Interactions between metal ions and carbohydrates. The coordination behavior of neutral erythritol to lanthanum and erbium ions

Deprotonation from an OH on myo-Inositol Promoted by μ2-Bridges with Possible Regioselectivity/Chiral Selectivity

Single-crystal structures of myo-inositol complexes with erbium ([Er₂(C₆H₁₁O₆)₂(H₂O)₅Cl₂]Cl₂(H₂O)₄, denoted ErI hereafter) and strontium (Sr(C₆H₁₂O₆)₂(H₂O)₂Cl₂, denoted SrI hereafter) are described. In ErI, deprotonation occurs on an OH of myo-inositol, although the complex is synthesized in an acidic solution, and the pK_a values of all of the OHs in myo-inositol are larger than 12. The deprotonated OH is involved in a μ₂-bridge. The polarization from two Er³⁺ ions activates the chemically relatively inert OH and promotes deprotonation. In the stable conformation of myo-inositol, there are five equatorial OHs and one axial OH. The deprotonation occurs on the only axial OH, suggesting that the deprotonation possesses characteristics of regioselectivity/chiral selectivity. Two Er³⁺ ions in the μ₂-bridge are stabilized by five-membered rings formed by chelating Er³⁺ with an O-C-C-O moiety. As revealed by the X-ray crystallography study, the absolute values of the O-C-C-O torsion angles decrease from ∼60 to ∼45° upon chelating. Since the O-C-C-O moiety is within a six-membered ring, the variation of the torsion angle may exert distortion of the chair conformation. Quantum chemistry calculation results indicate that an axial OH flanked by two equatorial OHs (double ax-eq motif) is favorable for the formation of a μ₂-bridge, accounting for the selectivity. The double ax-eq motif may be used in a rational design of high-performance catalysts where deprotonation with high regioselectivity/chiral selectivity is carried out.

Unexpected Deprotonation from a Chemically Inert OH Group Promoted by Metal Ions in Lanthanide-Erythritol Complexes

Single-crystal structures of five lanthanide-erythritol complexes are reported. The analysis of the chemical compositions and scrutinization of structural features in the single-crystal data of the complexes led us to find that unexpected deprotonation occurs on the OH group of erythritol of three complexes. Considering these complexes were prepared in acidic environments, where spontaneous ionization on an OH group is suppressed, we suggest metal ions play an important role in promoting the proton transfer. To find out why the chemically inert OH is activated, the single-crystal structures of 63 rare-earth complexes containing organic ligands with multiple hydroxyl groups (OLMHs) were surveyed. The formation of μ₂-bridges turns out to be directly relevant to the occurrence of deprotonation. When an OH group from an OLMH molecule participates in the formation of a μ₂-bridge, the polarization ability of the metal ions becomes strong enough to promote the deprotonation on the OH group. The above structural characteristics may be useful in the rational design of catalysts that can activate the chemically inert OH group and promote the relevant chemical conversions.

Crystal structures of two mononuclear complexes of terbium(III) nitrate with the tripodal alcohol 1,1,1-tris-(hy-droxy-meth-yl)propane

Two new mononuclear cationic complexes in which the TbIII ion is bis-chelated by the tripodal alcohol 1,1,1-tris-(hy-droxy-meth-yl)propane (H3LEt, C6H14O3) were prepared from Tb(NO3)3·5H2O and had their crystal and mol-ecular structures solved by single-crystal X-ray diffraction analysis after data collection at 100 K. Both products were isolated in reasonable yields from the same reaction mixture by using different crystallization conditions. The higher-symmetry complex dinitratobis[1,1,1-tris-(hy-droxy-meth-yl)propane]-terbium(III) nitrate di-meth-oxy-ethane hemisolvate, [Tb(NO3)2(H3LEt)2]NO3·0.5C4H10O2, 1, in which the lanthanide ion is 10-coordinate and adopts an s-bicapped square-anti-prismatic coordination geometry, contains two bidentate nitrate ions bound to the metal atom; another nitrate ion functions as a counter-ion and a half-mol-ecule of di-meth-oxy-ethane (completed by a crystallographic twofold rotation axis) is also present. In product aqua-nitratobis[1,1,1-tris-(hy-droxy-meth-yl)propane]-terbium(III) dinitrate, [Tb(NO3)(H3LEt)2(H2O)](NO3)2, 2, one bidentate nitrate ion and one water mol-ecule are bound to the nine-coordinate terbium(III) centre, while two free nitrate ions contribute to charge balance outside the tricapped trigonal-prismatic coordination polyhedron. No free water mol-ecule was found in either of the crystal structures and, only in the case of 1, di-meth-oxy-ethane acts as a crystallizing solvent. In both mol-ecular structures, the two tripodal ligands are bent to one side of the coordination sphere, leaving room for the anionic and water ligands. In complex 2, the methyl group of one of the H3LEt ligands is disordered over two alternative orientations. Strong hydrogen bonds, both intra- and inter-molecular, are found in the crystal structures due to the number of different donor and acceptor groups present.

