The series of molecular conductors and superconductors ET4[AFe(C2O4)3]·PhX (ET = bis(ethylenedithio)tetrathiafulvalene; (C2O4)2- = oxalate; A+ = H3O+, K+; X = F, Cl, Br, and I): influence of the halobenzene guest molecules on the crystal structure and superconducting properties.

An extensive series of radical salts formed by the organic donor bis(ethylenedithio)tetrathiafulvalene (ET), the paramagnetic tris(oxalato)ferrate(III) anion [Fe(C(2)O(4))(3)](3-), and halobenzene guest molecules has been synthesized and characterized. The change of the halogen atom in this series has allowed the study of the effect of the size and charge polarization on the crystal structures and physical properties while keeping the geometry of the guest molecule. The general formula of the salts is ET(4)[A(I)Fe(C(2)O(4))(3)]·G with A/G = H(3)O(+)/PhF (1); H(3)O(+)/PhCl (2); H(3)O(+)/PhBr (3), and K(+)/PhI (4), (crystal data at room temperature: (1) monoclinic, space group C2/c with a = 10.3123(2) Å, b = 20.0205(3) Å, c = 35.2732(4) Å, ß = 92.511(2)°, V = 7275.4(2) Å(3), Z = 4; (2) monoclinic, space group C2/c with a = 10.2899(4) Å, b = 20.026(10) Å, c = 35.411(10) Å, ß = 92.974°, V = 7287(4) Å(3), Z = 4; (3) monoclinic, space group C2/c with a = 10.2875(3) Å, b = 20.0546(15) Å, c = 35.513(2) Å, ß = 93.238(5)°, V = 7315.0(7) Å(3), Z = 4; (4) monoclinic, space group C2/c with a = 10.2260(2) Å, b = 19.9234(2) Å, c = 35.9064(6) Å, ß = 93.3664(6)°, V = 7302.83(18) Å(3), Z = 4). The crystal structures at 120 K evidence that compounds 1-3 undergo a structural transition to a lower symmetry phase when the temperature is lowered (crystal data at 120 K: (1) triclinic, space group P1 with a = 10.2595(3) Å, b = 11.1403(3) Å, c = 34.9516(9) Å, α = 89.149(2)°, ß = 86.762(2)°, γ = 62.578(3)°, V = 3539.96(19) Å(3), Z = 2; (2) triclinic, space group P1 with a = 10.25276(14) Å, b = 11.15081(13) Å, c = 35.1363(5) Å, α = 89.0829(10)°, ß = 86.5203(11)°, γ = 62.6678(13)°, V = 3561.65(8) Å(3), Z = 2; (3) triclinic, space group P1 with a = 10.25554(17) Å, b = 11.16966(18) Å, c = 35.1997(5) Å, α = 62.7251(16)°, ß = 86.3083(12)°, γ = 62.7251(16)°, V = 3575.99(10) Å(3), Z = 2; (4) monoclinic, space group C2/c with a = 10.1637(3) Å, b = 19.7251(6) Å, c = 35.6405(11) Å, ß = 93.895(3)°, V = 7128.7(4) Å(3), Z = 4). A detailed crystallographic study shows a change in the symmetry of the crystal for compound 3 at about 200 K. This structural transition arises from the partial ordering of some ethylene groups in the ET molecules and involves a slight movement of the halobenzene guest molecules (which occupy hexagonal cavities in the anionic layers) toward one of the adjacent organic layers, giving rise to two nonequivalent organic layers at 120 K (compared to only one at room temperature). The structural transition at about 200 K is also observed in the electrical properties of 1-3 and in the magnetic properties of 1. The direct current (dc) conductivity shows metallic behavior in salts 1-3 with superconducting transitions at about 4.0 and 1.0 K in salts 3 and 1, respectively. Salt 4 shows a semiconductor behavior in the temperature range 300-50 K with an activation energy of 64 meV. The magnetic measurements confirm the presence of high spin S = 5/2 [Fe(C(2)O(4))(3)](3-) isolated monomers together with a Pauli paramagnetism, typical of metals, in compounds 1-3. The magnetic properties can be very well reproduced in the whole temperature range with a simple model of isolated S = 5/2 ions with a zero field splitting plus a temperature independent paramagnetism (Nα) with the following parameters: g = 1.965, |D| = 0.31 cm(-1), and Nα = 1.5 × 10(-3) emu mol(-1) for 1, g = 2.024, |D| = 0.65 cm(-1), and Nα = 1.4 × 10(-3) emu mol(-1) for 2, and g = 2.001, |D| = 0.52 cm(-1), and Nα = 1.5 × 10(-3) emu mol(-1) for 3.

