Erich Dubler

Topotactic decomposition and crystal structure of white molybdenum trioxide-monohydrate: Prediction of structure by topotaxy

Abstract Single crystals of the white MoO3 · H2O modification (“α-molybdic acid”) were transformed by heating to 160°C into perfect pseudomorphs built up from oriented MoO3 crystallites of known structure. From the mutual orientation relationship of the unit cells of both phases involved in this topotactic reaction, as determined by X-ray photographs, a model for the so far unknown crystal structure of white MoO3 · H2O could be deduced. Independently, this structure was determined by X-ray diffractometer data then: space group P 1 , a = 7.388, b = 3.700, c = 6.673 A, α = 107.8, β = 113.6, γ = 91.2°, Z = 2. The structure was solved from the Patterson function and refined until R = 0.088. It is built up from isolated double chains of strongly distorted [MoO5(H2O)]-octahedra sharing two common edges with each other. This result agrees well with the model derived from topotaxy, and it becomes evident how the MoO3 lattice is formed through corner linking of the isolated double chains after the water molecules are removed. The study of topotactic phenomena seems rather generally applicable to deduce the main features of structures involved and for better understanding of structural relationships.

Thermal degradation of copper(1) thiolate clusters and the crystal structure of solvent-free (Ph4P)2 [Cu4(SPh)6]

Abstract Copper(I) thiolate clusters of the type (Ph4P)2- [Cu4(SPh)6] or ((CH3)nN)2[Cux(SPh)y] with or without solvent molecules and with x:y = 4:6 or 5:7 have been crystallized from different solvents. Their thermal degradation behavior was characterized by thermogravimetry and simultaneous mass spectrometry of the evolved molecules. The solvent-containing complexes lose the solvent in a first decomposition step between 100 and 160 °C. The subsequent degradation is dependent on the cation only, not on the Cu(I)S core type and finally leads to Cu1.96S. In the course of this decomposition intermediate products with the stoichiometry Cux(SPh)x, are formed. The crystal structure of solvent-free (Ph4P)2- [Cu4(SPh)6] (a=23.290(9), b=13.008(4), c= 25.622(6) A, β=107.31(3)°, Z=4, space group P21/a) has been solved and refined to R=6.9% for 2982 observed reflections. The structure consists of adamantan-type [Cu4S6]2- clusters and Ph4P+ cations. The mean CuCu distance within the cluster is 2.744 A CuS distances range from 2.252 to 2.315 A. Crystals of ((CH3)4N)2[Cus(SPh)7] have been shown by thermal analysis to contain one solvent molecule per formula unit. The crystal structure of this solvent-containing complex (a=12.244(10), b=20.058(11), c=11.506(5) A, a=103.59(5), β= 90.04(5), γ=82.98(6)°, Z=2, space group P 1 , R= 6.1% including 3409 observed reflections) exhibits [Cu5(SPh7]2- clusters and (CH3)4N+ cations and shows no significant deviations from data given in the literature for the ‘olvent-free’ complex.

The geometry of the neutral, protonated or coordinated purine derivatives hypoxanthine, xanthine, allopurinol and alloxanthine: quantum chemical and X-ray crystallographic studies

Abstract The structures of neutral, protonated and coordinated purine derivatives were calculated by semiempirical and ab initio geometry optimizations using MIDI or 6-31G ∗∗ basis sets. The predicted geometries agree well with the available crystallographic data and allow a systematic interpretation of the structural changes resulting from tautomerization, protonation or coordination. Protonation at a nitrogen atom induces alterations in the range 0.050-0.080 A of the CN and CC bond lengths of the pyrimidine or pyrazole ring. The corresponding CNC angles are increased by about 4° upon protonation in the oxopurines hypoxanthine and xanthine and in the pyrazolopyrimidines allopurinol and alloxanthine; the adjacent angles are reduced by approximately 3–4°°. The 1H,9H ⇌ 1H,7H tautomerization of neutral oxopurines results in changes in the respective CNC angles of approximately ±l° only. The pyrazolopyrimidines,, in contrast, show alterations of both neighboring bonding angles of the five-membered ring by about ± 6–8° upon 1 H,9H⇌1H,8H tautomerization. In contrast to the effects of protonation, the influence of metal coordination is very small, but still significant. Monodentate coordination at the pyrimidine ring of neutral hypoxanthine induces about 50% of the shifts effected by tautomerization and about 20% only of those resulting from protonation. Allopurinol, monodentately coordinating through N(8), shows structural changes of the pyrazole moiety up to a maximum of about 30% of those associated with an attachment of a hydrogen atom. The molecular electrostatic potential has been calculated for the optimized geometries of the free ligands at the ab initio level, using the MIDI basis set. Metal coordination of purine derivatives is discussed in terms of contour diagrams of the electrostatic potential in the molecular plane. Partial atomic charges have been fitted to the electrostatic potential and compared with charges derived according to various other methods.

