Michel Fleck

A unique example of a three component cocrystal of metal complexes

The synthesis, characterization and structure of a [3 × 1 + 2 × 1 + 1 × 2] cocrystal [(NiIIL1)2NaI(NO3)]·[{NiIIL1NaI(H2O)2}{NiIIL1}2(NO3)] derived from the hexadentate Schiff base compartmental ligand N,N′-ethylenebis(3-ethoxysalicylaldimine) (H2L1) are described. The compound crystallizes in the monoclinic system (space group C2/c). The structure consists of one trinuclear double-decker [(NiIIL1)2NaI]+ cation, one dinuclear [NiIIL1NaI(H2O)2]+ cation and two mononuclear [NiIIL1] moieties. Each of the two coordinated water molecules of the dinuclear unit is encapsulated in the O4 cavities of the two mononuclear [NiIIL1] moieties resulting in the formation of a tetranuclear self-assembly, which is further interlinked with the trinuclear sandwich species due to Ni⋯Ni interaction to result in an overall one-dimensional topology in the title compound. A unique example of a three component cocrystal of metal complexes, existence of NaI in two entirely different environments in spite of being surrounded by the same blocking ligand and structural resemblance of sodium(I) with 3d metal ions are the major outcomes of the present investigation.

Glycine glycinium picrate--reinvestigation of the structure and vibrational spectra.

The crystal of diglycine picrate (glycine glycinum picrate) has been obtained from an aqueous solution containing stoichiometric quantities of the components. The species crystallizes in the monoclinic system (space group P2(1)/c). The crystal structure was determined with high accuracy, IR and Raman spectra are discussed and compared with previous results, and the molecular structure is presented. It was shown that crystals of diglycine picrate obtained from the solution containing equimolar quantities may contain picric acid as impurity, which is the reason for the previously reported observation of second harmonic generation in this centrosymmetric crystal. With this example we want to point out the risk of misinterpretation of SHG signals in general.

Natural and synthetic compounds with kröhnkite-type chains: review and classification

Abstract The crystal structure of kröhnkite [Na2Cu(SO4)2·2H2O], which contains infinite chains composed of CuO6 octahedra corner-linked with SO4 tetrahedra, was originally determined 1952 by Dahlman. Since then, a large number of both minerals (e.g., collinsite, fairfieldite, etc.) and synthetic compounds with closely related struc-tures have been investigated, but the structural relation was not always recognised. In the present review we compare the structures of AnM(XO4)2·2H2O (A = mono- or divalent cation, n = 1, 2; M = di- or trivalent cation; X = penta- or hexavalent cation) compounds with kröhnkite-type infinite chains, and propose a structural classification into six types. The rod group symmetries of the chains are compared. Furthermore, the linkage of these chains to double chains (in krausite-type compounds) and sheets (in yavapaiite-, merwinite-, bafertisite-type and similar structures) is discussed, and the occurrence of octahedral-tetrahedral chains topologically identical to those in kröhnkite (referred to as kröhnkite-type) and similar chains (referred to as kröhnkite-like) in several related compounds is pointed out.

Salts of Amino Acids

Within this chapter, the fundamental properties of amino acids are presented. The basic chemical features of amino acids are the ubiquitous amino and acid groups; the residue of the molecule is usually referred to as side chain. Of an infinite number of conceivable amino acids, twenty (plus a few more or less frequent) members are found in proteins of living beings and thus play a crucial role in the chemistry of life. From a chemical point of view, the chirality of most amino acids is an important feature, which is discussed in regard with the nomenclature systems conventionally employed. Chirality is related with symmetry, both of the molecule and the crystal structure of amino acids (or their salts). Moreover, the chemical flexibility of amino acids, both in terms of symmetry and in terms of their amphoteric nature, is reviewed, thus forming the frame of reference for the following chapters which deal with the actual amino acid salts.

