Synthesis, structures and properties of macrocyclic nickel(II) supramolecules with imidazole pendants

Two new nickel(II) complexes with the composition [Ni(L+H)(CH₃CN)₂](ClO₄)₃ (1) and [Ni(L)(tp)]·6H₂O (2), (L = 3,10-bis{3-(1-imidazolyl)propyl}-1,3,5,8,10,12-hexaazacyclotetradecane, tp = terephthalate) have been synthesized and structurally characterized by a combination of analytical, spectroscopic and X-ray diffraction methods. The structure of 1 consists of monomeric cations of the formula [Ni(L+H)(CH₃CN)₂]³⁺ and perchlorate ions. The nickel(II) ion is six-coordinate with bonds to the four nitrogen atoms of the macrocycle and two nitrogen atoms of the axial acetonitrile ligands. One of the protonated imidazole pendants of the macrocycle is hydrogen bonded to the imidazole group of the neighboring nickel(II) macrocycle, forming an undulated 1D supramolecule. Then, the two 1D supramolecular chains are further interconnected by C-H···π interactions between the methyl group of the acetonitrile ligand and one of the imidazole groups to form a 2D double stranded supramolecular polymer. In the structure of 2, the 1D coordination polymer is formed with nickel(II) macrocycles and bridging terephthalate ions, where each 1D chain is interconnected with π-π interactions of pendant imidazole moieties of the macrocycles, resulting in the formation of a 2D supramolecule.     

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.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

EPR study of the oxidation reaction of nickel(0) phosphine complexes with Lewis and Brønsted acids

The oxidation of Ni(PPh₃)₄ with BF₃ · OEt₂, H₃CCOOH, and F₃CCOOH, and that of (PPh₃)₂Ni(C₂H₄) with BF₃ · OEt₂ is studied by EPR spectroscopy. The reaction of the Ni(0) complexes with BF₃ · OEt₂ gives Ni(II) complexes with which they react to form Ni(I) compounds with covalent Ni-F and Ni-B bonds that transform with excess BF₃ · OEt₂ into cationic paramagnetic Ni(I) complexes. Acetic acid also adds oxidatively to Ni(PPh₃)₄ to form a Ni(II) complex that reacts further to give Ni(I) hydride and carboxylate complexes. The Ni(I) hydride is transformed by the acid into the Ni(I) carboxylate with release of hydrogen, the amount of which depends on the rate of acid addition. The following Ni(I) complexes are identified in the reaction medium: [Ni(PPh₃)₃]BF₄, [(PPh₃)₂Ni(OEt₂)]BF₄, [(PPh₃)Ni(OEt₂)_n]BF₄, (PPh₃)₂NiBF₂, (PPh₃)₃NiOOCCH₃, and [(PPh₃)₂Ni(OEt₂)P(OEt)₃]BF₄. Oxidation schemes of Ni(0) complexes by Lewis and Brønsted acids are given.     

Pseudohalide supported mononuclear trans-Ni complexes of cationic and neutral dinitrogen heterocycles

Two mixed ligand complexes trans-[Ni(NCS)₄(PpzH)₂] (1) and trans-[Ni(NCO)₂(Imd)₄] (2) (where Ppz = piperazine; Imd = imidazole) were synthesized from one-pot reactions, and their crystal and molecular structures were determined. The reaction of NiCl₂·4H₂O with piperazine and KSCN in a 1:2:4 mole ratio in aqueous MeOH at room temperature under stirring condition affords 1. Whereas the reaction of NiCl₂·6H₂O with imidazole and NaOCN in a 1:4:2 mole ratio in aqueous MeOH at room temperature under stirring condition yields 2 quantitatively. The nickel ions are hexacoordinated by six nitrogen donor atoms of two different origin, thiocyanate and piperazinium ions in case of 1 and cyanate ion and neutral imidazole in case of 2, to form tetragonally elongated and quite regular octahedral arrangements. In 1, the average Ni-N_ppz distance is 2.198 Å is longer than the average Ni-N_thc distance at 2.070 Å, whereas, in case of 2, the average Ni-N_imd distance at 2.112 Å and is close to the average Ni-N_cyt distance at 2.107 Å. The reactions in other varying stoichiometries failed to provide the hitherto unknown complexes [Ni(NCS)₂(Ppz)₄] and [Ni(NCO)₄(ImdH)₂] confirming the ease of protonation on non-bonding of piperazine is more compared to that of imidazole.     

