Metal organic chemical vapour deposition (MOCVD) of bone mineral like carbonated hydroxyapatite coatings

For the first time, the MOCVD technique has been used to deposit carbonated hydroxyapatite onto Ti6AL4V substrates using volatile monomeric (liquid) complexes [Ca(beta-diketonate)(2)(L)] and P(OEt)(3).     

Vibrational study and fluorescence bands in the FT-Raman spectra of Ca(10-x)Pb(x)(PO4)6(OH)2 compounds

About 40 apatitic compounds, stoichiometric or not, with different substitutions like lead, sodium and cadmium were investigated using infrared, Raman and FT-Raman spectroscopies. In the Ca(10-x)Pb(x)(PO4)6(OH)2 sequence (x runs from 0 to 10), the evolution of the fluorescence bands observed by FT-Raman, only with stoichiometric entities apatites, is mainly regarded and explained. Important spectral changes concerning the OH- and the PO4(3-) entities occur when 4 < or = x < or = 7. The intensity ratio of the two components of the v1 PO4(3-) mode is shown to be a suitable method to determine the lead content. The weak OH...O hydrogen bonds involving the OH- ions, of which the disorder is discussed, are different for the lead and calcium hydroxyapatites. The evolution of the fluorescence bands, as well as the splitting of the v(OH) mode, are due to the lead distribution in the two sites, with a preference for sites II, of the hydroxyapatite structure. The effect of temperature is also reported.     

Cadmium removal from single- and multi-metal (Cd + Pb + Zn + Cu) solutions by sorption on hydroxyapatite

Heavy metal contamination of waters and soils is particularly dangerous to the living organisms. Different studies have demonstrated that hydroxyapatite has a high removal capacity for divalent heavy metal ions in contaminated waters and soils. The removal of Cd from aqueous solutions by hydroxyapatite was investigated in batch conditions at 25+/-2 degrees C. Cadmium was applied both as single- or multi-metal (Cd + Pb + Zn + Cu) systems with initial concentrations from 0 to 8 mmol L(-1). The adsorption capacity of hydroxyapatite in single-metal system ranged from 0.058 to 1.681 mmol of Cd/g of hydroxyapatite. In the multi-metal system competitive metal sorption reduced the removal capacity by 63-83% compared to the single-metal system. The sorption of Cd by hydroxyapatite follows the Langmuir model. Cadmium immobilization occurs through a two-step mechanism: rapid surface complexation followed by partial dissolution of hydroxyapatite and ion exchange with Ca resulting in the formation of a cadmium-containing hydroxyapatite.     

Colloidal and monocrystalline Ln3+ doped apatite calcium phosphate as biocompatible fluorescent probes

Ultrafine individualised mono crystalline Ca(10-x)(PO4)(6-x)(HPO4)x(OH)(2-x) deficient calcium hydroxyapatite nanocrystals displaying fluorescence under visible excitation are proposed for utilisation as biocompatible biological probes.     

Analysis of bone minerals by time-of-flight secondary ion mass spectrometry: a comparative study using monoatomic and cluster ions sources

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is an important tool for the analysis of bone minerals at implant surfaces. Most studies have been performed with monoatomic primary ion sources such as Ga(+) with poor secondary molecular ion production efficiency and only elemental distributions and minor fragments of bone minerals have been reported. By using cluster ion sources, such as Au(1-3) (+) and Bi(1-3) (+), identification of larger hydroxyapatite species at m/z 485, 541, 597 and 653, identified as Ca(5)P(3)O(12), Ca(6)P(3)O(13), Ca(7)P(3)O(14) and Ca(8)P(3)O(15), respectively, became possible. The ions appear to be fragments of the hydroxyapatite unit cell Ca(10)(PO(4))(6)(OH)(2). Each ion in the series is separated by 55.9 m/z units, corresponding to CaO, and this separation might reflect the columnar nature of the unit cell.     

Periodic ab initio study of structural and vibrational features of hexagonal hydroxyapatite Ca10(PO4)6(OH)2

Structural and vibrational features of hexagonal hydroxyapatite HA [Ca(10)(PO(4))(6)(OH)(2), space group P6(3)] are computed ab initio within a periodic approach using the CRYSTAL03 program and the B3LYP hybrid functional with a Gaussian-type basis set of polarized double zeta quality. Experimental lattice parameters and internal coordinates have been fully optimized and the final structure characterized by means of its band structure, density of states and Mulliken analysis. The full B3LYP harmonic vibrational spectrum of HA at Gamma point has also been computed and compares well with the available experimental IR and Raman data. Nevertheless, the presence of one negative frequency in the computed spectrum shows that, within the hexagonal symmetry imposed by the P6(3) group, the structure is a saddle point. This is at variance with the monoclinic structure (under P2(1)/b space group), which has been computed, with the same approach, to be a minimum of 17 kJ mol(-1) (per unit cell) more stable than the corresponding hexagonal HA structure.     

