Stephan Menzer

Structural and solution study on binary peptide and ternary peptide–nucleobase complexes of palladium(II)

The dipeptide complex [Pd(gly-L-hisNα)Cl]·1.5H2O 1(gly-L-hisNα= monoanion of glycylhistidine, deprotonated at the amide N) has been prepared and structurally characterized. Co-ordination of Pd is through the terminal amino group of the glycyl entity. N(π) of the imidazole ring of the histidine, and the deprotonated amide nitrogen. Reactions of 1 with the model nucleobases 1-methyluracil (Hmura), 1-methylcytosine (mcyt), 9-methyladenine (made), 9-ethylguanine (Hegua) and 6-methoxy-9-methyl-guanine (momgua) have been studied in solution by 1H NMR spectroscopy. The mcyt complex, [Pd(gly-L-hisNα,O)(Mcyt)]·3.5H2O (gly-L-hisNα,O = dianion of glycylhistidine, deprotonated at the amide N and the carboxylic acid group) has been structurally characterized. Nucleobase co-ordination is via N3. Proton NMR spectra of complexes of 1 with all model bases are indicative of rotamer formation and, with the purine bases, of linkage isomerism (N7, N1 and simultaneously with N7/N1). In weakly acidic, neutral or slightly alkaline media or with an excess of 1, Hegua and, most likely, also made form complexes of Pd3(nucleobase) stoichiometry with Pd binding through N1 and N7 and the third Pd linked to one of these Pd(gly-L-his) entities. As a consequence, the resonances of some of the aromatic protons of the histidine imidazole ring are shifted upfield by as much as 1 ppm. Complex stability constants have been determined by means of 1H NMR spectroscopy for a number of 1:1 complexes of 1 with model nucleobases. Competition experiments carried out at pD 7.1 indicate that 1 binds to the four model nucleobases in the following preference: Hegua-N7≈ mcyt-N3 made-N1 > made-N7 > mura-N3.

Preparation, X-ray structure and solution behavior of [Ag(9-EtGH-N7)2]NO3·H2O (9-EtGH=9-ethylguanine)

Abstract The preparation and X-ray structure of [Ag(9-EtGH-N7)2]NO3·H2O(9-EtGH=neutral 9-ethylguanine) is reported. The compound crystallizes in the triclinic system, space group P 1 with a=7.063(6), b=7.153(3), c=11.306(10) A, α=83.36(6), β=76.66(7), γ=81.44(6)°. The cation is centrosymmetric with Ag(I) coordinated via two N7 positions and Ague5f8N7 bond lengths of 2.11(1) A. Applying 109Ag NMR spectroscopy, complex formation constants for both the 1:1 complex (log β1=0.6) and the title compound (log β2=1.6) in Me2SO have been determined.

Dalton communications. Synthesis and structural characterisation of [Pd4(µ3-CH)(µ-Cl)3(PBut3)4]: a tetrahedral palladium cluster with a µ3-methylidyne ligand

The compound [Pd4(µ3-CH)(µ-Cl)3(PBut3)4] has been synthesised from [Pd2(dba)3](dba = dibenzylideneacetone), PBut3 and CHCl3 and characterised spectroscopically and by single-crystal X-ray analysis; it undergoes substitution reactions with Br– and tertiary phosphines and is a catalyst for the polymerisation of ethyne.

A trinuclear Pt adenine complex containing cis-(NH3)2PtII bound to N1 and (NH3)3PtII coordinated to N7

Abstract A compound of composition [Pt 3 (NH 3 ) 8 (9-MeA) 2 ](NO 3 ) 6 ·2H 2 O, where 9-MeA=9-methyladenine, C 6 H 7 N 5 , is reported which contains two (NH 3 ) 3 Pt II residues bound to 9-MeA via N7 and a cis -(NH 3 ) 2 Pt II entity bound to 9-MeA through N1. The two adenine rings are oriented head-to-head in the solid state, while in solution, an equilibrium between two rotamers (head-head, head-tail) exists. The X-ray structure is described, and based on it, the formation of related macrocyclic rings is proposed.

HgCl2 coordination to guanine derivatives: structural and spectroscopic studies on the interactions with 9-ethylguanine, 1,9-dimethylguanine and 2-amino-6-methoxy-9-methylpurine (6,9-dimethylguanine)

Abstract The coordination of HgCl2 to 9-ethylguanine, 1,9-dimethylguanine and 2-amino-6-methoxy-9-methylpurine (6,9- dimethylguanine) has been studied. The X-ray structures of the complexes HgCl2 (2-amino-6-methoxy-9-methyl- purine-N7) (1) (monoclinic, P21/m, a=10.160(3), b=6.222(1), c=11.060(3) A, β=116.11(2)°, Z=2) and {[HgCl2·(1,9- dimethyl-guanine-N7)]2HgCl2}n (2) (orthorhombic, Pbca, a=6.955(2), b=17.176(6), c=21.829(9) A, Z=4) are reported. Binding of HgCl2 is through N7 of the purine bases. In 1 discrete molecules are formed, while 2 is a linear polymer with (Hgue5f8Cl)n chains to which the guanine bases and chloro ligands are coordinated. The solution behavior is characterized by a rapid ligand exchange and low complex formation constants, log β1=0.4 (1), 1.3 (1:1 adduct of 2) and 1.0 [HgCl2·9-EtGH] (3).