Synthesis and spectral investigation of manganese(II), cadmium(II) and oxovanadium(IV) complexes with 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone): Crystal structure of manganese(II) and cadmium(II) complexes

The chelating behavior of 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone) (H₂dapa) towards manganese(II), cadmium(II) and oxovanadium(IV) ions has been studied by elemental analyses, conductance measurements, magnetic properties and spectral (IR, ¹H NMR, UV-Vis and EPR) studies. The IR spectral studies suggest the pentadentate nature of the ligand with pyridine nitrogen, two azomethine nitrogens and two carbonyl oxygen atoms as the ligating sites. Six coordinate structure for [VO(H₂dapa)]SO₄ · H₂O and seven coordinate structures for [Mn(H₂dapa)(Cl)(H₂O)]Cl · 2H₂O and [Cd(H₂dapa)Cl₂] · H₂O complexes have been proposed. Pentagonal bipyramidal geometry for [Mn(H₂dapa)(Cl)(H₂O)]Cl · 2H₂O and [Cd(H₂dapa)(Cl₂)] · H₂O complexes was confirmed by single crystal analysis. The X-band EPR spectra of the oxovanadium(IV) and manganese(II) complexes in the polycrystalline state at room (300 K) and also at liquid nitrogen temperature (77 K) were recorded and their salient features are reported.     

Two novel 1D complexes containing the dicyanoaurate ions incorporating gold-gold and hydrogen bonding interactions

Two novel 1D complexes, [Ni(hto){Au(CN)₂}₂][Ni(hto)](ClO₄)₂ · 4H₂O (hto = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.1^6,9]octadecane, in Scheme 1.) (1) and [Co(dien)₂][{Au(CN)₂}₃] · 2H₂O (dien = diethylenetriamine) (2) have been synthesized and characterized. The crystal structure of 1 confirmed the presence of nickel (II) chains via Au-Au interactions. The coordination geometry around the six-coordinate nickel (II) ion is slightly distorted octahedral with four nitrogen atoms of the macrocycle and two nitrogen atoms of the cyanides. The presence of Au-Au interactions have effectively increased the zero dimensional coordination polymer to a one dimensional system. In the complex 2, there are one cation, three anions, and two water molecules in the asymmetric unit. These components are interconnected through a combination of aurophilic attractions and hydrogen bonds and formed 1D chains.     

Magnetic and structural studies of novel tetranickel hydroxamates

The dinickel(II) compound [Ni₂(μ-OAc)₂(OAc)₂(μ-H₂O)(asy·dmen)₂]·2.5H₂O, 1; undergoes facile reaction in a 1:2 molar ratio with benzohydroxamic acid (BHA) in ethanol to give the novel nickel(II) tetranuclear hydroxamate complex [Ni₄(μ-OAc)₃(μ-BA)₃(asy·dmen)₃][OTf]₂·H₂O, 2, in which the bridging acetates, bridging two nickel atoms in 1, undergo a carboxylate shift from the μ₂-η¹:η¹ bridging mode of binding to the μ₃-η¹:η² bridging three nickel atoms in the tetramer. The structure of complex 2 was determined by single-crystal X-ray crystallography. The two monodentate acetates, water and two bidentate bridging acetates of two moles of complex 1 are replaced by three monodentate bridging acetates and three benzohydroxamates. Three nickel atoms in the tetramer, Ni(2), Ni(3) and Ni(4) are in a N₂O₄ octahedral environment, while the fourth nickel atom Ni(1) is in an O(6) octahedral environment. The Ni-Ni separations are Ni(1)-Ni(2) = 3.108 Å, Ni(1)-Ni(3) = 3.104 Å and Ni(1)-Ni(4) = 3.110 Å, which are longer than previously studied in dinuclear urease inhibited models but shorter than in the nickel(II) tetrameric glutarohydroxamate complex [Ni₄(μ-OAc)₂(μ-gluA₂)₂(tmen)₄][OTf]₂, isolated and characterized previously in this laboratory. Magnetic studies of the tetrameric complex show that the four Ni(II) ions are ferromagnetically coupled, leading to a total ground spin state S_T = 4. Three analogous tetranuclear nickel hydroxamates were prepared from AHA and BHA and the appropriate dinuclear complex with either sy·dmen or asy·dmen as capping ligands.     

