Bis Diamine Research Articles

Ionic Liquid Crystals Based on Loop-Shaped Copper(I) Complexes.

This paper describes the synthesis and characterization of liquid crystals based on loop-shaped cationic copper(I) complexes of a multidentate ligand. Their synthesis involves the one-pot reaction of an alkyloxy-decorated pyridine-aldehyde unit with a diamine (2,2'-(ethylenedioxy)bis(ethylamine)) spacer to form in situ a pyridine-imine quadridentate-N4-donor ligand, L, which is able to chelate a copper(I) center associated with various noncoordinating anions. All of these compounds were characterized by NMR, IR, and electronic absorption spectroscopy, and more particularly by X-ray diffraction and mass spectroscopy, enabling unambiguous assignment of the [ML]+ mononuclear nature of the cationic components. The presence of six flexible alkyloxy chains at each end of the ligand associated with the rigidity of the core complex causes induction of a liquid crystal state with a columnar self-organized architecture, where the columns are packed in a hexagonal two-dimensional network.

Comparison of the properties of polyimide nanocomposite films containing functionalized-graphene and organoclay as nanofillers

Poly(amic acid) (PAA) is prepared by the reaction of dianhydride 4,4′-biphthalic anhydride and diamine bis[4-(3-aminophenoxy)phenyl]sulfone in N,N’-dimethylacetamide. Two types of fillers were dispersed in the as-synthesized PAA via a solution intercalation method; polyimide (PI) hybrid films were synthesized under various heat treatment conditions. Octylamine (C8) was introduced into graphene sheets (C8-GS) and bentonite (C8-BTN), which were then used as nanofillers in the PI hybrid films. The synthesized nanofillers were used in varying amounts of 0.25–1.00 wt% with respect to the matrix PI. The thermal and morphological properties and optical transparency of the hybrid films were investigated and compared for both C8-GS and C8-BTN at varying nanofiller content. The C8-BTN nanocomposite showed superior thermal properties, and optical transparency, and the filler was well dispersed in the PI matrix compared to the C8-GS nanocomposite. The thermal stability of the hybrid films improved upon the addition of small amounts of the nanofiller. However, beyond a certain critical filler concentration, the thermal stability declined. These results were verified through the dispersion of fillers via transmission electron microscopy.

Comparison of Properties of Colorless and Transparent Polyimide Nanocomposites Containing Chemically Modified Nanofillers: Functionalized-Graphene and Organoclay.

Poly(amic acid) (PAA) was synthesized from dianhydride 4,4-(4,4-isopropylidenediphenoxy)bis(phthalic anhydride) and diamine bis [4-(3-aminophenoxy) phenyl] sulfone. Colorless and transparent polyimide (CPI) hybrid films were synthesized through thermal imidization after dispersing nanofillers using an intercalation method in a PAA solution. C16-GS and C16-MMT, in which hexadecylamine (C16) was substituted on graphene sheet (GS) and montmorillonite (MMT), respectively, were used as nanofillers to reinforce the CPI hybrid films. These two nanofillers were admixed in varying loadings of 0.25 to 1.00 wt%, and the morphology, thermal properties, and optical transparency of the hybrid films were investigated and compared. The results suggest that the thermal properties of the CPI hybrid films can be improved by adding only a small amount of nanofiller. Transmission electron microscopy results of the CPI hybrid film containing two types of fillers suggested that the fillers were well dispersed in the nano-size in the matrix polymer; however, some of the fillers were observed as agglomerated particles above the critical concentration of 0.50 wt%.

The effects of long and bulky aromatic pendent groups with flexible linkages on the thermal, mechanical and electrical properties of the polyimides and their nanocomposites with functionalized silica.

