The role of intermolecular interactions in the assemblies of Fe and Co tetrakis-isothiocyanatometalates with tris(1,10-phenanthroline)-Ru: Crystal structures of two dual-metal assemblies featuring octahedral cationic and tetrahedral anionic modules

Two new dual-metal assemblies: 2[Ru(phen)₃]²⁺·[Fe(SCN)₄]²⁻·2SCN⁻·4H₂O 1 and [Ru(phen)₃]²⁺·[Co(SCN)₄]²⁻2, (phen:1,10-phenanthroline), have been prepared and their structures were characterized by X-ray diffraction. In 1, the cationic octahedral enantiomers are arranged with a ΛΔΛΔΛ sequence supported by π-π stacking and the anionic inorganic tetrahedral units are oriented between these stacks by interacting with the nearby water molecules through strong O-H?O and O-H?S hydrogen bonds. In 2, homochiral double helices in the b-direction are revealed, with tetrakis-isothiocyanate Co^II anions arranged in the crystal to furnish one-dimensional (1D)-helical chains with S?S intermolecular interactions at 3.512(2) and 3.966(2) Å supporting [Ru(phen)₃]²⁺Λ- and Δ-helices with Ru?Ru shortest distance of 8.676(7) Å. In both 1 and 2, the supramolecular assembly is maintained by C-H?S hydrogen bonds extending between the phenanthroline aromatic carbons in the cationic nodes and the sulphur atoms of the isothiocyanates anions. Analysis of S?S interactions in isothiocyanate containing compounds using Cambridge structural database (CSD) showed an angle dependence categorizing these interactions into “type-I” and “type-II”.     

Synthesis and Characterization of Nitrato-Triamine-Metal(II) Complexes. Conglomerate Crystallization Part 55. Crystal Structure of [Ni(dien)(O2NO)(ONO2)] (I), {[Cu(dien)-(μ-ONO2)]NO3}∞ (II), [Zn(dien)(O2NO)(ONO2)] (III), [Ni(Medpt)(O2NO)(ONO2)] (IV) and [Cu(Medpt)(ONO2)2] (V)

In absolute ethanol and in the presence of triethylorthoformate, reactions of metal(II) nitrates with linear tridentate amines afforded metal complexes of the formula M(NNN)(NO₃)₂, where M = Ni²⁺, Cu²⁺ and Zn²⁺, and NNN = dien and Medpt. The compounds fall into three categories in accordance with their stereochemistry and mode of binding of the nitrato ligands. Compounds I, [Ni(dien)(O₂NO)(ONO₂)] and III, [Zn(dien)(O₂NO)(ONO₂)] are isomorphous and isostructural. They crystallize in the monoclinic space group P2₁/n with nearly identical cell constants. The stereochemistry of these two compounds is such that the terdentate dien ligand forms a fac MN₃ moiety with the two oxygens of the bidentate nitrato ligand trans to the terminal NH₂. These ligands form the base of the octahedral arrangement in which the sixth position, trans to the secondary nitrogen of the dien, is an oxygen of the monodentate nitrato ligand. Compound IV, [Ni(Medpt)(O₂NO)(ONO₂)] falls into the same category as I and III despite the fact that the two rings in the Ni-Medpt moiety are six-membered rings, unlike those in compounds I and III which are five-membered rings. Nevertheless, the nickel-amine arrangement is fac. The bidentate nitrato-oxygens are trans to the terminal NH₂ of the amine ligand, and the oxygen of the monodentate nitrato ligand is trans to the tertiary amine-nitrogen. Such stereochemistry is prevalent for nickel and zinc compounds. Interestingly, compound IV crystallizes as a conglomerate (space group P2₁2₁2₁). Compound II, {[Cu(dien)(μ-ONO₂)]NO₃}_∞ belongs to the second category and has a polymeric structure. The repeating fragment in the polymeric chain is a Cu(dien)-O fragment with the monodentate nitrato ligand occupying an equatorial position of the base. A second oxygen of the equatorial nitrate becomes an axial ligand for an adjacent Cu-N₃O fragment. In this way the substance propagates into an infinite chain. The repeating unit has an effective square pyramidal, five-coordinate, configuration. Finally, the compound crystallizes as a racemate. The second nitrate necessary for charge compensation of this copper(II) compound is ionic and its function is to hold the infinite chains of the lattice. The third category represented by compound V, [Cu(Medpt)(ONO₂)₂] contains two molecules in the asymmetric unit of the racemic lattice (monoclinic, space group P2₁/a). The structure of Cu-Medpt is unlike that of IV in that both species present in the asymmetric unit have the amine ligand in a mer configuration which together with a monodentate oxygen of a nitrato ligand form a base plane of a square pyramid. The fifth ligand of both Cu²⁺ ions is a second monodentate nitrato ligand. The stereochemical differences between the two Cu²⁺ ions are insignificant for the Cu-Medpt fragment, which share the same conformation and configuration. The major difference between the two species is the torsional angles defined by the Cu-O-N-O angles. The difference arises from variation in the hydrogens of the primary amine moieties selected by nitrato-oxygens to form intramolecular hydrogen bonds. Finally, there is a little variation in the equatorial Cu-ONO₂ stereochemistry because of steric hindrance, imposed by the Medpt, preventing large torsional angles by these nitrato ligands. This is evident by comparing the two copper species shown in Finally, nitrate-to-Br ligand exchange was found to take place when KBr pellets are prepared for IR spectral measurements.     