Zn(ii), Cd(ii) and Pb(ii) complexation with pyridinecarboxylate containing ligands

Herein, we report the coordination properties towards Zn(ii), Cd(ii) and Pb(ii) of two hexadentate ligands containing pyridinecarboxylate groups with ethane-1,2-diamine (bcpe) or cyclohexane-1,2-diamine (bcpc) backbones. The X-ray crystal structures of [Zn(bcpe)], [Cd(bcpe)] and [Cd(bcpc)] show hexadentate binding of the ligand to the metal ions, with the coordination polyhedron being best described as a severely distorted octahedron. The X-ray crystal structure of the Pb(ii) analogue shows the presence of tetrameric structural units [Pb(4)(bcpe)(4)] in which the four Pb(ii) ions are bridged by carboxylate oxygen atoms. While in the Zn(ii) and Cd(ii) complexes the bcpe ligand adopts a twist-wrap (tw) conformation in which the ligand wraps around the metal ion by twisting the pyridyl units relative to each other, for the Pb(ii) complex a twist-fold (tf) conformation, where a slight twisting of the pyridyl units is accompanied by an overall folding of the two pyridine units relative to each other is observed. Theoretical calculations performed at the DFT (B3LYP) level on the [Pb(bcpe)] and [Pb(bcpc)] systems indicate that the tf conformation is more stable than the tw form both in the solid state and in aqueous solution. The analysis of the natural bond orbitals (NBOs) indicate that the Pb(ii) lone-pair is polarized by a substantial 6p contribution, which results in a hemi-directed coordination geometry around the metal ion. Potentiometric studies have been carried out to determine the protonation constants of the ligands and the stability constants of the complexes with Zn(ii), Cd(ii), Pb(ii) and Ca(ii). The replacement of the ethylene backbone of bcpe by a cyclohexylene ring causes a very important increase in the stability constant of the Pb(ii) complex (ca. 2.3 logK units), while this effect is less important for Cd(ii) (ca. 1.4 logK units). However, the introduction of the cyclohexylene ring does not substantially affect the stability of the Zn(ii) and Ca(ii) complexes. The ligand bcpc shows Pb/Ca and Cd/Ca selectivities [10(8.9) and 10(9.8), respectively] superior to those of extracting agents, such as EDTA, already used in Pb(ii) and Cd(ii) removal from contaminated water and soils.     

Controlled synthesis of hydroxyapatite-supported palladium complexes as highly efficient heterogeneous catalysts

Achieving precise control of active species on solid surfaces is one of the most important goals in the development of highly functionalized heterogeneous catalysts. The treatment of hydroxyapatites with PdCl(2)(PhCN)(2) gives two new types of hydroxyapatite-bound Pd complexes. Using the stoichiometric hydroxyapatite, Ca(10)(PO(4))(6)(OH)(2), we found that monomeric PdCl(2) species can be grafted on its surface, which are easily transformed into Pd(0) particles with narrow size distribution in the presence of alcohols. Such metallic Pd species can effectively promote alcohol oxidation using molecular oxygen and are shown to give a remarkably high TON of up to 236 000. Another monomeric Pd(II) phosphate complex can be generated at a Ca-deficient site of the nonstoichiometric hydroxyapatite, Ca(9)(HPO(4))(PO(4))(5)(OH), affording a catalyst with Pd(II) structure and high activity for the Heck and Suzuki reactions. To the best of our knowledge, the PdHAP are one of the most active heterogeneous catalysts for both alcohol oxidation under an atmospheric O(2)() pressure and the Heck reaction reported to date. These Pd catalysts are recyclable in the above organic reactions. Our approach to catalyst preparation based on the control of Ca/P ratios of hydroxyapatites represents a particularly attractive method for the nanoscale design of catalysts.     