A novel diamine bis(4-aminophenyl)bis{3,4[(4-(8-quinolyloxymethyl carbonyl)]}methane, containing two long/bulky aromatic pendent chains was synthesized by incorporating aromatic and hetero aromatic groups with flexible linkages. Flexible, stretchable, thermally stable and processable polyimides were prepared by reacting this newly synthesized diamine with commercial tetracarboxylic acid dianhydrides like 3,3′,4,4′-benzophenone tetra carboxylic acid dianhydride (BTDA) and 4,4′-(4,4′-isopropylidenediphenoxy)diphthalic Anhydride (BPADA). Nanocomposites of polyimides were prepared using aromatic amine functionalized silica as a filler by solution casting method. The current work investigates the effects of incorporating long/bulky aromatic side chains and flexible linkages on the thermal, mechanical, electrical and optical properties of the polyimides and nanocomposites. The polyimides showed good thermal stability (T10% = 364 & 388), high flame resistance, low glass transition temperatures (Tg = 130 °C & 156 °C), very low dielectric constants (2.5 & 2.8 at 1 MHz) and good optical transparency. The neat polyimides displayed good elongation at break (133–155%) but possessed low tensile strength. The chemically imidized polyimides showed good solubility in low and high boiling solvents. Nanocomposites of polyimides based on aromatic amine functionalized silica exhibited enhanced properties with T10% values varying between 409–482 °C, Tg between 165–280 °C and higher dielectric constants (3–5.7 at 1 MHz).

Group IV diamine bis(phenolate) catalysts for 1-decene oligomerization

A family of three group IV based diamine bis(phenolate) catalysts, [M{2,2ʹ-(OC6H2-4,6-tBu2)2NHC2H4NH}(OiPr)2] (M = Ti (Cat1), Zr (Cat2), and Hf (Cat3)) were synthesized and characterized. These complexes were employed in 1-decene oligomerization using ([Ph3C][B(C6F5)4]) as an activator at 80 °C. NMR spectra of the di(isopropoxy) complexes confirmed C2-symmetrical structures. Cat2 demonstrated the highest activity followed by Cat3 and Cat1, whereas tacticity Cat1>Cat2>Cat3. The origin of this different performance was unveiled by DFT calculations. Interestingly, the increase of oligomerization temperature shifted PDI to the higher values. Moreover, kinetic studies employing population balance approach have been conducted, being outstanding that initiation rate constants were lower than propagation ones by a factor of 100. The precise study of termination reactions by NMR revealed that the significant termination reaction was the creation of two types of unsaturated bonds, i.e. vinylidene and vinylene. The obtained oligomers had viscosity index and pour point values comparable with commercial oils.

Synthesis and characterization of low-temperature polyamide 6 (PA6) copolyamides used as hot melt adhesives and derived from the comonomer of novel aliphatic diamine bis(2-aminoethyl) adipamide and adipic acid

A novel aliphatic PA6 copolyamide (PA6(BAEA/AA))-based hot melt adhesive was synthesized from ε-caprolactam with the organic salt of bis(2-aminoethyl) adipamide (BAEA) and adipic acid (AA), with BAEA/AA content ranges from 5 to 15 mol%. The chemical structures of BAEA diamine, BAEA/AA organic salt, PA6(BAEA/AA) copolyamides, and neat PA6 were obtained using FT-IR and 1H NMR. Determined by the comonomer compositions, the relative viscosity (ηr) and molecular weight (Mw) of the PA6(BAEA/AA) were from 2.29 to 2.74 and from 14,530 to 19,500 g mol−1, respectively. Adding the BAEA/AA structure strongly affected the crystallization behavior and thermal properties of the copolyamides. DSC results revealed that the melting temperature (Tm) of the copolyamides declined as the mole% of BAEA/AA increased in the range 5–15 mol%, and a TGA test revealed that the thermal decomposition of the copolyamides was similar to that of neat PA6. The Tm, glass transition temperature (Tg), and thermal stability (Td5%) with a BAEA/AA salt content of 10 mol% had the lowest values of 162.2, 40.3, 354.6 °C, respectively, while the fusion enthalpy (ΔHm) was lowest at 15 mol% (21.2 J g−1). Most remarkably, PA6(BAEA/AA) exhibits much better mechanical properties such as tensile strength (33.6–52.6 MPa) and elongation at breakage (114.7–584.5%), than the PA6 homopolymer. The peel strength of PA6 reached a maximum value of 53.4 N cm−1 at 10 mol% of BAEA/AA salt, and this value is better than those of commercial hot melt adhesives.

Coordinative chain transfer polymerization of 1-decene in the presence of a Ti-based diamine bis(phenolate) catalyst: a sustainable approach to produce low viscosity PAOs

A Ti-based diamine bis(phenolate) catalyst, [Ti{2,2′-(OC6H2-4,6-tBu2)2NHMePhMeNH}Cl2], was synthesized and fully characterized by elemental analysis and NMR spectroscopy.

