Robert O. Gould

The derivation of non-merohedral twin laws during refinement by analysis of poorly fitting intensity data and the refinement of non-merohedrally twinned crystal structures in the program CRYSTALS

Although non-merohedrally twinned crystal structures can normally be solved without difficulty, problems usually arise during refinement. Careful analysis of poorly fitting data reveals that they belong predominantly to certain distinct zones in which |Fo|2 is systematically larger than |Fc|2. In the computer program ROTAX, a set of data with the largest values of (|F_{o}^{\,2}| − |F_{c}^{\,2}|)/u(|F_{o}^{\,2}|) is identified and their indices transformed by rotations or roto-inversions about possible direct- and reciprocal-lattice directions. Matrices that transform the indices of the poorly fitting data to integers are identified as possible twin laws.

Template self-assembly of polyiodide networks

A range of metal thioether macrocyclic complexes has been used as templating agents in the preparation of extended multi-dimensional polyiodide arrays. A selection of unusual and intriguing polyiodides is described, and the role played by the size, shape and charge of the metal macrocyclic complex discussed.

Induced-fit recognition of DNA by organometallic complexes with dynamic stereogenic centers

Organometallic chemistry offers novel concepts in structural diversity and molecular recognition that can be used in drug design. Here, we consider DNA recognition by η6-arene Ru(II) anticancer complexes by an induced-fit mechanism. The stereochemistry of the dinuclear complex [((η6-biphenyl)RuCl(en))2-(CH2)6]2 + (3, en = ethylenediamine) was elucidated by studies of the half unit [(η6-biphenyl)RuCl(Et-en)]+ (2, where Et-en is Et(H)NCH2CH2NH2). The structures of the separated \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}R_{{\mathrm{Ru}}}^{*}R_{{\mathrm{N}}}^{*}\end{equation*}\end{document} and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}S_{{\mathrm{Ru}}}^{*}R_{{\mathrm{N}}}^{*}\end{equation*}\end{document} diastereomers of 2 were determined by x-ray crystallography; their slow interconversion in water (t½ ≈ 2 h, 298 K, pH 6.2) was observed by NMR spectroscopy. For 2 and 3 the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}R_{{\mathrm{Ru}}}^{*}R_{{\mathrm{N}}}^{*}\end{equation*}\end{document} configurations are more stable than \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}S_{{\mathrm{Ru}}}^{*}R_{{\mathrm{N}}}^{*}\end{equation*}\end{document} (73:27). X-ray and NMR studies showed that reactions of 2 and 3 with 9-ethylguanine gave rise selectively to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}S_{{\mathrm{Ru}}}^{*}R_{{\mathrm{N}}}^{*}\end{equation*}\end{document} diastereomers. Dynamic chiral recognition of guanine can lead to high diastereoselectivity of DNA binding. The dinuclear complex 3 induced a large unwinding (31°) of plasmid DNA, twice that of mononuclear 2 (14°), and effectively inhibited DNA-directed RNA synthesis in vitro. This dinuclear complex gave rise to interstrand cross-links on a 213-bp plasmid fragment with efficiency similar to bifunctional cisplatin, and to 1,3-GG interstrand and 1,2-GG and 1,3-GTG intrastrand cross-links on site-specifically ruthenated 20-mers. Complex 3 blocked intercalation of ethidium considerably more than mononuclear 2. The concept of induced-fit recognition of DNA by organometallic complexes containing dynamic stereogenic centers via dynamic epimerization, intercalation, and cross-linking may be useful in the design of anticancer drugs.

Stabilisation of trivalent platinum by structurally accommodating thiamacrocycles

The complex cation [Pt(1)2]2+[(1)= 1,4,7-trithiacyclononane] shows a quasi square based pyramidal structure with one non-bonding sulphur donor atom; electrochemical oxidation at +0.5 V. vs. Fc0/Fc+(Fc = ferrocene) at 20 °C in MeCN affords a paramagnetic platinum(III) species.