Protein adsorption behaviors onto photocatalytic Ti(IV)-doped calcium hydroxyapatite particles

The fundamental experiments on the adsorption behaviors of proteins onto photocatalytic Ti(4+)-doped calcium hydroxyapatite (TiHap) particles were examined comparing to those onto the calcium hydroxyapatite (CaHap) and commercially available typical titanium oxide (TiO(2)) photocatalyst (TKP-101). The heat treated TiHap and CaHap particles were also used after treated these particles at 650°C for 1h (abbreviated as TiHap650 and CaHap650, respectively). All the adsorption isotherms of bovine serum albumin (BSA), myoglobin (MGB) and lysozyme (LSZ) from 1×10(-4)mol/dm(3) KCl solution were the Langmuirian type. The saturated amounts of adsorbed BSA (n(s)(BSA)) for the CaHap650 particles was higher than that for CaHap. Similar results were observed for TiHap and TiHap650. The adsorption of LSZ exhibited the same result of BSA, while the saturated amounts of adsorbed LSZ (n(s)(LSZ)) value on the TiHap were much higher than CaHap. However, the saturated amounts of adsorbed MGB (n(s)(MGB)) are almost equal to those for the CaHap and TiHap nevertheless whether these particles were heat treated at 650°C or not. The TKP-101 exhibited extremely small adsorption capacity of all proteins due to its small particle size of ca. 4nm in diameter. The independence of the n(s)(MGB) value on the zeta potential (zp) of the particles was explained by the electrostatical neutrality of MGB molecules. On the other hand, the n(s)(LSZ) values were increased with increase in the negative zp of the particles. This fact was explained by increasing the electrostatic attractive forces between negatively charged particles and positively charged LSZ. However, the n(s)(BSA) values exhibit maxima for the heat treated TiHap650 and CaHap650 particles. This result was interpreted to the formation of β-TCP crystal phase by the heat treatment. The produced Ca(2+) ions by dissolution from β-TCP phase may exert as binders between BSA and surfaces of the heat treated particles.     

Effect of K(+) on the Stoichiometry of Carbonated Hydroxyapatite Obtained by the Hydrolysis of Monetite

This study investigates the stoichiometry and the thermal stability of K(+)- and CO(3)(2)(-)-containing apatites (KCAp's) obtained by the hydrolysis of monetite. The analysis results of the samples after drying reveal that the KCAp's start to lose carbonate at temperatures V(Ca) + CO(3)(2)(-) + V(OH)] and [Ca(2+) + PO(4)(3)(-) <--> K(+) + CO(3)(2)(-)], where V(X) stands for a vacancy in the X-sublattice. Moreover, a small part of the CO(3)(2)(-) ions are presumably incorporated according to [Ca(2+) + 2PO(4)(3)(-) <--> V(Ca) + 2CO(3)(2)(-)]. A comparison of the contributions of these fundamental mechanisms with the results for precipitated Na(+)- and CO(3)(2)(-)-containing apatites shows that no intrinsic coupling whatsoever exists between these mechanisms.     

Heavy-metal aromatic and conjugated species: rings, oligomers, and chains of tin in Li(9)(-)(x)EuSn(6+)(x), Li(9)(-)(x)CaSn(6+)(x), Li(5)Ca(7)Sn(11), Li(6)Eu(5)Sn(9), LiMgEu(2)Sn(3), and LiMgSr(2)Sn(3)

The title compounds were synthesized from the elements by heating the corresponding mixtures at high temperature. Their structures were determined from single-crystal X-ray diffraction. Li(9)(-)(x)()EuSn(6+)(x)(), Li(9)(-)(x)()CaSn(6+)(x)(), Li(5)Ca(7)Sn(11), and Li(6)Eu(5)Sn(9) contain columns of stacked aromatic pentagons of Sn(5)(6)(-) that are analogous to the cyclopentadienyl anion C(5)H(5)(-). The pentagons are separated with Ca(2+) or Eu(2+) in the columns and resemble a polymeric metallocene. In addition to the columns, the isostructural Li(9)(-)(x)()EuSn(6+)(x)() and Li(9)(-)(x)()CaSn(6+)(x)() contain isolated tin atoms and bent tin trimers while Li(5)Ca(7)Sn(11) and Li(6)Eu(5)Sn(9) contain flat zigzag hexamers and flat zigzag infinite chains of tin, respectively. The isostructural LiMgEu(2)Sn(3) and LiMgSr(2)Sn(3) do not contain columns of pentagons but only flat zigzag infinite chains of tin. The aromaticity of the pentagons and the conjugation of the pi-systems of the hexamers and the infinite chains are discussed. The title compounds are also characterized by magnetic and conductivity measurements.     

