Multidentate N-donor Ligand Research Articles

Five polyoxometalate-based inorganic–organic hybrid compounds constructed by a multidentate N-donor ligand: syntheses, structures, electrochemistry, and photocatalysis properties

Five inorganic–organic hybrid compounds, namely, [Cu6Na2(Htrb)4(Mo6O19)(MoO4)6] (1), [Zn3(Htrb)(Mo10O34)]·8H2O (2), [Zn2(Htrb)(β-Mo8O26)(H2O)2]·6H2O (3), [Co2(Htrb)(β-Mo8O26)(H2O)2]·6H2O (4), and [Co2(Htrb)(γ-Mo8O26)(H2O)6]·8H2O (5), have been synthesized under hydrothermal conditions, where Htrb = hexakis(1,2,4-triazol-ylmethy1)benzene. Their structures have been determined by single-crystal X-ray diffraction analyses and characterized by infrared spectra (IR), elemental analyses and powder X-ray diffraction (PXRD) patterns. In compound 1, eight Htrb ligands bridge six Cu(II) atoms to form a metal–organic Cu6(Htrb)8 cage. Neighboring cages are further linked by the arms of the Htrb ligands to generate a fascinating 3D framework. Interestingly, each inorganic [Mo6O19]2− anion was incorporated into the Cu6(Htrb)8 cage. In 2, adjacent [Mo10O34]8− anions are linked by the bridging oxygen atoms to form 1D inorganic molybdenum oxide chains, which are extended by Zn(II) atoms into a 2D layer. Adjacent layers are further linked by the Htrb ligands in hexadentate modes to yield a 3D framework. Compounds 3 and 4 are isostructural, where the [β-Mo8O26]4− anions are bridged by the metal atoms to yield an infinite chain. The chains are further joined together by the Htrb ligands to form a 3D (4,5,6)-connected net. In compound 5, the Co(II) atoms are bridged by the Htrb ligands to generate 1D chains, which are further extended through the Mo–N bond between the Htrb ligands and the [γ-Mo8O26]4− anions into a 3D (3,4,6)-connected net. Moreover, the optical band gaps, photoluminescence, electrochemistry and the photocatalytic properties for methylene blue (MB) degradation of 1–5 have also been investigated.

Three new inorganic–organic hybrid compounds constructed from two kinds of octamolybdate clusters and flexible multidentate N-donor ligand: syntheses, structures, electrochemistry, luminescence, and photocatalytic properties

Three inorganic–organic hybrid materials based on octamolybdates, d10 metals, and multidentate N-donor ligands, namely, [Zn4(htpmb)2(θ-Mo8O26)(H2O)6.5]·0.5H2O (1), [Zn6(htpmb)2(γ-Mo8O26)2(SO4)(H2O)6]·6.5H2O (2), and [Cd2(htpmb)(γ-Mo8O26)(H2O)2]·4.5H2O (3), where htpmb = hexakis(3-(1,2,4-triazol-4-yl)phenoxy-methyl)benzene, have been synthesized under hydrothermal conditions. Compound 1 shows a 3D framework based on a rare [θ-Mo8O26]4− isomer with binodal (5,6)-connected (32·43·5·63·7)(32·44·54·62·73) topology. Compound 2 displays a 3D framework with pentanodal (4,5,6,6,7)-connected (32·4·5·62)(32·42·52·63·8)(34·42·52·64·72·8)(34·42·52·66·9)(34·43·5·68·75) topology. Compound 3 exhibits a 3D framework with pentanodal (3,4,4,6,6)-connected (3·6·7)(32·4·62·7)(34·42)(32·66·76·10)(33·4·63·74·84) topology. Their structures have been characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD), thermogravimetric analysis, and optical band gaps. The luminescent properties and electrochemistry behaviors of compounds 1–3 have been studied. Moreover, the photocatalytic activities for methylene blue (MB) degradation of 1–3 under UV light irradiation have also been investigated in detail.