Silver thioether chemistry: Synthesis, X-ray crystal structure and redox properties of [Ag([18]aneS6)]+ ([18]aneS6 = 1,4,7,10,13,16-hexathiacyclooctadecane)

Abstract Reaction of AgNO3 with 1 molar equivalent of [18]aneS6 ([18]aneS6 = 1,4,7,10,13,16-hexathiacyclooctadecane) in water-MeOH (1:1 v/v) affords the complex cation [Ag([18]aneS6)]+. [Ag([18]aneS6)]PF6 crystallizes in the monoclinic space group I2/m with a = 5.295(4), b = 13.959(10), c = 13.951(9) A, β = 95.15(10)°, V = 1027 A3, Dc = 1.983 g cm−3, Z = 2. The complex cation has C2h(2/m) symmetry with AgI bound to all six thia donors of [18]aneS6 with two short [AgS(1) = 2.6665(12) A] and four significantly longer (AgS(4) = 2.7813(10) A) AgS distances. This 2+4 coordination of [18]aneS6 reflects the tendency of the d10 Ag+ ion to increase its coordination number with soft donor ligands. Chemical oxidation of [Ag([18]aneS6)]+ and [Ag([9]aneS3)2]+ at 293 K in highly acidic media affords the corresponding stable AgII species, which have been identified by ESR and UV—vis spectroscopy. These AgII species can only be generated electrochemically in MeCN at 293 K as transient intermediates. The enhanced stabilization of [M([9]aneS3)2]2+ (M = AgII) and [M([9]aneS3)2]3+ (M = FeIII, NiIII, PdIII) under acidic conditions is discussed.

Structural characterisation of hydroxo-bridged arene-ruthenium and -osmium complexes: Further reactions of hydroxo-bridged complexes

Abstract Reaction of [{M(η-C6H6)Cl2}2] with an excess of either aqueous NaOH or Na2CO3 followed by addition of Na[BPh4] gave two products, previously formulated as [η-C6H6(OH)M(OH)2,M(H2O)(η-C6H6)]BPh4 (II) and [(η-C6H6)M(OH)3M(η-C6H6)]BPh4·Me2CO (M = Ru (III), Os (IV)). X-ray structural analyses now reveal that the latter should be reformulated as the novel [M4(η-C6H6)4(μ2-OH)4(η4-O)](BPh4)2· tetramers containing a tetrahedrally coordinated O2− ion. In contrast, with substituted arenes the binuclear triple hydroxo-bridged cations of type III are formed as evidenced by the X-ray crystal structure determination of [Ru2-1,3,5-C6H3Me3)2(OH)3]Cl·3H2O (V). Reaction of these various hydroxo-bridged complexes with HX (X = Cl, Br, I) gives either [Ru2(η-arene)2X3]+ and/or [{Ru(η-arene)X2}2] whereas with CF3CO2H in the presence of arene, the dications [Ru(arene)(arene)]2+ are formed.

Areneruthenium(II) carboxylates: reactions with ligands and the X-ray structure of the p-cymene pyrazine complex [Ru(η-p-MeC6H4CHMe2)Cl(pyz)2]PF6