Natural abundance 43Ca solid-state NMR characterisation of hydroxyapatite: identification of the two calcium sites

Natural abundance (43)Ca solid-state NMR of hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2)) was performed at three different fields (8.45, 14.1 and 18.8 T). The two crystallographically distinct calcium sites of the apatite structure were spectroscopically resolved at 18.8 T. The (43)Ca NMR interaction parameters (delta(iso), C(Q) and eta(Q)) of each site were determined by multiple magnetic-field simulations. The peaks with delta(iso) = 11.2 +/- 0.8 and - 1.8 +/- 0.8 ppm, both with C(Q) = 2.6 +/- 0.4 MHz, were assigned to the Ca(II) and Ca(I) sites, respectively, on the basis of their relative intensities.     

Ca(1)(-)(x)Na(2)(x)Al(2)B(2)O(7): a structure with tunable density of Na(+) vacancies

A series of samples with the composition Ca(1)(-)(x)Na(2)(x)Al(2)B(2)O(7) (0 < x < or = 1) was investigated and a hexagonal structure with unusually large range of homogeneity (at least from x = 0.01 to 0.95) was revealed. The hexagonal phase consists of [Al(2)B(2)O(7)](infinity)(2)(-) lamellae stacked along the c axis, as in CaAl(2)B(2)O(7) and Na(2)Al(2)B(2)O(7). Nevertheless, the configuration and stacking sequence of the [Al(2)B(2)O(7)](infinity)(2)(-) lamellae are different in these three structures. In the hexagonal structure of Ca(1)(-)(x)()Na(2)(x)()Al(2)B(2)O(7), Ca and half Na cations (Na1) statistically occupy the same crystallographic site which is located between the [Al(2)B(2)O(7)](infinity)(2)(-) lamellae, the other half Na cations (Na2) distribute in the planes bisecting the [Al(2)B(2)O(7)](infinity)(2)(-) lamellae. Depending on the composition, the site occupation factor of Na2 site can vary in the same range as x, leading to a tunable density of Na(+) vacancies in the structure. The AlO(4) tetrahedra and BO(3) triangles in the structure tilt in appropriate ways to improve the bond valence sum of Na2 cations which are not sufficiently bonded to the anions.     

A comparative study of the metastable equilibrium solubility behavior of high-crystallinity and low-crystallinity carbonated apatites using pH and solution strontium as independent variables

Using solution strontium and pH as independent variables, the metastable equilibrium solubility (MES) behavior of two carbonated apatite (CAP) samples has been examined, a high-crystallinity CAP (properties expected to be similar to dental enamel) and a low-crystallinity CAP (properties expected to be similar to bone mineral). CAP samples were prepared by precipitation/digestion: (CAP A: high-crystallinity, 1.3 wt% CO3, synthesized at 85 degrees C; CAP B: low-crystallinity, 6.4 wt% CO3, synthesized at 50 degrees C). Baseline MES distributions were determined in a series of 0.1 M acetate buffers containing only calcium and phosphate (no strontium) over a broad range of solution conditions. To assess the influence of strontium, MES profiles were determined in a similar fashion with 20, 40, 60, and 80% of the solution calcium being replaced on an equal molar basis by solution strontium. To determine the correct function governing CAP dissolution, ion activity products (IAPs) were calculated from the compositions of buffer solutions based on the hydroxyapatite template (Ca(10-n)Sr(n)(PO4)6(OH)2 (n = 0-10)) and the calcium/hydroxide deficient hydroxyapatite template (Ca(9-n)Sr(n)(HPO4)(PO4)5OH (n = 0-9)). Findings: (a) for CAP A, at high solution strontium/calcium ratios, the MES profiles were essentially superimposable when the solution IAPs were calculated using the stoichiometry of Ca6Sr4(PO4)6(OH)2 and for CAP B by a stoichiometry of Ca7Sr2(HPO4)(PO4)5OH; (b) for CAP A, at low strontium/calcium ratios, the stoichiometry yielding MES data superpositioning was found to be that of hydroxyapatite and for CAP B, that of calcium/hydroxide deficient hydroxyapatite. When other stoichiometries were assumed, good superpositioning of the data was not possible.     

