Host–guest supramolecular interactions in the coordination compounds of 4,4′-azobis(pyridine) with MnX2(X = NCS–, NCNCN–, and PF6–): structural analyses and theoretical study

Three new Mn(II) coordination compounds {[Mn(NCNCN)2(azpy)]·0.5azpy}n (1), {[Mn(NCS)2(azpy)(CH3OH)2]·azpy}n (2), and [Mn(azpy)2(H2O)4][Mn(azpy)(H2O)5]·4PF6·H2O·5.5azpy (3) (where azpy = 4,4'-azobis-(pyridine)) have been synthesized by self-assembly of the primary ligands, dicyanamide, thiocyanate, and hexafluorophosphate, respectively, together with azpy as the secondary spacer. All three complexes were characterized by elemental analyses, IR spectroscopy, thermal analyses, and single crystal X-ray crystallography. The structural analyses reveal that complex 1 forms a two-dimensional (2D) grid sheet motif These sheets assemble to form a microporous framework that incorporates coordination-free azpy by host-guest pi center dot center dot center dot pi. and C-H center dot center dot center dot N hydrogen bonding interactions. Complex 2 features azpy bridged one-dimensional (ID) chains of centrosymmetric [Mn(NCS)(2)(CH3OH)(2)} units which form a 2D porous sheet via a CH3 center dot center dot center dot pi supramolecular interaction. A guest azpy molecule is incorporated within the pores by strong H-bonding interactions. Complex 3 affords a 0-D motif with two monomeric Mn(II) units in the asymmetric unit. There exist pi center dot center dot center dot pi, anion center dot center dot center dot pi, and strong hydrogen bonding interactions between the azpy, water, and the anions. Density functional theory (DFT) calculations, at the M06/6-31+G* level of theory, are used to characterize a great variety of interactions that explicitly show the importance of host-guest supramolecular interactions for the stabilization of coordination compounds and creation of the fascinating three-dimensional (3D) architecture of the title compounds.

Effect of anionic co-ligands on structure and magnetic coupling of bis(μ-phenoxo-bridged dinuclear copper(II) complexes

Two phenoxo bridged dinuclear Cu(II) complexes, [Cu2L2(NO2)(2)] (1) and [Cu2L2(NO3)(2)] (2) have been synthesized using the tridentate reduced Schiff-base ligand 2-[(2-dimethylamino-ethylamino)-methyl]-phenol (HL). The complexes have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. The structures of the two compounds are very similar having the same tridentate chelating ligand (L) and mono-dentate anionic ligand nitrite for 1 and nitrate for 2. In both complexes Cu(II) is penta-coordinated but the square pyramidal geometry of the copper ions is severely distorted (Addison parameter (tau) = 0.33) in 1 while the distortion is quite small (average tau = 0.11) in 2. These differences have marked effect on the magnetic properties of two compounds. Although both are antiferromagnetically coupled, the coupling constants (J = -140.8 and -614.7 cm (1) for 1 and 2, respectively) show that the coupling is much stronger in 2.

Peroxidative bromination and oxygenation of organic compounds: synthesis, X-ray crystal structure and catalytic implications of mononuclear and binuclear oxovanadium(V) complexes containing Schiffbase ligands

Treatment of of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H(2)L(1)) in methanol with aqueous NH(4)VO(3) solution in perchloric acid medium affords the mononuclear oxovanadium(V) complex [VOL(1)(MeOH)]-ClO(4) (1) as deep blue solid while the treatment of same solution of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H(2)L(1)) with aqueous solution of VOSO(4) leads to the formation of di-(mu-oxo) bridged vanadium(V) complex [VO(2)L(2)](2) (2) as green solid where HL(2) = (R,R)-N-salicylidene cyclohexane 1,2-diamine. The ligand HL(2) is generated in situ by the hydrolysis of one of the imine bonds of HL(1) ligand during the course of formation of complex [VO(2)L(2)](2) (2). Both the compounds have been characterized by single crystal X-ray diffraction as well as spectroscopic methods. Compounds 1 and 2 are to act as catalyst for the catalytic bromide oxidation and C-H bond oxidation in presence of hydrogen peroxide. The representative substrates 2,4-dimethoxy benzoic acid and para-hydroxy benzoic acids are brominated in presence of H(2)O(2) and KBr in acid medium using the above compounds as catalyst. The complexes are also used as catalyst for C-H bond activation of the representative hydrocarbons toluene, ethylbenzene and cyclohexane where hydrogen peroxide acts as terminal oxidant. The yield percentage and turnover number are also quite good for the above catalytic reaction. The oxidized products of hydrocarbons have been characterized by GC Analysis while the brominated products have been characterized by (1)H NMR spectroscopic studies.

