Crystalline cerium(IV) phosphates—II: The ion exchange characteristics with alkali metal ions

The ion exchange behavior of seven crystalline cerium(IV) phosphates towards some of the alkali metal cations is described. Only two of the compounds (A and C) possess ion exchange properties in acidic solutions. Four others show some ion exchange characteristics in basic media with some of the alkali cations. Compound G does not behave as an ion exchanger in solutions of pH < 12. Compounds B, D and F exchange Li⁺, but show very little Na⁺ uptake. Compound E undergoes ion exchange with Na⁺ and Cs⁺, but not with Li⁺. Both Li⁺ and Na⁺ are sorbed by compounds A and C. The results are indicative of structures which show steric exclusion phenomena.     

Variations of structures on changing the ratios of metal ions in rare Ca(II)–Zn(II) hetero-metallic self-assembled coordination polymers of hexamethylenetetramine and benzoate

Two rare hetero-metallic calcium(II)-zinc(II) complexes [CaZn₄(OBz)₁₀(μ₂-hmt)₂]_n (1) and [Ca₂Zn₄(OBz)₁₂(μ₂-hmt)₂]_n (2) have been synthesized using basic zinc carbonate, benzoic acid (HOBz), hydrated calcium chloride and hexamethylenetetramine (hmt) by varying the molar ratio of the reactants. Both the complexes have been analyzed by elemental analysis, IR spectroscopy and X-ray crystallography. The complex 1 is a 1D polymer which contains one calcium ion and four zinc atoms in the asymmetric unit together with ten benzoates and two hmts. The polymer has been constructed by the alternate joining of paddle-wheel Zn₂(OBz)₄ units and Zn₂Ca trinuclear species by μ₂-hmt bridging molecules connecting Zn²⁺ ions. Zinc atoms have five coordinate square pyramidal geometries and four coordinate tetrahedral geometries in Zn₂(OBz)₄ and Zn₂Ca moieties, respectively, whereas calcium atoms have six-coordinate distorted octahedral geometry. Complex 2 is also a 1D polymer but unlike complex 1, it contains four independent zinc and two independent calcium atoms in the asymmetric unit together with twelve benzoates and two hmts. By contrast, the polymeric structure of complex 2 has been formed by the connection of Zn₂Ca trinuclear species via μ₂ hmt bridging molecules at Zn centers. Complex 2 is also a 1D polymer but unlike complex 1, it contains four independent zinc and three independent calcium atoms in the asymmetric unit together with twelve benzoates and two hmts. All four zinc atoms are four coordinate with tetrahedral environments and the calcium atoms are six coordinated (two are located on a center of symmetry) exhibiting a distorted octahedral geometry.     

Interactions of metal ions with the intermediate of thiamine catalysis: Crystal structures of Cd(II), Hg(II) and Pt(II) complexes of 2-(α-hydroxybenzyl)thiamine

Five complexes of formulae Cd(HBT)X₃·H₂O, Hg₂X₅(HBT) (X=Cl, Br), and Pt(HBT)(NO₂)₃ were prepared by reacting CdX₂, HgX₂ and K₂Pt(NO₂)₄ with 2-(α-hydroxybenzyl)thiamine (HBT), an active intermediate of thiamine catalysis, and their crystal structures were determined by X-ray diffraction. The metal ion binds to the N(1′) site of the pyrimidine ring in each case, despite the different shapes and sizes of metal coordination units; a tetrahedral unit in the cadmium complexes, a double-metal unit consisting of two tetrahedral Hg(II) ions in the mercury complexes and a square-planar unit in the platinum complex. The HBT ligands in these complexes adopt the S conformation, as usually observed in C(2)-substituted derivatives of thiamine, with average torsion angles ϕ_T being ±99° and ϕ_P being ±175°. A ‘two-point’ anion-bridge between the amino group of the pyrimidine ring and the cationic thiazolium ring of the same molecule is found in all the structures, being of the form N(4′α)–H…X₁–M–X₂…thiazolium-ring (M=metal ion), which is one of the factors that affect the S conformation. Stacking interactions between the pyrimidine and phenyl rings play an important role in the molecular conformation and crystal packing. The intramolecular close contact between the oxygen of the C(2)-substituent and the sulfur of the thiazolium ring is also a common feature to these complexes, which gives the mechanistic implications.     