Cytotoxic Vanadium Complexes of Branched [ONNO]‐Type Diamine Bis(phenolato) Ligands

Vanadium complexes are attractive potential alternatives to platinum‐based anticancer drugs. Two vanadium(V) complexes, based on a common chelating tetradentate diaminobis(phenolato) ligand featuring a branched connectivity but differing in their labile ligands, were synthesized and characterized. Whereas the isopropoxido complex was obtained as a mixture of cis and trans isomers with regard to the orientation of the labile group vs. the amine sidearm, the salicylato‐containing complex was obtained as a single trans isomer. X‐ray structures of the complexes featured octahedral geometry for both. The two complexes exhibited high cytotoxic activity toward different cancer cells, often higher than that of cisplatin, including toward cisplatin‐resistant ovarian cancer cells. These complexes demonstrated rapid hydrolysis, releasing the labile ligand within several minutes, with no indications of release of free chelating ligand after water exposure, suggesting that polynuclear hydrolysis products are involved in the cellular activity.

Radical reactions of diamine bis(phenolate) vanadium(iii) complexes. Solid state binding of O2 to form a vanadium(v) peroxo complex.

[VCl3(THF)3] reacted with the sodium salt of a tripodal diamine bisphenolate ligand precursor Na2L2 to give a paramagnetic d2 complex [V(L2)Cl] (2). The reaction of 2 with oxygen is strongly dependent on the experimental conditions, affording [VO(L2)Cl] (6) or [V(η2-O2)(L2)Cl] (7). The formation of 7 involves the direct addition of O2 to V(iii) in the solid state with oxidation to V(v) without significantly disturbing the structure of 2. DFT calculations showed that compound 7 is an intermediate in the formation of 6 from 2. The reaction involves the cleavage of the η1-O-O bond in a proposed dimeric species. The overall reaction of 2 moles of vanadium(iii), complex 2, and one mole of O2 to yield two moles of product 6 is a favourable process with ΔG298 = -38.3 kcal mol-1. 7 is the first non-oxido peroxidovanadium(v) complex obtained directly from the reaction of a crystal and the second example of a structurally characterized complex of that type. Reactions of V(L1)Cl (1) and V(L2)Cl (2) with one equivalent of the nitroxyl radical TEMPO in toluene also result in the formation of oxido V(v) complexes, VO(L1)Cl (5) and VO(L2)Cl (6). The reaction of VO(OiPr)3 with Na2L2 afforded [VO(L2)(OiPr)] (8) in high yield. A major isomer having the V[double bond, length as m-dash]O moiety in the equatorial plane was characterised by X-ray diffraction although solution NMR data showed the presence of a minor species with the oxido ligand trans to the tripodal nitrogen, as in 6. Complexes 6 and 8 are very active and selective sulfoxidation catalysts of thioanisole, but no enantiomeric excess was obtained.

Facile fabrication of CO2 separation membranes by cross-linking of poly(ethylene glycol) diglycidyl ether with a diamine and a polyamine-based ionic liquid

In this study, a new family of poly(ethylene glycol) (PEG)-based membranes for CO2 separation was developed using PEG diglycidyl ether (PEGDE) cross-linked with a low-molecular-weight diamine (2,2′-(ethylenedioxy)bis(ethylamine)) and a polyamine-based ionic liquid (triethylenetetramine trifluoroacetate, [TETA][Tfa]) in a solvent-free process. A mass fraction up to 80% PEG dimethyl ether (PEGDME, average Mn~250) was added to the cross-linked matrix to enhance the gas transport properties. The cross-linking reaction mechanism, thermal stability of the resulting membranes, as well as water uptakes of the formed membranes were systematically investigated. The CO2, N2, and CH4 gas transport properties of these new membranes were studied. Both CO2/N2 and CO2/CH4 binary mixed gas separation performances of the membranes at various humidity levels were tested. The gas permeation results showed that the free PEGDME additive acts as plasticizer in the polymeric matrix, resulting in excellent CO2/ N2 and CO2/CH4 separation properties.

