M. Angustias Romero

Metal complexes of [1,2,4]triazolo-[1,5-a]pyrimidine derivatives

Abstract This article covers all the research work published until September 1998 about the coordination chemistry of 1,2,4-triazolo-[1,5-a]pyrimidine derivatives. The revision is mainly focused in the structural features of the compounds, obtained from single crystal X-ray diffraction. The references are classified according to the present metal atoms. These kind of ligands display a broad versatility when binding metal ions, monodentate binding through the endocyclic nitrogen atom at position 3 being however their main coordinating behaviour. Dimeric and polymeric structures are observed when a bidentate binding through N3–N4 or N3–N1, respectively, takes place. N1–O7 chelating binding mode has also been observed in a few cases. In some cases, dimers or polymers are also generated when the present auxiliary ligands are the ones that bridge the metal centres.

Molecular architecture of redox-active half-sandwich Ru(II) cyclic assemblies. Interactions with biomolecules and anticancer activity

Tetranuclear cationic open boxes non-covalently bind DNA major groove. By contrast, they covalently bind cysteine after ligand exchange reactions. In addition, these systems exhibit potent antitumour activity circumventing cisplatin resistance.

Structural and ab initio studies of AgAg bonding in the silver(I) dimer bis-μ-(5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine)dinitrato disilver(I)

Abstract This work is an attempt to address the issue of metal-metal bonding in d10 systems. The compound [Ag(dmtp)(NO3)]2, where dmtp represents the ligand 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine, has been prepared, characterized by thermal analysis and IR spectroscopy and its structure has been solved by X-ray diffraction. The compound is triclinic, space group P 1 , a = 5.1295(4), b = 9.6009(7), c = 10.332(2) A , α = 103.73(1), β = 99.14(1), γ = 97.67(1)°, Z = 2, Dcal = 2.200 g cm−3, R = 0.029 for 4144 observed reflections. The compound exhibits a [Ag2(dmtp)2]2+ core structure with two silver atoms bridged by the dmtp ligands via N3 and N4 to give eight-membered Ag2N4C2 rings. The nitrato groups are coordinated in a semibridging and semichelating way (distances AgO, 2.816(2) A for non-bridging and 2.653(2) and 2.749(2) A for bridging oxygens). The AgAg separation is 3.058(1) A, only 0.17 A greater than in metallic silver. In order to make checking of the possible AgAg bonding, a theoretical analysis has been performed, based on the properties of the charge density distribution derived from ab initio MO calculations using STO-3G∗ and 3-21G(∗) wavefunctions, a significant direction interaction between the two metal centres having been found. Similar conclusions have been obtained for the model compound [Ag(NHCHNH)]2 after performing a geometry optimization and using improved LANL2DZ wavefunctions that take into account relativistic effect.

Ternary copper(II) complexes with the versatile 4,7-dihydro-5-methyl-7-oxo-[1,2,4]triazolo[1,5-a]pyridine ligand

