Synthesis and Characterization of Novel Cobalt Carbonyl Phosphorus and Arsenic Clusters.

Phosphorus- and arsenic-containing cobalt clusters are an interesting class of compounds that continue to provide new structures with captivating bonding patterns. Although the first members of this family were reported 45 years ago, the number of such species is still limited within the broad family of transition metal complexes bearing pnictogen atoms. Herein, we present the reaction of Co2(CO)8 as a cobalt source with a number of phosphorus- and arsenic-containing compounds under variable reaction conditions. These reactions result in various known and novel cobalt phosphorus and cobalt arsenic clusters in which different nuclearity ratios between P/As and Co exist. All those clusters were characterized by X-ray structural analysis and partly by IR, 31P{1H} NMR, EI-MS and elemental analysis. This comprehensive study is the first detailed study in this field that reveals the richness of compounds that could be obtained only by modifying the ratio of used reactants and the involved reaction conditions.

Conversion of E4 (E4 =P4 , As4 , AsP3 ) by Ni(0) and Ni(I) Synthons - A Comparative Study.

The reactivity of white phosphorus and yellow arsenic towards two different nickel nacnac complexes is investigated. The nickel complexes [(L1 Ni)2 tol] (1, L1 =[{N(C6 H3 i Pr2 -2,6)C(Me)}2 CH]- ) and [K2 ][(L1 Ni)2 (µ,η1 : 1 -N2 )] (6) were reacted with P4 , As4 and the interpnictogen compound AsP3 , respectively, yielding the homobimetallic complexes [(L1 Ni)2 (µ-η2 ,κ1 :η2 ,κ1 -E4 )] (E=P (2 a), As (2 b), AsP3 (2 c)), [(L1 Ni)2 (µ,η3 : 3 -E3 )] (E=P (3 a), As (3 b)) and [K@18-c-6(thf)2 ][L1 Ni(η1 : 1 -E4 )] (E=P (7 a), As (7 b)), respectively. Heating of 2 a, 2 b or 2 c also leads to the formation of 3 a or 3 b. Furthermore, the reactivity of these compounds towards reduction agents was investigated, leading to [K2 ][(L1 Ni)2 (µ,η2 : 2 -P4 )] (4) and [K@18-c-6(thf)3 ][(L1 Ni)2 (µ,η3 : 3 -E3 )] (E=P (5 a), As (5 b)), respectively. Compound 4 shows an unusual planarization of the initial Ni2 P4 -prism. All products were comprehensively characterized by crystallographic and spectroscopic methods.

Iron ß-diiminate complexes with As2-, As4- and As8-ligands.

Different substituents at the ß-diiminato ligand in low-valent [LFe(tol)] (L = ß-diiminato) complexes fundamentally change their reactivity towards yellow arsenic. By using dmp (2,6-dimethylphenyl) as flanking groups, the tetranuclear complexes [(LFe)4As8] (L = L1 (1), L2 (2)) are isolated. For dipp (2,6-diisopropylphenyl) substituted ligands, dinuclear complexes [(LFe)2(cyclo-As4)] (L = L3 (3a), L4 (4a)) are obtained. Not only the choice of the ligand impacts the product formation, but also the temperature of the crystallization can shift their ratio in the solid state.

Element-Element Bond Formation upon Oxidation and Reduction.

The redox chemistry of [(Cp'''Co)2 (µ,η2 :η2 -E2 )2 ] (E=P (1), As (2); Cp'''=1,2,4-tri(tert-butyl)cyclopentadienyl) was investigated. Both compounds can be oxidized and reduced twice. That way, the monocations [(Cp'''Co)2 (µ,η4 :η4 -E4 )][X] (E=P, X=BF4 (3 a), [FAl] (3 b); E=As, X=BF4 (4 a), [FAl] (4 b)), the dications [(Cp'''Co)2 (µ,η4 :η4 -E4 )][TEF]2 (E=P (5), As (6)), and the monoanions [K(18-c-6)(dme)2 ][(Cp'''Co)2 (µ,η4 :η4 -E4 )] (E=P (7), As (8)) were isolated. Further reduction of 7 leads to the dianionic complex [K(18-c-6)(dme)2 ][K(18-c-6)][(Cp'''Co)2 (µ,η3 :η3 -P4 )] (9), in which the cyclo-P4 ligand has rearranged to a chain-like P4 ligand. Further reduction of 8 can be achieved with an excess of potassium under the formation of [K(dme)4 ][(Cp'''Co)2 (µ,η3 :η3 -As3 )] (10) and the elimination of an As1 unit. Compound 10 represents the first example of an allylic As3 ligand incorporated into a triple-decker complex.

The Influence of ß-diiminato Ligands on As4 Activation by Cobalt Complexes.

