Raffaele Battistuzzi

Copper(I) complexes of neutral, deprotonated and protonated 4,6-dimethylpyrimidine-2 (1H)-thione

SummaryThe following copper(I) complexes of 4,6-dimethylpyrimidine-2(1H)-thione (HL), its protonated cation (H2L+) and deprotonated anion (L−) have been prepared: CuL, Cu(HL)X (X = Cl, Br or I), Cu(HL)2X (X = C1 or Br), Cu2(HL)3Br2, Cu(H2L)X2 (X = Cl or Br), Cu3(HL)2LA2 (A = ClO4 or BF4 ). The i.r. spectra show that in all the HL and L− complexes and in the Cu(H2L)Br2 complex, the ligands are S, N coordinated to the metal ion, while in Cu(H2L)Cl2 only the thiocarbonylic sulphur is coordinated, probably bridging two copper(I) atoms. Thev(CuN) (288–317 cm−1 ) andv(CuS) (191–225 cm−1 ) have uniform frequency values in all the complexes. The halide ions are, in all their complexes, wholly or in part coordinated giving twov(CuX) bands which may indicate an asymmetrical Cu-X ⋯Cu halide bridging bond.

Redox interconversion of [ReV O]3+ ⇌ [ReIII]3+ centers in octahedral 4,6-dimethyl-pyrimidine-2-thiolate/triphenylphosphine rhenium (V) and rhenium (III) mixed complexes

Abstract Reaction of trans-[ReOX2(EtO)(PPh3)2] (X = Cl, Br, I) with 4,6-dimethylpyrimidine-2-(1H)-thione (pymSH) in 1:1 molar ratio in refluxing acetone, rapidly formed [ReOX2(pymS) (PPh3)] (X = Cl, Br, I) compounds and PPh3 in good yields. Upon increasing the refluxing time (5–6 h), the above products react in a 1:2 molar ratio producing the paramagnetic trans-[ReX2(pymS) (PPh3)2] (X = Cl, Br) species and triphenylphosphine oxide as a result of oxygen transfer from the [ReO]3+ core to the PPh3. The trans-[ReX2(pymS) (PPh3)2] (X = Cl, Br) species, in organic solvents at room temperature and in the presence of atmospheric oxygen, are easily oxidized back to [ReOX2(pymS) (PPh3)] with the concomitant formation of O = PPh3. These oxidation reactions most likely proceed through the loss of a PPh3 ligand on the reducing rhenium (III) center, which makes a coordination site available for the oxidative addition of dioxygen which produces a highly reactive rhenium-dioxygen intermediate ([ReX2(pymS) (PPh3)(O2)]). The time course of the aerial oxygenation reactions at room temperature was inferred from the rate [Km = (1.30 ± 0.05) × 10−2 h−1] of disappearance of the paramagnetic trans-[ReX2(pymS) (PPh3)2] (X = Cl, Br), species, monitored by VIS-NIR and 1H NMR spectroscopy. Spectroscopic (UV-VIS-NIR, 1H and 31P NMR), magnetic and electrochemical properties of the complexes are discussed.

Cobalt(II) perchlorate, tetrafluoroborate, nitrate and sulphate complexes with 4,6-dimethylpyrimidine-2(1H)-thione

Abstract Contrary to earlier reports in which no adducts of Co(II) metal ion with 4,6-dimethylpyrimidine-2(1H)-thione(HL) could be isolated starting from Co(ClO 4 ) 2 · 6H 2 O, we now report bis- and tris-ligand Co(II) complexes of the type [Co(HL) 2 (H 2 O) 2 ]X 2 · H 2 O (X = ClO 4 , BF 4 ), [Co(HL) 2 NO 3 ]NO 3 , [Co(HL) 2 SO 4 ] · 0.5H 2 O and [Co(HL) 3 ]X 2 · 0.5H 2 O (X = ClO 4 , BF 4 ). They have been synthesized by refluxing 2:1 and 3:1 mixtures of HL and CoX 2 · n H 2 O in ethanol-triethyl orthoformate. We also describe new Co(HL) 2 X 2 · n H 2 O complexes in which for X 2 = ClBr, ClI and BrI, n = 2; for X 2 = I 2 , n = 1 and for X 2 = (SCN) 2 , n = 0. Structural characterization of the complex species is made from electronic and vibrational spectra, magnetic susceptibility measurements in the solid state and conductivity measurements in DMF solution. The magnetic and electronic spectral data together with ligand-field parameters suggest a pseudo-octahedral environment for all the Co(II) complexes, with the exception of Co(HL) 2 SO 4 · 0.5H 2 O in which the Co(II) ion appears to be pentacoordinated. The IR spectra are consistent with a coordination involving N,S-chelation of the ligand through the non-protonated ring nitrogen atom and the exocyclic sulphur atom.

