Synthesis,molecular structure and reactivity of new biferrocenylpropane derivatives

New biferrocenylpropane derivatives FcC(CH₃)₂Fc′-C≡C–R [Fc?=?C₅H₅FeC₅H₄; Fc′?=?C₅H₅FeC₅H₃, R?=?C₆H₅ (L ₁ ), Fc (L ₂ )] and their complexes [FcC(CH₃)₂Fc′-C≡C–R][Co₂(CO)₆] [R?=?C₆H₅ (1); R?=?Fc (2)] have been synthesized by the Castro-Stephens coupling reaction and the reactions of ligands L ₁ , L ₂ with Co₂(CO)₈. Compounds L ₁ , L ₂ , 1 and 2 were characterized by elemental analysis, IR, ¹H (¹³C) NMR and MS, and the molecular structures of ligands L ₁ , L ₂ were determined by X-ray single crystal analysis. The electrochemical properties of L ₁ , L ₂ , 1 and 2 demonstrate two or three resolved one-electron redox processes.     

Polymerizations of methyl methacrylate and rac-lactide by zinc(II) precatalyst containing N-substituted 2-iminomethylpyridine and 2-iminomethylquinoline

The reaction of [ZnCl₂] with N-cyclopentyl-1-(quinolin-2-yl)methanimine (L_A), N-cyclohexyl-1-(quinolin-2-yl)methanimine (L_B), N-cyclohexyl-1-(pyridin-2-yl)methanimine (L_C), 2,6-diethyl-N-(pyridin-2-ylmethylene)aniline (L_D), N-cyclopentyl-1-(pyridin-2-yl)methanimine (L_E), and N-phenyl-(pyridin-2-yl)methanimine (L_F) in ethanol produced the bidentate [(NN′)ZnCl₂] complexes, [L_AZnCl₂], [L_BZnCl₂], [L_CZnCl₂], [L_DZnCl₂], [L_EZnCl₂] and [L_FZnCl₂], respectively. The molecular structures revealed that the zinc in [L_nZnCl₂] (L_n = L_A ? L_D) showed a distorted tetrahedral geometry involving two nitrogens of N,N’-bidentate ligands and two chloride ligands. Most of these initiators were effective for polymerization of methyl methacrylate (MMA) and polymerization of rac-lactide (rac-LA). [L_CZnCl₂] (with N-cyclohexyl substituted at imine-pyridine moiety) exhibited the highest catalytic activity for MMA polymerization in the presence of modified methylaluminoxane (MMAO) with an activity of 3.33 × 10⁴ g PMMA/mol·Zn·h at 60 °C, giving moderate syndiotactic poly methyl methacrylate (PMMA) with high molecular weight (9.62 × 10⁵ g/mol). The dimethyl derivatives [L_nZnMe₂] (L_n = L_A ? L_F), generated in situ, polymerized rac-LA with moderate activity and yielded a polylactide (PLA) with good number-average molecular weights and narrower polydispersity indices (PDIs). [L_AZnMe₂] effectively initiates the ring-opening polymerization (ROP) of rac-LA to attain heterotactic PLA (P_r = 0.91).     

Synthesis and structural characterization of new multiferrocenyl diyne ligands and their cobalt carbonyl complexes

New multiferrocenyl diyne ligands FcC(CH₃)₂Fc′–C≡C–C≡C–Fc [L ₁ ; Fc?=?C₅H₅FeC₅H₄; Fc′?=?C₅H₅Fe(1,3-disubstituted)C₅H₃], FcC(CH₃)₂Fc′–C≡C–C≡C–Fc′C(CH₃)₂Fc (L ₂ ) and their complexes [FcC(CH₃)₂Fc′–C≡C–C≡C–Fc][Co₂(CO)₆] _n [n?=?1, (1); n?=?2, (2)], [FcC(CH₃)₂Fc′–C≡C–C≡C–Fc′C(CH₃)₂Fc][Co₂(CO)₆] _n [n?=?1, (3); n?=?2, (4)] have been synthesized by the coupling reaction of terminal ferrocenylacetylene and the reaction of ligands L₁ and L₂ with Co₂(CO)₈. The composition and molecular structure of the ligands L₁ , L₂ and their cobalt complexes were characterized by element analysis, IR, ¹H(¹³C)NMR and MS. The electrochemical properties of compounds L₁ , L₂ , 1, 2, 3, 4 were studied by cyclic voltammetry(CV). The results of the electrochemical research reveal that all three ferrocenyl groups in L₁ become redox active centers, but there are only two (not four) ferrocenyl redox active centers in L₂ .     