Natural and synthetic compounds with kröhnkite-type chains. An update

Abstract The crystal structures of five new triclinic double salt dihydrates have been determined from single-crystal X-ray diffraction data. The following four compounds all contain kröhnkite-[Na2Cu(SO4)2·2 H2O]-type tetrahedral-octahedral chains: the three isotypic synthetic compounds K2Mg(CrO4)2·2 H2O (a = 5.674(1), b = 6.462(1), c = 7.517(2) Å, α = 110.38(3), β = 95.24(3), γ = 109.86(3)°, V = 236.0(1) Å3, R(F) = 0.036, space group P1̅, no. 2, Z = 1), K2Mg(MoO4)2·2 H2O (a = 5.884(1), b = 6.491(1), c = 7.700(1) Å, α = 111.67(2), β = 96.59(2), γ = 108.62(2)°, V = 249.8(1) Å3, R(F) = 0.019, space group P1̅, no. 2, Z = 1) and K2Mn(SeO4)2·2 H2O (a = 5.674(1), b = 6.608(1), c = 7.523(2) Å, α = 110.31(3), β = 95.69(3), γ = 108.35(3)°, V = 244.10(9) Å3, R(F) = 0.024, space group P1̅, no. 2, Z = 1), and the mineral messelite Ca2(Fe2+,Mn2+,Mg)(PO4)2·2 H2O (a = 5.480(1), b = 5.759(1), c = 6.569(1) Å, α = 90.18(3), β = 102.62(3), γ = 108.45(3)°, V = 191.3(1) Å3, R(F) = 0.022, space group P1̅, no. 2, Z = 1). The fifth compound, the synthetic dichromate K2Zn(Cr2O7)2·2 H2O (a = 6.794(1), b = 7.735(2), c = 7.834(2) Å, α = 88.97(3), β = 80.90(3), γ = 64.57(3)°, V = 366.5(2) Å3, R(F) = 0.036, space group P1̅, no. 2, Z = 1) is closely related to the kröhnkite-group; it contains Cr2O7 groups assuming the same bridging role that XO4 groups have in kröhnkite-type oxysalts. The atomic arrangements of the title compounds are described and structural relations with other kröhnkite-type and -like compounds are discussed. In addition, related yavapaiite-type sheet structures of AM′(XO4)2 compounds are briefly reviewed, including the rod group symmetry of the underlying kröhnkite-chain building unit. Twelve different space groups have been found for these sheet structures. The previously reported space group symmetries for α-NH4Fe(CrO4)2 (P21) and CsTa(PO4)2 (P1̅) are obviously incorrect and should be revised to P21/n and C2/m, respectively.

Compounds of glycine with halogen or metal halogenides : review and comparison

Abstract The large family of glycine halogenides and metal halogenides encompasses a high variety of different crystal structures. The role of the glycine molecule as a structural unit as a mono-, bi- or tridentate ligand, of the halogenide ions as well as the composition and condensation of the cationic polyhedra is discussed. With respect to the connectivity of the building units, five different structure families of glycine halogenides and glycine-metal halogenides can be distinguished. Parameters such as symmetry, ionic radii, electronegativity of cation and anion and their difference, charge, coordination number, hydration states, stoichiometric ratios and connectivity were weighed against each other in order to see if any correlations exist. The data suggest that cations with high electronegativities seem to promote formation of structures with a low grade of connectivity, i.e., isolated units, and vice versa.

Three novel non-centrosymmetric compounds of glycine: glycine lithium sulfate, glycine nickel dichloride dihydrate and glycine zinc sulfate trihydrate

The crystal structures of three compounds of glycine and inorganic materials are presented and discussed. The orthorhombic structure of glycinesulfatodilithium(I), [Li(2)(SO(4))(C(2)H(5)NO(2))](n), consists of corrugated sheets of [LiO(4)] and [SO(4)] tetrahedra. The glycine molecules are located between these sheets. The main features of the monoclinic structure of diaquadichloroglycinenickel(II), [NiCl(2)(C(2)H(5)NO(2))(H(2)O)(2)](n), are helical chains of [NiO(4)Cl(2)] octahedra connected by glycine molecules. The orthorhombic structure of triaquaglycinesulfatozinc(II), [Zn(SO(4))(C(2)H(5)NO(2))(H(2)O)(3)](n), is made up of [O(3)SOZnO(5)] clusters. These clusters are linked by glycine molecules into zigzag chains. All three compounds are examples of non-centrosymmetric glycine compounds.

Slow magnetic relaxation and electron delocalization in an S = 9/2 iron(II/III) complex with two crystallographically inequivalent iron sites

The magnetic, electronic, and Mössbauer spectral properties of [Fe(2)L(μ-OAc)(2)]ClO(4), 1, where L is the dianion of the tetraimino-diphenolate macrocyclic ligand, H(2)L, indicate that 1 is a class III mixed valence iron(II∕III) complex with an electron that is fully delocalized between two crystallographically inequivalent iron sites to yield a [Fe(2)](V) cationic configuration with a S(t) = 9∕2 ground state. Fits of the dc magnetic susceptibility between 2 and 300 K and of the isofield variable-temperature magnetization of 1 yield an isotropic magnetic exchange parameter, J, of -32(2) cm(-1) for an electron transfer parameter, B, of 950 cm(-1), a zero-field uniaxial D(9∕2) parameter of -0.9(1) cm(-1), and g = 1.95(5). In agreement with the presence of uniaxial magnetic anisotropy, ac susceptibility measurements reveal that 1 is a single-molecule magnet at low temperature with a single molecule magnetic effective relaxation barrier, U(eff), of 9.8 cm(-1). At 5.25 K the Mössbauer spectra of 1 exhibit two spectral components, assigned to the two crystallographically inequivalent iron sites with a static effective hyperfine field; as the temperature increases from 7 to 310 K, the spectra exhibit increasingly rapid relaxation of the hyperfine field on the iron-57 Larmor precession time of 5 × 10(-8) s. A fit of the temperature dependence of the average effective hyperfine field yields |D(9∕2)| = 0.9 cm(-1). An Arrhenius plot of the logarithm of the relaxation frequency between 5 and 85 K yields a relaxation barrier of 17 cm(-1).

