Structure-dependent spectroscopic and redox properties of copper(I) complexes with bidentate iminopyridine ligands

A series of iminopyridine ligands; cyclopropylpyridin-2-ylmethyleneamine (A), cyclopentylpyridin-2-ylmethyleneamine (B), cyclohexylpyridin-2-ylmethyleneamine (C), and cycloheptylpyridin-2-ylmethyleneamine, (D) and their copper(I) complexes, [Cu(L)₂]⁺ (1a-1d) and [Cu(L)(PPh₃)₂]⁺ (2a-2d) have been synthesized and characterized by CHN analyses, ¹H NMR and IR and UV-Vis spectroscopy. Structures of 1a, 1b, 1c and 2a were determined by X-ray crystallography. The coordination polyhedron about the Cu^I center in the complexes is best described as a distorted tetrahedron. The dihedral angles between the least-squares planes of the chelate ligands show considerable variation from 86.1° in 1a to 68.3° in 1b, indicating the importance of packing forces in the crystalline environment. The UV-Vis spectra of the complexes are characterized by first metal to ligand charge transfer bands increasing in wavelength with increasing size of the ring substituents in the ligands, except for the cyclopropyl compounds (1a and 2a), in good agreement with the variation of the dihedral angles between the ligand planes. Cyclic voltammetry of the complexes indicates a quasireversible redox behavior for the complexes. The bulkier ligands (PPh₃) inhibit the geometric distortion within the oxidized form and the redox potentials of complexes 2a-2d are shifted to more positive values, therefore.     

Coordination geometry isomerism induced by N-H?Cl, C-H?Cl, C-H?N, C-H?π and π?π supramolecular interactions in mercury(II) complexes with tripyridylimidazole chelating ligands

Reaction of HgCl₂ with trans-(±)2-(2,5-di(pyridin-2-yl)-4,5-dihydro-1H-imidazol-4-yl)pyridine (L1) and cis-(±)-(phenyl(2,4,5-tri(pyridin-2-yl)-4,5-dihydroimidazol-1- yl)methanone (L2) gives mononuclear complexes, 1 and 2. In these complexes L1 and L2 behave as tridentate and bidentate chelating ligands, giving distorted trigonal bipyramidal and tetrahedral coordination geometries, respectively. X-ray diffraction studies revealed a series of N-H?Cl, C-H?Cl, C-H?N and C-H?π interactions in 1 giving a 3D network, and N-H?Cl, C-H?Cl, C-H?π and π?π interactions in 2 giving a 2D network in the crystal lattice. Since both ligands should have a similar binding capacity to the mercury ions, the variations observed for coordination number and geometry should be a consequence of supramolecular stabilizing effects.     

Palladium(II) complexes obtained from 3,4-bis(cyanamido)cyclobutane-1,2-dione dianion

Three palladium(II) complexes have been synthesized, using 3,4-bis(cyanamido) cyclobutane-1,2-dione dianion (3,4-bis(cyanamido)squarate or 3,4-NCNsq²⁻): [Pd(en)(3,4-NCNsq)] · 1.5H₂O (1) (en=1,2-diaminoethane), [Pd(en)(3,4-(NC(O)NH₂)sq)] · 0.5H₂O (2) and K₃Na[Pd₂(3,4-(NCN)₂sq)₄] · 5H₂O (3). Complex 1 has been characterized by elemental analysis, IR and ¹³C NMR spectroscopies. Complexes 2 and 3 have been characterized by single-crystal X-ray diffraction. In complex 2, the unusual hydration of the cyanamido ligand was observed, it proceeds in the coordination sphere of the palladium and leads to a chelating urea squarate ligand. Complex 3 is an anionic dinuclear complex containing four bridging cyanamido squarate ligands. In complexes 2 and 3, the 3,4-NCNsq²⁻ ligand (hydrated or not) is, for the first time, coordinated to the metal atom by the two amido nitrogen atoms, either in a chelating mode (complex 2) or in a bridging mode giving a short Pd ? Pd distance of 2.8866(15) Å (complex 3). Electrochemical studies in acetonitrile and dmf solutions have been performed on complexes 1 and 3.     