Coordination polymers of lanthanides incorporating N,N′-ethylenebis(2-hydroxy-1-naphthylideneiminato): syntheses and crystal structures

Reaction of Ln(NO₃)₃?·?6H₂O with H₂napn (H₂napn?=?N,N′-ethylenebis(2-hydroxy-1-naphthylideneiminato)) and KSCN produces seven new coordination polymers, [La(H₂napn)(SCN)(C₂H₅OH)₂(NO₃)₂] _n (1), [La(H₂napn)₂(SCN)(NO₃)₂] _n (2), and [Ln(H₂napn)_1.5(NO₃)₃] _n [Ln?=?La(3), Sm(4), Eu(5), Dy(6), Er(7)]. Crystal structure analysis reveals that H₂napn functions as a bridging ligand, forming a 1-D chain polymer (1) and 2-D open-frameworks (2–7) with lanthanides. Each metal center of 1–7 is nine-coordinate. Lanthanide contraction is observed in 3–7.     

Electronic states of XC<Subscript>3</Subscript>H<Subscript>3</Subscript>Si five-membered rings (X = CH,N, P,and As)

Stable configurations of XC₃H₃Si five-membered rings, 1 _X and 2 _X (X = CH, N, P, and As) in the singlet and triplet states are found at B3LYP/6-311++G** level of theory. All the singlet states of 1 _X and 2 _X have lower potential energy than the triplet state. The ΔG _s−t differences between the singlet and triplet states of 1 _X and 2 _X changes at the B3LYP/6-311++G** level in the order (in kcal/mol): 1 _N (−17.56) > 1 _CH (−15.26) > 1 _P (−4.96) > 1 _As (−3.45) and 2 _CH (−15.26) > 2 _N (−9.21) > 2 _P (−7.39) > 2 _As (−6.15), respectively.     

X-ray structures of cobalt(III) complexes with bio-relevant pyrazolyl thiosemicarbazone: Indication of structural changes on the increasing bulkiness of the alkyl substituents on thiosemicarbazone moiety

X-ray crystallographic studies of cobalt(III) complexes of 5-methyl-3-formylpyrazole-N(4)-diethylthiosemicarbazone (HMP_zNEt₂), [Co(MP _z NEt ₂ ) ₂ ]Br·2H ₂ O, 5-methyl-3-formylpyrazole-N(4)-dipropylthiosemicarbazone (HMP_zNPr ₂ ), [Co(MP _z NPr ₂ ) ₂ ]Br·2H ₂ O and 5-methyl-3formylpyrazole-N(4)-dibutylthiosemicarbazone (HMP_zNBu ₂ ), [Co(MP _z NBu ₂ ) ₂ ]Br·H ₂ O, have been reported. In all the three complex species, X-ray crystallography has authenticated a CoN₄S₂ octahedral coordination with the pair of orthogonally coordinated NNS tridentate ligands in the monodeprotonated form of the ligand. The two azomethine nitrogen atoms are trans to each other, while the pyrazolyl ring nitrogens and the thiolato sulfurs are in cis positions. A gradual decrease in the dihedral angle between the coordinating ligands has been observed with increase in the bulkiness of the aliphatic side chains of the substituent on the thiosemicarbazone moieties. In all the three complexes, intraligand C–H···S contacts appear to arrest the free rotation of the side chains about the C(6)–N(5) single bond. ^†Deceased     

Aqua substitution from mononuclear Pt(II) complexes with 2-(pyrazol-1-ylmethyl)quinoline non-leaving ligands