Dissection of the difference between the group I metal ions in inhibiting GSK3β: a computational study

Glycogen synthase kinase 3β (GSK3β) is a serine/threonine kinase that requires two cofactor Mg(2+) ions for catalysis in regulating many important cellular signals. Experimentally, Li(+) is a competitive inhibitor of GSK3β relative to Mg(2+), while this mechanism is not experienced with other group I metal ions. Herein, we use native Mg(2)(2+)-Mg(1)(2+) GSK3β and its Mg(2)(2+)-M(1)(+) (M = Li, Na, K, and Rb) derivatives to investigate the effect of metal ion substitution on the mechanism of inhibition through two-layer ONIOM-based quantum mechanics/molecular mechanics (QM/MM) calculations and molecular dynamics (MD) simulations. The results of ONIOM calculations elucidate that the interaction of Na(+), K(+), and Rb(+) with ATP is weaker compared to that of Mg(2+) and Li(+) with ATP, and the critical triphosphate moiety of ATP undergoes a large conformational change in the Na(+), K(+), and Rb(+) substituted systems. As a result, the three metal ions (Na(+), K(+), and Rb(+)) are not stable and depart from the active site, while Mg(2+) and Li(+) can stabilize in the active site, evident in MD simulations. Comparisons of Mg(2)(2+)-Mg(1)(2+) and Mg(2)(2+)-Li(1)(+) systems reveal that the inline phosphor-transfer of ATP and the two conserved hydrogen bonds between Lys85 and ATP, together with the electrostatic potential at the Li(1)(+) site, are disrupted in the Mg(2)(2+)-Li(1)(+) system. These computational results highlight the possible mechanism why Li(+) inhibits GSK3β.     

New tetraaza macrocyclic complexes of palladium(II) and platinum(II) formed by the self-condensation of 5-amino-3-methyl-1-phenylpyrazole-4-carbaldehyde in the presence of metal ions. α-Amino ether and carbinolamine derivatives of the macrocyclic Schiff base metal complex

The self-condensation of 5-amino-3-methyl-1-phenylpyrazole-4-carbaldehyde (AMPC) in the presence of Pd^II and Pt^II ions yields the Pd^II and Pt^II complexes, [M(TAAP)]Cl₂, of the fully cyclized tetradentate macrocyclic ligand tetrapyrazolo[1,5,9,13]tetraazacyclohexadecine, (TAAP). Metathetical displacement of the chloride has led to isolation a series of complexes of the type [M(TAAP)]X₂, (X=I, ClO₄ and BF₄), the formulation of which is supported by elemental analysis, molar conductance and magnetic susceptibility measurements, and i.r. and u.v.–vis. spectra. Spectroscopic and other analytical results reveal that the complexes have square-planar stereochemistry with four donor nitrogen atoms coordinated to the metal ion in a planar array. The reaction which produces this new cyclic ligand is assumed to include the metal ion acting as a template for the condensation. Thus the probable mechanistic implications for the coordination template hypothesis are discussed to explain the formation of these new macrocyclic chelate compounds. Both Pd^II and Pt^II complexes appear to be sensitive to nucleophilic attack at the methine carbon, which is reversible upon acidification. The reaction of [Pt(TAAP)]²⁺ or [Pd(TAAP)]²⁺ with MeO^- or EtO^- ions results in the formation of partially solvolysed inner complexes containing two ionized -amino ether functions, stabilized by the macrocyclic chelate ring. Attempts to prepare discrete -carbinolamine derivatives were unsuccessful.     