The preparation of monomeric areneruthenium(II) acetates and trifluoroacetates [Ru(η-arene)X(O2CR)] and [Ru(η-arene)(O2CR)2](X = Cl or Br; R = Me or CF3; arene = C6H6, p-MeC6H4CHMe2, C6H3Me3-1,3,5, C6H2Me4-1,2,4,5, or C6Me6)(not all possible combinations) from the corresponding dihalides [{Ru(η-arene)X2}2] is described. Infrared spectra suggest that the complexes [Ru(η-arene)X(O2CR)] contain a bidentate carboxylate group and that [Ru(η-arene)(O2CR)2] contain one bi- and one uni-dentate carboxylate group, which are apparently equivalent on the n.m.r. time-scale at room temperature. Reaction of trifluoroacetic acid with [{Ru(η-C6Me6)Cl2}2] gives a complex of empirical formula Ru(η-C6Me6)Cl(O2CCF3)·CF3CO2H which may be a salt [(η-C6Me6)Ru(η-Cl)2(µ-O2CCF3)Ru(η-C6Me6)][H(O2CCF3)2]·CF3CO2H. Triphenylphosphine converts [Ru(η-C6Me6)(O2CR)2](R = Me or CF3) into [Ru(η-C6Me6)(O2CR)2(PPh3)] in which both carboxylate groups are unidentate. The trifluoroacetate group is completely displaced from [Ru(η-C6H6)Cl(O2CCF3)] by pyridine (py) or ethyldiphenylphosphine to give [Ru(η-C6H6)ClL2]+(L = py or PEtPh2), isolated as PF6– or BPh4– salts. The potentially binucleating ligands pyrazine (pyz), 4,4′-bipyridyl, and 1,3-dithiane react either with [Ru(η-C6H6)Cl(O2CCF3)] or with [{M(η-p-MeC6H4CHMe2)Cl2}2](M = Ru or Os) in the presence of NH4PF6 or NaBPh4 in methanol to give [M(η-arene)ClL2]+ salts in which only one donor atom of the ligand is co-ordinated, but pyz and [{Ru(η-p-MeC6H4CHMe2)Cl2}2] react in dry tetrahydrofurane to give the pyrazine-bridged species {Ru(η-p-MeC6H4CHMe2)Cl2}2(µ-pyz). The structure of the complex [Ru(η-p-MeC6H4CHMe2)Cl(pyz)2]PF6 has been verified by X-ray analysis. The crystals are triclinic, space group P, with a= 9.265(2), b= 9.684(4), c= 12.969(2)A, α= 86.51(2), β= 72.89(2), and γ= 85.59(2)°.

Gold thioether chemistry: synthesis, structure, and redox interconversion of [Au([9]aneS3)2]+/2+/3+([9]aneS3= 1,4,7-trithiacyclononane)

The crystal structure of [Au([9]aneS3)2]PF6 shows distorted tetrahedral S4 co-ordination at AuI with one [9]aneS3 bound in a unidentate manner [Au(1)–S(11) 2.302(6)A], and the other bound asymmetrically through three S-donors [Au(1)–S(21) 2.350(7), Au(1)–S(24) 2.733(8), Au(1)–S(27) 2.825(8)A]; oxidation of this complex affords the AuIII analogue [Au([9]aneS3)2]3+ which has a distorted octahedral stereochemistry [Au(1)⋯ S(1) 2.926(4), Au(1)–S(4) 2.348(4), Au(1)–S(7) 2.354(4)A]; the intermediate paramagnetic AuIII species has been identified by e.s.r. spectroscopy.

New routes to copper–lanthanoid complexes I: via a metallomacrocycle

We report the synthesis and structure of a novel hexanuclear copper complex of the anion of 6-methyl-2-hydroxypyridine (MeL), which undergoes reaction with lanthanum nitrate to give [La8Cu12(OH)24(NO3)22(MeLH)13(H2O)6][NO3]2[MeLH]2·CH2Cl2, a copper–lanthanoid complex with several unique structural features.

Synthesis and reactions of some triple alkoxo- and thioato-bridged areneruthenium(II) complexes. X-ray structure determination of [Ru2(η-C6H6)2(OMe)3][BPh4]

Reaction of [{Ru(η-arene)Cl2}2] (arene = C6H6, 1,4-MeC6H4CHMe2) with NaNH2 in CH3CN gives a dark oil which upon treatment with ROH/NaBPh4 (R = Me, Et) gives the triple bridged complexes [Ru2(η-arene)2(OR)3] [BPh4]. The structure of the benzene complex (R = Me) has been verified by X-ray analysis. The crystals are monoclinic, space group P21/n with a 11.725(4), b 15.573(5), c 18.739(2) A; β 103.29(2)°. These complexes undergo reactions with tertiary phosphines and hydrogen halides. There is also spectroscopic evidence for intermolecular exchange of the bridging alkoxo ligands on mixing pure solutions of the [M2(arene)2(OR)3]+ cations (M = Ru, Os). Reaction of [{Ru(η-arene)Cl2}2] with Pb(SEt)2 in CH3CN gives the analogous [Ru2(arene)2(SEt)3]+ cations.