The rates of aqua substitution from [Pt{2-(pyrazol-1-ylmethyl)quinoline}(H₂O)₂](ClO₄)₂, [Pt(H₂Qn)], [Pt{2-(3,5-dimethylpyrazol-1-ylmethyl)quinoline}(H₂O)₂](ClO₄)₂, [Pt(dCH₃Qn)], [Pt{2-[(3,5-bis(trifluoromethyl)pyrazol-1-ylmethyl]quinoline}(H₂O)₂](ClO₄)₂, [Pt(dCF₃Qn)], and [Pt{2-[(3,5-bis(trifluoromethyl)pyrazol-1-ylmethyl]pyridine}(H₂O)₂](ClO₄)₂, [Pt(dCF₃Py)], with three sulfur donor nucleophiles were studied. The reactions were followed under pseudo-first-order conditions as a function of nucleophile concentration and temperature using a stopped-flow analyzer and UV/visible spectrophotometry. The substitution reactions proceeded sequentially. The second-order rate constants for substituting the aqua ligands in the first substitution step increased in the order Pt(dCH₃Qn) < Pt(dCF₃Qn) < Pt(H₂Qn) < Pt(dCF₃Py), while that of the second substitution step was Pt(dCH₃Qn) < Pt(dCF₃Qn) < Pt(dCF₃Py) < Pt(H₂Qn). The reactivity trends confirm that the quinoline substructure in the (pyrazolylmethyl)quinoline ligands acts as an apparent donor of electron density toward the metal center rather than being a π-acceptor. Measured pK_a values from spectrophotometric acid–base titrations were Pt(H₂Qn) (pK_a1 = 4.56; pK_a2 = 6.32), Pt(dCH₃Qn) (pK_a1 = 4.88; pK_a2 = 6.31), Pt(dCF₃Qn) (pK_a1 = 4.07; pK_a2 = 6.35), and Pt(dCF₃Py) (pK_a1 = 4.76; pK_a2 = 6.27). The activation parameters from the temperature dependence of the second-order rate constants support an associative mechanism of substitution.     

Synthesis,structure and methyl methacrylate polymerization of cobalt(II), zinc(II) and cadmium(II) complexes with N,N′,N-bidentate versus N,N′,N-tridentate N,N′,N-bis((1H-pyrazol-1-yl)methyl)amines

Mononuclear Co(II), Zn(II) and Cd(II) complexes derived from bidentate or tridentate N,N′,N-bis((1H-pyrazol-1-yl)methyl)amines (L_n = L_A, L_B), where L_A is N,N-bis((1H-pyrazol-1-yl)methyl)-3-methoxypropan-1-amine and L_B is 3-methoxy-N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)propan-1-amine, have been synthesized and characterized. The geometry at Co(II) and Cd(II) for [L_ACoCl₂], [L_BCoCl₂] and [L_BCdBr₂] with N,N′,N-tridentate ligands (L_n = L_A, L_B) can be described as a distorted trigonal bipyramid achieved by coordinative interaction of N_pyrazole, two halides and the nitrogen of amine moiety. However, the molecular structure of four-coordinate [L_AZnCl₂] can be best described as tetrahedral, resulting in an eight-membered chelate ring. [L_ACoCl₂] polymerized methyl methacrylate in the presence of modified methylaluminoxane at 60 °C and resulted in poly(methylmethacrylate) (PMMA) with higher molecular weight and narrower polydispersity index compared to the other synthesized complexes. However, all the synthesized complexes yielded syndiospecific PMMA, characterized using ¹H NMR spectroscopy, with ca. 0.70.     

Synthesis,structural studies,and antibacterial activity of zinc,copper, and silver complexes derived from N′-(1-(pyrazin-2-yl)ethylidene)isonicotinohydrazide

The multidentate Schiff-base ligand N′-(1-(pyrazin-2-yl)ethylidene)isonicotinohydrazide (HL) has been prepared. Reaction with zinc, copper, and silver nitrate afford three complexes, [Zn(HL′)₂](NO₃)₂·3H₂O (1), {[Cu₂(L)₂(NO₃)(H₂O)₂]·NO₃}_n (2) and {[Ag₂(L)₂]·3H₂O}_n (3). These complexes have been characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. In 1, HL is a neutral tridentate ligand, whereas in 2 and 3, HL is a deprotonated tetradentate ligand. The hydrogen bonding interactions between NO₃^? and the host framework result in various supramolecular polymeric structures: a 2-D layer for 1 and 3-D network for 2 and 3. The antibacterial activities of these complexes have been investigated and the results indicate that 3 showed good antibacterial activities.     