Diamine bis(phenolate) and pendant amine bis(phenolate) ligands: catalytic activity for the room temperature palladium‐catalyzed Suzuki–Miyauracoupling reaction

A series of amine bis(phenolate) ligands bearing aryl substituents of varying steric bulk are reported and characterized using single‐crystal X‐ray diffraction, NMR spectroscopy and high‐resolution mass spectrometry experiments. Palladium complexes derived in situ from these ligands are evaluated as catalysts for the Suzuki–Miyaura coupling of phenylboronic acid and aryl bromides. High conversions are observed for these reactions in methanol solvent at low catalyst loadings (0.01 mol%), short reaction times (30 min) and mild temperatures (30°C). Conversion is observed for a range of substrates, and is found to depend on the nature of the external base and solvent employed. These findings demonstrate the utility of catalysts derived from late transition metal complexes of amine bis(phenolate) ligands, particularly those bearing bulky cumyl substituents. Copyright © 2015 John Wiley & Sons, Ltd.

Synthesis, characterization and catalytic properties for olefin polymerization of two new dimeric zirconium(IV) complexes having diamine-bis(phenolate) and chloride ligands

Reaction of the zirconium tetrachloride with one equivalent of the sodium salt of the diamine bis (phenolate) ligand, L1H2 (Me2NCH2CH2N-(CH2-2-OH-3,5-tBu-C6H2)2) or L2H2 (Me2NCH2CH2N-(CH2-2-OH-3,5-tBu-C6H2)(CH2-2-OH-C6H4)) in the presence of air led to formation of [Lig1ZrCl]2(μ-O) and [Lig2ZrCl]2(μ-O), respectively. These novel oxo-bridged dinuclear zirconium complexes were characterized by elemental analysis, 1H NMR spectroscopy and by single-crystal X-ray diffraction. Their reactivities in polymerization of ethylene and 1-octene, upon activation with Al(iBu)3/Ph3CB(C6F5)4 and MAO, were examined. It was found that lack of t-Bu substituents on one phenolate ring cause a significant decrease in catalytic activity but leads to polymers with improving properties, i.e., to poly(1-olefin)s with significantly higher stereoregularity and polyethylenes with higher molecular weight. In addition, the interaction of the [Lig1ZrCl]2(μ-O) precursors with MAO and with the Me3Al activator was investigated by 1H NMR spectroscopy giving an insight into the catalyst transformations in the course of the polymerization reaction.

Zr(iv) complexes containing salan-type ligands: synthesis, structural characterization and role as catalysts towards the polymerization of ε-caprolactone, rac-lactide, ethylene, homopolymerization and copolymerization of epoxides with CO2

Three new Zr(iv) complexes bearing salan-type diamine bis(phenolato) ligands were synthesized and their activities towards the ROP of ε-CL, rac-LA and homopolymerization, copolymerization and coupling of epoxides with CO2 were investigated.

Silarylene-containing poly(ether-amide)s obtained by Yamazaki–Higashi phosphorylation technique: use of bis(4-(4-aminophenoxy)phenyl)ethylmethyl silane

Aromatic poly(ether-amide)s (PEAs) based on -(R1,R2)diphenylsilane- and oxyether units were synthesized by direct polycondensation of a diamine and two dicarboxylic acids. For this, the diamine bis(4-(4-aminophenoxy)phenyl)ethylmethylsilane was obtained by reduction of the respective dinitro compound, which was synthesized by nucleophilic aromatic halogen displacement from 1-fluoro-4-nitrobenzene with bis(4-hydroxyphenyl)ethylmethylsilane in basic medium. New silicon-containing aromatic diamine and the PEAs were characterized by elemental analysis, FT-IR, 1H, 13C and 29Si NMR spectroscopy and the results were in agreement with the proposed structures. The incorporation of aliphatic units such as methyl and/or ethyl groups on the silicon atoms affected positively the solubility of the PEAs in organic polar solvents. When their thermal and optical properties were compared with two PEAs of similar structure, containing phenyl groups bonded to the silicon atoms, it was observed a decrease of the glass transition temperature and transmittance values, maintaining a high thermal resistance.