Complexation of the zinc(II) ion with 2,2′-bipyridine and 1,10-phenanthroline in 4-methylpyridine and solvation structure of the manganese(II), cobalt(II), nickel(II), and zinc(II) ions in 4-methylpyridine and 3-methylpyridine

Complexation of the zinc(II) ion with 2,2-bipyridine (bpy) and 1,10-phenanthroline (phen) has been calorimetrically studied in 4-methylpyridine (4Me-py) containing 0.1 mol dm^–3 (n-C₄H₉)₄NClO₄ as a constant ionic medium at 25°C. The formation of [ZnL]²⁺, [ZnL₂]²⁺, and [ZnL₃]²⁺ (L=bpy, phen), and their formation constants, reaction enthalpies and entropies were determined. Our EXAFS (extended X-ray absorption fine structure) measurements showed that the solvation structure of the manganese(II), cobalt(II), and nickel(II) ions is six-coordinate octahedral in 4Me-py and 3-methylpyridine (3Me-py), while that of the zinc(II) ion is four-coordinate tetrahedral in 4Me-py. Since [ZnL₃]²⁺ is expected to have an octahedral structure, a tetrahedral-to-octahedral structural change should take place at a certain step of complexation. The thermodynamic parameters, especially reaction entropies, indicate that the structural change occurs at the formation of [Zn(bpy)₂]²⁺ and [Zn(phen)]²⁺.     

A vibrational study of the metal—olefin bond in norbornadiene complexes of Rh(I), Pd(II) and Pt(II)

Vibrational assignments of the complexes [RhClC₇H₈]₂, PtCl₂C₇H₈, and PdCl₂C₇H₈ have been undertaken. A reinvestigation of the norbornadiene spectrum was necessary and a new set of assignments is given. The shift in energy of bands I and II and the out-of-plane olefinic CH wagging modes, as well as the relative energies of the bands associated with the metal—olefin motions are consistent with the total metal—norbornadiene interaction following the order Rh>Pt>Pd and the extent of the π component being ordered as Rh⋍Pt>Pd.     

3D Heterometallic (3d–4f) coordination polymers: A ferromagnetic interaction in a Gd(III)–Cu(II) couple

Four 3d–4f heterometallic coordination polymers, [Cu₃(IDA)₆Ln₂] · n(H₂O) [IDA =  iminodiacetate dianion; Ln = Gd, n = 3 (1); Ln = Nd, n = 6 (2); Ln = Sm, n = 6 (3)] and [Cu(Cl)(NTA)Sm(H₂O)₆] · (ClO₄) · (H₂O) (4) [NTA = nitrilotriacetate trianion], have heen synthesized and characterized by single crystal X-ray diffraction analysis. Complexes 1–3 are isomorphous, showing a 3D coordination framework having tubular channels filled by lattice water molecules running parallel to the c axis. Whereas complex 4 is a 1D polymer of alternating copper and samarium ions connected by NTA, and the chains get involved in H-bonding interactions resulting in a 3D network. A low temperature magnetic study reveals ferromagnetic interactions for complex 1. Thermogravimetric and X-ray powder diffraction analyses of 1, 2 and 3 show that the covalently bonded 3D network remains almost unaffected after deaquation.     

Weak interactions in imidazole-containing zinc(II)-based metal–organic frameworks

The self-assembly of the two zinc(II) metal–organic frameworks, [Zn₂(L)(bdc)₂]·3MeOH·4H₂O}_n ( 1 , L = 2-(pyridin-4-yl)-3H-imidazo[4,5-c]pyridine, H₂bdc = 1,4-benzenedicarboxylic acid) and [Zn₂(L)(bdc)₂]·2DMF·H₂O}_n ( 2 ), was achieved under mild reaction conditions. Both compounds 1 and 2 were structurally characterized by single-crystal X-ray diffraction analysis. Interestingly, the coordination modes of the ligand L in two structures are entirely different. Compounds 1 and 2 were made up of paddle wheel-shaped {Zn₂(O₂C)₄} secondary building unit (SBU) clusters, which adopted three-dimensional structures with a pcu topology. Rich weak interactions were observed in the structures of both 1 and 2 . The uncoordinated imidazole and pyridine moieties exhibited electron donor–acceptor interactions, π–π stacking, hydrogen bonding, and CH–π interactions. These interactions also facilitated the abilities of the framework to adsorb CO₂ molecules. Gas adsorption studies revealed that compound 1 selectively adsorbed CO₂ (131.1 cm³/g) over N₂ (23.5 cm³/g) and H₂ (36.5 cm³/g) at a pressure of 1 atm.     