A new synthetic pathway for tris-μ-disulfido-μ3-thio-triangulo-trimolybdenum(IV) complexes: preparation, characterization and structure of [Mo3S(S2)3(OOCCHSCH2COOH)3]2−

Abstract A new synthetic pathway for complexes containing the polynuclear core [Mo3S7]4+ is described: [Mo3S7(S2)3]2− reacts with HBr to [Mo3S7Br6]2− which seems to be a useful intermediate for further ligand substitution. A new complex with mercapto- succinic acid C4H6O4S (H3msa) as ligand could be prepared. 1H NMR and 13C NMR spectra and X-ray crystal structure analysis are in agreement with the bidentate coordination of mercapto-succinic acid, where S− and COO− are bound to the same molybdenum atom forming a five-membered ring. A monoclinic crystal, space group C2, of the composition [C18H30N3]2[Mo3S7(Hmsa)3][Mo3S7(Hmsa)2(msa)] Br·6H2O was used for X-ray diffraction. The cell parameters are a=21.968(7), b=13.423(13), c= 18.828(3) A, β=94.23°, Z=2, Dc=1.606 g/cm3, μ(Mo Kα)=13.51 cm−1. [Mo3S7(Hmsa)3]2− is stable in water and air, and it can be precipitated from aqueous solution by the addition of large three-fold charged cations. It can be deprotonated reversibly to [Mo3S7(msa)3]5− in water. The pK values are 3.95, 4.41, 5.02 (1 M KCl, 25 °C). To confirm the above described procedure as a useful approach for [Mo3S7]4+ complexes, a similar compound with 2-mercapto-benzoic acid was also prepared.

Isomer abundance of bis(β-diketonato) complexes of titanium(IV). Crystal structures of the antitumor compound budotitane [TiIV(bzac)2(OEt)2] and of its dichloro-derivative [TiIV(bzac)2Cl2] (bzac=1-phenylbutane-1,3-dionate)

The molecular tumor inhibiting titanium compound budotitane [Ti(IV)(bzac)(2)(OEt)(2)] (1) and its dichloro-derivative [Ti(IV)(bzac)(2)Cl(2)] (2) (bzac=1-phenylbutane-1,3-dionate) have been crystallized and characterized by X-ray crystallography and further physical methods. Budotitane (1) crystallizes in the tetragonal, non-centrosymmetric space group P4(1) with two molecules in the asymmetric unit. Both molecules adopt the cis-cis-trans configuration with the acetyl ends of the benzoylacetonate ligands in the trans position. The dichloro-derivative of budotitane, [Ti(IV)(bzac)(2)Cl(2)] (2) crystallizes in the monoclinic, centrosymmetric space group P2(1)/n with one molecule only in the asymmetric unit. In contrast to budotitane (1), (2) shows a cis-trans-cis arrangement with the benzoyl groups in the trans position. In both complexes there are equal numbers of Delta and Lambda enantiomers within the unit cell. The phenyl groups in (1) as well as in (2) are in approximately coplanar conjugation to the metal enolate rings. The thermal degradation of budotitane (1) was investigated in the temperature range from 25 degrees C up to 800 degrees C and reveals the formation of Ti(IV)O(bzac(2-)) as an intermediate and of the rutile phase of TiO(2) as a final product. It may be worthwhile to introduce budotitane in the form of isomerically pure crystals in the preparation of the drug used for future tests.

Cu(N,N′-dimethylthiourea)2NO3, a copper(I) complex exhibiting Infinite chains of edge-sharing CuS4 tetrahedra

Abstract Bis(N,N′-dimethylthiourea)copper(I)nitrate, Cu- (SC(NHCH3)2)2NO3, has been synthesized from an aqueous solution of copper(II) nitrate and N,N′- dimethylthiourea. Crystal data are a = 10.349(3), b = 12.197(2), c = 5.777(3) A, α =92.92(3), β = 98.84(3), γ = 68.03(2)°, V = 668.2 A3, space group P 1 , Z = 2. The crystal structure was solved by Patterson and Fourier methods from diffractometer data and refined to R and Rw of 0.038 and 0.041 including 3213 observed reflections. The compound exhibits a new structure type which has not yet been recognized in copper(I) sulfur complexes. Considerably distorted CuS4 tetrahedra are linked to isolated, infinite chains of the type [Cu(SR)2]nn+ by sharing opposite edges. The cationic chains are separated from each other by the nitrate anions, which do not coordinate to the metal atom. Shortest metal-to- metal distances within the chains are 2.865(1) and 2.934(1) A. The chains are bridged via NH···O hydrogen bonds involving the nitrate ions. A structural comparison between this compound and the copper(I) thiourea complexes hitherto known is presented.