Molecular conductors based on the mixed-valence polyoxometalates [SMo12O40]n- (n = 3 and 4) and the organic donors bis(ethylenedithio)tetrathiafulvalene and bis(ethylenedithio)tetraselenafulvalene.

The synthesis, crystal structure, and physical characterization of two new radical salts formed by the organic donors bis(ethylenedithio)tetrathiafulvalene (ET) and bis(ethylenediseleno)tetrathiafulvalene (BETS) and the Keggin polyoxometalate (POM) [SMo(12)O(40)](n-) are reported. The salts isolated are ET(8)[SMo(12)O(40)] x 10 H(2)O (1) (crystal data: (1) monoclinic, space group I2/m with a = 13.9300(10) A, b = 43.467(3) A, c = 13.9929(13) A, beta = 107.979(6) degrees, V = 8058.9(11) A(3), Z = 2) and BETS(8)[SMo(12)O(40)] x 10 H(2)O (2) (crystal data: monoclinic, space group I2/m with a = 14.0878(2) A, b = 44.1010(6) A, c = 14.0930(2) A, beta = 106.739(3) degrees, V = 8384.8 A(3), Z = 2). Both compounds are isostructural and consist of alternating layers of the organic donors (with an alpha or theta(42+40) packing mode) and POM anions. The structural data, as well as the magnetic susceptibility, ESR measurements, and band structure calculations, indicate that the Keggin POMs have been reduced by one electron in 1 and by two electrons in 2, leading to the POMs [SMo(12)O(40)](3-) and [SMo(12)O(40)](4-) in 1 and 2, respectively. At ambient pressure 1 is a classical semiconductor with a room temperature conductivity of about 1 S cm(-1) and an activation energy of about 130 meV. Salt 2 also exhibits an activated behavior although it does not follow a classical semiconducting regime. The conductivity of 2 under applied pressure shows an enhanced conductivity, in agreement with the analysis of the electronic structure, although no metallic behavior is detected below about 10 kbar.

Modular synthesis of heterobimetallic salen structures using metal templation.

A modular and general synthetic method is disclosed for nonsymmetrical heterobimetallic bis-salphen structures starting from a series of synthetically convenient monometalated triimine precursors. This methodology permits the introduction of various combinations of metal ions within the bis-salphen framework potentially useful in multifunctional materials.

Facile isolation of bisimines based on 3,3'-diaminobenzidine: direct access to unsymmetrical bimetallic salphen building blocks.

Diimines obtained from 3,3'-diaminobenzidine and tert-butyl-substituted salicylaldehydes in MeOH can be readily isolated in 60-90% yield and were obtained as a mixture of geometrical isomers. Two distinct diimine intermediates (4 and 5) with a higher molecular symmetry as related to the other isomeric diimine products were both isolated by crystallization of which 5 was subsequently used to demonstrate that nonsymmetrical bis-salphen complexes with different functional groups and metal centers can be assembled via a three-component one-pot procedure.

New BEDT-TTF/[Fe(C5O5)3]3- hybrid system: synthesis, crystal structure, and physical properties of a chirality-induced alpha phase and a novel magnetic molecular metal.