Synthesis, structures and luminescent properties of novel coordination polymers constructed by lanthanide salts and benzimidazole-5,6-dicarboxylic acid

Two three-dimensional (3D) novel lanthanide complexes with the H₂Lbenzimidazole-5,6-dicarboxylate [Ln₂L₃(H₂O)] [Ln = Eu (1), Tb (2)] and one two-dimensional (2D) novel lanthanide complex [Pr(L)(HL)H₂O]·H₂O (3) were synthesized by hydrothermal reaction at 180 °C and characterized by elemental analysis, infrared spectra and single-crystal X-ray diffraction. The result showed that complexes 1 and 2 are isostructural and build porous 3D networks by L²⁻ groups linking Ln(III) atoms via tetradentate (bridging and bridging) and pentadentate (bridging/chelating and bridging) coordination modes. Complex 3 is a eight-coordinated Pr(III) chain complex, exhibiting a 2D polymeric network with parallel Pr-carboxylate chains along the crystallographic c-axis. In addition, it is found that in these structures, coordination modes of L²⁻ and HL⁻ are versatile and can adopt different conformations according to distinct dimensions of polymeric structures. The photoluminescent properties of 1, 2 and thermogravimetric analyses of the three complexes were discussed in detail.     

Design, synthesis and coordination chemistry of sidearm substituted bisoxazoline ligands

We describe herein the design, synthesis and coordination chemistry of a novel ligand motif that combines a bisoxazoline with a third flexible chelating substituent (“tail”). Four such ligands (6-9) were synthesized from phenylglycine in 4-5 steps each in ca. 20% overall yield. Coordination of 6 and 7 to [Re(CO)₄Cl]₂ yielded crystals suitable for X-ray analysis. Likewise, crystals were obtained from coordination of 6 to FeCl₂. The solid state structures of the resulting complexes (10-12) reveal κ² binding of the bisoxazoline motif; however, the structures of complexes 10 and 12 show that the “tail” is poised above the metal center, demonstrating the potential for alternate binding modes in solution. The complexes exhibit a relatively planar 6-membered chelate structure, in contrast to the boat conformation typical of trispyrazolylborate complexes.     

Luminescence properties and solution dynamics of lanthanide complexes composed by a macrocycle hosting site and naphthalene or quinoline appended chromophore

The two-component ligand systems 1 and 2 which contain 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) as the hosting unit for the lanthanide cations, and naphthalene (which is devoid of any chelating ability) or quinoline units, respectively, as chromophores, were synthesized. The 1:1 complexes with Gd³⁺, Eu³⁺ and Tb³⁺ have been studied in aqueous solution. Relaxometric properties for Gd · 1 indicate that two water molecules (q = 2) are in the first coordination sphere of the metal ion whereas for Gd · 2, q < 2 is found. For Gd · 1, these results indicate that the naphthalene unit is not coordinated to the metal centre; for the case of quinoline, reasons for the lower hydration state are discussed. In case of Eu · 1, Tb · 1, Eu · 2, and Tb · 2 the absorption and luminescence spectra, the overall luminescence efficiencies, and the metal-centred lifetimes, were obtained both in water and deuterated water. The coordination features of these complexes were explored by comparing their luminescence properties, resulting in hydration state q = 2 and 1.4 for the cases of the complexes of 1 and 2, respectively. Use of the photophysical parameters in air-equilibrated water allowed the determination of the ligand-to-cation energy transfer efficiency, Φ_EnT, leading to the overall emission sensitization process. For Eu · 1, and Eu · 2, we found Φ_EnT = 0.034 and 0.078, respectively, supporting that also a non-coordinating chromophore like naphthalene, case of ligand 1, can transfer excitation energy to the metal centre.     

Synthesis, characterization and bioactivity of two novel trinuclear Cu(II)/Ni(II) complexes with pentadentate ligand N-2-methyl-acryloyl-salicylhydrazide

Two new trinuclear complexes, Cu₃L₂(py)₂ (1) and Ni₃L₂(py)₄ (2), have been synthesized and characterized, where L³⁻ is N-2-methyl-acryloyl-salicylhydrazidate. Central metal ion and two terminal metal ions in the two complexes are combined by two bridging deprotonated L³⁻ ligands, forming a bent trinuclear structure unit with an M-N-N-M-N-N-M core. The bent angles in complexes 1 and 2 are 167.6(1)° and 75.4(1)°, respectively. Three nickel ions in compound 2 exhibit alternating square-planar and octahedral geometries, while three copper ions in compound 1 follow square-planar mode. The studies in solution integrity and stability of compounds 1 and 2 show they are soluble and stable in DMF. UV-Vis titrations demonstrate compound 1 is stable in DMF even in the presence of excess metal ions. Antibacterial screening data indicate the two compounds all have stronger antimicrobial activities against the tested microorganisms than ligand. The trinuclear copper compound 1 is more active than monocopper compounds in the previous study, and the trinuclear nickel compound 2 is less active than tetranuclear nickel compound in the previous study.     