Synthesis, crystal structures and magnetic properties of a phenoxo-bridged dinuclear Cu(II) complex and a dicyanamide bridged novel molecular rectangle based on it

The phenoxo-bridged dinuclear Cu-II complex [Cu2L2-(NCNCN)(2)] (1) and the dicyanamide-bridged molecular rectangle [Cu4L4{mu(1,5)-(NCNCN)(2)}]center dot(ClO4)(2)(H2O)(2) (2) were synthesized using the tridentate reduced Schiff-base ligand HL {2-[(2-dimethylamino-ethylamino) methyl] phenol}. The complexes were characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Complex 2 was formed through the joining of the phenoxo-bridged dinuclear Cu2O2 cores of 1 via the mu(1,5)-bridging mode of dicyanamide. The structural properties of the Cu2O2 cores in two complexes are significantly different. The geometry of the copper ions is distorted trigonal bipyramid in 1 but is nearly square-pyramidal in 2. These differences have a marked effect on the magnetic properties of two compounds. Although both are antiferromagnetically coupled, the coupling constants (J = -185.2 and -500.9 cm(-1) for 1 and 2, respectively) differ considerably.

Synthesis and Electronic Structure of Dissymmetrical, Naphthalene-Bridged Sandwich Complexes [Cp′Fe(μ‑C10H8)MCp*]x (x = 0, +1; M =Fe, Ru; Cp′ = η5‑C5H2‑1,2,4‑tBu3; Cp* = η5‑C5Me5)

The dissymmetrical naphthalene-bridged complexes [Cp′Fe(μ-C10H8)FeCp*] (3; Cp* = η5-C5Me5, Cp′ = η5-C5H2-1,2,4-tBu3) and [Cp′Fe(μ-C10H8)RuCp*] (4) were synthesized via a one-pot procedure from FeCl2(thf)1.5, Cp′K, KC10H8, and [Cp* FeCl(tmeda)] (tmeda = N,N,N′,N′- tetramethylethylenediamine) or [Cp*RuCl]4, respectively. The symmetrically substituted iron ruthenium complex [Cp*Fe(μ-C10H8)RuCp*] (5) bearing two Cp* ligands was prepared as a reference compound. Compounds 3−5 are diamagnetic and display similar molecular structures, where the metal atoms are coordinated to opposite sides of the bridging naphthalene molecule. Cyclic voltammetry and UV/vis spectroelectrochemistry studies revealed that neutral 3−5 can be oxidized to monocations 3+−5+ and dications 32+−52+. The chemical oxidation of 3 and 4 with [Cp2Fe]PF6 afforded the paramagnetic hexafluorophosphate salts [Cp′Fe(μ-C10H8)FeCp*]PF6 ([3]PF6) and [Cp′Fe(μ-C10H8)RuCp*]PF6 ([4]PF6), which were characterized by various spectroscopic techniques, including EPR and 57Fe Mössbauer spectroscopy. The molecular structure of [4]PF6 was determined by X-ray crystallography. DFT calculations support the structural and spectroscopic data and determine the compositions of frontier molecular orbitals in the investigated complexes. The effects of substituting Cp* with Cp′ and Fe with Ru on the electronic structures and the structural and spectroscopic properties are analyzed.

