Max R. Taylor

The crystal structures of four models for the binding to DNA of cisplatinum derivatives containing a bidentate tertiary diamine

Abstract The compounds cis-[(TMED)Pt(9-MeG)2](PF6)2· 2H2O (1), cis-[(TMED)Pt(9-EtG)2](ClO4)2·2H2O(2). cis-[(TMED)Pt(DMX)2](PF6)2·4H2O (3) and cis-[(TMED)Pt(TMX)2](PF6)2·xH2O (x ≈ 4) (4), where TMED = N,N,N′,N′-tetramethylethylenediamine, 9-MeG = 9-methylguanine, 9-EtG = 9-ethylguanine, DMX = 1,3-dimethylxanthine and TMX = 1,3,9-trimethylxanthine, have been prepared and structurally characterized by X-ray methods. Compound 1 crystallises in space group Pn, with a = 10.675(1), b = 12.970(1), c = 12.016(1) A, β = 97.05(1)°, Z = 2. Compound 2 crystallizes in space group Pbca, with a = 13.886(1), b = 31.742(4), c = 14.958(2) A, Z = 8. Compound 3 crystallizes in space group C2/c, with a = 37.557(4), b = 12.215(2), c = 15.823(3) A, β = 90.47(1)°, Z = 8. Compound 4 cyrstallises in the space group C2/c, with a = 38.516(5), b = 12.078(2), c = 16.219(2) A, β = 97.88(1)°, Z = 8. Compounds 3 and 4 are structurally similar. Each [(TMED)Pt(Base)2]2+ cation shows square-planar coordination to Pt with the two independent purine ligands coordinated through N7 and arranged in a head-to-tail conformation. The structures are compared with each other and with related compounds in terms of their base/base and base/coordination plane dihedral angles, and their different crystalline environments.

Crystal structure of a zinc-(9-methyladenine) complex with N1 as the preferred binding site

Abstract The crystal structure analysis of a zinc-(9-methyladenine) complex has shown that in slightly acidic conditions, N1 of the base is a strong binding site and may be preferred over N7. Pairs of stacked bases are linked through metal-ligand and hydrogen bonds.

Compositional segregation and solid solution in the lead-dominant alunite-type minerals from Broken Hill, N.S.W.

Abstract A study of the composition and unit cell data of a suite of lead-rich minerals of the alunite-jarosite group from the oxidized zone of the ore body at Broken Hill, New South Wales, Australia, has revealed almost complete XO4 (X = As, P, S) solid solution in these minerals at this deposit. The species in the group noted are hidalgoite, hinsdalite, beudantite, segnitite and plumbogummite. These minerals at Broken Hill exhibit a number of growth textures, including oscillatory zoning, colloform banding and replacements. Zoning in these minerals is due to the segregation of Al- and Fe-rich members, and compositions indicate a strong coupling of Fe3+ with AsO43−and Al with PO43−.

Synthesis, structure and complexing capabilities of N,N′,N′′,N′′′-tetrakis(3-hydroxypropyl)cyclam

Abstract The synthesis of the new pendant arm macrocyclic ligand N,N′,N′′,N′′′ -tetrakis(3-hydroxypropyl)cyclam (THPC-14) has been accomplished, in quantitative yield, through the high pressure reaction of 1,4,8,11-tetraazacyclotetradecane (cyclam) with trimethylene oxide (oxetane). The molecular and crystal structure of this compound, which have been determined by X-ray crystallography, show the presence of both intermolecular and intermolecular hydrogen bonding, the former of which, together with an RSSR pattern of chiralities at the nitrogen atoms (the trans-IV configuration), preorganise the ligand unfavourably towards complexation. Formation constants have been determined for complexes of the ligand with Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ Hg 2+ and Pb 2+ by glass electrode potentiometry. In all cases the [M(THPC-14] 2+ complex is less stable than the complex formed from the related ligand N,N′,N′′,N′′′ -tetrakis(2-hydroxyethyl)cyclam (THEC-14), a fact which can be attributed to the formation of six-membered chelate rings by the pendant arms rather than five-membered chelate rings. Isolation of the octahedral complexes [Ni(THPC-14)](ClO 4 ) 2 and [Ni(THPC14)(NCS) 2 ] and a study of their spectral and magnetic properties indicates that pendant hydroxyl coordination occurs, but that this bonding is relatively weak facilitating easy substitution by isothiocyanate.