The coordination of lanthanide ions with picolinamide. The influence of different anions

Four kinds of structures varied with different rare earth ions and anions have been observed for lanthanide–picolinamide complexes.

Sugar-metal ion interactions: the coordination behaviors of lanthanum with erythritol

Three novel lanthanum chloride-erythritol complexes (LaCl(3)·C(4)H(10)O(4)·5H(2)O (LaE(I)), LaCl(3)·C(4)H(10)O(4)·3H(2)O (LaE(II)), and LaCl(3)·1.5C(4)H(10)O(4) (LaE(III)) were synthesized and characterized by single crystal X-ray diffraction, FTIR, far-IR, THz, and Raman spectroscopy. The coordination number of La(3+) is nine. LaE(I) and LaE(II) have similar coordination spheres, but their hydrogen bond networks are different. Erythritol exhibits two coordination modes: two bidentate ligands and tridentate ligands in LaE(III). Chloride ions and water coordinate with La(3+) or participate in the hydrogen-bond networks in the three complexes. Crystal structures, FTIR, FIR, THz, and Raman spectra provide detailed information on the structures and coordination of hydroxyl groups to metal ions in the metal-carbohydrate complexes.

Interactions between metal ions and carbohydrates. Spectroscopic characterization and the topology coordination behavior of erythritol with trivalent lanthanide ions

The coordination of carbohydrate to metal ions is important because it may be involved in many biochemical processes. The synthesis and characterization of several novel lanthanide-erythritol complexes (TbCl(3)·1.5C(4)H(10)O(4)·H(2)O (TbE(I)), Pr(NO(3))(3)·C(4)H(10)O(4)·2H(2)O (PrEN), Ce(NO(3))(3)·C(4)H(10)O(4)·2H(2)O (CeEN), Y(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (YEN), Gd(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (GdEN)) and Tb(NO(3))(3)·C(4)H(10)O(4)·C(2)H(5)OH (TbEN) are reported. The structures of these complexes in the solid state have been determined by X-ray diffraction. Erythritol is used as two bidentate ligands or as three hydroxyl group donor in these complexes. FTIR spectra indicate that two kinds of structures, with water and without water involved in the coordination sphere, were observed for lanthanide nitrate-erythritol complexes. FIR and THz spectra show the formation of metal ion-erythritol complexes. Luminescence spectra of Tb-erythritol complexes have the characteristics of the Tb ion.

Structural Characterization of Methanol Substituted Lanthanum Halides

The first study into the alcohol solvation of lanthanum halide [LaX(3)] derivatives as a means to lower the processing temperature for the production of the LaBr(3) scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {[La(micro-Br)(H(2)O)(7)](Br)(2)}(2) (1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric [La(H(2)O)(7)(MeOH)(2)](Br)(3) (2) compound was isolated where the La metal center retains its original 9-coordination through the binding of two additional MeOH solvents but necessitates the transfer of the innersphere Br to the outersphere. In an attempt to in situ dry the reaction mixture of 1 in MeOH over CaH(2), crystals of [Ca(MeOH)(6)](Br)(2) (3) were isolated. Compound 1 dissolved in MeOH at reflux temperatures led to the isolation of an unusual arrangement identified as the salt derivative {[LaBr(2.75)*5.25(MeOH)](+0.25) [LaBr(3.25)*4.75(MeOH)](-0.25)} (4). The fully substituted species was ultimately isolated through the dissolution of dried LaBr(3) in MeOH forming the 8-coordinated [LaBr(3)(MeOH)(5)] (5) complex. It was determined that the concentration of the crystallization solution directed the structure isolated (4 concentrated; 5 dilute) The other LaX(3) derivatives were isolated as [(MeOH)(4)(Cl)(2)La(micro-Cl)](2) (6) and [La(MeOH)(9)](I)(3)*MeOH (7). Beryllium Dome XRD analysis indicated that the bulk material for 5 appear to have multiple solvated species, 6 is consistent with the single crystal, and 7 was too broad to elucidate structural aspects. Multinuclear NMR ((139)La) indicated that these compounds do not retain their structure in MeOD. TGA/DTA data revealed that the de-solvation temperatures of the MeOH derivatives 4 - 6 were slightly higher in comparison to their hydrated counterparts.