The paramagnetic and chiral anion [Fe(C5O5)3]3- (C5O52-=croconate) has been combined with the organic donor BEDT-TTF (=ET=bis(ethylenedithio)tetrathiafulvalene) to synthesize a novel paramagnetic semiconductor with the first chirality-induced alpha phase, alpha-(BEDT-TTF)5[Fe(C5O5)3].5H2O (1), and one of the few known paramagnetic molecular metals, beta-(BEDT-TTF)5[Fe(C5O5)3].C6H5CN (2). Both compounds present layers of BEDT-TTF molecules, with the alpha or beta packing modes, alternating with layers containing the high-spin S=5/2 Fe(III) anions and solvent molecules. In the alpha phase, the alternation of the chiral [Fe(C5O5)3]3- anions along the direction perpendicular to the BEDT-TTF chains induces an alternation of the tilt angle of the BEDT-TTF molecules, giving rise to the observed alpha phase. The alpha phase presents a semiconductor behavior with a high room-temperature conductivity (6 S.cm-1) and an activation energy of 116 meV. The beta phase presents a metallic behavior down to ca. 120 K, where a charge localization takes place with a reentrance to the metallic state below ca. 20 K followed by a metal-semiconductor transition at ca. 10 K. The magnetic properties are dominated by the paramagnetic S=5/2 [Fe(C5O5)3]3- anion with an extra Pauli-type paramagnetism in the metallic beta phase. The ESR spectra confirm the presence of the high-spin Fe(III)-containing anion and show a progressive localization in the organic sublattice along with an antiferromagnetic coupling below ca. 120 K that, in the metallic beta phase, could be at the origin of the transition from the metallic to the activated conductivity regime. The correlation between crystal structure and conductivity behavior has been studied by means of tight-binding band structure calculations which provide a rationalization of the charge distribution and conductivity results.

Radical salts of bis(ethylenediseleno)tetrathiafulvalene with paramagnetic tris(oxalato)metalate anions.

The synthesis, crystal structure, and physical characterization of five new radical salts formed by the organic donor bis(ethylenediseleno)tetrathiafulvalene (BEST) and the paramagnetic tris(oxalato)metalate anions [M(C2O4)3]3- (M = FeIII and CrIII) are reported. The salts isolated are (BEST)4[M(C2O4)3].PhCOOH.H2O with MIII = Cr (1) or Fe (2) (crystal data: 1, triclinic, space group P(-)1 with a = 14.0999(4) A, b = 15.3464(4) A, c =19.5000(4) A, alpha = 76.711(5) degrees, beta = 71.688(5) degrees, gamma = 88.545(5) degrees, V = 3893.5(2) A3, and Z = 2; 2, triclinic, space group P(-)1 with a = 14.0326(3) A, b =15.1981(4) A, c =19.4106(4) A, alpha = 76.739(5) degrees, beta = 71.938(5) degrees, gamma = 88.845(5) degrees, V = 3824.9(2) A3, and Z = 2), (BEST)4[M(C2O4)3].1.5H2O with MIII = Cr (3) or Fe (4) (crystal data: 3, monoclinic, space group C2/m with a = 33.7480(10) A, b =12.3151(7) A, c = 8.8218(5) A, beta = 99.674(5) degrees, V = 3614.3(3) A3, and Z = 2; 4, monoclinic, space group C2/m with a = 33.659(6) A, b =12.248(2) A, c = 8.759(2) A, beta = 99.74(3) degrees, V = 3558.9(12) A3, and Z = 2), and (BEST)9[Fe(C2O4)3]2.7H2O (5) (crystal data: triclinic, space group P(-)1 with a =12.6993(3) A, b =18.7564(4) A, c = 18.7675(4) A, alpha = 75.649(5) degrees, beta = 107.178(5) degrees, gamma = 79.527(5) degrees, V = 3977.5(3) A3, and Z = 1). The structures of all these salts consist of alternating layers of the organic donors and tris(oxalato)metalate anions. In 1 and 2 the anionic layers contain also benzoic acid molecules H-bonded to the terminal oxygen atoms of the anions. In all salts the organic layers adopt beta-type packings. Along the parallel stacks the donors form dimers in 3 and 4, trimers in 5, and tetramers in 1 and 2. All the compounds are paramagnetic semiconductors with high room-temperature conductivities and magnetic susceptibilities dominated by the Fe- or Cr-containing anions.

A chirality-induced alpha phase and a novel molecular magnetic metal in the BEDT-TTF/tris(croconate)ferrate(III) hybrid molecular system.

The novel paramagnetic and chiral anion [Fe(C5O5)3]3- has been combined with the organic donor BEDT-TTF (= ET = bis(ethylenedithio)tetrathiafulvalene) to yield the first chirality-induced alpha phase and a paramagnetic metal.

Synthesis, structure, spectroscopy and redox chemistry of square-planar nickel(II) complexes with tetradentate o-phenylenedioxamidates and related ligands.