Solvent dependent anion dissociation limits copper(i) catalysed atom transfer reactions

Atom transfer radical addition (ATRA) and polymerisation (ATRP) reactions are commonly catalyzed by copper(I) complexes which react, reversibly, with a dormant alkyl halide initiator (RX) releasing a reactive organic radical R˙. The copper catalyst bears a multidentate N-donor ligand (L) and the active catalyst is simply Cu(I)L. The role of the catalyst in these reactions is to abstract a halogen atom from RX forming the corresponding higher oxidation state species Cu(II)LX. However, in order to perform its catalytic function (in multiple turnovers) the halido ligand must be released from the copper ion en route to regenerating the active catalyst Cu(I)L. In this work we investigate the kinetics of the Cu(I)LX/Cu(I)L equilibrium where L is the tridentate N,N,N',N'',N''-pentamethyl-diethylenetriamine (PMDETA). Using electrochemical analysis we find that the rate of formation of the active catalyst Cu(I)L is strongly dependent on solvent. We demonstrate that both the kinetics and thermodynamics of this simple ligand exchange reaction are critical in the overall reaction pathway.

Preparation and adsorption performance of 5-azacytosine-functionalized hydrothermal carbon for selective solid-phase extraction of uranium

A new solid-phase extraction adsorbent was prepared by employing a two-step “grafting from” approach to anchor a multidentate N-donor ligand, 5-azacytosine onto hydrothermal carbon (HTC) microspheres for highly selective separation of U(VI) from multi-ion system. Fourier-transform infrared and X-ray photoelectron spectroscopies were used to analyze the chemical structure and properties of resultant HTC-based materials. The adsorption behavior of U(VI) onto the adsorbent was investigated as functions of pH, contact time, ionic strength, temperature, and initial U(VI) concentration using batch adsorption experiments. The U(VI) adsorption was of pH dependent. The adsorption achieved equilibrium within 30min and followed a pseudo-second-order equation. The adsorption amount of U(VI) increased with raising the temperature from 283.15 to 333.15K. Remarkably, high ionic strength up to 5.0molL−1 NaNO3 had only slight effect on the adsorption. The maximum U(VI) adsorption capacity reached 408.36mgg−1 at 333.15K and pH 4.5. Results from batch experiments in a simulated nuclear industrial effluent, containing 13 co-existing cations including uranyl ion, showed a high adsorption capacity and selectivity of the adsorbent for uranium (0.63mmolUg−1, accounting for about 67% of the total adsorption amount).

A series of coordination polymers based on a multidentate N-donor ligand and different polycarboxylate anions: syntheses, structures and photoluminescent properties

A series of coordination polymers, namely, [Cd(4,4′-tmbpt)(o-bdc)(H2O)]·5.25H2O (1), [Cd(4,4′-tmbpt)(m-bdc)] (2), [Cd(4,4′-tmbpt)(5–OH–bdc)] (3), [Cd5Na2(4,4′-tmbpt)2(btc)4(H2O)3.5]·6.5H2O (4), [Cd3(4,4′-tmbpt)(btc)2(H2O)2]·H2O (5), [Zn(4,4′-tmbpt)(m-bdc)] (6), [Zn3(4,4′-tmbpt)2(p-bdc)3]·5.5H2O (7), and [Zn3(4,4′-tmbpt)(btc)2(H2O)2]·H2O (8), where 4,4′-tmbpt = 1-((1H-1,2,4-triazol-1-yl)methyl)-3,5-bis(4-pyridyl)-1,2,4-triazole, o-H2bdc = 1,2-benzenedicarboxylic acid, m-H2bdc = 1,3-benzenedicarboxylic acid, 5–OH–H2bdc = 5-hydroxy-1,3-benzenedicarboxylic acid, H3btc = 1,2,3-benzenetricarboxylic acid and p-H2bdc = 1,4-benzenedicarboxylic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), elemental analyses and powder X-ray diffraction (PXRD) analyses. Compounds 1, 3 and 7 display different 2D → 3D interdigitated structures. Compound 2 shows a 3D 6-connected framework with (412·63) topology. Compound 4 reveals a 3D (3,4,8)-connected net based on hexanuclear units. Compounds 5 and 8 are isostructural and display 3D (3,9)-connected frameworks based on trinuclear units. Compound 6 exhibits an unusual 2D → 3D polythreaded framework. The structural discrepancies of compounds 1–8 indicate that the presence of the different organic anions play important roles in the formation of the final structures of the coordination polymers. The luminescent properties were also investigated for the compounds 1–8.