Uric acid salts of magnesium: crystal and molecular structures and thermal analysis of two phases of Mg(C5H3N4O3)2•8H2O

Abstract Two structurally different phases of a uric acid salt of magnesium, Mg(hydrogenurate) 2 · 8H 2 O, have been prepared by crystallization from solution at pH = 7.5–8.0 and were investigated by x-ray crystallography, thermal analysis, and ir spectroscopy. Both phases are monoclinic, space group P2 1 /c with a = 9.573(2), b = 14.627(3), c = 7.170(1) A, β = 101.91(1)° (phase I) and a = 10.397(2), b = 14.306(3), c = 6.732(1) A, β = 104.64(2)° (phase II). The crystal structures of both phases (R = 0.053 and 0.051, respectively) contain isolated octahedral [Mg(H 2 O) 6 ] 2+ cations, hydrogenurate monoanions, and two molecules of water of crystallization per formula unit. The structural formula representing these facts is [Mg(H 2 O) 6 ] (hydrogenura-te) 2 ·2H 2 O. The tautomeric form of the hydrogenurate molecule corresponds to the tri-keto form of uric acid deprotonated at N(3). Differences in bond length between uric acid and the hydrogenurate molecule may be described in terms of three additional resonance structures distributing the formal negative charge at N(3) within the pyrimidine (but not the imidazole) ring. Deprotonation at N(3) significantly decreases the internal C-N-C angle at N(3). Alternating pairs of medium-strong intermolecular N-HO hydrogen bonds lead to infinite chains of hydrogenurate molecules extending along the b axis of the unit cells in both phases. The main difference between the two phases lies in their stacking pattern of the hydrogenurate molecules. Infrared data confirm the hydrogen bonding characteristics resulting from the crystal structure analysis. Thermogravimetric measurements and differential scanning calorimetry data show that the dehydration of both phases occurs in two distinct steps with Mg(hydrogenurate) 2 .6H 2 O as an intermediate phase. The first dehydration step (−2H 2 O) is a topotactic reaction with three-dimensional preservation of the main structure elements of the octahydrate in the structure of the hexahydrate.

Synthesis, characterization and crystal structure of copper(I) thiolates : [(C6H5)4P+]2[Cu4(C2H5S-)6].0.5C2H6O2 and [(C6H5)4P+][Cu7(C2H5S-)8]

Abstract The reaction of the monodentate ligand thioethane with (C 6 H 5 ) 4 PBr and Cu 2 O in organic solvents results in the crystallization of two new homoleptic polynuclear copper(I) thiolates: [(C 6 H 5 ) 4 P + ] 2 [Cu 4 (C 2 H 5 S − ) 6 ]·0.5C 2 H 6 O 2 ( 1 ) and [(C 6 H 5 ) 4 P + ][Cu 7 (C 2 H 5 S − ) 8 ] ( 2 ). Both compounds have been characterized by X-ray crystallography, thermal analysis, luminescence spectroscopy and IR spectroscopy. Compound 1 is triclinic, space group P 1 − with a = 12.066(5), b = 13.824(5), c = 19.112(3) A, α = 90.82(2), β = 101.85(2), γ = 93.53(3)° and Z = 2. Compound 2 is monoclinic, space group P 2 1 / c with a = 19.208(3), b = 16.975(4), c = 16.394(6) A, β = 108.68(2)° and Z = 4. The structure of 1 is built up by [(Cu 4 (RS − ) 6 ) 2− ] adamantane-type cluster units, separated by [(C 6 H 5 ) 4 P + ] cations. Compound 2 consists of copper(I) thiolate chains, also separated by [(C 6 H 5 ) 4 P + ] cations. In 2 , structural units of the stoichiometry Cu 7 (C 2 H 5 S − ) 10 are connected by common sharing of four sulphur atoms, leading to a chain of the stoichiometry Cu 7 (C 2 H 5 S − ) 8 . The shortest CuCu distance is 2.692(1) A in 1 and 2.736(2) A in 2 . Excitation at 450 nm of 1 in the solid state results in a weak emission at 665 nm, compound 2 exhibits in the solid state an intense luminescence at 591 nm upon excitation at 365 nm.