Synthesis, crystal and molecular structure, spectroscopic and electrochemical studies of μ-oxo-bis{oxo-bis (4,6-dimethylpyrimidine-2-thiolate)rhenium (V)} complex

Abstract The dinuclear oxo-rhenium (V), μ-O[ReO(Me2pymS)2]2 species was prepared by the reaction of 4,6-dimethylpyrimidine-2 (1H)-thione (Me2pymSH) with trans- [ReI2 (EtO) (PPh3)2] or trans- [ReO2py4]Cl·2H2O in different solvents. The compounds were characterized by elemental analysis, magnetic susceptibility, UV-VIS, IR and 1 H NMR spectroscopy and conductivity measurements. Cyclic voltammetry shows that the μ-O[ReO(Me2pymS)2]2 species, undergo a quasi-reversible single-electron process in which the oxygen-bridged dimeric framework is maintained. The structure of μ-O[ReO(Me2pymS)2]2 was determined by single-crystal X-ray diffraction methods. The dinuclear structure of [Re2O3 (Me2pymS)4] compound consists of two [ReO(Me2pymS)2] moieties bridged by an oxygen atom. The backbone ORe–O–ReO is almost linear and each rhenium (V) ion lies in the center of a distorted octahedron achieved through two deprotonated N,S-chelate ligands in the equatorial plane.

Crystal and molecular structures of 1-phenyl-4,6-dimethylpyrimidine-2-thionetetraaquacobalt(II) dinitrate complex and of two pyrimidine thiones

The crystal structures of 1-phenyl-4,6-dimethylpyrimidine-2-thionetetraaquacobalt(II) dinitrate (I)a=9.032(2),b=12.458(2),c=18.067(3)Å,β=103.25(3)°,Z=4;P21/c,R=0.049; 1-phenyl-4,6-dimethylpyrimidine-2-thione (II)a=12.005(3),b=10.090(2),c=9.649(2)Å,β=104.4(1)°,Z=4;P21/n,R=0.038; and 4,6-dimethylpyrimidine-2-thione (III)a=15.485(3),b=13.255(3),c=7.127(2)Å,β=104.3(1)°,Z=8,C2/c,R=0.041 are reported. In (I) the coordination around the cobalt(II) is distorted octahedral involving one ligand moleculevia sulphur and nitrogen atoms and four water molecules. It is relevant that the parameters in the complexed ligand are not different from those found in the uncomplexed one (II), excepting the distances on the nitrogen atom directly involved in the coordination. Bond distances and angles in compound (III) agree with those found in (II).

Synthesis, Magnetic, Spectroscopic and Electrochemical Studies of Mixed Pyrimidine-2-thiolate/triphenylphosphine Rhenium(V) and Rhenium (III) Complexes.

Abstract Equimolar amounts of trans -[ReOX 2 (OEt)(PPh 3 ) 2 ] (X=Cl, Br, I) precursors and potentially bidentate N , S -donor pyrimidine-2(1 H )-thione (pymSH) react in refluxing acetone to give mononuclear octahedral paramagnetic trans -[Re III X 2 (pymS)(PPh 3 ) 2 ] (X=Cl, Br, I) species. Starting from a metal–ligand molar ratio of 1:3, in the presence of N(C 2 H 5 ) 3 as deprotonating agent in refluxing ethanol, the same reaction proceeds stepwise, affording octahedral [ReO(pymS) 3 ] or [ReO(pymS) 3 ] and pentagonal-bipyramidal [Re(pymS) 3 PPh 3 ] complexes as a function of the reaction time. The compounds were characterized by elemental analysis, magnetic susceptibility, UV–Vis–NIR, IR and 1 H NMR spectroscopy and by cyclovoltammetric measurements. Reaction pathways and physico-chemical properties of the complexes are discussed.