Oligomeric poly(imide-amides)s containing side 1,8-naphthalimidyl groups: synthesis and characterization

Poly(imide-amide)s (PIAs) were synthesized from isophthalic acids, which have in position 5 a bulky group like 1,8-naphthalimidyl bonded to amino acids as flexible spacers, and the diamine bis(4-aminophenyl)diphenylsilane, which provides a polar group in the main chain. Glycine, l-alanine, l-phenylalanine, l-valine and p-aminobenzoic acid were used as amino acids. Polymers were obtained according to the Yamazaki method and characterized by elemental analysis, optical activity, IR and 1H, 13C and 29Si NMR spectroscopy. PIAs were soluble in aprotic polar solvents but not in common organic solvents, and obtained with low ηinh values, which was an indicative of low molecular weights species, probably of oligomeric nature. According to the polymeric structure, the only difference between PIAs is the structure of the amino acid residue, and in this sense it was possible to see an increase of the Tg values when the volume of the amino acid residue also increased, due to the lower possibility of internal mobility of the side chains. The higher Tg value was obtained with the PIA-e, which includes an aromatic ring as a side chain, derived from p-aminobenzoic acid. PIAs, in spite of the good TDT values obtained, were not thermally stable in the sense that the 10 % of weight lost was obtained at lower temperature than 400 °C, with the exception of PIA-e derived from p-aminobenzoic acid. However, there was an increase of the TDT values when the volume of the amino acid residue increases. The PIAs do not show good UV–vis transparence probably due to the low free volume of those including an aliphatic amino acid residue.

Synthesis, cytotoxic and hydrolytic studies of titanium complexes anchored by a tripodal diamine bis(phenolate) ligand.

The reactivity, cytotoxic studies and hydrolytic behaviour of diamine bis(phenolate) titanium complexes are reported. The reactions of [Ti((tBu2)O2NN')Cl]2(μ-O) (1) with LiO(I)Pr or HO(I)Pr in the presence of NEt3, aiming at the synthesis of the alkoxido derivative of 1 led to no reaction or to the synthesis of the monomeric complex [Ti((tBu2)O2NN')(O(i)Pr)2] (3), respectively. A small amount of the alkoxidotitanium dimer [Ti((tBu2)O2NN')(O(i)Pr)]2(μ-O) (2) crystallized out of a solution of 3 and DFT calculations showed that the transformation of 1 into 3 is a thermodynamically favorable process in the presence of a base (NEt3) (ΔG = -14.7 kcal mol(-1)). 2 was quantitatively obtained through the direct reaction of the ligand precursor H2((tBu2)O2NN') with titanium tetra(isopropoxido). Further reaction of 2 with an excess of TMSCl was revealed to be the most suitable method for the preparation of [Ti((tBu2)O2NN')Cl2] (4). 1 and 3 disclosed cytotoxic activity towards HeLa, Fem-x, MDA-MB-361 and K562 cells and 1 exhibited moderate binding affinity to FS-DNA. (1)H NMR hydrolysis studies attested the fast decomposition of 4 in the presence of D2O. The hydrolysis of 3 is slower and proceeds through the formation of [Ti((tBu2)O2NN')(OH)]2(μ-O) (5) that was crystallographically characterized. Upon D2O addition 1 immediately forms complex new species, stable in solution for long periods (weeks).

Silicon-containing oligomeric poly(imido-amides) with amino moieties. Synthesis, characterization and thermal studies

Silicon-containing oligomeric poly(imido-amides) (PIAs) were synthesized from dicarboxylic imido-acids containing a Si atom, which were obtained from dianhydrides, amino acids and p-aminobenzoic acid, were polymerized with the diamine bis(4-aminophenyl)diphenylsilane.

Oligomeric aliphatic/aromatic poly(amides) containing silicon in the main chain and phthalimide or tetrahalophthalimide moieties as side groups

Oligomeric aliphatic poly(amides) (PAs) with phthalimide or tetrahalophthalimide were obtained from aspartic and glutamic acids which reacted previously with phthalic or tetrahalophtalic anhydrides, and the diamine bis(4-aminophenyl)-diphenylsilane, by direct polycondensation according to the Yamazaki method. PAs were characterized by IR and 1H, 13C and 29Si NMR, inherent viscosity measurements and optical activity. The results showed low ηinh values due to the insolubility of the PAs in the reaction media. All PAs were soluble in aprotic polar solvents and partially soluble in other common solvents as CHCl3 and THF. The Tg values for the PAs derived from aspartic acid showed an increase when the size of the halogen atom is increased due to the more rigidity of the imide group. For those PAs derived from glutamic acid the influence of the side groups was less important due probably to the higher influence of the longer aliphatic main chain. The thermal degradation analysis showed that PAs have good TDT values with the exception of PA-7. The temperature for 50 % of weight loss for both PAs series was dependent on the nature of the halogen, showing an increase when the halogen was more electronegative. PAs do not showed good optical properties, with the exception of PA-1 and PA-6 without halogen atoms in the side chain, due to the increase of the volume of the side group which affects their mobility increasing their packing. It is possible to see a low increase of the transmittance when the aliphatic chain is increased from aspartic to glutamic acid due to an increase of the flexibility of the main chain.

