Zn(II) and Hg(II) complexes of naphthalene based thiosemicarbazone: Structure and spectroscopic studies

Synthesis, structure and spectroscopic characterization of 2-thiophenealdehyde-N(4)-napthylthiosemicarbazone and its complexes with biologically important Zn(II) and toxic Hg(II) metal ions have been reported. The crystal structure of the complexes reveals that both are distorted tetrahedral. In the Hg(II) complex the ligand is neutral and mondented where as in Zn(II) complex the ligand is bidented and anionic. Whereas conductivity measurement study shows both the complexes are molecular species. The beautiful changes in absorption spectra along with isosbestic points upon addition of respective metal salts to the ligand solution convincingly support the formation of metal complexes in solution phase. The other spectroscopic studies also show good correlation with their solid state structures.     

Squarato-metal(II) complexes. 1: Structural and magnetic characterization of squarato-bridged dinuclear nickel(II) and copper(II) complexes

A new series of dinuclear squarato-bridged nickel(II) and copper(II) complexes [Ni₂(2,3,2-tet)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (1), [Ni₂(aepn)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (2), [Cu₂(pmedien)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂.4H₂O (3) and [Cu₂(DPA)₂(μ_1,2-C₄O₄)(H₂O)₂](ClO₄)₂ (4) where is the dianion of 3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid), 2,3,2-tet = 1,4,8,11-tetraazaundecane, aepn = N-(2-aminoethyl)-1,3-propanediamine, pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine and DPA = di(2-pyridylmethyl)amine were synthesized and structurally characterized by X-ray crystallography. The spectral and structural characterization as well as the magnetic behaviour of these complexes is reported. In this series, structures consist of the groups as counter ions and the bridging the two M(II) centers in a μ-1,3- (1-3) and in a μ-1,2-bis(monodentate) (4) bonding fashions. The coordination geometry around the Ni(II) ions in 1 and 2 is six-coordinate with distorted octahedral environment achieved by N atoms of the amines and by one or two oxygen atoms from coordinated water molecules, respectively. In the Cu(II) complexes 3 and 4, a distorted square pyramidal geometry is achieved by the three N-atoms of the aepn or DPA and by an oxygen atom from a coordinated water molecule. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the M(II) centers. The complexes show weak antiferromagnetic coupling with ∣J∣ = 1.8-4.2 cm⁻¹ in the μ-1,3- bridged squarato compounds 1-3, and J = −16.1 cm⁻¹ in the corresponding μ-1,2- bridged squarato complex 4. The magnetic properties are discussed in relation to the structural data.     

A study on mono-, bis- and tris-N-functionalized 1,4,7-triazacyclononane with benzimidazolyl groups and their nickel(II) complexes

Three new ligands, 1-(benzimidazolyl-2-methyl)-1,4,7-triazacyclononane L¹, 1,4-bis(benzimidazolyl-2-methyl)-1,4,7-triazacyclonone L², and 1,4,7-tris-(benzimidazolyl-2-methyl)-1,4,7-triazacyclonane L³, were synthesized by a straightforward one-pot method. Their nickel(II) complexes , [NiL²CH₃CN](ClO₄)₂ · 2CH₃OH · H₂O (or [NiL²Cl] · ClO₄) and [Ni(H₋₂L³)] · H₂O were obtained and characterized by electrospray mass spectrum, ¹H NMR, CV and other physical methods. Their crystal structures were determined by X-ray analyses. The crystal structure of the nickel(II) complex of L¹ shows that two Ni(II) atoms are bridged by two Cl⁻ anions. A ferromagnetic exchange coupling and zero-field splitting effect exist in complex 1.     

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.     

Synthesis and characterization of nickel(II) and copper(II) complexes with tetradentate Schiff base ligands

The 1:1 condensation of 1,2-diaminopropane and 1-phenylbutane-1,3-dione at high dilution gives a mixture of two positional isomers of terdentate mono-condensed Schiff bases 6-amino-3-methyl-1-phenyl-4-aza-2-hepten-1-one (HAMPAH) and 6-amino-3,5-dimethyl-1-phenyl-4-aza-2-hexen-1-one (HADPAH). The mixture of the terdentate ligands has been used for further condensation with pyridine-2-carboxaldehyde or 2-acetylpyridine to obtain the unsymmetrical tetradentate Schiff base ligands. The tetradentate Schiff bases are then allowed to react with the methanol solution of copper(II) and nickel(II) perchlorate separately. The X-ray diffraction confirms the structures of two of the complexes and shows that the condensation site of the diamine with 1-phenylbutane-1,3-dione is the same.     