Inorganic–organic hybrid compounds based on octamolybdates and multidentate N-donor ligand: syntheses, structures, photoluminescence and photocatalysis

Six inorganic-organic hybrid compounds, namely, [Cu(2)(2,4'-tmbpt)(2)(β-Mo(8)O(26))(H(2)O)(2)]·7H(2)O (1), [Cu(2,4'-tmbpt)(γ-Mo(8)O(26))(0.5)(H(2)O)]·H(2)O (2), [Co(2,4'-Htmbpt)(2)(γ-Mo(8)O(26))(H(2)O)(2)] (3), [Zn(2,4'-Htmbpt)(2)(γ-Mo(8)O(26))(H(2)O)(2)] (4), [Ni(2,4'-tmbpt)(α-Mo(8)O(26))(0.5)(H(2)O)]·2.5H(2)O (5) and [Ag(2,4'-Htmbpt)(β-Mo(8)O(26))(0.5)] (6), have been synthesized under hydrothermal conditions (2,4'-tmbpt = 1-((1H-1,2,4-triazol-1-yl)methyl)-3-(2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole). The structures of compounds 1-6 have been determined by single-crystal X-ray diffraction analyses and characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD) analyses and thermogravimetric analyses (TGA). Compound 1 shows a 3D (3,4)-connected framework constructed by the 2D Cu(II)-organic fragments and [β-Mo(8)O(26)](4-) anions. Compound 2 exhibits a 2D layer structure based on Cu(II)-organic chains and [γ-Mo(8)O(26)] chains. The layers are extended into a 3D supramolecular framework by hydrogen-bonding interactions. Compounds 3 and 4 are isostructural, and display 1D chain structures. The chains are further interlinked by hydrogen-bonding interactions to form 3D supramolecular architectures. Compound 5 shows a 3D framework based on the 2D Ni(II)-organic fragments and [α-Mo(8)O(26)](4-) anions. In compound 6, the 1D chains constructed by the Ag(I) ions, 2,4'-Htmbpt ligands and [β-Mo(8)O(26)](4-) anions are extended by hydrogen-bonding interactions into a 2D supramolecular layer. Each layer threads into the adjacent layers, yielding a 2D → 3D interdigitated structure. Moreover, the photoluminescent properties of 4 and 6, the optical band gaps of 1-6, and the photocatalytic properties of 1-6 have also been investigated.

Influence of multidentate N-donor ligands on highly electrophilic zinc initiator for the ring-opening polymerization of epoxides

A set of multidentate ligands have been synthesized and used to stabilize the putative highly electrophilic zinc species initiating ring-opening polymerization (ROP) of cyclohexene oxide (CHO) and propylene oxide (PO). Reaction of the bidentate C 2-chiral bis(oxazoline) ligand ( R2,R3BOX: R 2 = (4 S)- tBu, R 3 = H ( a); R 2 = (4 S)-Ph, R 3 = H ( b); R 2 = (4 R)-Ph, R 3 = (5 S)-Ph ( c)) with Zn(R 1) 2 (R 1 = Et ( 1), Me ( 2)) led to the heteroleptic three-coordinate complexes ( R2,R3BOX)ZnR 1, 1a– c and 2a, which were isolated in 92–96% yield. Next, two pyridinyl-functionalized N-heterocyclic carbene (NHC) ligands have been designed and synthesized: the 1,3-bis(2-pyridylmethyl)imidazolinium salt ( d) and the protected NHC adduct 2-(2,3,4,5,6-pentafluorophenyl)-1,3-bis(2-pyridylmethyl)imidazolidine ( e). The reaction of ligands d and e with ZnEt 2 led directly to the formation of (NHC)ZnEt(Cl) 3d complex with ethane elimination and the adduct (NHC–C 6F 5(H))ZnEt 2 4e, respectively, in high yield. In situ combinations of selected complexes 1a– c, 3d and 4e with B(C 6F 5) 3 (1 or 2 equivalents) give active systems for ROP, with high productivity (3.3–5.9 10 6 g polym. mol Zn −1 h −1) and high molecular weight ( M n up to 132 10 3 g mol −1) for CHO polymerization. Although the in situ B(C 6F 5) 3-activated zinc species were not isolated, the sterically demanding BOX ligands ( 1c > 1b > 1a) and functionalized NHC ligands seem to enhance the stability of highly electrophilic zinc complexes over ligand redistribution, allowing a better control of the cationic ROP as reflected particularly for 3d and 4e complexes by their respective efficiency (42–88%).

Novel multidentate pyridyl/thiazolyl ligands containing terpyridine units: formation of dinuclear and trinuclear double helicate complexes.