Raman study of the metal—metal bonding in the molecules M2(CO)10-n(CNCH3)n(M = Mn,Re)

The effect of ligand substitution on the metal—metal bonding in the complexes M₂(CO)_10-n (CNCH₃)_n (M = Mn, Re) has been investigated by studying the metal—metal stretching mode in the Raman spectra. The result obtained suggests that CNCH₃ substitution weakens the metalmetal bond. This is related to the increased π-electron repulsion in the CNCH₃ substituted complexes. A study of the temperature dependence of the metal—metal stretching band shows the anharmonic nature of this motion.     

Complexation of N-acyl-N′-(p-toluenesulfonyl)hydrazines with nonferrous metal ions in ammoniac media

The complexation of N-acyl-N′-(p-toluenesulfonyl)hydrazines (ASHs) with copper(II), cobalt(II), nickel(II), zinc(II), cadmium(II), and silver(I) ions in ammoniac media was studied. The reagents were shown to form compounds with [M]: [ASH] ratios of 1: 1 and 1: 2 in solutions. ASH complexes with metal ions were preparatively separated and identified. The quantitative characteristics of complexation equilibria—the solubility products of precipitates—were found. The effects of ammonium salts and the length of a radical on the completeness of precipitation of M(II) cations with ASH were studied.     

The effects of redox-inactive metal ions on the activation of dioxygen: isolation and characterization of a heterobimetallic complex containing a Mn(III)-(μ-OH)-Ca(II) core

Rate enhancements for the reduction of dioxygen by a Mn(II) complex were observed in the presence of redox-inactive group 2 metal ions. The rate changes were correlated with an increase in the Lewis acidity of the group 2 metal ions. These studies led to the isolation of heterobimetallic complexes containing Mn(III)-(μ-OH)-M(II) cores (M(II) = Ca(II), Ba(II)) in which the hydroxo oxygen atom is derived from O(2). This type of core structure has relevance to the oxygen-evolving complex within photosystem II.     

Radiochemistry of organometallic compounds: Studies with implanted ions—II 59Fe+ ions in [CpFe(CO)2]2

Attempts to stimulate hot atom reactions by the use of implanted radioactive ions have been extended to ⁵⁹Fe⁺ bombardment of [CpFe(CO)₂]₂ and [CpFe(CO)₂]I targets. These show modest yields of the labelled target compounds and small yields of labelled FeCp₂ and Fe(CO)₅. These yields show an expected decrease with increasing ion dose, but no significant dependence on beam energy in the range 20–80 keV. The product yields are 6·0, 3·0, 0·4 and 0·8% respectively for [CpFe(CO)₂]₂ targets and 0·7, 8·7, 0·1 and 0·2% respectively for [CpFe(CO)₂]I targets.These yields are markedly smaller than those from the neutron-bombarded compounds, which is taken to indicate that the “pure” recoil cannot account for a substantial fraction of the yields following neutron capture. The predominant yield of the target compound in each case is construed to mean that the reaction occurs at or near the end of the trajectory, by a hot displacement. The present data cannot distinguish whether the displacement occurs within less than one or more than one normal vibrational period of the interstitial projectile atom.     

Copper(II), zinc(II) and mixed metal copper(II)-zinc(II) peroxocomplexes containing 2,2′,6′,2″-terpyridine

Summary Facile reaction of 2,2,6,2-terpyridine (L; terpy) with copper or zinc powders or their mixtures, in the presence of an excess of H₂O₂, leads to novel complexes [Cu(L)-(O₂ ^2–)]·3H₂O, [Zn(L)(O ₂ ^2– )]·H₂O and [Cu,Zn(L)₂(O ₂ ^2– )₂]· 4H₂O, respectively, which were isolated and characterized by elemental and micro- analysis, e.s.r., electronic, i.r. and thermogravimetric analysis in air and argon.     