Dinuclear nickel(II) and zinc(II) complexes of 2,6-bis[{bis(2-pyridylmethyl)amino}methyl]-4-methylphenol

Reaction of the symmetrical proligand H₂L with metal(II) acetate and a counteranion to promote crystallisation has given the homodinuclear complexes [Zn₂L(OAc)₂](BF₄)]·2MeOH and [Ni₂L(OAc)₂](BF₄)]·2MeOH the crystal structures of which are reported. These show the presence of a triply bridging (μ-cresolato)bis(μ-carboxylato) dimetal core.     

Syntheses and characterization of mono- and di-N-hydroxyethylated tetraaza macrocycles containing eight C-methyl groups and their nickel(II) and copper(II) complexes

New partially N-hydroxyethylated 14-membered tetraaza macrocycles 1,8-bis(2-hydroxyethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L²) and 1-(2-hydroxyethyl))-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L³) have been synthesized selectively by the one-step reaction of 2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L¹) with 2-hydroxyethyl bromide. The complexes [NiL³]²⁺, [CuL²]²⁺, and [CuL³]²⁺ have been prepared and characterized. The complex [CuL²](ClO₄)₂ has a square-pyramidal coordination geometry with one apical oxygen atom; only one of the two hydroxyethyl groups is coordinated to the metal ion. Electronic absorption spectra of [CuL³](ClO₄)₂ containing one hydroxyethyl pendant arm indicate that the geometry is similar to that of [CuL²](ClO₄)₂. Unexpectedly, the nickel(II) complex [NiL³](ClO₄)₂ has a severely distorted trigonal bipyramidal coordination geometry with the oxygen atom of the pendant arm at the equatorial position. The Ni---O bond distance of the nickel(II) complex is shorter, or not longer, than the Ni---N bond distances. The ligand in [CuL²]²⁺ is in the RRSS (trans-III) configuration, as usual, whereas that in [NiL³]²⁺ has the RRRR (trans-V) conformation. The coordination geometry and properties of [NiL³]²⁺ are quite different from those reported for other related nickel(II) complexes containing one functional pendant arm.     

Electronic spectrum and magnetic properties of a dinuclear nickel(II) complex with two nickel(II) ions of C2-twisted octahedral geometry

A dinickel(II) complex [Ni₂(sym-hmp)₂](BPh₄)₂·3.5DMF·0.5(2-PrOH) (1) was synthesized with a dinucleating ligand, 2,6-bis[(2-hydroxyethyl)methylaminomethyl]-4-methyl-phenol [H(sym-hmp)]. The complex 1 (C₉₀H_118.50B₂N_7.50Ni₂O₁₀) crystallized in the triclinic space group with dimensions a = 14.7446(4) Å, b = 15.4244(4) Å, c = 18.7385(6) Å, α = 86.9495(9)°, β = 76.7263(10)°, γ = 86.5370(8)°, and V = 4136.8(2) Å³ and with Z = 2; this is isomorphous to a previous cobalt(II) complex [Co₂(sym-hmp)₂](BPh₄)₂. Single-crystal X-ray analysis revealed a bis(μ-phenoxo)dinickel(II) core structure containing two distorted octahedral nickel(II) ions of C₂ symmetry. The order of the coordination bond lengths is Ni-O(phenoxo) < Ni-O(hydroxy) < Ni-N. The electronic spectrum of 1 was typical for the octahedral nickel(II) complexes, but the axial elongation and the C₂-twist of the equatorial plane were found after a detailed analysis. The bond angles obtained by the electronic spectrum agreed with the crystallographically obtained bond angles within 2.3°. The order of the AOM parameters was e_{σ,O(phenoxo)} > e_{σ,O(hydroxy)} > e_σ,N, which was consistent with the order of the coordination bond lengths. Magnetic susceptibility data for 1 were fitted well with the parameters 2J = −69.7 cm⁻¹, D = 0.00 cm⁻¹, g = 2.17, and TIP = 265 × 10⁻⁶ cm³ mol⁻¹. The result indicates significant antiferromagnetic exchange interaction and negligible zero-field splitting, while the isostructural cobalt(II) complex showed an anisotropic behavior.     

