Francesco Bigoli

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.

Synthesis, X-ray and spectroscopic characterization of obtained throught the one-step reaction of mbit·2I2 with tin metal powder (mbit = 1,1′-bis(3-methyl-4-imidazoline-2-thione)methane)

Abstract The reaction of the adduct mbit·2I2 (mbit = 1,1′-bis(3-methyl-4-imidazoline-2-thione)methane) with tin metal powder produces Sn(mbit)2I9, in mild conditions. An X-ray diffraction study on a crystal showed that the compound consists of a cation [SnI2(mbot)2]2+ having two I2 as counterions, interacting with two disordered diiodine molecules. In the cation, the metal atom lying on a symmetry centre exhibits a slightly distorted octahedral coordination with the two iodides at the apices in trans position, and with the two mbit molecules acting as bidentate chelating ligands through the sulfur atoms and forming an eight-membered ring, the tin metal atom included. The counterions I1 are slightly bent (I(2)–I(3)–I(4) 176.0(1)) and so asymmetric (I(2)–I(3) 2.841(6) I(3)−I(4) 3.016(5) A) that they can be better described as I ·I2 adducts. The presence of the two independent, centrosymmetric and disordered diiodine molecules as guests in the channel running parallel to [III] brings about I82 units of the type I2·I✓I2✓I·I2, here two triiodide ions realted by a sym centre are linked only for one third to I(5)–I(510), that is one of the two disordered guest I2 molecules (I(4)✓I(5) 3.22(I) A). Two I82 units related by a symmetry centre are held together through a non-negligible interaction (I(4)✓I(6) 3.55(1) A) involving the other disordered diiodine molecule (I(6)–I(6m)) giving rise to an octadecaioddide. Crystallographic data for C18H24N8S4I90Sn are as follows: the crystal is trigonal. M = 1783.77 space group R3, Z = 3, V = 3146(4) A ′, a = 18.100(6) A , α = 115.55(2)°, R = 0.0584 . In accordance with a description of the counterions as a sequence of the type I2·I✓I2✓I·I2. FT-Raman spectra do not show the peaks generally found in conventional triiodides, but those related to perturbed diiodine molecules.

Evaluation of thermodynamic parameters for highly correlated chemical systems: a spectrophotometric study of the 1 : 1 and 2 : 1 equilibria between I2 and 1,1′-methylenebis(3-methyl-4-imidazoline-2-thione)(mbit) and 1,1′-ethylenebis(3-methyl-4-imidazoline-2-thione)(ebit). Crystal and molecular structures of mbit·2I2 and ebit·2I2

The reactions of I2 with 1,1′-methylene- and 1,1′-ethylene-bis(3-methyl-4-imidazoline-2-thione)(mbit and ebit) have been investigated in CHCl3 solution at different temperatures by spectrophotometry. The experimental data have been processed using two different procedures of computer analysis: SUPERSPEC based on the conventional Gauss–Newton–Marquardt least-squares method; and POWELSPEC, based on Powells direct search method for the refinement of ΔH° and ΔS°. The ability of the two methods to identify the involved equilibria correctly was compared. Evidence for the stepwise formation of the 1 : 1 and 1 : 2 adducts has been obtained by the two methods for the mbit case, while POWELSPEC only was able to solve the ebit case satisfactorily. The crystal structures of the adducts mbit·2I2 and ebit·2I2 have been determined. They show that the thionic sulfur atoms co-ordinate two diiodine molecules, with S–I 2.683(2)(mbit·2I2) and 2.642(3)(ebit·2I2)A and with I–I 2.897(1) and 2.903(2)A respectively, the two S–I–I groups beings related by a two-fold axis. The structural features of the S–I–I linear group are in accordance with Fourier-transform IR and Raman spectral data and can be taken into account with a three-centre two-electron axial orbitally deficient bonding scheme.

The structures of bis(1H+,5H+-S-methylisothiocarbonohydrazidium) di-μ-chloro-octachlorodibismuthate(III) tetrahydrate and tris(1H+-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III)