Liquid crystalline guanidinium phenylalkoxybenzoates: towards room temperature liquid crystals via bending of the mesogenic core and the use of triflate counter ions

A series of guanidinium salts 1(C _n ) _m –4(C _n ) _m ?X bearing phenyl alkoxybenzoate cores have been synthesised and their mesomorphic properties have been investigated by polarising optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction experiments (small-angle X-ray scattering and wide-angle X-ray scattering). While compounds 1(C₁₂)₁?X and 3(C₁₂)₁?X with one alkoxy chain showed smectic A (SmA) phases irrespective of the counter ion, compounds 1(C₁₂)₂?OTf and 3(C₁₂)₂?OTf with two alkoxy chains displayed SmA phases and the corresponding chlorides 1(C₁₂)₂?Cl and 3(C₁₂)₂?Cl displayed Col_h. Guanidinium salts 1(C _n )₃–4(C _n )₃?X with three alkoxy chains showed Col_h phases. Whereas the use of cyclic guanidinium head groups rather than acyclic ones had only a minor influence on the mesophase properties, melting points were significantly decreased by bent core units instead of linear core units. Replacement of chloride counterions by triflate lead to a further depression of the clearing points and shifted the mesophase towards room temperature.     

Syntheses,structures, and fluorescent properties of three Zn(II) and Cu(II) complexes of different ligands derived from 3,6-bis(2-pyridyl)-1,2-dihydro-1,2,4,5-tetrazine

Three supramolecular complexes [Zn(HL₁ )₂(H₂O)₂(ZnCl₄)₂] (1), [Cu(L₂ )₂Cl₂] (2), and [Zn(L₃ )Cl₂] (3) have been synthesized and characterized by single crystal X-ray diffraction analysis (L₁ = 3,5-di(2-pyridyl)-4-amino-1,2,4-triazole, L₂ = 3,5-di(2-pyridyl)-1,2,4-triazole, and L₃ = 2-pyridinecarboxylic acid (pyridin-2-ylmethylene)-hydrazide). In 1, anion–π interactions between Cl^? and the π-systems of L₁ are observed and anion–π, hydrogen bonding and π–π stacking interactions link the two complex units of [Zn(HL₁ )₂(H₂O)₂]⁴⁺ and [ZnCl₄]^2? to form a 3-D supramolecular network. In 2, π–π stacking interactions between aromatic rings of 1,2,4-triazole and pyridine rings are observed; in 3, hydrogen bonding of Cl ··· H–N and π–π stacking interactions between parallel pyridine rings of L ₃ are observed. The mechanisms of rearrangement reactions of L to L₁ –L₃ are discussed. The fluorescent properties for solid 1 and 3 are also investigated.     

In quest of reversibility of Friedel-Crafts acyl rearrangements in the pyrene series

Friedel-Crafts acyl rearrangements in PPA of diacetylpyrenes (80–120 °C), dibenzoylpyrenes (80–200 °C), and bis(4-flurobenzoyl)pyrenes (80–120 °C) and Scholl reactions in AlCl₃/NaCl of dibenzoylpyrenes (140–200 °C) have been studied. The substrates were 1-AcPY, 2-AcPY, 1,3-Ac₂PY, 1,6-Ac₂PY, 1,8-Ac₂PY, 2,7-Ac₂PY, 1-BzPY, 1,6-Bz₂PY, 1,8-Bz₂PY, 1-4FBzPY, 1,6-4FBz₂PY, 1,8-4FBz₂PY. The mixtures of pyrene, 1-AcPY, 2-AcPY, 1,3-Ac₂PY, 1,6-Ac₂PY, 1,8-Ac₂PY, and 2,7-Ac₂PY were separated by HPLC. The following reversible intermolecular isomerizations were established: 1,6-Ac₂PY ? 1,8-Ac₂PY, 1,6-Bz₂PY ? 1,8-Bz₂PY, and 1,6-4'FBz₂PY ? 1,8-4'FBz₂PY, albeit not in high yields. The results substantiate Gore’s 1955 proposition that “The Friedel–Crafts acylation reaction of reactive aromatic hydrocarbons is a reversible process.” The isomerizations reported here differ from the few previously reported completely reversible intramolecular Friedel-Crafts acyl rearrangements. At ≥ 140 °C, in PPA and in AlCl₃/NaCl, 1,6-Bz₂PY and 1,8-Bz₂PY underwent a highly regioselective double Scholl reaction to give pyranthrone (3) and deacylations to 1-BzPy (and pyrene), followed by mono-Scholl reactions to give 8H-dibenzo[def,qr]chrysen-8-one (1), and 11H-indeno[2,1-a]pyren-11-one (2). The formation of 3 and not the expected tribenzo[a,ghi,o]perylene-7,16-dione (4) from 1,8-Bz₂PY indicates that 1,8-Bz₂PY has first undergone isomerization to 1,6-Bz₂PY. The present study confirms the linkage between Friedel-Crafts acyl rearrangements and the Scholl reaction.