Five manganese(II) complexes with seven- or eight-coordinated Mn(II), revealing different coordination modes for the nitrato ligands

Four seven-coordinated manganese(II) complexes [Mn(tpa)(η₁-NO₃)(η₂-NO₃)] (1), [Mn(bpia)(η₁-NO₃)(η₂-NO₃)] (2), [Mn(tpa)(η₁-NO₃)(η₂-NO₃)] (3), [Mn(tpa)(η₁-NO₃)(η₂-NO₃)] (4), and one octacoordinated manganese(II) complex [Mn(bppza)(η₂-NO₃)₂] (5) have been synthesized and characterized using the tripodal tetradentate ligands tpa, bpia, bipa, ipqa, and bppza (tpa: tris(2-pyridylmethyl)amine, bpia: bis(2-pyridylmethyl)(2-(N-methyl)imidazolylmethyl)amine, bipa: bis-(2-(N-methyl)imidazolylmethyl)(2-pyridylmethyl)amine, ipqa: (2-(N-methyl)imidazolylmethyl)(2-pyridylmethyl)(2-quinolylmethyl)amine, and bppza: bis(2-pyridylmethyl)(2-pyrazylmethyl)amine). The crystal structures for all compounds have been determined. 1, 2 and 3 crystallize in the triclinic space group , 4 crystallizes in the orthorhombic space group Pbca, whereas the eight-coordinated 5 crystallizes in the monoclinic space group P2₁/n. All compounds have one bidentate bound nitrate group in common. The coordination number and its geometry depend on the coordination mode of the second nitrate group. The coordination polyhedron for 1, 2, 3 and 4 is best described as an oblate octahedron and the one for 5 as a doubly oblate octahedron.     

Dinuclear terephthalato-bridged nickel(II) complexes. Structural characterization and magnetic properties

The dinuclear terephthalato-bridged nickel(II) complexes [Ni₂(cyclen)₂(μ-tp)](ClO₄)₂ (1) [Ni₂(trpn)₂(μ-tp)(H₂O)₂](ClO₄)₂ (2) and [Ni₂(3,3,3-tet)₂(μ-tp)(H₂O)₂](ClO₄)₂ · 2H₂O (3), where tp = terephthalate dianion, cyclen = 1,4,7,10-tetraazacyclododecane, trpn = tris(3-aminopropyl)amine and 3,3,3-tet = 1,5,9,13-tetraazatridecane, were synthesized and structurally characterized by X-ray crystallography. Their magnetic susceptibilities were also determined at variable temperatures over the range 2-300 K. The structures of these complexes consist of μ-tp bridging two Ni(II) centers in a bis(bidentate) bonding fashion in 1 and in bis(monodentate) bonding fashion in 2 and 3. The coordination geometry around the Ni(II) ions in these compounds has a distorted octahedral geometry with four nitrogen atoms from the amine ligand (cyclen, trpn or 3,3,3-tet) and two coordinated oxygen atoms supplied by the chelated carboxylate group of the bridged terephthalate ligand in 1, and by one tp-carboxylate-oxygen in 2 and 3. The sixth coordination site in the last two complexes 2 and 3 is achieved via an oxygen atom from a coordinated water molecule. The intradimer Ni…Ni distances in these complexes are 10.740, 11.428 and 11.537 Å for 1, 2 and 3, respectively. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Ni(II) centers. Also, the analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(bidentate) and bis(monodentate) coordination modes for the bridged terephthalate ligand in 1, 2 and 3, respectively. Despite the different coordination modes of the tp bridging ligand in these complexes, they all exhibit very weak antiferromagnetic coupling. The coupling constants J were found to be −2.2, −0.6 and −1.5 cm³ K mol⁻¹ for the complexes 1, 2 and 3, respectively. The structural and magnetic results of 1-3 are discussed in relation to the other related published μ-terephthalato dinuclear Ni(II) compounds.     