Abstract The structures of bis(1H + ,5H + -S-methylisothiocarbonohydrazidium) di-μ-chlorooctachlorodibismuthate(III) tetrahydrate: (C 2 H 10 N 4 S) 2 (Bi 2 Cl 10 )· 4H 2 O (compound [I]) and of tris(1H + -S-methylisothiocarbonohydrazidium) esachlorobismuthate(III): (C 2 H 9 N 4 S) 3 (BiCl 5.67 I 0.33 ) (compound [II]) were determined from single crystal X-ray diffractometer data. Both compounds crystallize as triclinic (P 1 - ); crystals [I] with Z = 1 formula unit in a cell of constants: a = 10.621(3), b = 9.989(5), c = 7.439(3) A, α = 88.31(2), β = 84.51(2), γ = 68.88(2)°, final R = 0.0427 for 2229 unique reflections with I ⩾ 2σ(I); crystals [II] with Z = 2 and cell dimensions: a = 14.109(4), b = 12.209(9), c = 8.206(7) A, α = 103.54(3), β = 104.95(2), γ = 81.96(2)°, final R = 0.0411 for 3637 unique reflections (1 ⩾ 2σ(I)). The structure of [I] is built up of diprotonated organic cations, water molecules and dinuclear centrosymmetric [Bi 2 Cl 10 ] 4− anions held together by N-H⋯Cl, N-H⋯O, O-H⋯Cl hydrogen bonds and Van der Waals interactions. The [Bi 2 Cl 10 ] 4− complex consists of two edge-sharing octahedra in which three pairs of bonds of similar length are observed (Bi-Cl av = 2.602(5), 2.712(4), 2.855(5) A). The structure of [II] consists of monoprotonated cations and [BiCl 5.67 I 0.33 ] 3− anions held together by a tridimensional network of hydrogen bonds. Each bismuth atom is octahedrally surrounded by six chlorine atoms, one of which is statistically substituted by a iodine atom.

A Spectro- and Conductometric Study of the Reaction of Imidazoline-2-selone Derivatives with Bromine − Crystal Structure of 1,2-Bis(3-methyl-4-imidazolin-2-ylium dibromoselenanide)ethane

The oxidative addition of Br2 to the imidazoline-2-selone derivatives 1a−c has been studied by spectrophotometric and conductometric techniques. The experimental results clearly indicate that this reaction involves the dications 2a−c, containing an Se−Se bond, as intermediates in the formation of the hypervalent 10-Se-3 selenium compounds 3a−c containing the Br−Se−Br group. The crystal structure of 1,2-bis(3-methyl-4-imidazolin-2-ylium dibromoselenanide)ethane (3c), a new stable hypervalent 10-Se-3 compound, is also reported.

Structural researches on copper(II) complexes with vitamin B6 derivatives: X-ray structures of bis(N-t-butyl-pyridoxylideneiminato)copper(II) and bis(N-t-butyl-pyridoxylideneiminato)copper(II)methanol (1:1/3)

Abstract The structures of bis(N-t-butyl-pyridoxylideneiminato)copper(II) (compound I) and bis(N-t-butyl-pyridoxylideneiminato)copper(II)methanol (1:1/3) (compound II) were determined from three-dimensional X-ray data collected by counter methods. Crystals (I) are monoclinic, space group C 2/c with Z = 8 in a unit cell of dimensions a = 11.19(1), b = 20.06(2), c = 23.99(2) A, β = 99.7(1)°. Crystals (II) are trigonal, space group R 3 c with Z = 18 and cell dimensions a = 16.82(3), c = 48.59(5) A . Compound (I) was refined to a final conventional R factor of 0.0403 for 2150 reflections with I ⩾ 2σ( I ) and compound (II) to a final R ( F ) of 0.0475 for 543 reflections with F ⩾ 6σ( F ). Both compounds show a C 2 symmetry but in (II) only, the copper atom lies on a crystallographic two-fold axis; the metal atom is chelated to two pyridoxylidene ligands through the imino N and the phenolato O in a flattened tetrahedral coordination with a θ value of 52.9(3)° for (I) and 47.1(7)° for (II). In (I) the OH⋯N hydrogen bonds form layers while in (II) they determine a trimeric unit which hosts a methanol molecule as guest. The layers or the trimers are held together by weak Van der Waals interactions.

Complexes of 4,5,6,7,-tetrathiocino[1,2-b:3,4-b']diimidazolyl-1,3,8,10-tetraethyl-2,9-dithione (Et4todit) with group IIb metal halides. Crystal and molecular structure of (Cd(II)Et4toditCl2)n

Abstract The capability of Et4todit (title ligand) to coordinate through the two CS groups forced at very distant positions has been used to prepare some new ligand-bridged polymeric complexes, having stoichiometry M(II)Et4toditX2 (M(II) = Zn, Cd, Hg; X=Cl, Br). IR spectral results show that the ligand binds via thionic sulphur in all isolated compounds, and the low frequency spectrum of (CdEt4toditX2)n gives a different pattern from the rest, which all are very similar and consistent with a tetrahedral stereochemistry. The X-ray structure of (CdEt4toditCl2)n shows that the crystals are orthorhombic, space group P21212, a=14.199(4), b=15.550(4), c= 10.575(3) A, Z=4. Solution and refinement of the structure gave final residuals R=0.0461 and Rw=0.0615 using 1402 observed reflections. Coordination around the metal is trigonal-bipyramidal. Apical sites are occupied by Cl atoms (Cl(1) and Cl(2)). Both bidentate ligand and Cl(2) are bridging to form a polymeric tridimensional structure.