Further study of the effect of macrocyclic pendant groups on the supramolecular architecture: Synthesis and structures of macrocyclic nickel (II) complexes with trans-butene dicarboxylate

Two nickel (II) complexes with the formula [NiL(H₂O)₂] · 6H₂O (1 · 6H₂O) and [NiH₂L(BDC)]_n (2), where L = 3,10-bis(3-propylcarboxyl)-1,3,5,8,10,12-hexaazacyclo-tetradecane, BDC = trans-butene dicarboxylate, have been synthesized and characterized by elemental analyses, IR spectra and single-crystal X-ray analyses. In 1, the Ni(II) ion is six-coordinated with four nitrogen atoms from the macrocyclic ligand in the equatorial plane and two water molecules in axial position. In 2, the structure is made up of one-dimensional chain of [NiH₂L]²⁺ units with BDC²⁻ anions, in which the Ni(II) ion is also six-coordinated with four nitrogen atoms from the macrocyclic ligand in the equatorial plane and two carboxylate oxygen atoms from the BDC²⁻ group in axial position. In 2, the 1D chains are aligned in a parallel mode.     

Synthesis, crystal structures and magnetic studies of terephthalato- and fumarato-bridged dinickel(II) complexes with tripodal poly-benzimidazole ligand

Two novel dinuclear nickel(II) complexes [Ni₂(ntb)₂(μ-tp)(H₂O)_1.61(CH₃OH)_0.39](NO₃)₂·5.13CH₃OH·2.25H₂O (1) and [Ni₂(ntb)₂(μ-fum)(H₂O)(CH₃OH)](NO₃)₂·6CH₃OH·H₂O (2) (tp = terephthalate dianion, fum = fumarate dianion, ntb = tris(2-benzimidazolylmethyl)amine) containing tetradentate poly-benzimidazole ligand were synthesized and structurally characterized by IR spectra, UV-Vis, elemental analysis and X-ray crystallography. The Ni(II) ions in 1 and 2 have distorted octahedral geometry with four nitrogen atoms of ntb, one oxygen atom of water and one oxygen atom supplied by the carboxylate group of the bridged dicarboxylato ligand. Complexes 1 and 2 consist of terephthalato- and fumarato-bridged dinickel(II) centers in bis(monodentate) bonding fashion. The Ni?Ni distances are 11.333 Å for 1 and 8.966 Å for 2. The magnetic susceptibility measurements at variable temperature show that two complexes exhibit weak antiferromagnetic interactions between nickel(II) ions with J values of −0.25 cm⁻¹ and −0.36 cm⁻¹, respectively.     

Synthesis, spectroscopy and magnetism of novel metal complexes of 3-aminoflavone (3-af). X-ray crystal structure of 3-af and [Cu(3-af)2(NO3)2]

The synthesis and characterization of four new complexes with the bioactive ligand 3-aminoflavone (3-af) are reported. The complexes of general formula [M(3-af)₂(H₂O)₂](NO₃)₂ · nH₂O], where M = Co(II), Ni(II), and Zn(II), and n = 0, 2, 0, respectively, and [Cu(3-af)₂(NO₃)₂] compound were prepared and studied. In particular, to investigate the binding in detail, the crystal structures of the free ligand (3-af) and [Cu(3-af)₂(NO₃)₂] (1) were determined. The new coordination compounds were identified and characterized by elemental analysis, magnetic measurements, and infrared and ligand-field spectra. The crystal structure of the Cu(II) complex reveals that the ligand acts as a N,O-bidentate chelate ligand forming a five-membered ring with the copper(II) ion. The copper(II) ion is octahedrally surrounded by the two amino nitrogens and two carbonyl oxygens from two chelating organic ligands in trans arrangement. Two molecules of coordinated nitrate anions occupy axial positions. The spectral and magnetic properties are in accordance with the structural data of the copper(II) compound. From X-ray powder-diffraction patterns and IR spectra, the complexes of nickel(II) (2) and cobalt(II) (3) were found to be mutually isomorphous. The results of the spectroscopic studies suggest a mononuclear structure of 2 and 3 complexes. The variable-temperature (1.8-300 K) magnetic susceptibility data of 2 indicate a weak ferromagnetic interaction. The magnetic behavior of complex 3 is characteristic of cobalt(II) systems with an important orbital contribution via spin-orbit-coupling and also suggests a weak ferromagnetic interaction.     

