Marina Biagini Cingi

4-Amino-3-methyl-1,2,4-Δ2-triazoline-5-thione: an example of thione-thiol tautomerism and stabilization of Cu(I) and Au(I) complexes☆

Two complexes of Cu(I) (1) and Au(I) (2) with the ligand 4-amino-3-methyl-1,2,4-Δ2-triazoline-5-thione (HL) have been prepared. Potentiometric and spectrophotometric studies on the ligand show that the thiol is the prevalent form in solution while in the solid state the thione form is present. Preliminary ab initio calculations of the molecular electrostatic potential maps for the ligand HL are in good agreement with reactivity and studies in solution. Both compounds crystallize in the monoclinic system, 1 in the P21/m space group with unit cell parameters a = 6.829(2), b = 6.218(2), c = 8.540(3) A, β = 105.68(2)°, Dcalc = 2.180 g cm−3 and V = 349.1(2) A3 or Z = 2, 2 in the C2/m space group with unit cell parameters a = 15.902(6), b = 6.606(5), c = 6.707(3) A, β = 109.37(2)°, Dcalc = 2.462 g cm−3 and V = 664.7(6) A3 for Z = 2.5563 and 742 observed reflections for 1 and 2, respectively, were used in the refinement which converged to R and Rw values of 0.0388 and 0.0528 for 1 and 0.0432 and 0.0540 for 2. The structure of complex 1 presents an unusual phenomenon of disorder with the Cu atoms statistically distributed in two independent positions and the complex can be described as assuming a non-molecular cationic structure. The crystal structure of 2 consists of discrete [Au(HL)2]+ and Cl− ions.

Preparation, spectroscopic and magnetic characterization of a new series of two-dimensional transition metal compounds. The x-ray structure of poly-bis(thiocyanato-N)-bis-μ- [1,2,4] triazolo [1,5-a] pyrimidine-N1,N3)iron(II)

The synthesis of a series of polynuclear compounds of general formula [M(tp) 2 (NCS) 2 ] n (M = Mn, Fe, Co, Ni and tp = [1,2,4]triazolo[1,5− a ]pyrimidine, C 5 H 4 N 4 ) is described. The compounds are X-ray and IR isostructural and were further characterized by ligand field and magnetic susceptibility measurements. The structure of the iron compound was determined by X-ray diffraction methods. It crystallizes in the orthorhombic space group Aba 2, with a =8.028(2), b =20.422(6), c =10.129(5) A. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrtx least-squares to R = 0.040 for 706 observed reflections. The structure consists of octahedral iron complexes in which the metal atom is coordinated by two nitrogen atoms from two monodentate NCS groups and by four nitrogen atoms from four symmetry-related tp molecules; each organic ligand bridges two metal atoms through both non-bridgehead triazole nitrogen atoms, joining the octahedral complexes in a layered system where the Fe···Fe distance is 6.49 A.

Synthesis and spectroscopic characterization of a new class of heterotetranuclear compounds with thiocyanate groups as bridging ligands. The X-ray structure of bis-(μ-tetrakis(thiocyanato-S)mercury(II)-N,N′)diaquahexakis(5.7-dimethyl[1,2,4] triazolo[1,5-a] pyrimidine-N3) dicobalt(II)

Abstract The synthesis and characterization of a novel type of heterotetranuclear compounds of general formula [MHg(dmtp) 3 (SCN) 4 (H 2 O)] 2 [M = Mn, Co, Ni(II) and dmtp = 5,7-dimethyl[1,2,4] triazolo[1,5-a] pyrimidine] are described. Infrared spectra show the presence of both S-coordinating and N,S-bridging thiocyanate ligands. Ligand-field spectra indicate an ocahedral coordination geometry for the transition-metal ions. The structure of one of the three, mutually isomorphous, compounds was determined by X-ray diffraction methods. Crystals of [CoHg(dmtp) 3 (SCN) 4 (H 2 O)] 2 are triclinic, space groups P 1 with a = 11.481(9), b = 13.975(11), c = 11.479(8) A, α = 101.08(6), β = 90.11(7), γ = 77.24(6)°, Z = 1. The structure was solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.038 for 2392 independent observed reflections. The structure consists of centrosymmetric heterotetranuclear complexes formed by thiocyanate groups bridging heterometals. Mercury is tetrahedrally coordinated by sulphur atoms from thiocyanate groups (HgS bonds ranging from 2.457 to 2.601 A), two of which bridge two centrosymmetric Co atoms. Three N atoms from dmtp ligands and one oxygen from a water molecule complete the octahedral coordination of Co (CoN bonds: 2.11, 2.14 and 2.18 A; CoO w bond: 2.08 A). Intramolecular hydrogen bonds between water hydrogens and N atom sfrom a dmtp molecule and a non-bridging thiocyanate group respectively stabilize the tetranuclear species. Magnetic suspectibility studies indicate that the magnetic exchange between the metal ions is very weak.