In a systematic study of the activation of As4 , three [LCo(tol)] (L=ß-diiminato) complexes have revealed different steric and electronic influences. 2,6-Diisopropylphenyl (Dipp) and 2,6-dimethylphenyl (dmp) flanking groups were used, one of the ligands with H backbone substituents (ß-dialdiminate L0 ) and two with Me substituents (ß-diketiminates L3 and L1 ). In the reaction with As4 , different dinuclear products [(LCo)2 As4 ] (LM=L0 (1), L1 (2), L3 (3)) were isolated, with all showing differently shaped [Co2 As4 ] cores in the solid state: octahedral in 1, prismatic in 2, and asterane-like in 3. Thermal treatment of 3 leads to the abstraction of one arsenic atom to yield [(L3 Co)2 As3 ] (4). All products were comprehensively characterized by single-crystal X-ray diffraction, FD-MS, and 1 H NMR spectroscopy. A rational explanation for the different reactivity is also proposed and DFT calculations shed light on the nature of the highly flexible [Co2 As4 ] cores.

Nacnac-Cobalt-Mediated P4 Transformations.

A comparison of P4 activations mediated by low-valent ß-diketiminato (L) cobalt complexes is presented. The formal Co0 source [K2 (L3 Co)2 (µ2 :η1 ,η1 -N2 )] (1) reacts with P4 to form a mixture of the monoanionic complexes [K(thf)6 ][(L3 Co)2 (µ2 :η4 ,η4 -P4 )] (2) and [K(thf)6 ][(L3 Co)2 (µ2 :η3 ,η3 -P3 )] (3). The analogue CoI precursor [L3 Co(tol)] (4 a), however, selectively yields the corresponding neutral derivative [(L3 Co)2 (µ2 :η4 ,η4 -P4 )] (5 a). Compound 5 a undergoes thermal P atom loss to form the unprecedented complex [(L3 Co)2 (µ2 :η3 ,η3 -P3 )] (6). The products 2 and 3 can be obtained selectively by an one-electron reduction of their neutral precursors 5 a and 6, respectively. The electrochemical behaviour of 2, 3, 5 a, and 6 is monitored by cyclic voltammetry and their magnetism is examined by SQUID measurements and the Evans method. The initial CoI -mediated P4 activation is not influenced by applying the structurally different ligands L1 and L2 , which is proven by the formation of the isostructural products [(LCo)2 (µ2 :η4 ,η4 -P4 )] [L=L3 (5 a), L1 (5 b), L2 (5 c)].

Influence of the nacnac Ligand in Iron(I)-Mediated P4 Transformations.

A study of P4 transformations at low-valent iron is presented using ß-diketiminato (L) Fe(I) complexes [LFe(tol)] (tol=toluene; L=L(1) (1 a), L(2) (1 b), L(3) (1 c)) with different combinations of aromatic and backbone substituents at the ligand. The products [(LFe)4 (µ4 -η(2) :η(2) :η(2) :η(2) -P8 )] (L=L(1) (2 a), L(2) (2 b)) containing a P8 core were obtained by the reaction of 1 a,b with P4 in toluene at room temperature. Using a slightly more sterically encumbered ligand in 1 c results in the formation of [(L(3) Fe)2 (µ-η(4) :η(4) -P4 )] (2 c), possessing a cyclo-P4 moiety. Compounds 2 a-c were comprehensively characterized and their electronic structures investigated by SQUID magnetization and (57) Fe Mössbauer spectroscopy as well as by DFT methods.

Versatile structures of group 13 metal halide complexes with 4,4'-bipy: from 1D coordination polymers to 2D and 3D metal-organic frameworks.

A systematic structural study of complexes formed by aluminium and gallium trihalides with 4,4'-bipyridine (bipy) in 2 : 1, 1 : 1, and 1 : 2 stoichiometric ratios has been performed. Molecular structures of 11 complexes in the solid state have been determined for the first time. Complexes of 2 : 1 composition are molecular, while complexes of 1 : 1 composition form metal-organic frameworks of different kinds: an ionic 3D network (three interpenetrated lvt nets for AlCl3bipy), an ionic 2D network for AlBr3bipy and GaBr3bipy and a 1D coordination polymer in the case of GaCl3bipy. Thus, the nature of the Lewis acid plays a critical role in the structural type of the complex in the solid state. Incorporation of excess bipy molecules into (GaCl3bipy)∞ (formation of crystallosolvate) leads to an unprecedented change of the molecular structure from a non-ionic 1D coordination polymer to an ionic 2D metal organic framework [GaCl2bipy2](+)[GaCl4](-)·2bipy. As indicated by the temperature-dependent XRD study, removal of bipy by heating in a vacuum restores the non-ionic 1D structure. Quantum chemical computations for simple cluster model systems (up to eight Al and Ga atoms) reveal that ionic forms are slightly favourable, although the energy differences between the ionic and non-ionic structures are not large. These theoretical predictions are in good agreement with experimental findings. Thus, even relatively simple cluster models may be used to indicate the structural preferences in the solid state. Both experimental and computational IR frequency shifts of the in-plane ring bending mode of bipy upon complexation correlate well with the M-N bond distances in the complexes.

