The addition of 2,2'-bipyridine to [U(Tp(Me2))(2)I] (1) results in the displacement of the iodide and the formation of the cationic uranium(III) complex [U(Tp(Me2))(2)(bipy)]I (2). This compound was isolated as a dark-green solid in good yield and characterized by IR and NMR spectroscopies, and its molecular structure was determined by single-crystal X-ray diffraction. Studies of its magnetic properties revealed a frequency dependence of magnetization with a blocking temperature of 4.5 K and, at lower temperatures, a slow relaxation of magnetization with an energy barrier of 18.2 cm(-1), characteristic of single-molecule-magnet behavior.

The electrocrystallization from solutions of cyanobenzene-ethylenedithio-tetrathiafulvalene (CNB-EDT-TTF) in the presence of different anions X = ClO4(-), PF6(-), and I3(-), affords a new type of 2D molecular metals with composition (CNB-EDT-TTF)4X based on an unprecedented bilayer structure of the donors induced by effective head to head interdonor interactions through the nitrile groups, which is responsible for 2D metallic systems with unusual properties such as the higher band filling, larger effective mass of carriers, and almost degenerated double Fermi surfaces.

Starting from the first organic spin ladder reported, a dithiophene‐tetrathiafulvalene salt ((DT‐TTF)2[Au(mnt)2]) (mnt = maleonitriledithiolate), two different approaches to enlarge the family of organic spin‐ladder systems are described. The first approach consists of a molecular variation of the donor; to that purpose, the new TTF derivative ethylenethiothiophene‐tetrathiafulvalene (ETT‐TTF, 3), is synthesized and structurally characterized. From this donor a new ladder‐like structure compound, (ETT‐TTF)2[Au(mnt)2] (4), isostructural with (DT‐TTF)2[Au(mnt)2], is obtained. However, the magnetic properties of 4 do not follow the known spin‐ladder behavior owing to orientational disorder exhibited by the ETT‐TTF molecules in the crystal structure. In the second approach, the acceptor complex is changed, either in the nature of the ligand or in the metal. With the [Au(i‐mnt)2]– salt (i‐mnt = iso‐maleonitriledithiolate), the new ladder‐like compound (DT‐TTF)2[Au(i‐mnt)2] (5), isostructural with 4, is obtained, but only as a minority product. Two other compounds with a different anion generated in situ, bearing a Au(I) dimeric core, were also isolated; (DT‐TTF)9[Au2(i‐mnt)2]2 (6) as the most abundant phase and (DT‐TTF)2[Au2(i‐mnt)2] (7) as another minority phase. Salt 7 is characterized by X‐ray crystallography as a chiral compound, due to the torsion of the ligands around the central Au–Au bond. The magnetic properties of (DT‐TTF)2[Au(i‐mnt)2] (5) indicate that it follows a spin‐ladder behavior and the electron paramagnetic resonance (EPR) data is fitted to the Troyer and Barnes and Riera equations with the parameters Δ/kB = 71 K, J∥/kB = 86 K, and J⟂/kB = 142 K, indicating a J⟂/J∥ ratio of 1.65. The change of the gold complex [Au(mnt)2] for its copper analogue, [Cu(mnt)2] also leads to a ladder‐like structure, (DT‐TTF)2[Cu(mnt)2] (8), which is isostructural with the gold analogue and with salts 4 and 5. The fully ionic salt (DT‐TTF)[Cu(mnt)2] (9) is also obtained. The magnetic properties demonstrated that compound 8 is the third organic spin‐ladder system of this family, and the values found by a fitting to the ladder equations were Δ/kB = 123 K, J∥/kB = 121 K, and J⟂/kB = 218 K, corresponding to a J⟂/J∥ ratio of 1.75, similar to that of 5 and close to that of an ideal spin ladder.

We report the synthesis of the iron(III) complex of the hexadentate Schiff base ligand nsal2trien obtained from the condensation of triethylenetetramine and 2 equiv. of 2-hydroxy-1-naphthaldehyde. The study of the salt [Fe(nsal2trien)]SCN (1) by magnetic susceptibility measurements and Mössbauer spectroscopy reveals a rather unique behavior that displays thermally induced spin crossover (SCO) with two well-separated steps at 250 (gradual transition) and 142 K (steep transition). Single crystal X-ray structures were obtained at 294, 150, and 50 K, for the high spin (HS), intermediate (Int), and low spin (LS) phases. The HS and LS phases are isostructural, and based on a single Fe(III) site (either HS or LS) an unusual symmetry break occurs in the transition to the Int ordered phase, where the unit cell includes two distinct Fe(III) sites and is based on a repetition of the [HS-LS] motif. The two-step SCO behavior of 1 must result from the existence of structural constraints preventing the full conversion HS ↔ LS in a single step.

