Antiprismatic Coordination Environment Research Articles

Syntheses and X-ray Crystal Structures of Zirconium(IV) and Hafnium(IV) Complexes Containing Monovacant Wells−Dawson and Keggin Polyoxotungstates

The syntheses and crystal structures of a series of zirconium(IV) and hafnium(IV) complexes with Dawson monovacant phosphotungstate [alpha2-P2W17O61](10-) and in situ-generated Keggin monovacant phosphotungstate [alpha-PW11O39](7-), which was obtained by a reaction of [alpha-PW12O40](3-) with Na2CO3, are described. K15H[Zr(alpha2-P2W17O61)2].25H2O (K-1), K16[Hf(alpha2-P2W17O61)2].19H2O (K-2), (Et2NH2)10[Zr(alpha-PW11O39)2].7H2O (Et2NH2-3), and (Et2NH2)10[Hf(alpha-PW11O39)2].2H2O (Et2NH2-4), being afforded by reactions in aqueous solutions of monolacunary Dawson and Keggin polyoxotungstates with ZrCl2O.8H2O and HfCl2O.8H2O followed by exchanging countercations, were obtained as analytically pure, homogeneous colorless crystals. Single-crystal X-ray structure analyses revealed that the Zr(IV) and Hf(IV) ions are in a square antiprismatic coordination environment with eight oxygen atoms, four of them being provided from each of the two monovacant polyanion ligands. Although the total molecular shapes and the 8-coordinate zirconium and hafnium centers of complexes 1-4 are identical, the bonding modes (bond lengths and bond angles) around the zirconium(IV) and hafnium(IV) centers were dependent on the monovacant structures of the polyanion ligands. Additionally, the characterization of complexes 1-4 was accomplished by elemental analysis, TG/DTA, FTIR, and solution (31P and 183W) NMR spectroscopy.

Synthesis and structural characterization of lanthanide(iii) nitrate complexes of a tetraiminodiphenol macrocycle in the solid state and in solution

The lanthanide(III) complexes [Ln(LH2)(NO3)3] 1-11(La-Er), 15(Y) and [Ln(LH2)(NO3)2(H2O)](NO3) 12-14 (Tm-Lu) of the tetraiminodiphenolate macrocycle L2- have been prepared by the transmetallation reaction between [Pb(LH2)(NO3)2] and Ln(NO3)3.nH2O. In these compounds, the uncoordinated imino nitrogens are protonated and are hydrogen bonded to the phenolate oxygens. The X-ray crystal structures of the La (1), Ho (10) and Lu (14) compounds have been determined. Compounds 1 and 10, in which all the three nitrates are bound in bidentate fashion, are isostructural with distorted bicapped square antiprism geometry for the metal centre. In [Lu(LH2)(NO3)2(H2O)](NO3) 14, of the two metal bound nitrates one is bidentate and the other is unidentate, while the metal centre obtains a distorted square antiprism coordination environment. Proton NMR spectra of the paramagnetic lanthanide complexes have been studied in detail. Contributions of contact and pseudo-contact shifts to the lanthanide induced isotropic shifts (LIS) of the macrocycle protons have been separated and good agreement has been obtained between the calculated LIS values and the experimentally observed values. Analysis of the NMR data has led us to conclude that all the complexes in dimethyl sulfoxide solution attain similar configurations. The absorption and emission spectral characteristic of several compounds have been investigated. The complexes of samarium (5) and europium (6) on photoexcitation at 400 nm exhibit well-resolved luminescence spectra at 77 K both in the solid state and a methanol-ethanol (1 : 4) glassy matrix. For the terbium (8) and dysprosium (9) complexes, however, the observed luminescence peaks are less resolved and weak in intensity.

Structural and NMR investigations of the ternary adducts of twenty alpha-amino acids and selected dipeptides with a chiral, diaqua-ytterbium complex.

A detailed investigation of the nature of the binding of each of the 20 common alpha-amino acids and various selected dipeptides to a chiral, diaqua-ytterbium complex in aqueous solution has been carried out. Analysis of the dipolar 1H NMR paramagnetic shifts suggests that the alpha-amino acids form a common chelated structure within a nine-coordinate mono-capped square antiprismatic coordination environment, with the amine N axially disposed. Crystal structures of nine chelated YbL1-amino acid adducts (Gly, Ala, Ser, Thr, Met) confirm this. The ternary complexes with dipeptides (e.g. Gly-Ala, Gly-Ser, Gly-Met, Gly-Asp, Gly-Asn, Gly-His, Ser-Met, Asp-Phe, His-Gly) also favour the terminal amine as the axial donor with the proximate amide group binding to generate a five-ring chelate. Evidence for chelation through side-chain functionality was found only in the case of N-terminal Asp. The chiral environment about the ytterbium ion upon amino acid binding has also been probed using near-IR circular dichroism spectroscopy.

A new microporous structure constructed by a lanthanide-carboxylate coordination polymer

A novel microporous structure constructed by a lanthanide-carboxylate coordination polymer of [Nd(C 8H 5NO 4) 1.5(H 2O) 2]·2H 2O is reported. Nd 3+ ion is in the distorted square anti-prism coordination environment. Both carboxyl groups of each ligand link Nd 3+ ions in the same fashion to engender the open-framework structure along Y-axis. Pendant groups in microporous structure join guest water molecules via hydrogen bond.

Rare Earth Ion Center in Distorted Square Anti-Prism Coordination Environment: A Novel Three-Dimensional Coordination Polymer with Channels

Abstract The hydrothermal synthesis and the structure of the coordination polymer [La2(ATPT)3·(H2O)5] (H2O)2 (ATPT=2-aminoterephthalic acid) were reported. The Rare-earth ion center was in the distorted square anti-prism coordination environment. These carboxyl groups linking La3+ ion centers engendered one-dimension channels with pending groups. Guest water molecules in these channels joined these pending groups via hydrogen bond.

Poly[[tetraaquapraesodymium(III)-μ-(iminiodiacetato-O,O':O':O'',O''':O''')] dichloride hydrate

The title compound, [Pr(C 4 H 6 NO 4 )(H 2 O) 4 ]Cl 2 .H 2 O, consists of [Pr(OOCCH 2 NH 2 CH 2 COO)(H 2 O) 4 ] sheets, Cl - ions and solvent water molecules. Within the sheets, each Pr ion is linked by four bridging iminiodiacetate ligands and is further coordinated by four water molecules giving a distorted bicapped square antiprism coordination environment with an average Pr-O distance of 2.573 (2) A. The Cl - ions and the solvent water molecules lie between these sheets and form numerous hydrogen bonds with the coordinated water and the -NH 2 + - group of the ligand.