A series of four-coordinate square-planar nickel(II) complexes of o-phenylenebis(N'-methyloxamidate)(L1) and related o-phenylene(N'-methyloxamidate)oxamate (L2) and o-phenylenebis(oxamate)(L3) tetradentate ligands have been synthesized and characterized structurally, spectroscopically and electrochemically. The parent nickel(II)-L1 complex presents an intense MLCT band in the UV region (lambda max = 357 nm) and a distinctive 1 s --> 4p CT satellite in the Ni K-edge XANES spectrum (E = 8339.2 eV). These features together with the short Ni-N(amidate) bond lengths (1.85-1.93 A) as revealed by the analysis of the Ni K-edge EXAFS spectrum and confirmed by single-crystal X-ray diffraction are typical of square-planar low spin (S = 0) Ni(II) ions. The dianionic nickel(II) complexes, [Ni(II)L(i)](2-)(i = -3), experience two redox processes in acetonitrile at 25 degrees C. The first redox process, at moderately low potentials (E1 = 0.12-0.52 V vs. SCE), is a reversible one-electron metal-centered oxidation to the corresponding monoanionic nickel(III) complexes, [Ni(III)L(i)]-. The second redox process, at relatively high potentials (E2 = 0.86-1.04 V vs. SCE), is a quasireversible to irreversible one-electron oxidation largely centered on the o-benzenediamidate fragment of the non-innocent ligand, yielding the corresponding neutral nickel(iii) complexes with a o-benzosemiquinonediimine pi-cation radical ligand, [Ni(III)(L(i))*+]. The singly and doubly oxidized species of the parent nickel(II)-L1 complex have been prepared by chemical oxidation and characterized spectroscopically in acetonitrile at -40 degrees C. The stable singly oxidized nickel(III)-L1 species presents an intense LMCT band in the NIR region (lambda max = 910 nm) and a rhombic X-band EPR spectrum (g1 = 2.193, g2 = 2.080 and g3 = 2.006) characteristic of square-planar low spin (S = 1/2) Ni(III) ions. The unstable double oxidized nickel(III)-L1 pi-cation radical species exhibits a rather intense visible band (lambda max = 645 nm) that is tentatively assigned as a MLCT transition from the Ni(III)-benzosemiquinone type ground state to the Ni(IV) excited state.

Electronic factors affecting second-order NLO properties: case study of four different push-pull bis-dithiolene nickel complexes.

The paper presents a detailed experimental and theoretical study of the four mixed nickel-bisdithiolene complexes [Ni(Pr(i)(2)pipdt)(dmit)] (1b, Pr(i)(2)pipdt = 1,4-diisopropyl-piperazine-3,2-dithione; dmit = 1,3-dithiolo-2-tione-4,5-dithiolato), [Ni(R(2)pipdt)(mnt)] (2b", R = 2-ethylhexyl; mnt = maleonitriledithiolato), [Ni(Pr(i)(2)timdt)(dmit)] (3b, Pr(i)(2)timdt = 1,3-diisopropyl-imidazoline-2,4,5-trithione), and [Ni(Pr(i)(2)timdt)(mnt)] (4b), and their models. All the complexes, with common (C(2)S(2))Ni(C(2)S(2)) core and two different terminal groups, are uncharged and square-planar coordinated. Previous measurements of the first molecular hyperpolarizability indicated that some of the species are potential NLO chromophores due to the pi-delocalized character of two frontier levels (HOMO and LUMO) which is asymmetrically perturbed by the combination of one push (R(2)pipdt, R(2)timdt) with one pull ligand (dmit and mnt). The X-ray structure of complex 1b is presented and its geometry is compared with those available in the literature for the four types of complexes under study. The results of electrochemical and spectroscopic measurements (oxidation and reduction potentials, IR, dipole moment, molecular absorptivities, etc.) indicate rather different responses between the pairs of complexes 1-2 and 3-4. Hence, DFT calculations on the model compounds 1a-4a, where hydrogen atoms replace the alkyl groups of R(2)pipdt and R(2)timdt, have been carried out to correlate geometries and electronic structures. Moreover, the first molecular hyperpolarizabilities have been calculated and their components have been analyzed with the simplest two-level approximation. The derived picture highlights the different roles of the two push and pull ligands, but also the peculiar perturbation of the pi-electron density induced by the terminal CS(3) grouping of the ligand dmit.