than the effective constants of the corresponding phosphonoacetate and methylenediphosphonate complexes. The structure of Be(pcp)(H2O)(2) was determined by X-ray powder diffraction methods and consists of discrete molecules interconnected by an extended 2D network of hydrogen bonds, resulting in a stacking of double layers with a polar core and a lipophilic surface. Crystal data: C13H16BeO6P2, fw 339.21, monoclinic P2(1)/c, a 16.174(1) Angstrom, b = 8.979(1) Angstrom, c = 10.929(1) Angstrom, beta = 90.398(9)degrees, V = 1587.2(3) Angstrom(3), Z = 4

Coordinated water/anion hydrogen bonds and Pd-H bond acidity in cationic palladium(II) aquo hydrides and the x-ray crystal and molecular structures of trans-[(Cy3P)2Pd(H)(H2O)]BF4 (Cy = cyclohexyl)

Palladium(II) bis(tricyclohexylphosphine) cationic hydrides have been obtained by oxidative addition of the strong acids [H3O+][BF3OH-] or [H3O+][BF4-] to (PCy3)2Pd, 1; by this route, the compounds trans-[(Cy3P)2Pd(H)(H2O)]X (X = BF3OH, 2; X = BF4,4) have been isolated and characterized. A strong dependence of the stability of trans-[(Cy3P)2Pd(H)(L)]X complexes upon the L-X combinations was observed. When L = H2O, stable cationic hydrides are obtainable only with fluorine-containing anions (BF3OH-, BF4-, or PF6-), while immediate decomposition to 1 was observed when the metathesis of X- with BPh4- or B(n-Bu)4- was attempted. Stable complexes with X = BPh4 could be isolated when L = MeCn. No reaction was observed when 1 was reacted with [Et2OH+][BF4-]. These findings can be explained in principle by two hypotheses: (i) when the strength of the M-L bond is not sufficient to stabilize the [(R3P)2Pd(H)(L)]X complexes, further thermodynamic assistance is furnished by hydrogen-bond formation between the metal-bonded ligand L and the X counteranion, and/or (ii) depending upon the nature of L, the cationic hydrides are sufficiently acidic to decompose reactive anions such as BPh4- or B(n-Bu)4-. IR and crystallographic data on trans-[(Cy3P)2Pd(H)(H2O)]BF4 show the existence, in the solid state, of strong hydrogen bonds between the Pd-bound water molecule and the BF4- anion. A conductivity study on 4 and on the related hydride trans-[(Cy3P)2Pd(H)(MeCN)]BF4, 5, shows the existence of large concentrations of ions both in 4 and 5 solutions, though the values of LAMBDA-M (10-20% lower for 4 as compared to 5) could account for the presence in 4 of appreciable amounts of the hydrogen-bonded species. The aquohydride 4 has evidenced its acidic behavior by protonating strong and weak bases (Ph3C-, OH-, Et3N, and PCy3), and further information on its acid-base behavior has been obtained through the study of exchange reactions with D2O. The aquodeuteride trans-[(Cy3P)2Pd(D)(H2O)]BF4. 9, can in fact be obtained by reacting for a few minutes a solution of complex 4 with D2O while the d3 derivative trans-[(Cy3P)2Pd(D)(D2O)]BF4, 10, can only be obtained after prolonged reaction times. Complex 2 behaves similarly, and trans-[(Cy3P)2Pd(D)(H2O)]BF3OD, 11, or trans-[(Cy3P)2Pd(D)(D2O)]BF3OD, 12, can be prepared by controlling the reaction times with D2O. These data suggest that the acidity of the hydridic hydrogen is higher than the acidity of the hydrogens of the PdOH2 moiety. The last hypothesis is further confirmed by the reaction of trans-[(Cy3P)2Pd(D)(H2O)]BF4 with Ph3CLi, which yields a 70/30 Ph3C-d/Ph3C-h mixture. Crystals of 4 are monoclinic, C2/c, a = 30.587 (6) angstrom, b = 13.408 (4) angstrom, c = 19.121 (5) angstrom, beta = 99.23 (3)-degrees, V = 7740.2 angstrom 3, Z = 8, R = 0.040 for 3077 reflections with F(o) > 4-sigma-(F(o)

Complex formation equilibria of phosphocreatine with sodium, potassium and magnesium ions

The formation of complexes between phosphocreatine, H2O3PNHC(=NH)N(CH3)CH2CO2H, and the ions Na+, K+ and Mg2+ have been investigated under physiological conditions (aqueous solution, T=37degreesC and I=0.25 mol dm(-3)) by means of P-31 NMR spectroscopy. Only 1:1 complexes have been identified. Stability constants have been determined with the aid of the new computer program HYPNMR-2000. log(10) K values were found to be -0.5(2),-0.3(2) and 1.43(3), respectively. The formation constant for the potassium complex is two orders of magnitude less that the literature value

Stepwise electron-induced demolition of the Ni-I sigma-bond in complexes with tetradentate tripodal ligands: A theoretical rationalization of structural and electrochemical results

The X-ray structural analysis of the compound [(pp3)Nil]BPh4 (complex d), pp3 = P(CH2CH2PPh2)3, is presented. The complex cation has an almost regular trigonal bipyramidal geometry (TBP) with distances Ni-I and Ni-Pax of 2.546(2) and 2.142(3) \uc5, respectively. This structure completes a series of strictly related nickel complexes, namely [(np3)Nil]I, complex a; (np3)Nil, complex b; (np3)Ni, complex c; [(pp3)NiHClO4), complex e; [np3 = N(CH2CH2PPh2)3] The complexes are redox derivatives [Ni(II), Ni(I), Ni(O)] that can be isolated via chemistry and/or electrochemistry. In the solid state complexes c and e have a trigonal pyramidal (TP) structure, whereas, electrochemical measurements suggest that in solution the TBP structure with a very elongated Ni-I bond can also have a finite lifetime. EHMO calculations offer a satisfying interpretation of the main structural trends in complexes a rarr e, in particular, those relative to axial bond stretching, and clarify the different roles of phosphine vs. the amine axial donor. Moreover, the correlation is discussed between the electrode potentials and the nature of the Ni-I sgr* MO that accepts or releases the electrons exceeding thed 8 configuration of Ni(II)