Structural Diversity and Multielectron Reduction Reactivity of Samarium(II) Iodido-ß-diketiminate Complexes Dependent on Tetrahydrofuran Content.

The molecular structures of complexes [Sm(Nacnac)I(thf)n] (Nacnac = HC(C(Me)Ndipp)2-, dipp = 2,6-diisopropylphenyl, thf = tetrahydrofuran) depending on the number of thf ligands are studied. The complete removal of thf from a known complex [Sm(Nacnac)I(thf)2] leads to a tetranuclear product [Sm(Nacnac)I]4 (4). The partial removal of thf results in mixtures of dinuclear [Sm2(Nacnac)2I2(thf)] (2), trinuclear [Sm3(Nacnac)3I3(thf)] (3), and tetranuclear [Sm4(Nacnac)4I4(thf)2] (4*) complexes and 4, depending on the conditions. The reaction of solvent-free SmI2 with 1 equiv of K(Nacnac) results mainly in [Sm(Nacnac)2] (1), while the interaction of 4 with certain amounts of thf allows obtaining pure 2 and 3 (with the admixture of 4*). Complex 4* is the exact dimer of 2, and both compounds are stable in solutions. Reactions with 3 and 4 as reductants are studied. 4 is oxidized by I2 to stoichiometrically yield two products, mixed-valent tetranuclear [Sm4(Nacnac)4I5] (5) and binuclear [Sm(Nacnac)I2]2 (6) complexes. In the reaction of 4 with nBu3PTe, a trinuclear complex [Sm3(Nacnac)3(µ-I)3(µ3-E)2] (8, E = I or Te) is formed in small amounts, with the formation of 6 as the second product. 3 serves as a two-electron reductant in the reaction with nBu3PTe to yield a trinuclear complex [Sm3(Nacnac)3I3(µ-Te2)] (7). Complexes 2, 4, 4*, 5, 6, and 8 possess a unique flat SmxIy core of heavy atoms, which is assumed to be a consequence of the Nacnac ligand geometry.

Doping of Carbon Nanotubes with Encapsulated Phosphorus Chains.

Single-walled carbon nanotubes (SWCNTs) are a perfect host for the formation of one-dimensional phosphorus structures and to obtain hybrid materials with a large P-C ratio. This work presents a procedure for high-yield phosphorus filling of commercial Tuball SWCNTs and efficient removal of phosphorus deposits from the external nanotube surface. We probed white and red phosphorus as precursors, varied the synthesis temperature and the ampoule shape, and tested three solvents for sample purification. High-resolution transmission electron microscopy and Raman spectroscopy indicated crystallization of interior phosphorus in a form resembling fibrous red phosphorus. An aqueous sodium hydroxide solution allowed removing the majority of external phosphorus particles. Thermogravimetric analysis of the product determined ∼23 wt % (∼10 atom %) of phosphorus, and the X-ray photoelectron spectroscopy (XPS) data showed that ca. 80% of it is in the form of elemental phosphorus. Externally purified SWCNTs filled with phosphorus were used to study the interaction between the components. Raman spectroscopy and core-level XPS revealed p-type SWCNT doping. Valence-band XPS data and density functional theory calculations confirmed the transfer of the SWCNT electron density to the encapsulated phosphorus.

Radical Anions, Radical-Anion Salts, and Anionic Complexes of 2,1,3-Benzochalcogenadiazoles.

By means of cyclic voltammetry (CV) and DFT calculations, it was found that the electron-acceptor ability of 2,1,3-benzochalcogenadiazoles 1-3 (chalcogen: S, Se, and Te, respectively) increases with increasing atomic number of the chalcogen. This trend is nontrivial, since it contradicts the electronegativity and atomic electron affinity of the chalcogens. In contrast to radical anions (RAs) [1].- and [2].- , RA [3].- was not detected by EPR spectroscopy under CV conditions. Chemical reduction of 1-3 was performed and new thermally stable RA salts [K(THF)]+ [2].- (8) and [K(18-crown-6)]+ [2].- (9) were isolated in addition to known salt [K(THF)]+ [1].- (7). On contact with air, RAs [1].- and [2].- underwent fast decomposition in solution with the formation of anions [ECN]- , which were isolated in the form of salts [K(18-crown-6)]+ [ECN]- (10, E=S; 11, E=Se). In the case of 3, RA [3].- was detected by EPR spectroscopy as the first representative of tellurium-nitrogen π-heterocyclic RAs but not isolated. Instead, salt [K(18-crown-6)]+ 2 [3-Te2 ]2- (12) featuring a new anionic complex with coordinate Te-Te bond was obtained. On contact with air, salt 12 transformed into salt [K(18-crown-6)]+ 2 [3-Te4 -3]2- (13) containing an anionic complex with two coordinate Te-Te bonds. The structures of 8-13 were confirmed by XRD, and the nature of the Te-Te coordinate bond in [3-Te2 ]2- and [3-Te4 -3]2- was studied by DFT calculations and QTAIM analysis.