The interaction of transition metals with the coenzyme α-lipoic acid: synthesis, structure and characterization of copper and zinc complexes

Abstract The reaction of DL-α-lipoic acid or DL-α-lipoamide with copper(I) chloride in acidic aequeous solution leads to the copper(I) lipoic acid complexes catena -poly[Cu 1 (lip 0 )Cl[ form I ( A ) and form II ( B ) and poly[Cu I 3 (lip 0 ) 2 Cl 3 ] ( C ). From an aqueous suspension of lipoic acid, crystals of the copper(II) lipoic acid complex [{;Cu 11 (lip − ) 2 > 2 ] ( D ) and of the zinc(II) complex [Zn 11 (lip − 2 (H 2 O) 2 ] ( E ) can be grown on the surface of pressure pills of the corresponding insoluble metal hydroxide salts. The crystal structures of A, B, C and E have been established by X-ray diffraction. Crystal data are as follows A : monoclinic, In the three copper(I) complexes A, B and C , α-lipoic acid is coordinating to the metal atom via its cyclic disulfide group and bridges two adjacent copper atoms. Five-membered rings of the type CuClCuSS- are building blocks in each of these three structures. A four-fold bridging μ 4 -chlorine atoms is observed in C . The structure of E is built up by neutral molecular [Zn 11 (lip − ) 2 (H 2 O) 2 ] unitsl the anionic α-lipoic acid ligand is coordinating via its bidentate, chelating carboxylate group. A trend is evident, whereby the SS bond distance of the cyclic disulfide unit increases and the CSSC torsion angle decreases upon coordination to metal ions. This geometrical influence upon coordination may be paralleled by an increase of the corresponding ring strain and, hence, by an enhanced redox reactivity of the disulfide moiety of α-lipoic acid. Spectroscopic and variable temperature magnetic studies indicate the presence of dimeric [Cu II 2 (lip − ) 4 ] unit with antiferromagnetic coupling (−2 J = 315 cm −1 ) between the copper(II) centers in D .

Molecular structures and solid-solid phase transitions of trinuclear CpCo[P(O)(OR)2]32M complexes

SummaryThe trinuclear complexes {CpCo[P(O)(OMe)2]3}2Co and {CpCo[P(O)(OEt)2]3}2M, where M=Mg, Ca, Sr, Ba, Pb, Mn, Co, Ni, Cu, Zn, Cd or Hg, have been studied by x-ray diffraction methods and the crystal structures of {CpCo[P(O)(OR)2]3}2M [R=Me with M=Co (1) and R = Et with M = Cu (2)] have been solved by the heavy atom technique. Complex (2) crystallizes in the triclinic space group P 1 with two crystallographically independent molecules per unit cell. The cell dimensions area = 12.195(3) Å,b = 20.429(6) Å, c = 12.518(3) Å,α = 102.39(2)°, β=120.15(2)°, γ=92.28(2)°. The molecule contains two cobalt atoms and one copper atom in a linear arrangement with copper situated on a center of symmetry. Each of the cobalt atoms is bonded to a cyclopentadienyl ring and is connected to the central copper atom by three phosphonate groups acting as bridging ligands. Disorder phenomena within these phosphonate groups are best described as an enhanced thermal motion corresponding mainly to a rotation around the Co-Cu-Co axis. The CuO6 coordination octahedra exhibit a small (4+2) distortion.The electronic spectrum of this copper complex has been measured in solution and in the solid state and is in accord with the Jahn-Teller distorted octahedral coordination of the copper ion found in the x-ray structure.Complex (1) is monoclinic, space group P21/c with two formula units per cell. Its molecular structure shows the same general features as the copper complex. The coordination of the central cobalt atom is regularly octahedral within the limits of error. Parts of the phosphonate P(O)(OMe)2 groups are disordered over two distinct sites in the crystal with occupancy factors ofca. 0.75 and 0.25.D.s.c. measurements of the trinuclear compounds containing disordered P(O)(OEt)2 groups show phase transitions occurring in the 160–230 K temperature range that are best discussed in terms of order-disorder transitions. From d.s.c. measurements of the corresponding complexes with P(O)(OMe)2 ligands, there are no phase transitions visible in the 100–300 K range.