Synthesis, structures and properties of dinuclear cadmium(II) complexes based on polybenzimidazole binucleating ligands

Three novel cadmium(II) complexes [Cd₂(tbpo)(O₂CC₆H₄-p-NO₂)₂]ClO₄·3CH₃OH (1) [Cd₂(bbap)(O₂CC₆H₄-p-NO₂)₂]ClO₄·4.5CH₃OH·0.75H₂O (2) and [Cd(ntb)(O₂CC₆H₄-p-NO₂)]ClO₄·4CH₃OH (3) have been synthesized and characterized by IR, elemental analysis, ¹H NMR and X-ray crystallography, where tbpo⁻ and bbap⁻ are anions of N,N,N′,N′-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane and 2,6-bis[bis(2-benzimidazolylmethyl)aminomethyl]-4-methylphenol, respectively; ntb is tris(2-benzimidazolymethyl)amine. Complexes 1 and 2 contain μ-phenolate-bridged and μ-alkoxo-bridged dicadmium(II) cores with the Cd1?Cd2 separation of 3.671 Å for complex 1 and 3.718 Å for 2. One of the 4-nitrobenzoate anions bridged the two cadmium(II) ions in syn-anti mode through its carboxylate group, the other 4-nitrobenzoate is only coordinated with Cd2 in bidentate chelating mode. The two central cadmium(II) atoms are in trigonal bipyramidal and pentagonal bipyramidal geometry. In complex 3, the cadmium(II) atom is coordinated with four nitrogen atoms of ntb and one carboxylate oxygen atom of 4-nitrobenzoate in distorted trigonal bipyramidal geometry. Experiment shows that there is a higher affinity of 4-nitrobenzoate anion as coligand with the dinuclear [Cd₂(tbpo)]³⁺ and [Cd₂(bbap)]³⁺ cores than that with the mononuclear [Cd(ntb)]²⁺ core.     

Crystal structure of six and seven coordinate manganese(II) complexes with penta and hexadentate pyridylmethyl ligands

Two six-coordinated manganese(II) complexes [Mn(pydien)Cl](ClO₄) · C₂H₅OH (1), [Mn(pydien)NCS](ClO₄) (2) and two seven-coordinated manganese(II) complexes [Mn(pydado)Cl](ClO₄) (3), [Mn(pydado)NCS](ClO₄) (4) have been obtained using linear penta and hexadentate ligands pydien and pydado (pydien: 1,7-bis(2-pyridylmethyl)-1,4,7-triazaheptane and pydado: 1,10-bis(pyridylmethyl)-1,10-diaza-4,7-dioxadecane). The crystal structures for all compounds have been determined. 1 and 3 crystallize in the triclinic space group , 2 crystallizes in the orthorhombic space group Pbca, whereas 4 crystallizes in the monoclinic space group P2₁/c. The bound anion (chloro or isothiocyanato) in complexes 1 and 2 has no influence on the geometry of six-coordinate manganese(II) complexes, whereas the geometry and the wrapping of the hexadentate ligand (pydado) around Mn²⁺ cation depend on the nature of the bound anion. The complex 3 has a capped octahedron geometry with the two pyridyl groups in trans position, while the geometry of complex 4 can be described as pentagonal bipyramid with one pyridyl group and a thiocyanate anion in the axial positions.     

Synthesis and structures of pyridinecarboxylate-containing zinc(II) complexes in dien and tren system

Four new zinc(II) complexes [Zn(dien)(μ-nic)]₂(BPh₄)₂·2CH₃OH (1), {[Zn(dien)(isonic)]BPh₄}_n (2), [Zn(tren)(nic)]BPh₄ (3) and [Zn(tren)(isonic)]BPh₄ (4) (dien/tren = diethylenetriamine/triethylenetriamine, nic/isonic = nicotinate/isonicotinate anion) were synthesized and structurally characterized by IR, ¹H NMR and single crystal X-ray diffraction. In the zinc(II) complexes of dien, both nicotinate and isonicotinate connect the zinc(II) ions via N,O-bis-monodentate mode. Complex 1 contains a centrosymmetric dinuclear unit bridged by two nicotinate anions in anti-parallel way. Complex 2 is characterized by an infinite one-dimensional zigzag chain bridged by isonicotinate anion in an end-to-end mode. The Zn···Zn distance is 6.782 for 1 and 8.805 Å for 2. While in the complexes of tren, both 3 and 4 are mononuclear complexes with nicotinate and isonicotinate coordinated to zinc(II) ion through only one oxygen atom of their carboxylate groups. The zinc(II) ions in all of the four complexes are in a distorted trigonal bipyramidal geometry. Complex 3 forms a dinuclear unit and complex 4 forms an infinite 2D sheet structure through intermolecular H-bonds. In all of the crystal lattices, the counterions act to balance the electronic charge at the same time to construct different 3D structures through noncovalent interactions such as C-H···π, N-H···π and van der Waals interactions.     