Electrochemistry of 4,6-dimethyl-2-thiopyrimidine and 4,6-dimethyl-1-phenyl-2-thiopyrimidine in dimethylformamide

Abstract The electrochemical behaviour of 4,6-dimethyl-2-thiopyrimidine (LH) and 4,6-dimethyl-1-phenyl-2-thiopyrimidine (LΦ) and their protonated forms was investigated in dimethylformamide on Hg electrodes. Adsorption processes affect the oxidation mechanism of both the compounds and the formation of Hg(I) complexes was observed. The electrochemical reduction of LH provides an example of the so-called “father—son reaction” but this kind of mechanism cannot occur with LΦ. Only in the species LH is a proton present which can be abstracted by the product of the first electron transfer LH · − while LΦ can be protonated by the solvent. However, in the presence of strong acids, for both molecules LH and LΦ the formation of the dimer from the radical anion obtained in the first electron transfer is kinetically preferred to the father—son reaction.

Complexes of tetramethylthiourea with zinc(II), cadmium(II) and mercury(II) halides

Abstract Several complexes of tetramethylthiourea with zinc(II), cadmium(II) and mercury(II) halides were prepared and their i.r. (4000-400 cm−1) and far-i.r. (400-60 cm−1) spectra are reported. Possible structures for these complexes are suggested. The metal sulphur stretching vibrations were observed mainly in the region 260-190 cm−1 and in the order Hg > Zn > Cd. The molecular weights in nitrobenzene and molar conductivities in methanol were measured and are generally consistent with the proposed structures.

The hydrogen bonding effect on the halobismuthate(III) geometry: thermal, spectroscopic and structural properties of halobismuthate complexes of 4,6-dimethylpyrimidine-2(1H)-thione

Abstract Reactions involving Bi(III) halides and 4,6- dimethylpyrimidine-2(1H)-thione (L) in HX solution result in the formation of [HL]3[BiX6]·2H2O (X=C1, Br) and [HL]3[Bi2I9]. These compounds together with the organic molecule in the form of the hydrochloride, (HLCl) were characterized by means of spectroscopic and thermogravimetric measurements. For HLCl·H2O (1) and [HL]3[BiCl6]·2H2O (2), X-ray structures were determined. In 1, which crystallizes in the space group Pca21, with four molecules in the cell, the structure consists of roughly planar protonated organic molecules stacked along the [100] axis and built up by hydrogen bonds involving chlorine atoms and water molecules. For 2, the space group is P21/n, Z=4, the structure contains [BiCl6]3− anions, protonated organic molecules stacked along the [010] axis and water molecules which form strong hydrogen bonds with the [BiCl6]3− anions. The final R indices are 0.0320 and 0.0465 for 1 and 2, respectively.

Zinc(II), cadmium(II) and mercury(II) complexes of 4,6-dimethyl-pyrimidine-2(1H)-one

Abstract The following zinc(II), cadmium(II) and mercury(II) complexes of 4,6-dimethylpyrimidine-2(1H)-one (L) have been prepared and investigated by conductometric,IR and Raman methods: MX 2 L 2 (M = Zn, X = Cl, Br(CHCl 3 , I(CHCl 3 , CF 3 COO; M = Cd, X = Cl, Br CF 3 COO; M = Hg, X = Cl, CF 3 COO), Cd 2 I 4 L 3 , Hg 3 X 6 L 2 (X = Cl, Br), Hg 3 X 6 L 4 (X = Br, I), MX 2 L 4 ·6H 2 O (M = Zn, Cd, X = CIO 4 , BF 4 ; M = Hg, X = CIO 4 . The ligand is principally bonded through the unprotonated nitrogen atom and in some complexes also through the carbonylic oxygen atom. The zinc halide complexes are tetrahedrally coordinated, the trifluoroacetate ion is coordinated as a monodentate ligand.