Abstract The synthesis and structural characterization by X-ray crystallography, thermal, spectroscopic and magnetic methods of the ternary copper(II) complexes [Cu(Hmtpo-N3)2(H2O)2](NO3)2·2H2O (1), [Cu(mtpo-N3)2(η2-en)(H2O)]·1.5H2O (2), [ Cu(mtpo -N 3 )-(η 2 - mtpo -N′,O 7 )(η 2 - tn )]2 H 2 O ( 3 ), [ Cu(mtpo -N 3 ) 2 ( py ) 2 ( H 2 O ) 2 ] (4), [Cu(mtpo-N3)2(η2-bpy)(H2O)]·2H2O (5), and [Cu(mtpo)-N3)2(η2-phen)(H2O)2] (6) is reported (Hmtpo = 4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo[1,5-a]pyridine, en = 1,2-ethylenediamine, tn = 1,3-rmpropanodiamine, py = pyridine, bpy = 2,2′bipyridine, phen = 1,10-phenanthroline). Crystals of 1 are monoclinic, space group C2/c, with unit cell dimensions a = 19.473(2), b = 8.603(3), c = 15.198(3) A , β = 122.230(6)°, V = 2153.7(8) A3, Z = 4. The structure was refined to final R = 0.042 for 1659 reflections with I≥3.0σ(1). Crystals of 2 are monoclinic, P21/n with a = 13.029(4), b = 11.388(2), c = 13.518(4) A , β = 101.52(3)° V = 1965(1) A 3 , Z = 4, and R = 0.038 for 2707 reflections. Crystas of 3 are triclinic, P l , with a = 10.241(2), b = 12.271(2), c = 9.296(1) A , α = 107.69(1)°, β = 113.95(1)° γ = 84.421(1)°, V = 1016.7(3) A3, Z = 2, and R = 0.036 for 3554 reflections. Crystals of 4 are monoclinic, P21/c, with a = 8.561(1), b = 10645(1), c = 13.882(7) A , β = 103.530(7)°, V = 12.30.3(2) A 3 , Z = 2, and R = 0.056 for 1837 reflections. Crystals of 5 are triclinic, P l , with a = 13.236(6), b = 14.395(5), c = 9.033(2) A , α = 95.14(3)°, β = 106.27(2)°, γ = 68.31(3)°, V = 1534(1) A 3 , Z = 2, and R = 0.075 for 3252 reflections. Crystals of 6 are monoclinic. C2/c, with a = 11.439(1), b = 11.791(1), c = 19.718(3) A , β = 106.20(1)°, V = 2553.9(5) A 3 , Z = 4, and R = 0.048 for 2057 reflections. The X-ray crystal structure show that Hmtpo, both in its neural and monoanionic forms, binds the central atom preferentially through N3, nevertheless, compound 3 presents an unusual N1, O7 chelate, which is analogous to the rare 6-oxo-purines N7, 06 chelate. Further, the Cu(II) polyhedron in this set of complexes follows a trend to higher coordination numbers with increasing π-acid character of the auxilliary ligands. Finally, the coordination potential of the Hmtpo ligand is discussed on the basis of molecular orbital semi-empirical PM3 calculations, performed for the neutral and monoanionic forms of Hmtpo.

Thermally induced interconversions of metal-pyrimidine-4,6-dicarboxylate polymers: a structural, spectroscopic, and magnetic study.

Continuing our work on the structural and magnetic aspects of the one-dimensional (1-D) coordination polymers of the [M(pmdc)(H(2)O)(2)] x H(2)O kind (M = Fe, Co, Ni, Cu, Zn; pmdc = pyrimidine-4,6-dicarboxylate), we have combined ab initio X-ray powder diffraction methods with in situ thermodiffractometry and thermal analyses to characterize the selective and reversible transformation of the [M(pmdc)(H(2)O)(2)] x H(2)O compounds (M = Fe, Co, Ni, Cu) into the bis-hydrated [M(pmdc)(H(2)O)(2)] counterparts by moderate heating, which is followed by an irreversible transformation into two-dimensional (2-D) anhydrous species. The structural features of the transient bis-hydrated species and of the completely dehydrated one are described for M = Cu. Remarkably, the first dehydration process does not alter the 1-D nature of the [M(pmdc)(H(2)O)(2)] chains; on the contrary, the second dehydration gives rise to the loss of the axially coordinated water molecules with a concomitant condensation of the 1-D chains into 2-D layers through ancillary carboxylate bridging groups. The magnetic properties of the anhydrous [M(pmdc)] species (M = Co, Ni, Cu) have been investigated, showing that these phases behave as 1-D antiferromagnets with interchain interactions. Notably, in the case of the [Ni(pmdc)] system, a weak ferromagnetic ordering, arising from a spin canting phenomenon with a blocking temperature of 13 K, is observed.

Molecular orbital calculations on 6-amino-1,3 dimethyl-5-nitrosouracil. Crystal structure of its copper(II) complex

Abstract Molecular orbital calculations have been performed for 6-amino-1,3-dimethyl-5-nitrosouracil (HADNU) and its monoanion with the MOPAC program, discussing the role of the MOs of the latter in coordination. The copper complex of this derivative, [Cu(ADNU)2(H2O)2], has been synthesized and its structure has been determined by X-ray diffraction. The metal atom lies on a crystallographic inversion centre that relates the two bidentate [through N(5) and N(6)] pyrimidine moieties and the two water molecules that complete the octahedral environment. The characterization of the compound has been completed by the study of its vis-NIR diffuse reflectance and IR spectra, thermal behaviour and magnetic susceptibility measurements.