Preparation, spectroscopic and magnetic characterization of two pseudo layered copper(II) systems. The x-ray structures of bis(thiocyanato-N)bis([1,2,4] triazolo[1,5-a]pyrimidine-N3)copper(II) and dichlorobis([1,2,4]triazolo[1,5-a]pyrimidine-N3)copper(II)

Abstract The structures of α-Cu(NCS)2(tp)2 (1) and CuCl2(tp)2 (2), with tp = [1,2,4]triazolo[1,5-α]pyrimidine, C5H4N4, have been determined by single crystal X-ray diffraction methods. 1 is monoclinic, space group P21/c, with a = 11.669(2), b = 8.808(2), c = 7.951(2) A, β = 102.52(2)° and Z = 2. 2 is also monoclinic, space group P1/c, with a = 9.546(1), b = 8.958(1), c = 8.082(1) A, β = 107.32(1)° and Z = 2. Both compounds show essentially layered structures with the copper atoms square planarly coordinated by two nitrogen atoms (trans) from N3-coordinating tp ligands and by two donor atoms (trans) from anions [N atoms from thiocyanate ligand in 1 and Cl atoms from chloride ligands in 2; in 1 CuN (tp ligand) = 2.035(5) and CuN(thiocyanate group) = 1.935(6) A, in 2 CuN(tp ligand) = 2.021(4) and CuCl = 2.297(1) A]; the coordination is completed to octahedral by two nitrogen atoms from adjacent tp molecules which N1-coordinate axially to the metals at relatively long distances (CuN = 2.633(6) in 1 and 2.692(4) A in 2) so that in both compounds two-dimensional systems parallel to each other are formed. The structural properties of the two compounds are correlated to their IR, UV and ESR spectra and magnetic susceptibilities.

Synthesis, characterization and X-ray structure of hetero-polynuclear thiocyanates of iron(II) and mercury(II) with 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine-N3 and water as ligands

Abstract The synthesis and characterization of heteronuclear compounds of formula FeHg(NCS) 4 (dmtp) 2 (H 2 O 1.5 ( I ), FeHg(NCS) 4 (dmtp) 2 (H 2 O) ( II ) and FeHg(NCS) 4 (dmtp)(H 2 O) 2 ·(Me 2 CO) ( III ) with dmtp = 5,7-dimethyl[1,2,4]triazolo[1,5- a ] pyrimidine (C 7 H 8 N 4 ) are described. Infrared spectra of these compounds have shown the presence of both S-coordinating and N,S-bridging thiocyanate ligands; moreover, ligand field spectra have indicated an octahedral coordination geometry for the iron ions. The structures of these compounds were elucidated by X-ray diffraction methods. Crystals of I are triclinic, space group P 1 , with a = 16.318(10), b = 18.389(14), c = 10.089(4) A, α = 105.15(4), β = 101.24(6), γ = 83.31(9)°, Z = 2; crystals of II are monoclinic, space group P 2 1 / n , with a = 11.599(7), b = 16.54(5), c = 14.766(10) A, β = 98.47(5)°, Z = 4; crystals of III are monoclinic, space group P 2/ n , with a = 12.285(7), b = 13.689(6), c = 7.562(5) A, β = 96.28(3)°, Z = 2. The structures were solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.044 for I , 0.038 for II and 0.058 for III . The structure of I consists of two different octahedral complexes, [Fe(NCS) 3 (dmtp) 2 (H 2 O)] ( a ) and [Fe(NCS) 2 (dmtp) 2 (H 2 O) 2 ] ( b ) (in which nitrogen atoms from both thiocyanate groups and dmtp ligands besides water molecules are involved in coordination), and tetrahedral [Hg(SCN) 4 ] complexes bridging either two or three iron atoms. In II [Hg(SCN) 4 ] and [Fe(NCS) 3 (dmtp) 2 (H 2 O)] complexes are present, the octahedral iron complex differing from the complex ( a ) only in the mutual orientations of the dmtp molecules. The structure of III consists of [Hg(SCN) 4 ] and [Fe(NCS) 3 (dmtp)(H 2 O) 2 ] complexes together with acetone molecules of crystallization; the octahedral iron complex, involving only one dmtp molecule, can be derived from the complex ( b ) replacing a dmtp molecule by a thiocyanate ligand. The thiocyanate groups which bridge heterometals determine one -, two - and three -dimensional systems in I , III and II respectively.