Three new multidentate N-donor ligands L 1–L 3, which contain a combination of pyridyl and thiazolyl donor units, have been prepared starting from 2,2′:6′,2″-terpyridine. The extended linear sequence of ortho-linked N-donor heterocycles (five for L 1; six for L 2; and seven for L 3) is reminiscent of the well-known oligopyridines, although they have different coordination properties due to the presence of five-membered thiazolyl rings which result in natural breaks of the ligand backbone into distinct bidentate or terdentate domains. Thus, the pentadentate ligand L 1 partitions into terdentate and bidentate domains to give a dinuclear double helicate [M 2(L 1) 2] 4+ with Cu(II). The hexadentate ligand L 2 partitions into two terdentate domains to give dinuclear double helicates [M 2(L 2) 2] 4+ with six-coordinate first-row transition metals dications (M=Ni and Co). The heptadentate ligand L 3 partitions into two terminal bidentate and a central terdentate domains to give a trinuclear double helicate [Cd 3(L 3) 2] 6+ with Cd(II). The formation of these complexes highlights the fact that the thiazole group is instrumental in instructing the partitioning of the ligand, which in turn controls the formation of the helicate complexes.

New multidentate ligands for supramolecular coordination chemistry: double and triple helical complexes of ligands containing pyridyl and thiazolyl donor units

Four new multidentate N-donor ligands L1–L4 have been prepared which contain a combination of pyridyl and thiazolyl donor units. The syntheses of these ligands are facile and high-yielding, being based on reaction of an α-bromoacetyl unit with a thioamide to form the thiazolyl ring. The extended linear sequence of ortho-linked N-donor heterocycles (four for L1, six for L2; five for L3; and six for L4) is reminiscent of the well-known linear oligopyridines, although these new ligands are much easier to make and have significantly different geometric coordination properties because the presence of the five-membered thiazolyl rings results in natural breaks of the ligand backbone into distinct bidentate or terdentate domains. Thus, the tetradentate ligand L1 partitions into two bidentate domains to give dinuclear triple helicates [M2(L1)3]4+ with six-coordinate first-row transition metal dications (M = Co, Cu, Zn). The hexadentate ligand L2 partitions into two terdentate domains to give dinuclear double helicates [M2(L2)2]4+ with six-coordinate metal ions (M = Cu, Zn). In the double helicate [Cu2(L3)2]4+ the pentadentate ligand L3 only uses its two terminal bidentate binding sites, resulting in four-coordinate Cu(II) centres and a non-coordinated pyridyl residue in the centre of each of the two ligand strands. These pendant pyridyl residues are directed towards each other to give a potentially two-coordinate cavity between the metal ions in the centre of the helicate. Similarly, in the double helicate [Cu2(L4)2]4+ the metal ions are only four-coordinate, with each ligand having its central bipyridyl unit un-coordinated. This results in a potentially four-coordinate cavity between the two metal ions in the centre of the helicate. These easy-to-prepare ligands offer a great deal of scope for the development of multinuclear helicates.

Hexafluoropentanedionatosilver(I) complexes stabilised by multidentate N-donor ligands: crystal structure of a charge-separated salt species soluble in supercritical carbon dioxide

A tetrahydrofuran suspension of silver(I) oxide reacted with Hhfpd (1,1,1,5,5,5-hexafluoropentane-2,4-dione) to give in situ ‘[Ag(hfpd)]’ after removal of the solvent in vacuo. Addition of equimolar ratios of multidentate amines to toluene solutions of the ‘[Ag(hfpd)]’ led to the isolation of several hexafluoropentanedionatosilver(I) complexes, [Ag(hfpd)(L–L)] [L–L = Me 2 NCH 2 CH 2 NHMe (trimen) 1, Me 2 N(CH 2 ) 2 NMe(CH 2 ) 2 NMe 2 (pmdien) 2 or Me 2 N(CH 2 ) 2 NMe(CH 2 ) 2 NMe(CH 2 ) 2 NMe 2 (hmten) 3]. Addition of only half a molar equivalent of hmten to a toluene solution of ‘[Ag(hfpd)]’ led to the synthesis of [Ag(hmten)][Ag(hfpd) 2 ] 4. The products have been characterised by a variety of methods including microanalysis, IR, 1 H and 13 C NMR spectroscopy and mass spectrometry and all complexes dissolve readily in supercritical carbon dioxide. Complexes 2 and 4 have been further characterised by X-ray crystallography. The structure of 2 contains a monomeric five-co-ordinate silver(I) cation in which the two chelating oxygens and two of the three amine nitrogens are in an almost planar arrangement. In comparison, the structure of 4 reveals a charge-separated salt; one of the silver atoms is exclusively co-ordinated to two hfpd ligands in a pseudo-tetrahedral arrangement, whilst the other is encapsulated by an hmten molecule.