Platinum group metal-ketoxime complexes: crystal structure of hydrogen fac-tris(dimethylviolurato)ruthenate(II) heptahydrate

Eight complexes of the anions of monomethyl− and dimethylvioluric acids with the metals ruthenium, rhodium, palladium and platinum have been isolated

Molecular orbital study of 8-azaxanthine derivatives and crystal structure of 1,3-dimethyl-8-azaxanthine monohydrate

Abstract The crystal and molecular structure of 1,3-dimethyl-8-azaxanthine (HDAX) monohydrate has been determined by X-ray diffraction. The compound exhibits the N8-H tautomer in the solid state and hydrogen-bonded dimers are formed. Molecular orbital calculations have been performed for this compound, its analogues 1,3-dimethyl-2-thio-8-azaxanthine, 3-methyl-8-azaxanthine and 3-methyl-2-thio-8-azaxanthine and their anionic forms with the mopac program. The most stable tautomer is shown to be N7-H for the neutral compounds. Calculations have also been performed for the hydrogen-bonded dimer (HDAX·H2O)2, a stabilization energy of −19.76 kcal mol−1 having been found, which may explain why the N8-H tautomer is found in the solid state. The role of the molecular orbitals in possible coordination to metal ions is discussed for all the species.

Mononucleotide recognition by cyclic trinuclear palladium(ii) complexes containing 4,7-phenanthroline N,N bridgesElectronic supplementary information (ESI) available: ORTEP view of the [((S,S)-dach)Pd(4,7-phen)]36+ cations in the crystal structure of 2b. Experimental details of the partial crystal structure solution of 2b. See http://www.rsc.org/suppdata/dt/b4/b402602k/

Reaction of [(dach)Pd(NO3)2] entities (dach = (R,R)-1,2-diaminocyclohexane, (S,S)-1,2-diaminocyclohexane) and 4,7-phenanthroline (phen) providing, respectively, 90 and 120 degrees bond angles, leads to the formation of two novel positively charged homochiral cyclic trinuclear metallacalix[3]arene species [((R,R)-1,2-diaminocyclohexane)Pd(phen)]3(NO3)6 (2a) and [((S,S)-1,2-diaminocyclohexane)Pd(phen)]3(NO3)6 (2b). These species have been characterised by 1)H NMR and X-ray diffraction methods (2b), showing that they possess accessible cavities suited for supramolecular recognition processes. We prove, indeed, from 1H NMR studies the inclusion of mononucleotides inside the cavity of the trinuclear species [(ethylenediamino)Pd(phen)]3(6+) (1), [((R,R)-1,2-diaminocyclohexane)Pd(phen)]3(6+) (2a) and [((S,S)-1,2-diaminocyclohexane)Pd(phen)]3(6+) (2b) in aqueous solution. Association constants (K(ass)) range from 85 +/- 6 M(-1) for the interaction between [(ethylenediamine)Pd(phen)]3(6+) and adenosine monophosphate to 37 +/- 4 M(-1) for the interaction between [(1,2-diaminocyclohexane)Pd(phen)]3(6+) and thymidine monophosphate. We invoke the synergy of electrostatic, anion-pi and pi-pi interactions to explain the recognition of mononucleotides inside the cavity of the metallacalix[3]arenes.

Metal complexes of theophylline-7-acetic acid. Crystal structure of a nickel(II) compound containing non-coordinated theophylline-7-acetate ion

Abstract The solids obtained by interaction of theophylline-7-acetic acid with the metal ions nickel(II), cobalt(II) and palladium(II) have been studied by standard thermal and spectroscopic methods. The structure of the compound formed with nickel(II), hexaaqua nickel(II) theophylline-7-acetate tetrahydrate, has been solved by X-ray diffraction, this being the first example of a metal salt of an anionic purine derivative in which there is not a direct metal-purine bond. Powder X-ray diffraction demonstrates that the cobalt compound is isostructural to the nickel one. A trans-square planar structure with the ligand bound to the palladium via N(9) is proposed for the palladium compound [PdCl2(theophylline-7-acetic acid)2].