Nature of Bonding in Donor-Acceptor Interactions Exemplified by Complexes of N-Heterocyclic Carbenes with 1,2,5-Telluradiazoles.

Comprehensive structural, spectroscopic, and quantum chemical analyses of new donor-acceptor complexes between N-heterocyclic carbenes and 1,2,5-telluradiazoles and a comparison with previously known complexes involving tellurenyl cations showed that the dative C-Te bonds cannot be solitarily described with only one Lewis formula. Canonical Lewis formulas that denote covalency and arrows emphasizing ionicity complement each other in varying extents. Evaluation of the relative weights of these resonance forms requires proper bonding description with a well-balanced toolbox of analytical methods. If for conciseness only, one resonance form is used, it must be the most significant one according to the analytical evaluation. If unclear, all significant resonance forms should be displayed.

Cooperative reduction by Ln(2+) and Cp*(-) ions: synthesis and properties of Sm, Eu, and Yb complexes with 3,6-di-tert-butyl-o-benzoquinone.

The first examples of samarium, europium, and ytterbium complexes with 3,6-di-tert-butyl-o-benzoquinone(3,6-dbbq) in the form of catecholate have been obtained by reactions of the quinone with the corresponding lanthanocenes, [LnCp2*(thf)n] (n = 1 or 2) in solution. In the course of the reactions lanthanide ions lose one or two Cp* ligands, which take part in reduction of a quinone molecule into a catecholate anion (dbcat, 2(-)). As a result of the reactions, Sm and Yb clearly yield dimeric complexes[(LnCp*)2(dbcat)2], where each Ln ion loses one Cp* ligand. Eu forms a trimeric complex [(EuCp*)-(Eu·thf)2(dbcat)3], in which one Eu ion is coordinated by one Cp* ligand, while two Eu ions have lost all Cp* ligands and are coordinated by THF molecules instead. Magnetic properties corroborate the assignment of oxidation states made on the basis of single-crystal X-ray diffraction: all the quinone ligands are present in the catecholate state; both Sm/Yb ions in the dimers are in the +3 oxidation state, whereas the Eu trimer contains two Eu(II) and one Eu(III) ions. Cyclovoltammetry studies show the presence of two reversible oxidation waves for all complexes, presumably concerned with the redox transitions of the dbcat ligands.

Synthesis and Properties of the Heterospin (S1 = S2 = (1)/2) Radical-Ion Salt Bis(mesitylene)molybdenum(I) [1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazolidyl.

Low-temperature interaction of [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1) with MoMes2 (Mes = mesitylene/1,3,5-trimethylbenzene) in tetrahydrofuran gave the heterospin (S1 = S2 = (1)/2) radical-ion salt [MoMes2](+)[1](-) (2) whose structure was confirmed by single-crystal X-ray diffraction (XRD). The structure revealed alternating layers of the cations and anions with the Mes ligands perpendicular, and the anions tilted by 45°, to the layer plane. At 300 K the effective magnetic moment of 2 is equal to 2.40 µB (theoretically expected 2.45 µB) and monotonically decreases with lowering of the temperature. In the temperature range 2-300 K, the molar magnetic susceptibility of 2 is well-described by the Curie-Weiss law with parameters C and θ equal to 0.78 cm(3) K mol(-1) and -31.2 K, respectively. Overall, the magnetic behavior of 2 is similar to that of [CrTol2](+)[1](-) and [CrCp*2](+)[1](-), i.e., changing the cation [MAr2](+) 3d atom M = Cr (Z = 24) with weak spin-orbit coupling (SOC) to a 4d atom M = Mo (Z = 42) with stronger SOC does not affect macroscopic magnetic properties of the salts. For the XRD structure of salt 2, parameters of the Heisenberg spin-Hamiltonian were calculated using the broken-symmetry DFT and CASSCF approaches, and the complex 3D magnetic structure with both the ferromagnetic (FM) and antiferromagnetic (AF) exchange interactions was revealed with the latter as dominating. Salt 2 is thermally unstable and slowly loses the Mes ligands upon storage at ambient temperature. Under the same reaction conditions, interaction of 1 with MoTol2 (Tol = toluene) proceeded with partial loss of the Tol ligands to afford diamagnetic product.

