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Mixed-ligand Pt(II) dithione-dithiolato complexes: influence of the dicyanobenzodithiolato ligand on the second-order NLO properties

The mixed-ligand dithiolene complex [Pt(Bz(2)pipdt)(dcbdt)] (1) bearing the two ligands Bz(2)pipdt = 1,4-dibenzyl-piperazine-3,2-dithione and dcbdt = dicyanobenzodithiolato, has been synthesized, characterized and studied to evaluate its second-order optical nonlinearity. The dithione/dithiolato character of the two ligands gives rise to an asymmetric distribution of the charge in the molecule. This is reflected by structural data showing that in the C(2)S(2)PtS(2)C(2) dithiolene core the four sulfur atoms define a square-planar coordination environment of the metal where the Pt-S bond distances involving the two ligands are similar, while the C-S bond distances in the C(2)S(2) units exhibit a significant difference in Bz(2)pipdt (dithione) and dcbdt (dithiolato). 1 shows a moderately strong absorption peak in the visible region, which can be related to a HOMO-LUMO transition, where the dcbdt ligand (dithiolato) contributes mostly to the HOMO, and the Bz(2)pipdt one (dithione) mostly to the LUMO. Thus this transition has ligand-to-ligand charge transfer (CT) character with some contribution of the metal and undergoes negative solvatochromism and molecular quadratic optical nonlinearity (μβ(0) = -1296 × 10(-48) esu), which was determined by the EFISH (electric-field-induced second-harmonic generation) technique and compared with the values of similar complexes on varying the dithiolato ligand (mnt = maleonitriledithiolato, dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato). Theoretical calculations help to elucidate the role of the dithiolato ligands in affecting the molecular quadratic optical nonlinearity of these complexes.

(n-Bu4N)2[Fe(dcbdt)2]2. Synthesis, crystal structure and magnetic characterisation

Abstract The ( n -Bu 4 N) 2 [Fe(dcbdt) 2 ] 2 complex, where 4,5-dicyanobenzene-1,2-dithiolate (dcbdt), was prepared and characterised by X-ray diffraction, Mossbauer spectroscopy and magnetisation measurements. The crystal structure as determined by single crystal X-ray diffraction is triclinic, space group P 1 with cell parameters a =9.5660(1) A, b =13.0200(2) A, c =16.0850(2) A, α =67.554°(1), β =86.797°(1), γ =70.523°(1), V =1738.77(4) A 3 and it consists in strongly dimerised [Fe(dcbdt) 2 ] − units, which are stacked side by side as chains along a . The magnetic susceptibility shows that the [Fe(dcbdt) 2 ] − units have a low spin S =1/2 configuration and, besides a strong intradimer antiferromagnetic interaction, present also a significant interdimer antiferromagnetic interaction mediated by short side contacts.

Structure and physical properties of (n-Bu4N)2 [Au(dcbdt)2]5

[(n-Bu) 4 N] 2 [Au(dcbdt) 2 ] 5 was obtained as brown thin plate shaped crystals by electrochemical oxidation of (n-Bu) 4 N [Au(dcbdt) 2 ], a Au complex with 4,5-dicyanobenzene-1,2-dithiolate (dcbdt) recently prepared. Cyclic voltammetry and optical spectroscopy studies indicate a mixed valence state. The crystal structure is triclinic and presents slightly pentamerised segregated stacks of the complex along (1,2,0) Single crystal electrical conductivity (σ RT ∼10 S/cm, Ea=13.5 meV) and thermopower measurements (S RT =6μ V/K) suggest a degenerate semiconducting behaviour. The static susceptibility measurements give an almost temperature independent paramagnetic value of 3 5×10 4 emu/mol. These and EPR results are discussed in relation to the crystal structure.

Conductors based on metal-bisdicyanobenzodithiolate complexes☆

Abstract The physical properties of the partially oxidised complexes [( n -Bu) 4 N] 2 [M(dcbdt) 2 ] 5 with M=Au and Ni (dcbdt=4,5-dicyanobenzene-1,2-dithiolate) are compared and related to the different electronic bandfilling and their slightly different structure. Both compounds present a triclinic structure, space group P- 1, with pentamerised segregated stacks of the complex along [-2 1 0]. The lower electrical conductivity with a larger activation energy, as well as the larger magnitude of thermopower and paramagnetic susceptibility, of the Ni compound are a consequence of both its different electronic bandfilling and more pronounced modulation of the stacking.

[Fe(qdt)2]− salts; an undimerised FeIII bisdithiolene complex stabilised by cation interactions

(n-Bu)4N[Fe(qdt)2] provides the first example of an undimerised FeIII bisdithiolene complex with well isolated square planar coordinated [Fe(qdt)2]− units, due to short apical Fe⋯H, Fe⋯C and S⋯H contacts with the cations, while the tetraphenylarsonium salt of this complex presents the usual dimerisation as [Fe(qdt)2]22−, with square-based pyramidal coordination of Fe.

Synthesis and crystal structure of copper and gold complexes of 1,2,5-thiadiazole-3,4-dithiolate. Charge transfer salt with TTF

Abstract The M(tdas)2 complexes (tdas2−=1,2,5-thiadiazole-3,4-dithiolate) with M=CuII, CuIII and AuIII were obtained as tetrabuthylammonium and tetraphenilphosphonium salts and characterised. The crystal structure of (n-Bu4N)n[M(tdas)2], M=Cu(2) and Au(4) were determined by X-ray crystallography as well as that of the charge transfer salt (TTF)2[Au(tdas)2]2 (5).

Charge transfer salts based on M(dcbdt)2 complexes (M=Au and Ni)

BEDT-TTF [Au(dcbdt) 2 ] and TMTSF [Co(dcbdt) 2 ] (dcbdt = 4,5-dicyanobenzene-1,2-dithiolate) were obtained as small single crystals by electrocrystallisation. BEDT-TTF [Au(dcbdt) 2 ] is triclinic, space group P1, and its structure consists in alternated donor acceptor stacks, responsible for electrical insulating properties. TMTSF [Co(dcbdt) 2 ] presents semiconducting properties with a relatively high electrical conductivity (σ RT ∼10-150 S/cm, E a =78 meV) and its thermopower (S RT ∼ 9 μV/K) has a temperature dependence suggesting a two band conduction mechanism.

Charge transfer salts based on Cu(qdt)2, Ni(qdt)2 and Au(qdt)2 anions

Metal bis(quinoxaline-2,3-dithiolate) complexes, M(qdt) 2 , were used as counterions of radical-cation salts commonly employed in the preparation of one-dimensional conductors. We report the synthesis of the new complex Au(qdt) 2 as the tetraphenylphosphonium salt and the preparation of (bedt-ttf)M(qdt) 2 , (tmtsf) M(qdt) 2 and (ttf)M(qdt) 2 with M=Au and Cu, and (ttf) 3 [Ni(qdt) 2 ] 2 . Their electrical conductivity and thermoelectric power were measured showing in all cases activated behaviour, with room temperature values of σ ranging from 10 -7 to 10 -3 S cm -1 , the highest value being for (bedt-ttf)Au(qdt) 2 which has a gap 2Δ=0.32 eV. Preliminary E.S.R results for (ttf)Cu(qdt) 2 are also presented.