Spectroscopic and TDDFT studies of N-phenyl-N′-(3-triazolyl)thiourea) compounds with transition metal ions

Reaction of N-phenyl-N′-(3-triazolyl)thiourea) (H₃L) with M(ClO₄)₂ (M = Co(II) (1), Ni(II) (2) and Cu(II) (3)) afforded [M(H₂L)₂] complexes, which were characterized experimentally and theoretically using different analytical, and spectral tools. The susceptibility of Staphylococcus aureus and Escherichia coli bacteria towards H₃L and its complexes was evaluated. The thiourea ligand coordinates to the 3d-metal ions via C–S^?, and triazole nitrogen yielding coordination compounds between the tetrahedral, and square-planar geometries (“flattened” tetrahedron, D₂d symmetry). Full geometry optimization, vibrational analyses, and natural bond orbital analyses of the proposed conformations of 1–3 were executed at B3LYP/def2-SVP to gain some knowledge about the local minima structures, natural charge of the coordinated metal ion, electronic configuration as well as the hybridization of M–L bonds. The electronic structures of the local minimum structures of 1–3 were investigated by time-dependent density functional theory calculations. Coordination of the thiourea ligand to Co(II) and Cu(II) ions did alter the toxicity against the tested microbes, while chelation of Ni(II) ion gave rise to inactive species.     

Complexes of cadmium(II) and mercury(II) ions with cytidine or cytidine-5′-monophosphate in ternary systems including tetramines

Interactions between Hg(II) and Cd(II) ions in binary systems with 3,3,3-tet (1,11-diamino-4,8-diazaundecane) and in ternary systems with Cyd (cytidine) or CMP (cytidine-5′-monophosphate) and 3,3,3-tet or Spm (1,12-diamino-4,9-diazadodecane, spermine) have been studied. The presence of the following species has been detected: MH _x (3,3,3-tet), M(3,3,3-tet), M(3,3,3-tet)(OH) _x and M(Cyd or CMP)(PA), M(Cyd or CMP)(H _x PA) (M?=?Cd or Hg, PA?=?3,3,3-tet or Spm). Overall stability constants (log β) have been determined and equilibrium constants for complex formation (log?K _e) calculated. The mode of coordination in these species has been proposed on the basis of the equilibrium and ¹³C NMR, ³¹P NMR and IR studies. Unlike the biogenic amine Spm, its homologue 3,3,3-tet coordinates with Cd(II) and Hg(II) ions with the involvement of all available donor nitrogen atoms. In Cd(Cyd)(3,3,3-tet) the {N5} chromophore is formed, while in Cd(Cyd)(Spm) the {N4} chromophore is involved (only three nitrogen atoms from Spm are involved in metallation). Introduction of the polyamine into the system Cd(II)/CMP (at pH below 7) leads to changes in coordination mode in the anchoring Cd(CMP) complex and the phosphate group of CMP is involved in bonding. In ternary systems, Hg(II)/Cyd(or CMP)/tetramine, the nitrogen atom N(3) and the phosphate group of the nucleotide take part in coordination. The presence of PA in the inner coordination sphere does not change the mode of metal–CMP coordination with respect to that in the binary system.     

Why Doesn't all-trans-1,2,3,4,5,6-Hexaspiro(THF)cyclohexane complex metal ions?

Despite the inherent preference for placing alkyl substituents, rather than alkoxy substituents, in equatorial positions, all-trans-hexaspiro(THF)cyclohexane strongly favors the all-O-equatorial conformer. Ab initio and density functional calculations on a series of cyclohexane derivatives containing one, two, or three spiro(THF) units demonstrate that this preference results from at least two important factors. First, when oxygen atoms are attached to adjacent carbons, the gauche effect favors the di-O-equatorial arrangement. In trans-1,2-dispiro(THF)cyclohexane, the single gauche interaction overcomes the inherent steric preference for projecting the two oxygen atoms axially. Similarly, in the all-trans-hexaspiro(THF)cyclohexane the six gauche interactions in the all-O-equatorial conformer overpower the inherent conformational biases of the six isolated spiro(THF) moieties. Nevertheless, the gauche effect only partially accounts for the more than 20 kcal/mol conformational bias calculated for this molecule. There is also another factor, the high energetic cost associated with projecting multiple alkoxy substituents axially on the same face of a cyclohexane scaffold. The calculations find the energetic cost of each 1,3-diaxial interaction is about 2 kcal/mol larger between alkoxy substituents than between alkyl substituents.