The approach to 4d/4f-polyphosphides.

The first 4d/4f polyphosphides were obtained by reaction of the divalent metallocenes [Cp*2Ln(thf)2] (Ln = Sm, Yb) with [{CpMo(CO)2}2(µ,η2:2-P2)] or [Cp*Mo(CO)2(η3-P3)]. Treatment of [Cp*2Ln(thf)2] (Ln = Sm, Yb) with [{CpMo(CO)2}2(µ,η2:2-P2)] gave the 16-membered bicyclic compounds [(Cp2*Ln)2P2(CpMo(CO)2)4] (Ln = Sm, Yb) as the major products. From the reaction involving samarocene, the cyclic P4 complex [(Cp*2Sm)2P4(CpMo(CO)2)2] and the cyclic P5 complex [(Cp*2Sm)3P5(CpMo(CO)2)3] were also obtained as minor products. In each reaction, the P2 unit is reduced and a rearrangement occurred. In dedicated cases, a P-P bond formation takes place, which results in a new aggregation of the central phosphorus scaffold. In the reactions of [Cp*2Ln(thf)2] (Ln = Sm, Yb) with [Cp*Mo(CO)2P3] a new P-P bond is formed by reductive dimerization and the 4d/4f hexaphosphides [(Cp*2Ln)2P6(Cp*Mo(CO)2)2] (Ln = Sm, Yb) were obtained.

Bis(toluene)chromium(I) [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolidyl and [1,2,5]thiadiazolo[3,4-b]pyrazinidyl: new heterospin (S1 = S2 = ½) radical-ion salts.

Bis(toluene)chromium(0), Cr(0)(η(6)-C7H8)2 (3), readily reduced [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1) and [1,2,5]thiadiazolo[3,4-b]pyrazine (2) in a tetrahydrofuran solvent with the formation of heterospin, S1 = S2 = ½, radical-ion salts [3](+)[1](-) (4) and [3](+)[2](-) (5) isolated in high yields. The salts 4 and 5 were characterized by single-crystal X-ray diffraction (XRD), solution and solid-state electron paramagnetic resonance, and magnetic susceptibility measurements in the temperature range 2-300 K. Despite the formal similarity of the salts, their crystal structures were very different and, in contrast to 4, in 5 anions were disordered. For the XRD structures of the salts, parameters of the Heisenberg spin Hamiltonian were calculated using the CASSCF/NEVPT2 and broken-symmetry density functional theory approaches, and the complex magnetic motifs featuring the dominance of antiferromagnetic (AF) interactions were revealed. The experimental χT temperature dependences of the salts were simulated using the Van Vleck formula and a diagonalization of the matrix of the Heisenberg spin Hamiltonian for the clusters of 12 paramagnetic species with periodic boundary conditions. According to the calculations and χT temperature dependence simulation, a simplified magnetic model can be suggested for the salt 4 with AF interactions between the anions ([1](-)···[1](-), J1 = -5.77 cm(-1)) and anions and cations ([1](-)···[3](+), J2 = -0.84 cm(-1)). The magnetic structure of the salt 5 is much more complex and can be characterized by AF interactions between the anions, [2](-)···[2](-), and by both AF and ferromagnetic (FM) interactions between the anions and cations, [2](-)···[3](+). The contribution from FM interactions to the magnetic properties of the salt 5 is in qualitative agreement with the positive value of the Weiss constant Θ (0.4 K), whereas for salt 4, the constant is negative (-7.1 K).

X-(Diiodoarsanyl)benzoic acid (X = 3 and 4).

The title compounds, 4-(diiodoarsanyl)benzoic acid, (I), and 3-(diiodoarsanyl)benzoic acid, (II), both [As(C(7)H(5)O(2))I(2)], which possess a -COOH coordinating group, form molecular crystal structures composed of hydrogen-bonded dimers, the packing differences of which are caused by the relative position of the diiodoarsanyl groups. The para isomer, with Z' = 1, crystallizes in a layered structure with shortened contacts of the As atoms to only the arene rings of adjacent molecules. In contrast, the meta isomer, with Z' = 3, forms separate rectangular blocks of three ribbons, each composed of dimeric molecular units positioned almost directly above each other and with the As atoms possessing only two As···I contacts to the I atoms of neighbouring molecules.