Chromium(III) Complexes with Quadridentate Amines. Crystal Structure of [cis-β-Cr(trien)(C2O4)] Cl·2H2O (I) and [Cr2(μ-OH)2(μ-tren)2] Br4·2H2O (II)

[cis-g-Cr(trien) C₂O₄)] Cl·2H₂O (I) (CrC₈H₂₂N₄O₆Cl) crystallizes at 22°C, from deionized water solution as a racemate in space group Pn (No. 7). Lattice constants are: a = 7.193(2), b = 9.1545(12), c = 11.469(2) Å; g = 100.994(13)°; V = 741.3(3) ų and D_calc = 1.603 gcm^-3 (MW = 357.75, Z = 2). A total of 2251 data were collected, using MoK f radiation ( u = 0.71703 Å), over the range 4 h 2 è h 60°; of these, 1441 (independent and with I S 2 σ (I)) were used in the structural analysis. Data were corrected for absorption ( w = 9.81 cm^-1) and the transmission coefficients ranged from 0.8676 to 0.9942. The final R (F) and R_w(F) residuals were 0.0338 and 0.0764, respectively. The cations of (II) exist in the lattice as enantiomeric pairs. [Cr₂( w -OH)₂( w -tren)₂]Br₄ ·2H₂O (II) (Cr₂C₁₂H₄₂N₈O₄Br₄) crystallizes in the monoclinic space group P2₁/n (No. 14) with a = 10.835(2) Å, b= 7.859(3) Å, c = 16.397(2) Å, g = 105.45(2)°, V = 1345.7(5) ų3 and D_calc = 1.940 g cm^-1 (MW = 786.18, Z = 4). A total of 2467 data were collected, using MoK f radiation ( u = 0.71703 Å), over the range 4 h 2 è h 50°; of these, 1450 (independent and with I S 2 σ ( I )) were used in the structural analysis. Data were corrected for absorption ( w =67.79 cm^-1) and the transmission coefficients ranged from 0.5589 to 0.9949. The final R(F) and R_w(F) residuals were 0.0481 and 0.1408, respectively for 2385 observed reflections with ( I S 2 σ ( I )). In the complex cation, the two Cr(III) centers are in a distorted octahedral environment and are bridged by two hydroxide groups and two ethylamine arms, one from each tren ligand, which spans over the binuclear core. Within the bridging moiety, the Cr···Cr separation is 3.005(2) Å, the ° Cr-OH-Cr = 101.3(2)° and ° O-Cr-O = 78.7(2)°, while the average Cr-N bond distance trans to the hydroxo groups (2.085(6) Å) is shorter than the corresponding cis Cr-N distance (2.104(5) Å).     

High-performance liquid chromatography ofα-amino acids on a polystyrene resin with fixed ligands of the type (R)-N′, N′-dibenzyl-1,2-propanediamine

Summary A cross-linked polystyrene resin with fixed ligands of the type (R)-N, N-dibenzyl-1,2-propanediamine in the form of a copper(II) complex displays high enantio-selectivity in ligand-exchange chromatography of amino acids. A microbore column (100 mm×1 mm i.d.) packed with angular particles of dp=5–10 m generated up to 3500 theoretical plates, enabling a complete resolution of a mixture of three racemic amino acids into six components under isocratic conditions.12th publication in the series dealing with the ligand-exchange chromatography of racemates. Previous publications: ref. [1].     

外消旋硫代缩水甘油醚在多糖基质手性柱上的手性拆分

在自行合成的3种多糖基质的手性固定相上直接拆分了7种外消旋硫代缩水甘油醚，初步探讨了手性化合物结构在手性识别过程中对手性拆分的影响，并对手性固定相的手性识别能力进行了评价。     

Separation of unmodified α-amino acid enantiomers by reverse phase HPLC

Summary A novel chiral phase system is presented for the resolution of unmodified α-amino acid racemates which is composed of a reverse phase packing coated with N-alkyl-L-hydroxyproline (where alkyl is n-C₇H₁₅-, n-C₁₀H₂₁- and n-C₁₆H₃₃-) and a hydro-organic eluent containing copper(II)acetate. The factors controlling retention and enantioselectivity such as concentration of Cu(II)ion and pH of the eluent, addition of NH₄Ac to the eluent, type and content of organic solvent of hydro-organic eluent and column temperature were examined. The extremely high enantioselectivity observed (α up to 16) is assumed to be caused by a three site sorbate-sorbent interaction involving bidentate coordination of two amino acids to a Cu(II)ion and hydrophobic attractions between hydrocarbon side chains of amino acids and the n-octadecyl groups of the support. The efficiency and selectivity of the system permits resolution of up to 7 racemic amino acids into enantiomers within 35 minutes on a conventional HPLC apparatus. 13th publication in the series dealing with the ligand-exchange chromatography. Previous publication: ref. [1].     

Investigation of Structural Relationships between Racemic Alkali and Ammonium Hydrogen Tartrates and their Chiral Counterparts

Single crystals of racemic anhydrous alkali and ammonium hydrogen tartrates of the composition M(C₄H₅O₆) with M = K, Rb, Cs, NH₄ as well as M_xM′_1?x(C₄H₅O₆) with {M = K, M′ = Rb, x = 0.5}, {M = K, M′ = NH₄, x = 0.56} and {M = Rb, M′ = NH₄, x = 0.61} were obtained from the reaction of D,L‐tartaric acid with the corresponding hydroxides MOH and / or M′OH. These compounds form an isostructural series (monoclinic, P2₁/c, Z = 4). The structures consist of alternating tartrate anion layers and cation layers. Each tartrate layer is held together by a number of hydrogen bonds and contains exclusively either the D or the L‐form of the tartrate. Structural analogies between these crystals and their chiral counterparts are investigated. The smilarity of cell parameters between racemic and chiral structures is shown to be a consequence of certain packing features that occur in both groups.