     

Non-conventional multi-arm ester liquid crystal derived from cholic acid: synthesis,thermal and optical behaviour

ABSTRACT

With cholic acid as the core, five multi-arm ester liquid crystals were synthesised with different terminal substituents. B₁–B₅ were mesogenic arms which were linked to multifunctional chiral core cholic acid. The effect of electron-withdrawing and electron-donating groups on the mesogenic behaviour of the compounds was discussed. All products were structurally well characterised by elemental analysis, ¹HNMR, and FT-IR. The phase behaviours were investigated by means of polarised optical microscopy and differential scanning calorimetry. B₂, B₄, B₅ and C₂, C₄, C₅ and D₂, D₄, D₅ exhibited typical nematic texture and belonged to thermotropic enantiotropic nematic liquid crystals. B₃, C₃ and D₃ also displayed typical nematic texture of thermotropic monotropic nematic liquid crystal. B₁, C₁ and D₁ did not have mesogenic performance. Wider mesogenic range for 81.6°C of C₅ whose terminal substituent is nitro on heating cycle while 121.1°C on cooling cycle. The results indicated that terminal substituents have a pretty important effect on the mesogenic phase and range of multi-arm liquid crystal compounds. The mesomorphic behaviour of compounds with polar groups terminally substituted performance much better than those without polar groups. In this ester multi-arm liquid crystal system, electron-withdrawing groups terminally substituted behave better than those electron-donating groups substituted.     

Heteroleptic ruthenium(II)/(III) 2,2′-bipyridine/1,10-phenanthroline complexes incorporating bidentate Schiff base N,O-ligands

Eight substituted bidentate Schiff base ligands HOC₆H₄CH=N-R (HL) (HL1: R = 4-ClC₆H₄, HL2: R = 2-ClC₆H₄, HL3: R = 4-NO₂C₆H₄, HL4: R = 4-MeC₆H₄, HL5: R = 2,6-Me₂C₆H₃, HL6: R = 2,46-Me₃C₆H₂, HL7: R = CH₂C₆H₅, and HL8: R = n-Pr) were synthesized by the typical condensation reaction. Interaction of cis-[Ru(bpy)₂Cl₂]?2H₂O (bpy = 2,2′-bipyridine) with one equivalent of HL ligand in the presence of KPF₆ afforded the cationic ruthenium(II) complexes of the type [Ru(bpy)₂(L)](PF₆) (1–8). The reaction of cis-[Ru(phen)₂Cl₂]?2H₂O (phen = 1,10-phenanthroline) and HL1 under similar condition gave complex [(phen)₂Ru(L)](PF₆) (1a). Treatment of cis-[Ru(phen)₂Cl₂]?2H₂O with two equivalents of HL in the presence of KPF₆ resulted in isolation of the cationic ruthenium(III) complexes of the type [Ru(phen)(L)₂](PF₆) (9-16). All complexes have been spectroscopically characterized. The structures of 1a?CH₂Cl₂, 2?½CH₂Cl₂, 3?CH₃CN, 5?½H₂O, 6, 12?½HOCH₂CH₂OH, 13?CH₃CN, 15?H₂O, and 16 have been determined by single-crystal X-ray diffraction.     