The reaction of the tripodal tris-amido U(III) complex [U{(SiMe 2 NPh) 3 -tacn}] (tacn ¼ 1,4,7triazacyclononane), 1, with 0.0625 and 0.25 equiv. of elemental sulfur affords the sulfide-bridged U(IV) complex [{U((SiMe 2 NPh) 3 -tacn)} 2 (m-S)], 2, and the terminal persulfide U(V) complex [U{(SiMe 2 NPh) 3 -tacn}(h 2 -S 2 )], 4, respectively, in good yield. Two different electronic structures, U(V) persulfide and U(IV) supersulfide, were computed for complex 4 at the DFT level. The results show that complex 4 is best described as a U(V) persulfide species with a significant sulfur contribution. X-ray, magnetism and electrochemistry data support this description. Complex 4 is the first example of a terminal U(V) persulfide and of a two-electron reduction of S 8 by a U(III) complex. Complex 4 behaves as a S-atom transfer agent when reacted with PPh 3 , affording the persulfide-bridged diuranium(IV) complex [{U((SiMe 2 NPh) 3 -tacn)} 2 (m-h 2 :h 2 -S 2 )], 5, and S]PPh 3 .

The Fe(III) complexes Fe(5-Br-qsal)2Ni(dmit)2·solv with solv = CH2Cl2 (1) and (CH3)2CO (2) were synthesized, and their structural and magnetic properties were studied. While magnetization and Mössbauer spectroscopy data of 1 showed a gradual spin transition, compound 2 evidenced an abrupt transition with a thermal hysteresis of 13 K close to room temperature (T1/2 ↓ ∼273 K and T1/2 ↑ ∼286 K). A similar packing arrangement of segregated layers of cations and anions was found for 1 and 2. In both low-spin, LS, structures there are a large number of short intra- and interchain contacts. This number is lower in the high-spin, HS, phases, particularly in the case of 1. The significant loss of strong π-π interactions in the cationic chains and short contacts in the anionic chains in the HS structure of 1 leads to alternating strong and weak bonds between cations along the cationic chains and the formation of unconnected dimers along the anionic chains. This is consistent with a significant weakening of the extended interactions in 1. On the other hand, in the HS phase of 2 the 3D dimensionality of the short contacts observed in the LS phases is preserved. The effect of distinct solvent molecules on the intermolecular spacings explains the different spin crossover behaviors of the title compounds.

A series of new M[(dcbdt) 2 ]−z complexes of the dicyanobenzodithiolate (dcbdt) ligand with a range of transition metals (M = Co, Pd, Pt, Cu, Au and Zn) in different oxidation states (z = 0.4, 1, 2) were prepared as their nBu 4 N salts and characterised by X-ray diffraction, cyclic voltammetry, EPR and static magnetic susceptibility. Their properties are discussed in comparison with the Ni and Fe analogues described by us recently. The structures of these complexes belong to four distinct groups: i) the Zn II compound 10 is triclinic P1 with the metal in a tetrahedral coordination geometry; ii) other M II complexes [M = Pt (8), Pd (7), Co (3) and Cu (5)] are monoclinic C2/m, and are isostructural with the Ni II analogue, presenting a perfectly planar square geometry; iii) the Co III compound 4 is triclinic P1 , and isostructural with the Fe and Ni analogues, with a strong dimerisation of the M(dcbdt) 2 units

The gold and nickel bisdithiolene complexes based on new highly extended ligands incorporating fused tetrathiafulvalene and thiophene moieties (alpha-tdt=thiophenetetrathiafulvalenedithiolate and dtdt=dihydro- thiophenetetrathiafulvalenedithiolate), were prepared and characterised by using cyclic voltammetry, single crystal X-ray diffraction, EPR, magnetic susceptibility and electrical transport measurements. These complexes, initially obtained under anaerobic conditions as diamagnetic gold monoanic [nBu(4)N][Au(alpha-tdt)(2)] (4), [nBu(4)N][Au(dtdt)(2)] (3) and nickel dianionic species [(nBu(4)N)(2)][Ni(alpha-tdt)(2)] (8), [(nBu(4)N)(2)][Ni(dtdt)(2)] (7), can be easily oxidised to the stable neutral state just by air or iodine exposure. The monoanionic complexes crystallise in at least two polymorphs, all of which have good cation and anion segregation in alternated layers, the anion layers making a dense 2D network of short SS contacts. All of the neutral complexes, obtained as microcrystalline or quasi amorphous fine powder, present relatively large magnetic susceptibilities that correspond to effective magnetic moments in the range 1-3 mu(B) indicative of high spin states and very high electrical conductivity that in case of the Ni compound can reach sigma(RT) approximately 250 S cm(-1) with a clear metallic behaviour. These compounds are new examples of the still rare single-component molecular metals.