Spectrophotometric study, crystal and molecular structure of the 1:1 complex between 1,3-dithiolane-2-thione and diiodine

Abstract The reaction of 1,3-dithiolane-2-thione (dtt) with diiodine has been investigated by spectrophotometric methods in CHCl3. The formation of a 1:1 charge-transfer complex between the reagents has been observed. The use of a general computer program has allowed to refine the formation constants and the extinction coefficients simultaneously in the whole 260–550 nm explored range. While the formation constant is rather lower (K20° = 45 ± 1 mol−1 dm3), the—ΔHo is comparable with those generally found in other moderately strong thione-donors. An X-ray crystal structure analysis of the title compound has shown that the crystals are triclinic, space group PI, with a = 7.675(6), b = 9.955(7), c = 6.161(6) A, a = 90.08(2), β = 104.23(2), γ = 95.18(2)° and Z = 2. The molecular structure shows that the sulfur-thioamide atom of the ligand acts as the donor with respect to the diiodine molecule, and the S—I—I linkage is nearly linear [176.5(1)°]. The I—I bond length is 2.823(2) A. The only significant changes ...

The crystal and molecular structure of bis(thiocarbohydrazide-N,S)cadmium dichloride

The crystals of bis(thiocarbohydrazideN,S)cadmium dichloride, Cd(SC(NHNH 2 ) 2 ) 2 Cl 2 , belong to monoclinic space group P2 1 /c. The structure of the compound, determined from three-dimensional data, consists of trans -octahedral complexes where the ligand molecule forms pentatomic chelate rings with N,S as donor atoms. The chlorine atoms lie along the normal to the plane containing metal and organic molecules. The distances CdN=2.34(3) and CdS=2.59(1) A are slightly shorter than those found in non-chelate cadmium complexes; CdCl=2.73(1) A is very close to the sum of ionic radii. The configuration of the ligand, with on -NH 2 group turned towards SC, repeats that of crystallized thiocarbohydrazide. Some differences, however, in distances, planarity, and angles between complexed or free ligand can be detected. The complexes are held together in layers parallel to (102) by weak hydrogen bonds NH⋯Cl.

Preparation and characterization of polymeric compounds of copper(I) halogenides with Et4todit=4,5,6,7-tetrathiocino[1,2-b:3,4-b′]diimidazolyl-1,3,8,10-tetraethyl-2,9-dithione. Crystal and molecular structures of [Cu(I)(Et4todit)I]n and [Cu(I)(Et4todit)I]n·n/2Me2CO

Abstract The complexes [Cu(II)(Et4todit)X2] (Et4todit=title ligand, X=Cl or Br) are reduced at very positive reduction potential. Cyclic voltammograms on their CH2Cl2 solutions exhibit a quasi-reversible process with E 1 2 =0.68 (Cl) and 0.48 (Br) V versus SCE. The reduced species have been chemically prepared by reacting CuX2 (X=Cl and Br) with Et4todit in the presence of an appropriate reducing agent. When the reducing agent is hydroquinone in organic solvents, yellow products analyzed as Cu2(Et4todit)X2 are obtained by concentration. When the reducing agent is I− in MeeCO, the obtained product gives instead an elemental analysis according to Cu(Et4todit)I (compound 1), which can also crystallize with 1 2 Me2CO (compound 2). X-ray results on crystals of compounds 1 and 2 have shown that the compounds crystallize in the orthorhombic crystal system; space group P212121, Z=4, with a=19.792(5), b=14.167(4), c=8.537(4) A (compound 1) and a=22.088(7), b=14.414(6), c=8.807(6) A (compound 2). The coordination around Cu(I) is trigonal in both compounds and involves the iodide ion and two S atoms of two ligand molecules related by a screw axis. Both metal and ligand are bridging and polymeric chains parallel to b are formed. The solvent in 2 produces a different disposition of the adjacent chains and as a consequence interactions of the type S···S between the chains are observed only in this compound. IR spectroscopic results agree with a thionic-sulfur coordination. Moreover in the low-frequency region, bands attributed to the metal-halogen vibrations are observed and their positions suggest that Cl and Br are bridging while the I atom is terminal as shown by X-ray results.