Synthesis and structure of dimeric anthracene-9-carboxylato bridged dinuclear erbium(III) complex, [Er(2)(9-AC)(6)(DMF)(2)(H(2)O)(2)]

We study the influence of the bulky aromatic rings, e.g. anthracence-9-carboxylic acid (9-ACA) with a large conjugated pi-system on the structure and spectroscopic properties of [Er(2)(9-AC)(6)(DMF)(2)(H(2)O)(2)] complex where 9-AC=anthracence-9-carboxylato and DMF=N,N'-dimethylformamide. The complex has been prepared from the erbium chloride and 9-ACA in the mixture of H(2)O:DMF solution (4:1, v/v) followed by pH adjustment to 6. The complex is crystallized in a monoclinic system with space group P2(1)/n. The two Er(III) ions are double bridged by the deprotonated carboxyl groups of two 9-AC anions (O1 and O1A), forming an eight-coordination number. The chelating bidentate (O,O), chelating-bridging tridentate (O,O,O') and monodentate of 9-AC anions are observed in the dinuclear [Er(2)(9-AC)(6)(DMF)(2)(H(2)O)(2)] complex. The Er-Er distance is 4.015A in the dimeric unit. Intramolecular O-Hcdots, three dots, centeredO and C-Hcdots, three dots, centeredO hydrogen bonds as well as numerous of intermolecular C-Hcdots, three dots, centeredpi interactions between the anthracene rings by edge-to-face interactions linked the dinuclear dimeric units into two-dimensional supramolecular network in a propeller-arrangement. Electronic absorption spectra of the Er(III) complex and its salt were measured. The emission spectrum of the complex is composed of a broad band due to the emission of intraligand pi*-->pi transition from the 9-AC anions and a shoulder peak originating from the 4f-4f emission transition of the Er(III) ions. The complex has a high thermal stability which can be attributed to the effectively increase the rigidity of the 9-AC anions.

Interactions of calcium nitrate with pyranosides in water: a 13C NMR study

The 13C NMR spectra of methyl alpha- and beta-D-galactopyranosides, and methyl alpha- and beta-D-glucopyranosides were recorded and show that the Delta(deltaC-4) values for methyl alpha- and beta-D-galactopyranosides increase most rapidly, whereas those for methyl alpha- and beta-D-glucopyranosides vary hardly with increasing molality of calcium nitrate. It can be concluded that ax-OH-4 interacts more strongly with Ca2+ than eq-OH-4 group, namely, the Ca2+ ion interaction with ax-OH-4 leads to a stronger deshielding of the C-4 atom. Compared with other C atoms, the chemical shifts of both C-1 and C-5 atoms in these two types of glycosides decrease relatively rapidly as molality of calcium nitrate increases, indicating that the nitrate ion attractions for these glycosides cause a relatively strong enhancing shielding effect of C-1 and C-5 atoms.

Chelation-controlled regioselectivity in the lanthanum-promoted monobenzoylation of monosaccharides in water

Monosaccharides are selectively converted to monobenzoates in a base-catalyzed reaction with benzoyl methyl phosphate (BzMP) and a lanthanum salt in water. Yields are reported in terms of formation of the ester, which competes with hydrolysis of BzMP, to give an estimate of the efficiency of the conversion of the sugar. Higher conversions can be achieved using excess reagent. Regioselectivity is influenced by the structure of the glycoside. For example, the reaction leads to different product distributions from alpha- and beta-anomers of the glycosides. The reaction combination provides a basis for efficient ester formation in specific geometric situations, providing a means of identification as well as modification.