Diversity of linking modes byN,N′-p-phenylenedimethylenebis(pyridin-4-one) [p-XBP4] in the novel ‘linked lantern’framework complex{[Nd2(p-XBP4)6(H2O)4](p-XBP4)(H2O)3(ClO4)6}n

The title compound has a complex framework structure in which pairs of nNd atoms are linked by four p-XBP4 ligands to form n‘lanterns’ which are further connected by interwoven nNd–(p-XBP4)–Nd bridges, and yet again by nnon-coordinated p-XBP4 molecules hydrogen bonded to aqua ligands non the Nd centres.

The influence of the chelate effect on supramolecular structure formation: synthesis and crystal structures of zinc thiourea and thiosemicarbazide complexes with terephthalate

The lability of the ligand with a potential hydrogen bond donor–hydrogen bond donor arrangement was found to be the predominant factor in determining the structures of the adducts formed between zinc(II) complexes of thiourea [tu, NH2C(S)NH2] and thiosemicarbazide [tsc, NH2C(S)NHNH2] and the terephthalate anion [tere, C6H4(CO2–)2-1,4]. Reaction of [Zn(tsc)2][NO3]2, containing the bidentate thiosemicarbazide ligand, with sodium terephthalate led to a hydrogen-bonded structure, [Zn(tsc)2(OH2)2][tere]·2H2O, 1, in which the cations and anions are linked into chains through charge-augmented double hydrogen bonds between two NH protons on the tsc ligands and two oxygen lone pairs on the carboxylate. This chain formation is similar to that previously observed for related nickel complexes, although there are major differences in the way in which these chains are linked together into sheets. In contrast to the thiosemicarbazide complex, the reaction of [Zn(tu)4][NO3]2, containing unidentate thiourea ligands, with sodium terephthalate led to the formation of a co-ordinatively-bonded polymer, [Zn2(µ-tu)(tu)2(µ-tere)2]·4H2O, 2, in which the terephthalate anions have displaced some of the thiourea ligands from each zinc co-ordination sphere. The zigzag tapes formed by the terephthalate ligands bridging zinc atoms are linked together into double strands via bridging thiourea ligands.

Synthesis of [Au(NH3)2]+ salts and the crystal structure of [Au(NH3)2]Br

The complexes [Au(NH2R)2]X (R = H, Me, Et or But; X = Br, SbF6 or BF4) have been synthesised and characterised by IR, NMR spectra and by thermal gravimetric and differential scanning calorimetry techniques; the single-crystal structural determination of [Au(NH3)2]Br has confirmed the linear co-ordination about gold and highlighted some interesting bond-length differences compared to [Ag(NH3)2]NO3.

Complex array structures formed by metal complexes ofN,N′-p-phenylenedimethylenebis(4-methylpyridin-2-one)

The syntheses of the ‘extended reach’ ligand nN,N′-p- nphenylenedimethylenebis(4-methylpyridin-2-one) (L) and of a range of its nmetal complexes with Mn n II n, Co n II n, Ni n II n, nZn n II n, Cd n II n, Y n III n, and lanthanide ions nhave been accomplished. X-Ray studies showed that in the compound n{[MnL n 3 n](ClO n 4 n) n 2 n} n + nn n octahedrally co-ordinated manganese centres are nconnected by L nbridges so as to form a three-dimensional array of contiguous rhomboidal n‘boxes’. The analogous compounds with Co n II n, nNi n II n, Zn n II n and Cd n II n have the same nstructure. The polymeric compound n{[Cu n 4 nL n 5 nCl n 8 n]·2MeOH} n n n n forms a complex array of cross-linked chains containing nboth four- (distorted tetrahedral) and five-co-ordinate (distorted nsquare pyramidal) copper centres in equal proportions.

Dalton communication. Synthesis and crystal structure of {[Au2(dien)2]2+}n(dien = diethylenetriamine), an infinite linear polymer based on weak gold–gold contacts

The complex {[Au2(dien)2][BF4]2}n(dien = diethylenetriamine) has been synthesised and characterised by IR and NMR spectroscopy; the crystal structure of its ethanol solvate revealed that the molecular cation has a 16-atom ring structure and an interesting polymeric structure based on weak gold–gold contacts which extends infinitely in the (111) direction.