Crystal structure of 2:1 molecular complexes of caffeine with hexaaquamagnesium(II) bromide and hexaaquamanganese(II) triiodide iodide

Abstract The crystal structures of (C 8 H 10 N 4 O 2 ) 2 Mg(OH 2 ) 6 Br 2 (I) and (C 8 H 10 N 4 O 2 ) 2 Mn(OH 2 ) 6 I·I 3 (II) have been determined by X-ray diffraction methods; crystals of I are triclinic, space group P 1 , with Z = 1, in a unit cell of dimensions: a = 9.620(7), b = 10.779(8), c = 7.645(6) A , α = 107.03(7), β = 108.88(7), γ = 72.71(8)°; crystals of II are monoclinic, space group P 2 1 /n, with Z = 4, in a unit cell of dimensions a = 12.406(8), b = 29.652(12), c = 9.419(6) A , β = 108.39(7)°. The structures of I and II have been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.046 for I and 0.090 for II. Both compounds contain octahedral hexaaquametal(II) cations, uncoordinated caffeine molecules and bromide anions in I and triiodide and iodide anions in II, held together by a network of hydrogen bonds. The triiodide anions are unsymmetrical [I(1)I(2) = 2.89, I(2)I(3) = 2.95 A , I(1)I(2)I(3) = 178°], arranged in linear systems with a weak ‘head-to-tail’ interaction, the distance being of 3.62 A .

Spectroscopic study and x-ray structure of bis(N-methylimidazole)bis(2,4,6-trichlorophenolato)cobalt(II)

Abstract The preparation, spectroscopic study and X-ray structure of the mixed-valence compound Pt(NMIz)4− PtCl6 are described; NMIz stands for N-methyl-imidazole. The crystal and molecular structure has been determined by a single crystal X-ray analysis using three-dimensional diffractometer data. The compound crystallizes in the triclinic system, with four formula units in the unit cell, space group F 1 and lattice parameters a = 15.228(11), b = 17.855(12), c = 11.177(8) A, α = 91.98(6), β = 106.94(6), γ = 115.76(7)°. The structure was solved and refined using the heavy-atom method and subsequent least-squares techniques. Refinements using 2335 observed reflections (Mo-Kα radiation) led to final values for R and Rw of 0.077 and 0.075 respectively. The Pt(II) ions are surrounded in a square-planar geometry by four NMIz ligands (Pt−N = 1.986−2.012(14) A and N−Pt−N = 92.6(6)°). Pt(IV) is octahedrally coordinated by the six Cl− ions (Pt−Cl = 2.313−2.323(6) and Cl−Pt−Cl = 88.3−89.9(2)°). In addition there is an interaction between the Pt(NMIz)2+4 ions and the PtCl2−6 ions (with Pt⋯Cl = 3.538(5) A and Pt(II)⋯Cl-Pt(IV) = 144.1°) and Pt(II). Pt(IV) = 5.588 A), resulting in chain-type behaviour along the c-axis. Optical, infrared and far-infrared spectra agree with this structure. No clear intervalence charge-transfer absorption could be detected which might be related to the relatively long Pt(II)⋯Pt(IV) distance in this compound.

Synthesis and characterization of mononuclear complexes containing 3-acetylamino-1,2,4-triazole (aat). X-ray structure of [Co(aat)2(H2O)2]Br2

Abstract The spectroscopic characteristics of the isostructural compounds [M(aat) 2 (H 2 O) 2 ]X 2 (aat = 3-acetylamino-1,2,4-triazole; M = Co, Cu, X = Br, CI; M = Ni, X = Cl) are described. The structure of [Co(aat) 2 (H 2 O) 2 ]Br 2 has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P 2 1 / a with a = 9.686(3), b = 14.433(4), c = 6.169(2) A, β = 92.84(2)° and Z = 2. The structure was refined to final R and R ′ values of 0.033 and 0.039 for 1066 observed reflections. In the mononuclear cationic complex, having an imposed crystallographic C i symmetry, the cobalt atom is surrounded in a slightly distorted octahedral arrangement by two axial water molecules (CoOw = 2.108(5) A) and in the equatorial plane by two oxygen atoms (CoO(1) = 2.100(4) A) and two triazole nitrogen atoms (CoN(3) = 2.063(5) A) from two aat chelating ligands. The complex cations are associated in chains, with interposed bromide anions, by hydrogen bonding system.