Binuclear zinc(II) complexes with the anti-inflammatory compounds salicylaldehyde semicarbazone and salicylaldehyde-4-chlorobenzoyl hydrazone (H(2)LASSBio-1064)

Complexes [Zn(2)(HL(1))(2)(CH(3)COO)(2)] (1) and [Zn(2)(L(2))(2)] (2) were synthesized with salicylaldehyde semicarbazone (H(2)L(1)) and salicylaldehyde-4-chlorobenzoyl hydrazone (H(2)LASSBio-1064, H(2)L(2)), respectively. The crystal structure of (1) was determined. Upon recrystallization of previously prepared [Zn(2)(HL(2))(2)(Cl)(2)] (3) in 1:9 DMSO:acetone crystals of [Zn(2)(L(2))(2)(H(2)O)(2)]center dot[Zn(2)(L(2))(2)(DMSO)(4)] (3a) were obtained. The crystal structure of 3a was also determined. All crystal structures revealed the presence of phenoxo-bridged binuclear zinc(II) complexes. (C) 2011 Elsevier Ltd. All rights reserved.

Dinuclear Azide-Bridged Copper(II) Complex as Building Block for the Assembly of a 2D-Supramolecular Array

A novel Schiff base-copper(II) complex [Cu(2)L(2)(N(3))(2)](ClO(4))(2) 1, where L = (4-imidazolyl)ethylene-2-amino-1-ethylpyridine (apyhist), containing azide-bridges between adjacent copper ions in a dinuclear arrangement was isolated and characterized both in the solid state and in solution by X-ray crystallography and different spectroscopic techniques. Azide binding constants were estimated from titrations of the precursor [CuL(H(2)O)(2)](2+) solutions with sodium azide, giving rise to the azido-bridged species, [Cu(2)L(2)(N(3))(2)](2+). Raman spectra showed asymmetric stretching band at 2060 cm(-1), indicating the presence of azido ligands with a symmetric mu(1,) (1) binding geometry. EPA spectra, in frozen methanol/water solutions at 77 K, exhibited characteristic features of copper centers in tetragonal pyramidal coordination geometry, exhibiting magnetic interactions between them. Further, in solid state, two different values for magnetic coupling in this species were obtained, J/k = -(5.14 +/- 0.02) cm(-1) attributed to the mu(1, 1) azide-bridge mode, and J`z`/k = -(2.94 +/- 0.11) cm(-1) for the interaction between dinuclear moieties via water/perchorate bridges. Finally, an attempt was made to correlate structure and magnetic data for this dinuclear asymmetric end-on azido bridged-copper(II) 1 complex with those of another correlated dinuclear system, complex [Cu(2)L(2)Cl(2)](ClO(4))(2) 2, containing the same tridentate diimine ligand, but with chloro-bridged groups between the copper centres.

Synthesis, spectroscopic characterization and radiosensitizing properties of acetato-bridged copper(II) complexes with 5-nitroimidazole drugs

Three novel acetato-bridged dinuclear copper(II) complexes with 5-nitroimidazoles (CuAcNtrim) and the known copper-acetato-metronidazole have been prepared by an environment-friendly route and spectroscopically characterized. The CuAcNtrim compounds of formula [Cu(2)(mu-O(2)CCH(3))(4)Ntrim(2)], where Ntrim = metronidazole (1), secnidazole (2), tinidazole (3) or nimorazole (4), exhibit dimeric copper-acetato paddle-wheel structures with Ntrim axial ligands coordinated to copper(II) ions through the N(3) atoms of the imidazole rings. EPR data indicate antiferromagnetic behavior for this novel series of copper complexes. The constant coupling has been found to decrease along with the increasing of basicity of the Ntrim axial ligand. The CuAcNtrim complexes and the correspondent Ntrim parent drugs have shown radiosensitizer properties for Hep2 (human larynx cancer) cell line in vitro. The best enhancement of radiosensitizer activity upon coordination of the Ntrim drug to copper(II) has been found for the nimorazole compound which has the strongest Cu-Ntrim bond and exhibits the highest lipophilicity within the series of CuAcNtrim complexes. (C) 2010 Elsevier B.V. All rights reserved.