Synthesis and crystal structure determination of some novel zinc(II) macrocyclic heptaaza Schiff-base complexes with two 2-aminoethyl pendant arms

Abstract Three heptadentate Zn(II) macrocyclic bis(pendant donor) Schiff-base complexes, [Zn Ln](ClO4)2 (n=5, 6, 7) have been prepared via the Zn(II) templated [1+1] condensation of 2,6-diacetylpyridine with branched hexaamines, and characterised by X-ray diffraction, IR, 1H and 13C NMR spectroscopy. The ligands are 15-, 16- and 17-membered pentaaza macrocycles with two pendant 2-aminoethyl groups [L5=2,13-dimethyl-6,9-bis(2-aminoethyl)-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18), 2, 12, 14, 16-pentaene, L6=2,14-dimethyl-6,10-bis(2-aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19), 2, 13, 15, 17-pentaene and L7=2,15-dimethyl-6,11-bis(2-aminoethyl)-3,6,11,14,20-pentaazabicyclo[14.3.1]eicosa-1(20),2,14,16,18-pentaene]. The crystal structure of [Zn L5](ClO4)2, was determined by X-ray diffraction and showed that the complex cation that had formed consisted of a pentagonal bipyramidally coordinated Zn(II) ion, centrally located in a pentaaza macrocycle, with two pendant amines coordinating on opposite sides of a plane defined by the macrocycle and the metal ion. The spectroscopic characterisation of the three complexes is consistent with them all having this basic structure.

On the structure of aragonite -- Lawrence Bragg revisited.

The structure of aragonite was first determined by Lawrence Bragg in 1924 in what is the now standard space-group setting Pnma (No. 62). Subsequent studies have all taken his structure as their starting points, despite Braggs own stated doubts and some earlier etching studies which indicated that the underlying symmetry may really be polar. We have reinvestigated the structure and found that there are many reflections with significant intensity among those that should be systematically extinct in Pnma. Some of these reflections have been subjected to further experimental analysis and have been shown not to be due to Renninger effects. A possible model that satisfies these observations is one where the true structure is in space group P1; and the structure is twinned about the three axial twofold rotation axes of Pnma. The space group P1 cannot be ruled out. Evidence for these conclusions is presented. The crystal chemistry of aragonite is revisited and described in terms of the stuffed alloy CaC. The carbonate group is confirmed to be non-planar in the crystal.

The crystal structure of kintoreite, PbFe 3 (PO 4 ) 2 (OH,H 2 O) 6

Abstract The crystal structure of kintoreite, PbFe3(PO4)2(OH,H2O)6, has been refined. The mineral is rhombohedral, R3̅m with a = 7.3310(7), c = 16.885(2) Å, Z = 3; the structure has been refined to R = 3.0% and Rw = 3.0% using 183 observed reflections [I > 2σ(I)]. Kintoreite has the alunite-type structure which consists of sheets of corner-sharing Fe(O,OH)6 octahedra parallel to (001). The sheets are composed of clusters of three comerlinked octahedra which are tilted so that the three apical O atoms form the base of the XO4 tetrahedra. The clusters of octahedra are linked to similar groups by corner-sharing to form six membered rings. The Pb cations occupy the cavities between pairs of octahedral sheets and are surrounded by six oxygen atoms from the tetrahedra and six oxygen atoms from the octahedra to form a very distorted icosahedron. The mean bond lengths for the various coordination polyhedra are X−O 1.55 Å, (X= P, As, S); Fe−(O, OH) 2.01 Å; Pb−O 2.84 Å. The composition of the crystal used in the refinement was PbFe3(PO4)1.3(AsO4)0.4(SO4)0.3(OH,H20)6. The XO4 anions are disordered, as in beudantite, rather than being ordered, as they are claimed to be in corkite.