The crystal chemistry of Ca(10-y)(SiO4)3(SO4)3Cl(2-x-2y)F(x) ellestadite

Fluor-chlorellestadite solid solutions Ca(10)(SiO(4))(3)(SO(4))(3)Cl(2-x)F(x), serving as prototype crystalline matrices for the fixation of hazardous fly ash, were synthesized and characterized by powder X-ray and neutron diffraction (PXRD and PND), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The lattice parameters of the ellestadites vary linearly with composition and show the expected shrinkage of unit cell volume as fluorine (IR = 1.33 ?) displaces chlorine (IR = 1.81 ?). FTIR spectra indicate little or no OH(-) in the solid solutions. All compositions conform to P6(3)/m symmetry where F(-) is located at the 2a (0, 0, (1)/(4)) position, while Cl(-) is displaced out of the 6h Ca(2) triangle plane and occupies 4e (0, 0, z) split positions with z ranging from 0.336(3) to 0.4315(3). Si/S randomly occupy the 6h tetrahedral site. Ellestadites rich in Cl (x ≤ 1.2) show an overall deficiency in halogens (<2 atom per formula unit), particularly Cl as a result of CaCl(2) volatilization, with charge balance achieved by the creation of Ca vacancies (Ca(2+) + 2Cl(-) →□(Ca) + 2□(Cl)) leading to the formula Ca(10-y)(SiO(4))(3)(SO(4))(3)Cl(2-x-2y)F(x). For F-rich compositions the vacancies are found at Ca(2), while for Cl-rich ellestadites, vacancies are at Ca(1). It is likely the loss of CaCl(2) which leads tunnel anion vacancies promotes intertunnel positional disorder, preventing the formation of a P2(1)/b monoclinic dimorph, analogous to that reported for Ca(10)(PO(4))(6)Cl(2). Trends in structure with composition were analyzed using crystal-chemical parameters, whose systematic variations served to validate the quality of the Rietveld refinements.     

Theoretical and experimental studies of substitution of cadmium into hydroxyapatite

Substitution of cadmium into bulk hydroxyapatite Ca((10-x))Cd(x)(PO(4))(6)(OH)(2) (CdHA: x = 0.12, 1.3, 2.5) is studied by combining X-ray diffraction data from synchrotron radiation, Fourier transform infra-red spectroscopy (FTIR) and density functional theory (DFT) calculations. Energetic and electronic analyses are carried out for several configurations of Cd substitution for Ca at both cationic sites. Rietveld analysis shows preferential occupation of the Ca2 site by cadmium. FTIR data suggest a non-negligible covalent character of Cd-OH. The much-discussed cation site preference for substitution is determined on the basis of relaxed-lattice energetics, and interpreted in terms of chemical concepts; theory indicates that the Ca2 site is clearly favored and this preference is related to the more covalent character of this site compared to that of site 1.     

Macrocyclic receptor showing extremely high Sr(II)/Ca(II) and Pb(II)/Ca(II) selectivities with potential application in chelation treatment of metal intoxication

Herein we report a detailed investigation of the complexation properties of the macrocyclic decadentate receptor N,N'-Bis[(6-carboxy-2-pyridil)methyl]-4,13-diaza-18-crown-6 (H(2)bp18c6) toward different divalent metal ions [Zn(II), Cd(II), Pb(II), Sr(II), and Ca(II)] in aqueous solution. We have found that this ligand is especially suited for the complexation of large metal ions such as Sr(II) and Pb(II), which results in very high Pb(II)/Ca(II) and Pb(II)/Zn(II) selectivities (in fact, higher than those found for ligands widely used for the treatment of lead poisoning such as ethylenediaminetetraacetic acid (edta)), as well as in the highest Sr(II)/Ca(II) selectivity reported so far. These results have been rationalized on the basis of the structure of the complexes. X-ray crystal diffraction, (1)H and (13)C NMR spectroscopy, as well as theoretical calculations at the density functional theory (B3LYP) level have been performed. Our results indicate that for large metal ions such as Pb(II) and Sr(II) the most stable conformation is Δ(δλδ)(δλδ), while for Ca(II) our calculations predict the Δ(λδλ)(λδλ) form being the most stable one. The selectivity that bp18c6(2-) shows for Sr(II) over Ca(II) can be attributed to a better fit between the large Sr(II) ions and the relatively large crown fragment of the ligand. The X-ray crystal structure of the Pb(II) complex shows that the Δ(δλδ)(δλδ) conformation observed in solution is also maintained in the solid state. The Pb(II) ion is endocyclically coordinated, being directly bound to the 10 donor atoms of the ligand. The bond distances to the donor atoms of the pendant arms (2.55-2.60 ?) are substantially shorter than those between the metal ion and the donor atoms of the crown moiety (2.92-3.04 ?). This is a typical situation observed for the so-called hemidirected compounds, in which the Pb(II) lone pair is stereochemically active. The X-ray structures of the Zn(II) and Cd(II) complexes show that these metal ions are exocyclically coordinated by the ligand, which explains the high Pb(II)/Cd(II) and Pb(II)/Zn(II) selectivities. Our receptor bp18c6(2-) shows promise for application in chelation treatment of metal intoxication by Pb(II) and (90)Sr(II).     