Extension ladders - synthesis and characterisation of new spacer-bridged tetraorganodistannoxanes

Preliminary results are described on the synthesis and characterization of novel spacer-bridged tetraorganodistannoxanes, {[[R(Cl)Sn]₂(CH₂)₂]O}₄ (n = 5 &ndash; 8, 10, 12; R = CH₂SiMe₃) containing particularly long organic spacers. In the solid state, these compounds reveal typical double-ladder structures with eight tin atoms per molecule, whereas in solution a partial and reversible rearrangement takes place to form tetraorganodistannoxanes, {[[R(Cl)Sn]₂(CH₂)_n]O}₂ (n = 5 &ndash; 8, 10, 12; R = CH₂SiMe₃), having four tin atoms per molecule.<br />

Synthesis and structure of new oligomethylene-bridged double ladders. How far can the layers be separated?

The synthesis of the &alpha;,&omega;-bis[dichloro(trimethylsilylmethyl)stannyl]alkanes, (Me₃SiCH₂)C1₂Sn(CH₂)_<i>n</i>SnCl₂(CH₂SiMe₃) (<b>13</b>, <i>n</i>=5; <b>14</b>, <i>n</i>=6; <b>15</b>, <i>n</i>=7; <b>16</b>, <i>n</i>=8; <b>17</b>, <i>n</i>=10; <b>18</b>, <i>n</i>=12) and the corresponding oligomethylene-bridged diorganotin oxides [(Me₃SiCH₂)(O)Sn(CH₂)_<i>n</i>Sn(O)(CH₂SiMe₃)]_<i>m</i> (<b>19</b>, <i>n</i>=5; <b>20</b>, <i>n</i>=6; <b>21</b>, <i>n</i>=7; <b>22</b>, <i>n</i>=8; <b>23</b>, <i>n</i>=10; <b>24</b>; <i>n</i>=12) is reported. The reaction of the diorganodichlorostannanes <b>13&ndash;18</b> with the corresponding diorganotin oxides <b>19&ndash;24</b> provided the spacer-bridged tetraorganodistannoxanes {[(Me₃SiCH₂)ClSn(CH₂)_<i>n</i>SnCl(CH₂SiMe₃)]O}₄ (<b>25</b>, <i>n</i>=5; <b>26</b>, <i>n</i>=6; <b>27</b>, <i>n</i>=7; <b>28</b>, <i>n</i>=8; <b>29</b>, <i>n</i>=10; <b>30</b>, <i>n</i>=12). Compounds <b>13&ndash;30</b> have been identified by elemental analyses and multinuclear NMR spectroscopy. Compounds <b>25, 27, 29</b> and <b>30</b> have also been characterised by single crystal X-ray diffraction analysis and electrospray mass spectrometry. For the latter the essential double ladder motif is maintained for all <i>n</i> in the solid state, but subtle changes in alignment of the ladder planes occur. Separation between the two layers of the double ladder ranges from approx. 8.7&nbsp; &Aring; (for <b>25</b>, <i>n</i>=5) to approx. 15 &Aring; (for <b>30</b>, <i>n</i>=12). In solution there is some dissociation of the double ladders into the corresponding dimers. The degree of dissociation is favoured by increasing oligomethylene chain length <i>n</i>.<br /><br /><br />

Oligomethylene-bridged dinuclear triorganotin triflates and diphenylphosphinates. Ion pairing in the solid state and electrolytic dissociation in solution of [Ph2Sn(CH2)nSnPh2X](O3SCF3) (X = OH, O2PPh2; n = 1-3)