The crystal structure of mawbyite, PbFe 2 (AsO 4 ) 2 (OH) 2

Abstract The crystal structure of mawbyite, PbFe2(AsO4)2(OH)2 has been refined. The mineral is monoclinic, C2/m with a = 9.066(4), b = 6.286(3) c = 7.564(3) Å, β = 114.857(5)° Z = 2; the structure has been refined to a conventional R = 4.3% using 361 observed reflections [I> 3σ(I)]. The structure contains chains of edgesharing Fe(O,OH)6 octahedra which are linked by AsO4 tetrahedra and Pb atoms in distorted square antiprismatic co-ordination. The hydrogen bonding network in the structure has been modelled using bond valence calculations. Mawbyite is confirmed to be isostructural with tsumcorite and dimorphous with carminite and the relationship between these two structures is discussed.

Structural requirements for rapid metal ion ingress into hydroxyethylated tetraaza macrocycles

Abstract Synthesis of two new bis(2-hydroxyethyl)_substituted cyclam (1,4,8,11-tetraazacyclotetradecane) 1,4-bis(2-hydroxyethyl)-8,11-dimethylcyclam (1,4-DMHEC-14) and 1,11-bis(2-hydroxyethyl)-4,8-dimethylcyclam (1,11-DMHEC-14), has enabled a study of the effects of partial hydroxyethylation of the nitrogen atoms in a macrocyclic ligand framework to be made. The ligands were synthesised through the reaction of ethylene oxide with the appropriately methylated cyclam precursor. Stability constants for complexes of these ligands with Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ Cd 2+ Hg 2+ and Pb 2+ have been measured by potentiometric titration and are generally intermediate between those shown by tetramethylcyclam (TMC-14) and tetrakis(2-hydroxyethyl)cyclam (THEC-14), consistent with a lower level of ligand stabilisation through internal hydrogen bond formation than in THEC-14. Equilibration times noted during the potentiometric titrations indicate that these bis(2-hydroxyethyl) ligands, like THEC-14 and unlike TMC-14, facilitate rapid entry of the metal ion into the macrocyclic annulus demonstrating that two pendant 2-hydroxyethyl arms, when located on adjacent nitrogen atoms, are sufficient to generate facilitated entry. The crystal structures of both [Ni(1,4-DMHEC-14)](ClO 4 ) 2 and [Ni(l,II-DMHEC14)](ClO 4 ) 2 have been determined by a combined molecular mechanics and X-ray crystallography study and show that in each isomer both pendant donors are coordinated in a trans -relationship, in addition to the four nitrogen atoms, giving rise to octahedral stereochemistry. In the former case the ligand is in the trans -III configuration whereas the latter complex has a trans -II geometry.

Synthesis, X-ray Characterization, NMR and Ab Initio Molecular-Orbital Studies of some Cadmium(II) Macrocyclic Schiff-Base Complexes with Two 2-Aminoethyl Pendant Arms

Three new pendant arm Schiff-base macrocyclic complexes, [CdLn]2+ (n = 5, 6, 7), have been prepared via cyclocondensation of 2,6-diacetylpyridine with three different branched hexaamines in the presence of Cd(II). The ligands are 15-, 16- and 17-membered pentaaza macrocycles having two 2-aminoethyl pendant arms [L5 = 2,13-dimethyl-6,9-bis(aminoethyl)-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, L6 = 2,14-dimethyl-6,10-bis(aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19),2,13,15,17-pentaene and L7 = 2,15-dimethyl-6,11-bis(aminoethyl)-3,6,11,14,20-pentaazabicyclo[14.3.1]eicosa-1(20),2,14,16,18-pentaene]. All complexes were investigated by IR, 1H and 13C NMR, COSY(H,H) and HETCOR(H,C) spectroscopy and X-ray diffraction. In the solid state structure of each complex the Cd(II) ion is situated centrally within an approximately planar pentaaza macrocyclic ring, binding to the five nitrogen atoms, and also to the two pendant amines which are located on opposite sides of the macrocyclic plane. ab initio HF-MO calculations using a standard 3-21G* basis set have been used to verify that these similar basic structures correspond to energy minima in the gas phase.