Construction of acetate-bridged dicopper(II) hybrid organic–inorganic networks with calix[4]arene-derived nitrogenous ligands

The reactions of mono-, bis- and tetrapicolyl-p-tert-butylcalix[4]arene derivatives functionalised in the phenolic positions (L ¹ –L ⁴ ) with copper(II) acetate resulted in the formation of discrete complexes or extended coordination polymers. The centrosymmetric dimer [Cu₂(μ-O₂CCH₃)₄(L ¹ )₂] 1, obtained with monodentate L ¹ , has square pyramidal coordination around the copper centres and a cone conformer of monopicolyl-calix[4]arene acting as an axial ligand, with a molecule of acetonitrile hosted within its cavity. The potentially bidentate L ² acts as a monodentate ligand, affording the complex [Cu₂(μ-O₂CCH₃)₄(L ² )₂] 2, which based on spectroscopic and combustion analysis data has a similar coordination sphere around Cu(II). Compound L ³ bridges two dicopper units in the coordination polymer [Cu₂(μ-O₂CCH₃)₄(μ-L ³ )] _n 3, with the calixarene hosting a molecule of tetrahydrofuran. Finally, compound L ⁴ reacts with 4 equivalents of copper(II) acetate, presumably generating a two-dimensional coordination polymer formulated as [{Cu₂(μ-O₂CCH₃)₄}₂(L ⁴ )] 4.     

Theoretical study on the mechanism of OH + HCNO reaction

A detailed mechanistic study of the OH + HCNO reaction, in which the products P _i with i=1, 2, . . . ,7 are involved, is carried out by means of CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE computatio-nal method to determine a set of reasonable pathways. It is shown that P ₆ (CO + H₂NO) and P ₃ (HNO +HCO) are the major product channels with a minor contribution from P ₅ (NO + H₂CO), whereas the other channels for P ₁ (H₂O + NCO), P ₂ (NH₂ + CO₂), P ₄ (HCN + HO₂) and P ₇(CO + H₂ + NO) are less favorable. All these theoretical results are in harmony with experimental facts.     

Syntheses and structures of three disulfoxide uranyl complexes

Three disulfoxide uranyl complexes [UO₂(DBSOB)(NO₃)₂] _n (1), [UO₂(DBM)₂]₂(DBSOB) (2), and [UO₂(PMBP)₂]₂(DBSOB) (3) (DBSOB = 1,4-di(butylsulfinyl)butane, HDBM = dibenzoylmethane, HPMBP = 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone) were synthesized and characterized. The [UO₂(NO₃)₂] groups are connected by bridging disulfoxide ligands DBSOB to form a 1-D zigzag chain in 1. Two [UO₂(DBM)₂] or [UO₂(PMBP)₂] groups are connected by a bridging DBSOB to form the dimeric structures of 2 or 3, respectively. Complexes 1, 2, and 3 are the first structurally characterized disulfoxide–actinide compounds. Thermal stabilities of 1, 2, and 3 were investigated.     

Cu(II) coordination polymers stabilized by pyridine-2,6-dicarboxylate anion and pyrazole derivatives through ligand hydrolysis

Abstract

2,6-Pyridinedicarbonyldichloride (PDD) was treated with pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole in the presence of trimethylamine at room temperature. Reactions afforded 2,6-bis(pyrazolyl-1-carbonyl)pyridine (1), 2,6-bis(3-methylpyrazolyl-1-carbonyl)pyridine (2) and 2,6-bis(3,5-dimethylpyrazolyl-1-carbonyl)pyridine (3). 1-3 were treated with copper ion under ambient conditions in open air. Such coupling of 1 and 2 with copper led to coordination polymers 6 and 7, bearing 1D architectures, of general formulas [Cu(C₇H₃NO₄)(C₃H₄N₂)]_n and [Cu(C₇H₃NO₄)(C₄H₇N₂)]_n (C₇H₃NO₄?=?2,6-pyridinedicarboxylate ion, C₃H₄N₂?=?pyrazole and C₄H₇N₂?=?3-methylpyrazole), respectively. Under the same experimental conditions, 3 instead forms a mononuclear Cu(II) complex (8). Structures of 1-3 and 6-8 were determined with X-ray diffraction. The solid state structures reveal that short-range intermolecular interactions in the ligands afford 1D (1) and 2D (2 and 3) supramolecular chains, respectively. 6 and 7 both crystallize in the orthorhombic system, space group P2₁2₁2₁. 1–3 were also characterized with elemental analysis and NMR spectroscopy. The magnetic susceptibility measurements indicate that both complexes are paramagnetic with effective moments of 1.75 (6) and 1.90 (7) µ_B at 300 K. The voltammetric signatures of 6 and 8 show two steps reversible redox behavior as evidenced by the appearance of two cathodic waves with corresponding anodic peaks in the backward scan.     