Supramolecular assembly driven by hydrogen-bonding and π-π stacking interactions based on copper(II)-terpyridyl complexes

Six 2D and 3D supramolecular complexes [Cu(L1)(O₂CCH₃)₂] · H₂O (1), [Cu₂(L2)₂(μ₂-O₂CCH₃)₂](BF₄)₂ (2), [Cu₂(L1)₂(BDC)(NO₃)₂] · 0.5H₂O (3) [Cu₂(L2)₂(BDC)(NO₃)₂] (4), [Cu₂(L3)₂(BDC)(NO₃)₂] · 0.5H₂O (5) and [Cu₂(L2)₂(BDC)(H₂O)₂](BDC) · 8H₂O (6) (L1 = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine, L2 = 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine, L3 = 4′-phenyl-2,2′:6′,2″-terpyridine, BDC = 1,4-benzenedicarboxylate), have been prepared and structurally characterized by X-ray diffraction crystallography. In complexes 1, 3, and 4, 1D channels are formed through C-H?O and C-H?N hydrogen-bonding interactions, and further linked into 3D structure via C-H?O and O-H?O interactions. Complex 2 is a 2D layer constructed from intermolecular C-H?F and π-π stacking interactions. In the structure of 6, the BDC²⁻ ions and solvent water molecules form a novel 2D layer containing left- and right-handed helical chains via hydrogen-bonds, and an unusual discrete water octamer is formed within the layer. In 2, 4, 6 and [Ag₂(L2)₂](PF₆)₂ (7) the bonding types of pendent pyridines of L2 depending on the twist about central pyridines are involved in intramolecular (2 and 4), intermolecular (6) or coordination bonds (7) in-twist-order of 5.8°, 3.7°, 28.2° and 38.0°, respectively. Differently, the pendent pyridines of L1 in 1 and 3 form intermolecular hydrogen bonds despite of distinct corresponding twist angles of 25.1° (1) and 42.6°(3). Meanwhile, π-π stacking interactions are present in 1-6 and responsible for the stabilization of these complexes.     

S versus O alkylation and coordination in zinc complexes containing the bulky heteroscorpionate alkoxy ligand bis(3,5-dimethylpyrazol-2-yl) diphenylmethanol

A series of zinc complexes containing the tripodal heteroscorpionate ligand bis(3,5-dimethylpyrazol-2-yl)diphenylmethanol (L2H) have been synthesized and characterized by X-ray crystallography. The L2H/Zn complexes were designed to model the N₂OX coordination (with the zinc-bound O being a reactive nucleophile) that is characteristic of many protease and amidase zinc enzymes. The pseudotetrahedral mononuclear complexes characterized include [(L2)ZnI] (1), [(L2)Zn(CH₃)] (2), and [(L2)Zn(SPh)] (3). Alkylation of (1) with methyl iodide has revealed a modest nucleophilicity of the chelated zinc-bound alkoxide, and produces the penta-coordinate [(L2OCH₃)ZnI₂] (4) which contains a weakly bound ether in the fifth coordination site. However, when the coordination sphere also includes a thiolate sulfur as in (3), reaction with methyl iodide produces exclusive alkylation at the sulfur to produce thioanisole and (1). The coordination of the ether in the neutral (4) can be strengthened by reaction with various silver salts, Ag⁺X⁻, to produce other penta-coordinate complexes [(L2OCH₃)ZnI(Tf)] (5) and [(L2OCH₃)ZnI(H₂O)]BF₄ (6) which show enhanced coordination of the ether.     

Mono- and dinuclear manganese(II) complexes derived from the cis/trans isomers of 2,4,5-tris(2-pyridyl)-4,5-dihydroimidazole