Synthesis, reactivity, structural studies and magnetic properties of 4-amino-1,4-dihydro-3-methyl-1,2,4-triazole-5-thione copper complexes

By reaction of CuCl2 with 4-amino-1,4-dihydro-3-methyl-1,2,4-triazole-5-thione (HL) in a 4 : 1 molar ratio and in a 12 mol dm–3 HCl medium, at room temperature, the complex [CuCl2(HL)]·H2O 1 was isolated in an orthorhombic form. With an excess of CuCl2 a polymeric complex [{Cu2Cl4(HL)}n]·nH2O 2 was isolated, while introduction of a bar of metallic copper gave a polymeric mixed-valence CuI–CuII(1 : 2) complex [{Cu3Cl5(OH2)(HL)2}n]·2nH2O 3. Crystals of 1 are orthorhombic, space group Pbca, a= 16.256(1), b= 15.611(2), c= 7.327(1)A and Z= 8. Crystals of 2 are orthorhombic, space group Pbca, a= 12.900(3), b= 12.965(5), c= 14.250(5)A and Z= 8. Crystals of 3 are monoclinic, space group P21/a, a= 34.099(8), b= 8.704(3), c= 7.163(3)A, β= 96.14(2)° and Z= 4. The structures have been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.0393, 0.0582 and 0.0467 for 1132, 1346 and 3177 observed reflections respectively. In 1 the triazole acts as a chelating ligand through the sulfur and the aminic nitrogen atoms and the co-ordination of CuII is fundamentally square planar. In 2 the ligand acts in a tridentate manner, chelating and bridging through the iminic nitrogen atom. The [Cu2Cl4(HL)] units can be considered as inner salts and are joined in a head-to-tail fashion forming zigzag polymeric chains. In 3 the two independent ligands present different behaviours; one chelates a CuII atom as in 1, while the other acts as a µ3 ligand chelating another CuII atom and bridging through the iminic nitrogen and the sulfur atoms two CuI atoms. The magnetic properties were investigated by measurements of electron paramagnetic resonance microwave absorption. For all compounds S=½ spectra were observed with spectroscopic g constants in the range ca. 2.05–2.20. The resulting single-ion g tensors are typical of a tetragonal elongated copper(II) ion where covalency plays a relevant role due to the presence of the SCNN chelating structure. The magnetic local axes deduced on this basis are strictly related to the copper co-ordination planes (obtained from the structural data) confirming the oxidation state II for all the copper atoms except for the tetrahedral CuI in 3.

Spectrophotometric study of the reactions of proton and copper (II) with arsenazo I in aqueous solution

The systems of proton and/or copper(II) ion with Arsenazo I (H6L) have been characterized at 25 °C and I= 1.0 mol dm–3(KCl) using u.v.–visible spectrophotometry. The cumulative mixed protonation constants of the ligand L6– are log β011= 12.114(19), log β021= 21.871(18), log β031= 29.506(16), log β041= 32.155(6), and log β051= 34.298(6). Complexing reactions and equilibrium constants of the copper(II)–Arsenazo I system are given by (i)–(v) below. Both mixed and mononuclear Cu2++ H++ L6–⇌[Cu(HL)]3– log β111= 23.529(29)(i), Cu2++ L6–⇌[CuL]4– log β101= 16.797(58)(ii), 2Cu2++ 2H++ L6–⇌[Cu2(H2L)] log β221= 31.878(31)(iii), Cu2++ HL5–⇌[Cu(HL)]3– log K111011= 11.415(35)(iv), 2Cu2++ H2L4–⇌[Cu2(H2L)] log K221021= 10.007(36)(v) complexes have been found, the former includes a diprotonated dinuclear species in solutions at higher metal-to-ligand ratios and hydrogen ion concentrations, the latter a monoprotonated mononuclear species prevailing at lower metal-to-ligand ratios and at higher pH values. Data have been analysed by using two computer programs: the least-squares program LETAGROPVRID, version SPEFO, and the program SQUAD. The experimental spectra are compared with the calculated ones and the constants are discussed in connection with those of similar compounds reported in the literature. Accurate molar absorption coefficients are computed and the resolved spectral bands are discussed and assigned. Tentative structures of the proposed complexes are given.