Syntheses, crystal structures and properties of Cd(II) and Co(II) complexes with 4,4′-dipyridylsulfide ligand

Two new coordination polymers [Cd(dps)₂Cl₂] (1) and [Co(dps)₂(H₂O)₂]·(abs)₂(H₂O)₂ (2) (dps = 4, 4′-dipyridylsulfide, Habs = 4-amino benzenesulfonic acid) have been synthesized under similar conditions and characterized by elemental analysis, fluorescence spectra and single crystal X-ray diffraction. Compound 1 displays a dps-bridged 2D puckered, grid-like layer, which is further linked by C-H?Cl hydrogen bonds to form a 3D supramolecular architecture. Compound 2 shows a dps-bridged double-stranded chain structure, which is extended by N-H?O and O-H?O hydrogen bonds generating a 3D network. Solid-state fluorescence results reveal that both complexes can emit strong emission bands, at 467 nm and 518 nm for 1 and 344 nm for 2, respectively. Magnetic measurements show that there are weak antiferromagnetic interactions between the adjacent Co(II) ions in 2.     

Hydrogen-bonded copper(II) and nickel(II) complexes and coordination polymeric structures containing reduced Schiff base ligands

Complexes [Cu(HSas)(H₂O)] · 2H₂O (H₃Sas = N-(2-hydroxybenzyl)-l-aspartic acid) (1), [Cu(HMeSglu)(H₂O)] · 2H₂O (H₃MeSglu = (N-(2-hydroxy-5-methylbenzyl)-l-glutamic acid) (2), [Cu₂(Smet)₂] (H₂Smet = (N-(2-hydroxybenzyl)-l-methionine) (3), [Ni(HSas)(H₂O)] (4), [Ni₂(Smet)₂(H₂O)₂] (5), and [Ni(HSapg)₂] (H₂Sapg = (N-(2-hydroxybenzyl)-l-aspargine) (6) have been synthesized and characterized by chemical and spectroscopic methods. Structural determination by single crystal X-ray diffraction studies revealed 1D coordination polymeric structures in 2 and 4, and hydrogen-bonded network structure in 5 and 6. In contrast to previously reported coordination compounds with similar ligands, the phenol remains protonated and bonded to the metal ions in 2 and 4, and also probably in 1. However, the phenolic group is non-bonded in 6.     

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.     

Synthesis, structures and magnetic properties of nicotinato-copper(II) complexes with polybenzimidazole and polyamine ligands

Four novel nicotinato-copper(II) complexes containing polybenzimidazole and polyamine ligands were synthesized with formula [Cu₂(bbma)₂(nic)₂](ClO₄)₂·CH₃OH·0.5H₂O (1), [Cu₂(dien)₂(nic)₂](ClO₄)₂·2CH₃OH (2), [Cu(ntb)(nic)]ClO₄·H₂O (3) and [Cu(tren)(nic)]BPh₄·CH₃OH·H₂O (4), in which bbma is bis(benzimidazol-2-yl-methyl)amine, dien is diethylenetriamine, ntb is tris(2-benzimidazolylmethyl)amine, tren is tris(2-aminoethyl)amine and nic is nicotinate anion. All of the complexes were characterized by elemental analysis, IR and X-ray diffraction analysis. Complexes 1 and 2 contain centrosymmetric dinuclear entity with the two Cu(II) atoms bridged by two nicotinate anions in an anti-parallel mode. The Cu···Cu separation is 7.109 Å for 1 and 6.979 Å for 2. Complexes 3 and 4 are mononuclear with nicotinate coordinated to Cu(II) ion by the carboxylate O atom in 3 and the pyridine N atom in 4. All of the complexes exhibit abundant hydrogen bonds to form 1D chain for 1, 3, 4 and 2D network for 2. Magnetic susceptibility measurements over the 2-300 K range reveal very weak ferromagnetic interaction between the two Cu(II) ions in 1 and antiferromagnetic interaction in 2 mediated by nicotinate ligand, with J value to be 0.15 and −0.19 cm⁻¹, respectively.     