Two new manganese(II) complexes, [Mn(L1)(L1H)(ClO₄)(H₂O)][ClO₄]₂·0.5CH₃CN·H₂O (1) [L1 = trans-(±)2-(2,5-di(pyridin-2-yl)-4,5-dihydro-1H-imidazol-4-yl)pyridine)] and [Mn₂(μ-L2)₂(H₂O)₃(CH₃CN)₃][ClO₄]₄·2CH₃CN (2) [L2 = cis-(±)2-(2,5-di(pyridin-2-yl)-4,5-dihydro-1H-imidazol-4-yl)pyridine)], have been prepared and examined by single-crystal X-ray diffraction analysis, showing that complex 1 is a mononuclear compound, whereas complex 2 is a dinuclear species. The cis/trans isomers L1 and L2 have similar coordination properties, but behave as bidentate and tridentate chelating ligands, respectively, giving distorted octahedral metal coordination geometries. X-ray diffraction studies revealed that the molecular and crystal structures are stabilized by a series of intra- and intermolecular interactions. In both cases extended supramolecular networks are generated, in compound 1 through O-H···O, O-H···N, N-H···O, N-H···N, C-H···O, C-H···N, C-H···π and π···π interactions, and in compound 2 through O-H···O, O-H···N, C-H···O and π···π interactions. The observed structural differences between the two metal complexes might be a consequence of these stabilizing effects.     

Coordination polymers derived from a bis-pyridyl-bis-amide ligand: Supramolecular structural diversities and anion binding properties

Six new coordination polymers namely [{Cu(μ-L1)(CH₃COO)₂}]_∝1a, [{Cu(μ-L1)₂(CH₃COO)₂]_∝1b, [{Cu(μ-L1)₂(H₂O)₂}(NO₃)₂]_∝2, [{Cu(μ-L1)₂(H₂O)₂}(ClO₄)₂]_∝3, [{Cu(μ-L1)(H₂O)₂(μ-SO₄)}·3H₂O]_∝4a and [{Cu(μ-L1)₂SO₄}·X]_∝4b (L1 = N,N′-bis-(3-pyridyl)terephthalamide) have been synthesized. Single crystal structures of five coordination polymers namely 1a, 2-4b and the free ligand L1 are discussed in the context of the effect of conformation dependent ligating topology of the ligands, hydrogen bonding backbone, counter anions on the resultant supramolecular structures observed in these coordination polymers. It was revealed from the single crystal X-ray structure analysis that conformation dependent ligating topology of the bis-amide ligand L1, counter anion’s ligating strength dependent metal: ligand ratio, hydrogen bonding ability of the ligand as well as counter anions are responsible for the formation of 1D zigzag, 1D looped chain, 2D corrugated sheet in 1a, 2-3, 4a−4b, respectively. By following in situ coordination polymer crystallization technique, anion binding and separation studies have also been performed; nitrate anion has been separated as neat coordination polymer crystals from a complex mixture of anions.     

Synthesis, characterization, and reactivity of zinc carboxylate complexes of 2,3-pyridine dicarboxylic acid and (3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)acetic acid

Ethylenediammonium tris-2,3-pyridine dicarboxylato zinc(II) trihydrate (enH₂)₂[ZnL₃]·2H₂O (1) (where H₂L = 2,3-pyridine dicarboxylic acid, en = ethylenediamine) and a mixed metal coordination polymer with composition [Na₂ZnL′₃(OAc)(H₂O)₃]_n (2) {where L′ = anion of (3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)acetic acid} are synthesized and characterized. The complex 1 is mono nuclear complex with three coordinating carboxylate anion along with nitrogen chelating zinc ion and there is three uncoordinated carboxylate group one each from three ligand molecules making a complex anion of zinc(II). The zinc(II) ion are in distorted octahedral coordination geometry. In this complex diprotonated ethylenediamines serve as cations. The complex 2 has a polymeric structure with one acetate and three carboxylate of L′ binding to zinc ion provides a tetrahedral environment and these ligands further hold dinuclear units of tri-aquated sodium ions; each dinuclear sodium units are bridged by one water molecule make the coordination polymer. The catalytic ability of these two complexes 1 and 2 towards carbon-carbon bond formation reaction between 3,4-dimethoxy benzaldehyde and acetone are studied. Both the complexes as well as sodium salt of L′ are found to be catalyst for such reactions.     