The condensation of [Ph₂(OH)Sn(CH₂)<i>_n</i>Sn(OH)Ph₂] (<b>1-3</b>; <i>n</i> = 1-3) with HO₃SCF₃ and HO₂PPh₂ provided [Ph₂Sn(CH₂)_<i>n</i>SnPh₂(OH)](O₃SCF₃) (<b>4-6</b>; <i>n</i> = 1-3) and [Ph₂(O₂PPh₂)Sn(CH₂)_<i>n</i>Sn(O₂PPh₂)Ph₂] (<b>10-12</b>; <i>n</i> = 1-3), respectively. The reaction of [Ph₂Sn(CH₂)_<i>n</i>SnPh₂(OH)](O₃SCF₃) (<b>4-6</b>; <i>n</i> = 1-3) with HO₂PPh₂ and NaO₂PPh₂ gave rise to the formation of [Ph₂Sn(CH₂)_<i>n</i>SnPh₂(O₂PPh₂)](O₃SCF₃) (<b>7-9</b>; <i>n</i> = 1-3) and [Ph₂(OH)Sn(CH₂)_<i>n</i>Sn(O₂PPh₂)Ph₂] (<b>13-15</b>; _<i>n</i> = 1-3), respectively. In the solid state, compounds <b>4-9</b> comprise ion pairs of cationic cyclo-[Ph₂SnCH₂SnPh₂(OH)]₂²⁺, cyclo-[Ph₂Sn(CH₂)<i>_n</i>SnPh₂(OH)]⁺ (<i>n</i> = 2, 3), and cyclo-[Ph₂Sn(CH₂)_<i>n</i>SnPh₂(O₂PPh₂)]⁺ (<i>n</i> = 1-3) and triflate anions. In MeCN, the eight-membered-ring system cyclo-[Ph₂SnCH₂SnPh₂(OH)]₂²⁺ appears to be in equilibrium with the four-membered-ring system cyclo-[Ph₂SnCH₂SnPh₂(OH)]⁺. In contrast, compounds <b>10-15</b> show no ionic character. Compounds <b>1-15</b> were characterized by multinuclear NMR spectroscopy in solution and in the solid state, IR spectroscopy, conductivity measurements, electrospray mass spectrometry, osmometric molecular weight determinations, and X-ray crystallography (<b>4, 5, 7,</b> and <b>12</b>). <br /><br />

Incorporation of group 14 elements into siloxane-bridged paracyclophanes cyclo-[p,p´-Me2SiC6H4EMe2C6H4SiMe2O]2 (E = C, Si, Ge, Sn)§

The bis(arylene silanes) <i>p,p'</i>-HMe₂SiC₆H₄EMe₂C₆H₄SiMe₂H (E = C (<b>10</b>), Si (<b>11</b>), Ge (<b>12</b>), Sn(<b>13</b>)) were prepared by the in situ Grignard reaction of <i>p,p'</i>-BrC₆H₄CMe₂C₆H₄Br, Mg turnings, and HSiMe₂Cl (for <b>10</b>) and the Grignard reaction using <i>p</i>-HMe₂SiC₆H₄Br, Mg turnings, and Me₂ECl₂ (E = Si for <b>11</b>, Ge for <b>12</b>, Sn for <b>13</b>). The oxidation of <b>10-13 </b>using Pearlman's catalyst, Pd(OH)₂/C, in aqueous THF provided the bis(arylene silanols) <i>p,p'</i>-HOMe₂SiC₆H₄EMe₂C₆H₄SiMe₂OH (E = C (<b>14</b>), Si (<b>15</b>), Ge (<b>16</b>), Sn(<b>17</b>)). The HCl-catalyzed condensation of <b>14-17</b> in highly diluted solutions of acetone/water afforded the siloxane-bridged paracyclophanes cyclo-[<i>p,p'</i>-Me₂SiC₆H₄EMe₂C₆H₄SiMe₂O]₂ (<b>6-9</b>) that incorporate the group 14 elements E = C, Si, Ge, and Sn. Compounds<b> 6-17</b> were investigated by multinuclear solution and solid-state NMR spectroscopy and <b>6</b> and <b>9</b> also by X-ray crystallography.<br />

The first spacer-bridged tetraorganodistannoxanes with a mixed double ladder structure