Restriction of apical coordination in the square-planar nickel(II) complexes of meso-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane with axially oriented C-methyl groups

Crystal structures of nickel(II) complexes coordinated with cyclam-type macrocyclic tetraamine, meso-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane (L) in two complex salts 1 and 2 have been determined by single-crystal X-ray crystallographic analysis. Complexes in both salts adopted trans-III structure, but the C-methyl groups of L adopted equatorial configuration in 1, while axial in 2. Complex 2 is the first example of complex of cyclam-type tetraamine with only axially oriented C-methyl groups. Complex in 1 adopted six-coordinated octahedral geometry with two water molecules occupying two apical sites, while in 2, apical sites were vacant resulting in four-coordinated square-planar geometry. UV-Vis spectra in various solutions also revealed the formation of octahedral six-coordinated complex for 1 but not for 2. Network of hydrogen bonds involving chloride ion, water, and N-H of L was present in crystals of both 1 and 2. Convenient synthetic paths for 1 and 2 are also presented.     

Different coordination modes of Hdipic and dipic ligands to nickel(II) ions in a same environment (dipic = 2,6-pyridinedicarboxylate, dipicolinate)

Two new nickel(II) complexes of the composition [Ni(cyclam)(Hdipic)₂] · 2H₂O (1) and [Ni(cyclam)(H₂O)₂][Ni(dipic)₂] · 2.5H₂O (2) (cyclam = 1,4,8,11-tetraazacyclotetradecane) have been prepared and structurally characterized by a combination of analytical, spectroscopic, thermogravimetric, and crystallographic methods. The structure of 1 shows that the central nickel(II) ion is coordinated axially by two monodentate Hdipic ligands. The discrete neutral complex 1 further extends its structure by hydrogen bonding interactions to form a one-dimensional supramolecule. The structure of 2 consists of two independent nickel(II) centers. Water molecules instead of dipic ligands prefer to coordinate to the Ni1 ion forming a divalent cation [Ni(cyclam)(H₂O)₂]²⁺. Two dipic ligands coordinate to the second Ni2 ion forming a divalent anion [Ni(dipic)₂]²⁻. The divalent cations and anions are charge-balanced, resulting in a molecular salt. The divalent cations and anions are interconnected by multiple types of hydrogen bonding interactions.     

Synthesis, structure and property of manganese(II) complexes with mixed tetradentate imidazole-containing ligand and benzenedicarboxylate

Three new coordination complexes [Mn(L)(H₂O)₂](1,4-BDC)·2H₂O (1), [Mn(L)_0.5(1,4-BDC)]CH₃OH·H₂O (2) and [Mn(L)(H₂O)₂](1,2-HBDC)₂·2H₂O (3) were synthesized by solvothermal reactions of 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene (L) and 1,4-benzenedicarboxylic acid (1,4-H₂BDC) or 1,2-benzenedicarboxylic acid (1,2-H₂BDC) with Mn(II) salt, and characterized by single crystal X-ray diffraction, IR, thermogravimetric and elemental analyses. In complexes 1 and 3, each ligand L links four Mn(II) atoms to form two-dimensional (2D) cationic network with non-coordinated 1,4-BDC²⁻ and 1,2-HBDC⁻ anions lying in the voids between the two adjacent layers, respectively. The 2D layers are further connected together by hydrogen bonds to give three-dimensional (3D) supramolecular structures. However, the 1,4-BDC²⁻ in 2 acts not only as counteranion, but also as bridging ligand leading to the formation of 2-fold interpenetrated 3D framework with pcu (primitive cubic unit) topology. The Mn(II) atoms bridged by carboxylate groups in 2 show antiferromagnetic interactions.