One-dimensional helical coordination polymers of cobalt(II) and iron(II) ions with 2,2′-bipyridyl-3,3′-dicarboxylate (BPDC)

One-dimensional (1-D) helical coordination polymers, [M^II(H₂O)₃(BPDC)]_n · nH₂O (M = Co (1), Fe (2)), have been prepared by the self-assembly of cobalt(II) and iron(II) ions, respectively, with 2,2′-bipyridyl-3,3′-dicarboxylic acid (H₂BPDC) in an aqueous solution. X-ray crystal structures of compounds 1 and 2 show that each metal ion displays a distorted octahedral coordination geometry including three water oxygen atoms, one oxygen atom of the carboxylate of a BPDC²⁻ belonging to the adjacent metal ion and two nitrogen atoms from the BPDC²⁻ acting as a chelating ligand. In 1 and 2, one carboxylate oxygen atom of coordinated BPDC²⁻ binds to the neighboring metal ion, which give rise to 1-D helical coordination polymers. The helical chains of 1 and 2 are linked by the hydrogen bonding interactions between the carboxylate oxygen atom of the BPDC²⁻ ion belonging to a chain and the water molecule of the adjacent helical chain, which lead to 2-D networks extending along the ab plane. The supramolecules 1 and 2 show isomorphous structures regardless of the metal ions.     

S-allyl-3-(2-pyridyl-methylene)dithiocarbazate ligand and its manganese(II), cobalt(III) and nickel(II) complexes

A new NNS tridentate ligand, S-allyl-3-(2-pyridyl-methylene)dithiocarbazate (HL) has been prepared. Three coordination complexes, Mn(L)₂ (1), [Co(L)₂]NO₃ (2) and Ni(L)₂ (3) (L⁻ is the deprotonated monoanionic form of HL) have been synthesized and characterized by elemental analysis, molar conductivity, FT-IR, ¹H NMR and UV-Vis spectroscopy. 1 and 3 are neutral complexes, while 2 is cationic with nitrate as the counter ion. Single crystal X-ray diffraction analysis shows that bis-chelate complexes have a distorted octahedral geometry in which two ligands in thiolate tautomeric form coordinate to the metal center through N atoms of the pyridine and imino moieties and one S atom. Molecular geometry from X-ray analysis, molecular geometry optimization, atomic charges distribution and bond analysis of the ligand and complexes have been performed using the density functional theory (DFT) with the B3LYP functional.     

Synthesis, characterisation and crystal structures of a few coordination complexes of nickel(II), cobalt(III) and zinc(II) with N′-[(2-pyridyl)methylene]salicyloylhydrazone Schiff base

Four new coordination complexes, Ni^II(L)₂ (1), [Co^III(L)₂]ClO₄ (2), [Zn(HL)(L)]ClO₄ · H₂O (3) and [Zn(L)₂][Zn(L)(HL)]ClO₄ · 7H₂O (4) (where L is a monoanion of a Schiff base ligand, N′-[(2-pyridyl)methylene]salicyloylhydrazone (HL) with NNO tridentate donor set), have been synthesised and systematically characterised by elemental analysis, spectroscopic studies and room temperature magnetic susceptibility measurements. Single crystal X-ray diffraction analysis reveals that 1 is a neutral complex, while 2-4 are cationic complexes. Among them, 4 is a rare type of cationic complex with two molecules in the asymmetric unit. The ligand chelates the metal centre with two nitrogen atoms from the pyridine and imino moieties and one oxygen atom coming from its enolic counterpart. All the reported complexes show distorted octahedral geometry around the metal centres, with the two metal-N (imino) bonds being significantly shorter than the two metal-N (Py) bonds.     

Neutral and cationic palladium(II) and platinum(II) complexes of 2,2′-dipyridylamine with saccharinate: Syntheses, spectroscopic, structural, fluorescent and thermal studies

Four palladium(II) and platinum(II) complexes of 2,2′-dipyridylamine (dpya) with saccharinate (sac), cis-[Pd(dpya)(sac)₂]·H₂O (1), cis-[Pt(dpya)(sac)₂]·H₂O (2), [Pd(dpya)₂](sac)₂·2H₂O (3) and [Pt(dpya)₂](sac)₂·2H₂O (4), have been synthesized and characterized by elemental analysis, IR, NMR, TG-DTA and X-ray diffraction. In 1 and 2, the metal ions are coordinated by two N-bonded sac ligands, and two nitrogen atoms of dpya, resulting in a neutral square-planar coordination sphere, while in 3 and 4, the metal ions are coordinated by two dpya ligands to generate square-planar cationic species, which are stabilized by two sac counter-ions. The mononuclear species of 1 and 2 interact each other through weak intermolecular N-H?O, C-H?O and π?π interactions to form a three-dimensional network, while the ions of 3 and 4 are connected by N-H?N and OW-H?O hydrogen bonds into one-dimensional chains. On heating at 250 °C, the solid cationic complexes of 3 and 4 convert to corresponding anhydrous neutral complexes of 1 and 2 after elimination of a dpya ligand. In addition, all complexes 1-4 are luminescent at room temperature and their emissions seem to be attributed to the MLCT fluorescence.     