Dihaloheptasilanes X2Si[SiMe(SiMe3)2]2 as potential precursors for silylenes, disilenes and cyclotrisilanes

The synthesis of new dihaloheptasilanes X₂Si[SiMe(SiMe₃)₂]₂ (X=Cl: 2, Br: 3, I: 4) was performed by treating dihydridoheptasilane 1 (X=H) with CCl₄, HCBr₃ or HCI₃. Difluoroheptasilane 6 (X=F) was prepared from either diphenylheptasilane 5 (X=Ph), triflic acid (HOTf), and LiF with concomitant isolation of heptasilanes 7 (X₂=Ph and OTf), 8 (X₂=F and Ph), and 9 (X₂=F and OTf), or by halogen exchange from 2 using ZnF₂. Crystal structures of 2, 3, 4, and 5 are reported. The reduction of 2 with Li, Na or KC₈ resulted in the instantaneous formation of various cyclotrisilanes, while the reduction of 3 gave exclusively the unsymmetrical cyclotrisilane (E)-1-methyl-2,3,3-tris[methylbis(trimethylsilyl)silyl]-1,2-bis(trimethylsilyl)cyclotrisilane 10, which was characterized by X-ray crystallography. A mechanism for the formation of cyclotrisilanes via a silylsilylene-to-disilene rearrangement is proposed. Attempts to prepare the tetradekasilane [(Me₃Si)₂MeSi]₂SiH–SiH[SiMe(SiMe₃)₂]₂ (by reductive dehalogenation of either HClSi[SiMe(SiMe₃)₂]₂ 13 or HISi[SiMe(SiMe₃)₂]₂ 18), or the tetradekasilane [(Me₃Si)₂MeSi]₂SiPh–SiPh[SiMe(SiMe₃)₂]₂ (by reductive dehalogenation of either PhClSi[SiMe(SiMe₃)₂]₂ 14 or PhISi[SiMe(SiMe₃)₂]₂ 19) as precursors for the disilene [(Me₃Si)₂MeSi]₂Si=Si[SiMe(SiMe₃)₂]₂ failed. 14 was characterized by X-ray crystallography. All compounds described were also characterized by multinuclear NMR spectroscopy and elemental analysis.     

Ten complexes constructed by two reduced Schiff base tetraazamacrocycle ligands: syntheses,structures, magnetic and luminescent properties

Ten new complexes, [Cu₂(L¹)(NO₃)₂]·2H₂O (1), [Cu₄(L¹)₂]·4ClO₄·H₂O (2), [Cu₂(L¹)(H₂O)₂]·(adipate) (3), [Cu₆(L¹)₂(m-bdc)₄]·2DMF·5H₂O (4), [Cu₂(L¹)(Hbtc)]·5H₂O (5), [Cu₂(L¹)(H₂O)₂]·(ntc)·3H₂O (6), [Co₂(L²)]·[Co(MeOH)₄(H₂O)₂] (7), [Co₃(L²)(EtOH)(H₂O)] (8), [Ni₆(L²)₂(H₂O)₄]·H₂O (9) and [Zn₄(L²)(OAc)₂]·0.5H₂O (10), have been synthesized. 1 displays a [Cu₂(L¹)(NO₃)₂] monomolecular structure. 2 shows a supramolecular chain including [Cu₂L¹]²⁺. In 3, two Cu(II) ions are connected by L¹ to form a [Cu₂(L¹)(H₂O)₂]²⁺ cation. In 4, the m-bdc anions bridge Cu(II) ions and L¹ anions to form a layer. Both 5 and 6 display 3-D supramolecular structures. 7 consists of both [Co₂L²]^2? and [Co(MeOH)₄(H₂O)₂]²⁺ units. 8 and 9 show infinite chain structures. In 10, Zn(II) dimers are linked by L² to generate a 3-D framework. The magnetic properties for 4 and 8 and the luminescent property for 10 have been studied.