The reaction of Me₃SiCH₂Cl₂Sn(CH₂)₃SnCl₂Ph (<b>6</b>) with (<i>t</i>Bu₂SnO)₃ gave a statistical mixture of the corresponding tetraorganodistannoxanes whereas the reaction of the spacer-bridged ditin tetrachlorides RCl₂Sn(CH₂)₄SnCl₂R (<b>3</b>, R = Me₃CCH₂; <b>4</b>, R = Me₂CHCH₂; <b>10</b>, R = Me₃SiCH₂) with the polymeric spacer-bridged ditin oxides [R(O)Sn(CH₂)₄Sn(O)R]_<i>n</i> (<b>7</b>, R = Me₂CHCH₂; <b>8</b>, R = Me₃CCH₂; <b>11</b>, R = Me₃SiCH₂) provided the mixed double ladder compounds {[R(Cl)Sn(CH₂)₄Sn(Cl)R][R(Cl)Sn(CH₂)₄Sn(Cl)R']O₂}₂ (<b>9</b>, R = Me₃CCH₂, R' = Me₂CHCH₂; <b>12</b>, R = Me₃CCH₂, R' = Me₃SiCH₂) in almost quantitative yield. In solution, <b>9</b> and <b>12</b> are in equilibrium with their corresponding dimers, as was evidenced by ¹¹⁹Sn NMR spectroscopy, molecular mass determination, and electrospray mass spectrometry. The molecular structures of <b>9</b> and <b>12</b> were established by single crystal X-ray diffraction.<br />

Trimethylene-bridged tetraorganodistannoxanes{[Me3SiCH2(RCOO)Sn(CH2)3Sn(OOCR)CH2SiMe3]O}n(R=Ph,2,4-Me2C6H3): control of structure by variation of R*

The synthesis of trimethylene-bridged carboxylate-substituted tetraorganodistannoxanes {[Me_3SiCH_2(RCOO)Sn(CH_2)_3Sn(OOCR)CH_2SiMe_3]O}_n (1, R = Ph; 2, R = 2,4-Me_2C_6H_3) is reported. Depending on the structure of R, in the solid state these compounds are either dimers (1, n = 2, cis-isomer) with a ladder-type structure or tetramers (2, n = 4) with a double ladder-type structure.<br /><br /><br />

Comparison of tissue dosimetry in the mouse following chronic exposure to arsenic compounds

Several chronic bioassays have been conducted in multiple strains of mice in which various concentrations of arsenate or arsenite were administered in the drinking water without a tumorigenic effect. However, one study (Ng et al., 1999) reported a significant increase in tumor incidence in C57Bl/6J mice exposed to arsenic in their drinking water throughout their lifetime, with no tumors reported in controls. A physiologically based pharmacokinetic model for arsenic in the mouse has previously been developed (Gentry et al., 2004) to investigate potential differences in tissue dosimetry of arsenic species across various strains of mice. Initial results indicated no significant differences in blood, liver, or urine dosimetry in B6C3F1 and C57Bl/6 mice for acute or subchronic exposure. The current work was conducted to compare model-predicted estimates of tissue dosimetry to additional kinetic information from the (C57Bl/6 x CBA)F1 and TgAc mouse. The results from the current modeling indicate that the pharmacokinetic parameters derived based on information in the B6C3F1 mouse adequately describe the measured concentrations in the blood/plasma, liver, and urine of both the (C57Bl/6 x CBA)F1 and TgAc mouse, providing further support that the differences in response observed in the chronic bioassays are not related to strain-specific differences in pharmacokinetics. One significant finding was that no increases in skin or lung concentrations of arsenic species in the (C57Bl/6 x CBA)F1 strain were observed following administration of low concentrations (0.2 or 2 mg/L) of arsenate in the drinking water, even though differences in response in the skin were reported. These data suggest that pharmacodynamic changes may be observed following exposure to arsenic compounds without an observable change in tissue dosimetry. These results provided further indirect support for the existence of inducible arsenic efflux in these tissues. <br />