Do solid-state structures reflect Lewis acidity trends of heavier group 13 trihalides? Experimental and theoretical case study.

Lewis acidity trends of aluminum and gallium halides have been considered on the basis of joint X-ray and density functional theory studies. Structures of complexes of heavier group 13 element trihalides MX(3) (M = Al, Ga; X = Cl, Br, I) with monodentate nitrogen-containing donors Py, pip, and NEt(3) as well as the structure of the AlCl(3)·PPh(3) adduct have been established for the first time by X-ray diffraction studies. Extensive theoretical studies (B3LYP/TZVP level of theory) of structurally characterized complexes between MX(3) and nitrogen-, phosphorus-, arsenic-, and oxygen-containing donor ligands have allowed us to establish the Lewis acidity trends Al > Ga, Cl ≈ Br > I. Analysis of the experimental and theoretical results points out that the solid state masks the Lewis acidity trend of aluminum halides. The difference in the Al-N bond distances between AlCl(3)·D and AlBr(3)·D complexes in the gas phase is small, while in the condensed phase, shorter Al-N distances for AlBr(3)·D complexes are observed with 9-fluorenone, mdta, and NEt(3) donors. The model based on intermolecular (H···X) interactions in solid adducts is proposed to explain this phenomenon. Thus, the donor-acceptor bond distance in the solid complexes cannot always be used as a criterion of Lewis acidity.

Reciprocal interactions between MK-801, sleep deprivation and recovery in modulating rat behaviour.

Increasing evidence indicates that sleep deprivation alters behavioural responses to various pharmacological agents which might be associated to changes in receptor systems. The present work addressed the effects of sleep deprivation and recovery on behavioural changes induced by MK-801, and investigated whether such effects are related to changes in NMDA receptor (NMDAR) binding. Male Wistar rats were deprived of sleep for 96 h using the platform method (SD group), or were sleep deprived and then allowed to recover sleep for 24 h (SR group). Animals were treated with saline or 0.05, 0.10 or 0.20 mg/kg MK-801 before testing in an open field arena and elevated plus maze. A separate set of animals was sacrificed for [³H]MK-801 binding analysis in 40 brain regions. MK-801-induced hyperlocomotion was facilitated in a dose-dependent fashion after SR, while SD-induced increase in grooming was antagonized by the drug. Anxiolytic effects of 0.05 and 0.10 mg/kg MK-801 were unaffected by SD or SR conditions. No significant differences among groups were found in NMDAR binding. These findings indicate that the combined effects of MK-801 and sleep deprivation and recovery interact in a complex fashion to affect rat behaviour. They further suggest that such effects cannot be attributed to altered NMDAR binding in brain.

Ethanol-induced behavioral sensitization is associated with dopamine receptor changes in the mouse olfactory tubercle.

Accumulating evidence points to the mesolimbic and the nigrostriatal dopamine systems as critical to behavioral sensitization induced by several drugs of abuse. In the present study, we analyzed D1 and D2 binding to brain regions related to these dopaminergic systems during the expression of ethanol-induced behavioral sensitization. The first experiment was performed to demonstrate the effectiveness of the ethanol treatment schedule and challenge used to induce the expression of the behavioral sensitization phenomenon. The second experiment was conducted to study D1 and D2 alterations in several brain regions during the expression of this phenomenon. Mice were ip treated with ethanol or saline for 21 consecutive days and 24 h after the last injection they received an ethanol or a saline challenge injection. Five minutes later, the animals were observed in an open-field for locomotion quantification or were sacrificed and their brains were submitted to autoradiographic binding analyses. No differences among the groups were found for D1 binding levels in all the brain regions analyzed. However, ethanol-sensitized mice showed reduced levels of D2 binding in the olfactory tubercle when compared to the other groups. Our data suggest that D2 receptor changes in the olfactory tubercle seem to play an important role in the expression of ethanol-induced behavioral sensitization.

Beneficial effects of vitamin C and vitamin E on reserpine-induced oral dyskinesia in rats: critical role of striatal catalase activity.

Oral dyskinesias are implicated in a series of neuropathologies and have been associated to an increase in oxidative stress. Several antioxidants, including vitamin E, decrease reserpine-induced oral dyskinesia (OD) in rodents and we have described a protective role of striatal catalase against the development of OD. The aim of this study was to verify the effects of vitamin C alone or in combination with vitamin E on reserpine-induced OD as well as to determine a possible role of catalase in the antidyskinetic property of these vitamins. Different doses of vitamin C attenuated reserpine-induced increase in OD. A similar treatment with an effective dose of vitamin C concomitant to an effective dose of vitamin E potentiated the antidyskinetic effect of both vitamins when administered alone. The administration of these vitamins alone produced an increase in striatal catalase activity that likewise was potentiated by their combined administration. In addition, the antidyskinetic property of vitamin E and vitamin C was abolished by a concomitant treatment with the catalase inhibitor aminotriazole. These results indicate a beneficial effect of these vitamins and reinforce the critical role of striatal catalase against the development of oral dyskinesias.