New salts of amino acids with dimeric cations

Among salts of amino acids there are compounds with the composition 2A..HX, which consist of dimeric A...A+ cations with short symmetric or asymmetric hydrogen bonds between zwitter-ionic and protonated moieties. These species are materials liable to undergo phase transitions or possess interesting nonlinear optical properties. Here, we report the preparation of 20 new salts with dimeric cations from aqueous solutions, including compounds of glycine, betaine, β- alanine, L-alanine, L-phenylalanine, L-threonine, L-valine, L-leucine and L-proline, with BF4-, ClO4-, Cl-, Br-, HSeO3-, and HC2O4-; as anions. The prepared salts are characterized by IR and Raman spectroscopy. Some of them are grown in form of good quality single crystals, which allowed the determination of their crystal structure.

Third update on compounds with kröhnkite-type chains : the crystal structure of wendwilsonite [Ca2Mg(AsO4)2·2H2O] and the new triclinic structure types of synthetic AgSc(CrO4)2·2H2O and M2Cu(Cr2O7)2·2H2O (M = Rb, Cs)

As part of a comprehensive crystal-chemical study and classification of minerals and synthetic compounds with krohnkite-type or -like chains of octahedra bridged by tetrahedra, the crystal structures of wendwilsonite from Schneeberg, Saxony, Germany, with composition Ca 2 (Mg 0.90 ,Co 0.10 )(AsO 4 ) 2 ·2H 2 O, and of three new synthetic double-metal dichromate(VI) dihydrates have been determined from single-crystal X-ray diffraction data. Wendwilsonite is monoclinic [space group P 2 1 / c (no. 14), a = 5.806(1), b = 12.923(3), c = 5.628(1) A β = 107.49(3)°, V = 402.75(14) A 3 , Z = 2; R(F) = 1.42%] and adopts type D in the classification of Fleck et al. (2002b); it is isotypic with the three arsenates brandtite, roselite, zincroselite, and the sulphate krohnkite. Infinite krohnkite-type tetrahedral-octahedral chains [(Mg,Co)(AsO 4 ) 2 (H 2 O) 2 ] 2- are separated by Ca 2+ cations. A very strong hydrogen bond (O…O = 2.5294(18)A) links adjacent chains. Hydrothermally synthesised, orange AgSc(CrO 4 ) 2 ·2H 2 O is triclinic [space group P 1 (no. 2), a = 5.586(1), b = 6.054(1), c = 7.432(1)A, α = 110.74(3), β = 90.21(3), γ = 117.34(3)°, V = 204.56(6) A 3 , Z = 1; R (F) = 3.48%] and represents a novel structure type, designated G, among compounds containing krohnkite-type chains. The structure is metrically pseudo-monoclinic and closely related to those of the monoclinic subtypes F1 ( C 2/ c ) and F2 ( C 2/ m ). AgSc(CrO 4 ) 2 ·2H 2 O also represents the first Ag and Sc compound based on a krohnkite-type chain. The structure is based on infinite tetrahedral-octahedral chains [Sc(CrO 4 ) 2 (H 2 O) 2 ] 2- separated by Ag 1+ cations. The Ag atom exhibits a [4+4]-coordination, with the AgO 8 polyhedron closely resembling a strongly sheared cube. Rb 2 Cu(Cr 2 O 7 ) 2 ·2H 2 O and isotypic Cs 2 Cu(Cr 2 O 7 ) 2 ·2H 2 O were both grown at room temperature as orange blades from slightly acidic aqueous solutions. They represent a new, triclinic structure type containing krohnkite-like octahedral-tetrahedral chains based on bridging Cr 2 O 7 groups [space group P 1 (no. 2), a = 7.272(1) / 7.462(2), b = 7.648(2) / 7.819(2), c = 7.772(2) / 7.847(2)A, α = 91.89(3) / 93.19(3), β = 99.72(3) / 99.57(3), γ = 115.79(3) /116.34(3)°, V = 380.84(15) / 400.23(15) A 3 , Z = 1; R(F) = 3.03 / 2.99%]. The Cu atoms show a Jahn-Teller-distorted ’octahedral’ coordination environment, approaching an unusual [2+2+2]-coordination. Hydrogen bonding is weak. A distinct positive correlation between the size of the alkali cation and the Cr-O-Cr angle in the few known alkali metal dichromates with krohnkite-like chains is demonstrated.