Adsorption of Some Essential Amino Acids on Hydroxyapatite

Samples of synthetic hydroxyapatite, Ca(10)(PO(4))(6)(OH)(2), obtained by wet method and calcined at 1173 K in air were used in an adsorption study of some essential amino acids, mainly histidine, methionine, and tryptophan. Adsorption isotherms were obtained using aqueous solutions of concentration range 2.7x10(-2)-1.3x10(-3) M at 303, 318, and 343 K, under near neutral conditions. The mode of adsorption was studied using IR spectroscopy. The results are discussed in terms of the dependence of the adsorption process both on the functional groups on the hydroxyapatite and on the solution chemistry of the aqueous amino acids solutions. Copyright 2001 Academic Press.     

Structure Refinement and Two-Center Luminescence of Ca(3)La(3)(BO(3))(5):Ce(3+) under VUV-UV Excitation

A series of Ca(3)La(3(1-x))Ce(3x)(BO(3))(5) phosphors were prepared by a high-temperature solid-state reaction technique. Rietveld refinement was performed using the powder X-ray diffraction (XRD) data, which shows occupation of Ce(3+) on both Ca(2+) and La(3+) sites with a preferred location on the La(3+) site over the Ca(2+) site. The prepared samples contain minor second phase LaBO(3) with contents of ～0.64-3.27 wt % from the Rietveld analysis. LaBO(3):1%Ce(3+) was prepared as a single phase material and its excitation and emission bands were determined for identifying the influence of impurity LaBO(3):Ce(3+) luminescence on the spectra of the Ca(3)La(3(1-x))Ce(3x)(BO(3))(5) samples. The luminescence properties of Ca(3)La(3(1-x))Ce(3x)(BO(3))(5) samples under vacuum ultraviolet (VUV) and UV excitation were investigated, which exhibited two-center luminescence of Ce(3+), assigned to the Ce(1)(3+) center in the La(3+) site and Ce(2)(3+) center in the Ca(2+) site, taking into account the spectroscopic properties and the Rietveld refinement results. The influences of the doping concentration and the excitation wavelength on the luminescence of Ce(3+) in Ca(3)La(3(1-x))Ce(3x)(BO(3))(5) are discussed together with the decay characteristics.     

Oxidation products of calcium and strontium bis(diphenylphosphanide)

The tetrahydrofuran adducts [(thf)(4)M(PPh(2))(2)] (M = Ca, Sr) are air sensitive and can easily be oxidized by chalcogens. Metalation of diphenylphosphane oxide, diphenylphosphinic acid, and diphenyldithiophosphinic acid as well as salt metathetical approaches of the potassium salts with MI(2) allow the synthesis of [(thf)(4)Ca(OPPh(2))(2)] (1), [(dmso)(2)Ca(O(2)PPh(2))(2)] (2), [(thf)(3)Ca(O(2)PPh(2))I](2) (3), [(thf)(3)Ca(S(2)PPh(2))(2)] (4), [(thf)(2)Ca(Se(2)PPh(2))(2)] (5), [(thf)(3)Sr(S(2)PPh(2))(2)] (6), [(thf)(3)Sr(Se(2)PPh(2))(2)] (7), and [(thf)(2)Ca(O(2)PPh(2))(S(2)PPh(2))](2) (8), respectively. The diphenylphosphinite anion in 1 contains a phosphorus atom in a trigonal pyramidal environment and binds terminally via the oxygen atom to calcium. The diphenylphosphinate anions act as bridging ligands leading to polymeric structures of calcium bis(diphenylphosphinates). Therefore strong Lewis bases such as dimethylsulfoxide (dmso) are required to recrystallize this complex yielding chain-like 2. The chain structure can also be cut into smaller units by ligands which avoid bridging positions such as iodide and diphenyldithiophosphinate (3 and 8, respectively). In general, diphenyldithio- and -diselenophosphinate anions act as terminal ligands and allow the isolation of mononuclear complexes 4 to 7. In these molecules the alkaline earth metals show coordination numbers of six (5) and seven (4, 6, and 7).