[N,N'-Bis(2,6-diisopropylphenyl)acenaphthene-1,2-diimine-1κ2N,N']heptacarbonyl-1κC,2κ3C,3κ3C-di-µ3-tellurido-triiiron(II)(2 Fe-Fe).

The sterically hindered title complex, [Fe(3)Te(2)(C(36)H(40)N(2))(CO)(7)], was obtained by substitution of two carbonyl groups in the [Fe(3)(µ(3)-Te)(2)(CO)(9)] cluster by the bulky redox-active N,N'-bis(2,6-diisopropylphenyl)acenaphthene-1,2-diimine (dpp-BIAN) ligand. The asymmetric unit contains two molecules of the same geometry. The C=N bond lengths in dpp-BIAN indicate a rather low level of electron transfer from the cluster core to the dpp-BIAN ligand.

Dimerization of pentanuclear clusters [Fe3Q(AsMe)(CO)9] (Q = Se, Te) as a conversion pathway to novel cubane-like aggregates.

The first examples of carbonyl heterocubane-type clusters, [Fe(4)(µ(3)-Q)(2)(µ(3)-AsMe)(2)(CO)(12)] (2, Q = Se (a), Te (b)), which simultaneously contain elements of group 15 and 16, were obtained by thermolysis of [Fe(3)(µ(3)-Q)(µ(3)-AsMe)(CO)(9)] (1) in acetonitrile. The clusters 2 possess a cubic Fe(4)Q(2)As(2) core with alternating Fe and Q/As atoms. The coordination environment of the Fe atoms is close to octahedral, and those of Q or As atoms are tetrahedral, which determines the distorted cubic cluster core geometry. The second main products of thermolysis are the clusters [Fe(6)(µ(3)-Q)(µ(4)-Q)(µ(4)-AsMe)(2)(CO)(12)] (3a,b), whose core contains double the elemental composition of the initial cluster 1. In the case of the Se-containing cluster two other minor products [Fe(4)(µ(4)-Se)(µ(4)-SeAsMe)(CO)(12)] (4) and [Fe(3)(µ(3)-AsMe)(2)(CO)(9)] (5) are formed. Based on the structures and properties of the products, a reaction route for the conversion of 1 into 2 is proposed, which includes the associative formation of the clusters 3 as intermediates, unlike the dissociative pathways previously known for the transformations of similar clusters of the type [Fe(3)Q(2)(CO)(9)].

Heterospin pi-heterocyclic radical-anion salt: synthesis, structure, and magnetic properties of decamethylchromocenium [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolidyl.

Decamethylchromocene, Cr(II)(eta(5)-C(5)(CH(3))(5))(2) (2), readily reduced [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1) in a tetrahydrofuran solvent at ambient temperature with the formation of radical-anion salt [2](+)[1](-) (3) isolated in 97% yield. The heterospin salt 3 ([2](+), S = 3/2; [1](-), S = 1/2) was characterized by single-crystal X-ray diffraction as well as magnetic susceptibility measurements in the temperature range 2-300 K. The experimental data together with theoretical analysis of the salt's magnetic structure within the CASSCF and spin-unrestricted broken-symmetry (BS) density functional theory (DFT) approaches revealed antiferromagnetic (AF) interactions in the crystalline 3: significant between anions [1](-), weak between cations [2](+), and very weak between [1](-) and [2](+). Experimental temperature dependences of the magnetic susceptibility and the effective magnetic moment of 3 were very well reproduced in the assumption of the AF-coupled [1](-)...[1](-) (J(1) = -40 +/- 9 cm(-1)) and [2](+)...[2](+) (J(2) = -0.58 +/- 0.03 cm(-1)) pairs. The experimental J(1) value is in reasonable agreement with the value calculated using BS UB3LYP/6-31+G(d) (-61 cm(-1)) and CASSCF(10,10)/6-31+G(d) (-15.3 cm(-1)) approaches. The experimental J(2) value is also in agreement with that calculated using the BS DFT approach (-0.33 cm(-1)).

[{(eta(5)-C(5)Me(5))(2)Sm}(4)P(8)]: a molecular polyphosphide of the rare-earth elements.

[{(eta(5)-C(5)Me(5))(2)Sm}(4)P(8)], a molecular polyphosphide of the rare-earth elements having a realgar core structure, was synthesized by a one-electron redox reaction of divalent samarocen and white phosphorus.