Electrochemical synthesis and crystal structure of iron(II), cobalt(II), nickel(II) and copper(II) complexes of dianionic tetradentate N4 Schiff base ligand

The electrochemical oxidation of anodic metal (iron, cobalt, nickel and copper) in an acetonitrile solution of the potentially chelating Schiff base N,N(dithiodiethylenebis-(aminylydenemethylydene)-bis(1,2-phenylene)ditosylamide (H₂L) afforded stable complexes of empirical formula [ML]. The compounds obtained have been characterized by microanalysis, IR spectroscopy and ES-MS mass spectrometry. The crystal and molecular structures of [FeL]·CH₃CN (1) [CoL]·CH₃CN (2), [NiL]·CH₃CN (3) and [CuL]·CH₃CN (4) have been determined by X-ray diffraction in all complexes, the metal atom is in a distorted tetrahedral environment with the Schiff base acting as a tetradentate N4 donor.     

Neutral and cationic rare-earth metal alkyl complexes that contain bis(2-methoxyethyl)(trimethylsilyl)amine, a neutral [ONO]-type ligand

Neutral tris(trimethylsilylmethyl) complexes [Ln(CH₂SiMe₃)₃(L)] (Ln = Sc (1), Lu (2)) and cationic bis(trimethylsilylmethyl) complexes [Ln(CH₂SiMe₃)₂(L)(THF)]⁺[BPh₄]⁻, (Ln = Sc (3), Lu (4)) that contain bis(2-methoxyethyl)(trimethylsilyl)amine (L = Me₃SiN(CH₂CH₂OMe)₂) as a neutral, tridentate ligand were synthesized and characterized by NMR spectroscopy. X-ray structural analysis was performed for the scandium complex 1 and exhibited a distorted octahedral coordination geometry with a facially arranged ligand at the neutral scandium center. NMR spectroscopy corroborated the coordination of the tertiary amine function of the ligand to the metal. Complexes 3 and 4 expand the still limited range of cationic rare-earth metal alkyl complexes with known neutral, multidentate ligands.     

Hydrothermal synthesis of copper complexes of 4′-pyridyl terpyridine: From discrete monomer to zigzag chain polymer

Seven copper complexes [Cu(L1)I₂] (1), [Cu₂(L1)₂I₂]₂[Cu₂(μ-I)₂I₂] (2), [Cu(L2)I₂] (3), [Cu₂(L2)(μ-I)I(PPh₃)] (4), [Cu₄(L2)₂(μ-I)₂I₂] (5), {[Cu(L2)I]₂[Cu₂(μ-I)₂I₂]}_n (6) and [Cu₂(L2)(μ-I)₂]_n (7) have been prepared by reactions of ligands: 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine (L1) and 4′-(3-pyridyl)-2,2′:6′,2″-terpyridine (L2) with CuI in hydrothermal conditions, respectively. By alternating the oxidations states of the metal centers, increasing stoichiometric metal/ligand ratio and introducing a second ligand, the compounds, were successfully developed from mononuclear (1 and 3) to multinuclear (2, 4 and 5) and polymers (6 and 7). The synthesis of these compounds may provide an approach for the construction of coordination compounds of 4′-pyridyl terpyridine with different nuclearity.     

Exploring the effect of chain length of bridging ligands in coordination complexes and polymers derived from mixed ligand systems of pyridylnicotinamides and dicarboxylates

The supramolecular structural diversities in mixed ligand systems derived from a series of dicarboxylate anions with varying chain lengths and N-donor exo-bidentate ligand equipped with hydrogen bonding capable amide backbone with Co(II)/Zn(II) metal centers are analyzed. In this context, two complexes namely (Co(L1)₂(malonate)(H₂O)₂} (1a), {Zn(L1)₂(malonate)(H₂O)₂} (1b) and one coordination polymer namely {[Co(μ-L1)(μ-glutarate)(H₂O)] · H₂O}_n (4) (where L1 = N-(4-pyridyl)nicotinamide) have been synthesized and crystallographically characterized. The main aim of this work is to explore the effects of chain lengths of the anionic carboxylate ligands such as malonate, succinate, maleate, and glutarate, in determining the final architecture of coordination compounds based on the mixed ligands. Analyses of the structures revealed that the length of the bridging ligands have prominent effect in the formation of hierarchical structures.