Toward the Understanding of Radical Reactions: Experimental and Computational Studies of Titanium(III) Diamine Bis(phenolate) Complexes

Radical reactions of titanium(III) [Ti((tBu2)O2NN')Cl(S)] (S = THF, 1; S = py, 2; (tBu2)O2NN' = Me2N(CH2)2N(CH2-2-O-3,5-(t)Bu2C6H2)2) are described. Reactions with neutral electron acceptors led to metal oxidation to Ti(IV), [Ti((tBu2)O2NN')Cl(TEMPO)] (4) being formed with the TEMPO radical and [Ti((tBu2)O2NN')Cl2] (9) with PhN═NPh. [Ti((tBu2)O2NN')Cl2] was also formed when [Ti((tBu2)O2NN')Cl(S)] was oxidized by [Cp2Fe][BPh4], but the [Cp2Fe][PF6] analogue yielded [Ti((tBu2)O2NN')ClF] (8). The reactions of [Ti((tBu2)O2NN')Cl(S)] with O2 gave [Ti((tBu2)O2NN')Cl]2(μ-O) (3). The DFT calculated Gibbs energy for the above reaction showed it to be exergonic (ΔG298 = -123.6 kcal·mol(-1)). [Ti((tBu2)O2NN')(CH2Ph)(S)] (S = THF, 5; py, 6) are not stable in solution for long periods and in diethyl ether gave 1:1 cocrystals of [Ti((tBu2)O2NN')(CH2Ph)2] (7) and [Ti((tBu2)O2NN')Cl]2(μ-O) (3), most probably resulting from a disproportionation process of titanium(III) followed by oxygen abstraction by the resulting Ti(II) species. The oxidation of [Ti((tBu2)O2NN')(κ(2)-{CH2-2-(NMe2)-C6H4})] (10), which is a Ti(III) benzyl stabilized by the intramolecular coordination of the NMe2 moiety, led to a complex mixture. Recrystallization of this mixture under air led to a 1:1 cocrystal of two coordination isomers of the titanium oxo dimer (3). In one of these isomers, one metal is pentacoordinate and the dimethylamine moiety of the diamine bis(phenolate) ligand is not bonded to the metal, displaying a coordination mode of the ligand never observed before. The other titanium center is distorted octahedral with two cis-phenolate moieties. In the second unit, the coordination of the two ancillary ligands to the titanium centers reveals mutually cis-phenolate groups in one-half of the molecule and trans-coordinated in the other titanium center, keeping a distorted octahedral environment around each titanium.

Diamine bis(phenolate) samarium complexes: Synthesis and structures

Samarium complexes supported by the diamine bis(phenol) proligand H2(tBu2O2NN′)=Me2N(CH2)2N{CH2-(2-OH-3,5-tBu2-C6H2)2} were prepared and structurally characterized. [Sm(tBu2O2NN′)]2(μ-Cl)2 (1) was obtained from reaction of SmCl3 with K2(tBu2O2NN′) in THF, DME or pyridine. The reaction of 1 with LiNEt2 gave a zwitterionic bimetallic complex of Sm and Li, [Sm(tBu2O2NN′)2Li] (2) that formed upon ligand redistribution and did not allow the isolation of the expected diethylamido derivative. Analogously treatment of Sm{N(SiMe3)2}3 with H2tBu2O2NN′ led to a zwitterionic samarium complex [Sm(tBu2O2NN′)(tBu2O2N(H)N′)] (3) that also displays a 2ligand:1Sm ratio. In 3 the samarium is formally an ate centre and the tripodal nitrogen of one of the ligands is protonated. The reaction of 1 with Li[2-(CH2NMe2)C6H4] proceeded through chloride metathesis to give [Sm(tBu2O2NN′)(κ2-{2-(CH2NMe2)-C6H4})] (4).