Heterometallic Ni/Zn amine complexes possessing extended 2D and 3D hydrogen-bonded networks prepared from zinc oxide

Five novel heterometallic Ni/Zn coordination compounds [Ni(en)₃][ZnCl₄] (1), [Ni(en)(Hea)₂][ZnCl₄] (2), [Ni(dien)₂][ZnCl₄] (3), [Ni(en)₃][ZnCl₄] · 2DMSO (4) and [Ni(en)₃][Zn(NCS)₄] · CH₃CN (5), where en = ethylenediamine (ethane-1,2-diamine), Hea = monoethanolamine (2-aminoethanol) and dien = diethylenetriamine (1,4,7-triazaheptane), have been synthesized by means of the open-air reaction of zinc oxide, nickel chloride (or nickel powder), NH₄X (X = Cl, NCS) and ligand (en, dien, Hea) in non-aqueous solvents, such as DMSO, DMF, CH₃OH and CH₃CN. The choice of a counter-anion in the initial ammonium salt as well as selection of the ligand and solvent provides an effortless approach to the controlled assembly of two- or three-dimensional extended networks assisted by hydrogen bonding. Crystallographic investigations reveal that 1, 2 and 5 possess 3D, while 3 and 4 exhibit 2D H-bonded crystal structures. The structures of the compounds exhibit six-coordinated Ni(II) centers and four-coordinated Zn(II) centers in distorted octahedral and tetrahedral geometries, respectively.     

Synthesis, crystal structure and interaction with DNA and HSA of (N,N'-dibenzylethane-1,2-diamine) transition metal complexes

A new ligand, N,N′-dibenzylethane-1,2-diamine (L) and its four transition metal(II) complexes, ML₂(OAc)₂ · 2H₂O (M = Cu, Ni, Zn, Co), have been synthesized and characterized by elemental analysis, mass spectra, molar conductivity, NMR and IR. Moreover, the crystals structure of Cu(II) and Ni(II) complexes characterized by single crystal X-ray diffraction showed that the complexes have a similar molecular structure. Ni(II) has an regular octahedral coordination environment complexes, but typical Jahn Teller effect influenced Cu(II) in an elongated octahedral environment. The interaction between complexes and calf thymus DNA were studied by UV and fluorescence spectra measure, which showed that the binding mode of complexes with DNA is intercalation. Under physiological pH condition, the effects of Cu(OAc)₂L₂ · 2H₂O and Ni(OAc)₂L₂ · 2H₂O on human serum albumin were examined by fluorescence. The results of spectroscopic measurements suggested that the hydrophobic interaction is the predominant intermolecular force. The enthalpy change ΔH⁰ and the entropy change ΔS⁰ of Cu(OAc)₂L₂ · 2H₂O and Ni(OAc)₂L₂ · 2H₂O were calculated to be −11.533 kJ mol⁻¹ and 46.339 J mol⁻¹ K⁻¹, −11.026 kJ mol⁻¹ and 46.396 J mol⁻¹ K⁻¹, respectively, according to the Scatchard’s equation. The quenching mechanism and the number of binding site (n ≈ 1) were also obtained from fluorescence titration data.     

Syntheses, crystal structure and theoretical investigation of novel heteroleptic complexes of nickel(II) with N-R-sulfonyldithiocarbimate and phosphine ligands

Five new complexes of general formula: [Ni(RSO₂NCS₂)(dppe)], where R = C₆H₅ (1), 4-ClC₆H₄ (2), 4-BrC₆H₄ (3), 4-IC₆H₄ (4) and dppe = 1,2-bis(diphenylphosphino)ethane and [Ni(4-IC₆H₄SO₂NCS₂)(PPh₃)₂] (5), where PPh₃ = triphenylphosphine, were obtained in crystalline form by the reaction of the appropriate potassium N-R-sulfonyldithiocarbimate K₂(RSO₂NCS₂) and dppe or PPh₃ with nickel(II) chloride in ethanol/water. The elemental analyses and the IR, ¹H NMR, ¹³C NMR and ³¹P NMR spectra are consistent with the formation of the square planar nickel(II) complexes with mixed ligands. All complexes were also characterized by X-ray diffraction techniques and present a distorted cis-NiS₂P₂ square-planar configuration around the Ni atom. Quantum chemical calculations reproduced the crystallographic structures and are in accord with the spectroscopic data. Rare C-H···Ni intramolecular short contact interactions were observed in the complexes 1-5.     

Study on synthesis, structure, and DNA-binding of Ni, Zn complexes with 2-phenylquinoline-4-carboylhydrazide

2-Phenylquinoline-4-carboylhydrazide (HL), and its novel nickel(II), zinc(II) complexes [M(HL)₂(L)]·2H₂O·NO₃ (M = Ni (1), M = Zn (2)), have been synthesized and characterized by elemental analysis, molar conductivity, and IR spectra. The crystal structure of [Ni(HL)₂(L)]·2H₂O·NO₃ obtained from ethanol solution was determined by X-ray diffraction analysis, crystallized in the rhombohedral system, space group , Z = 18, a = 31.913(3) Å, b = 31.913(3) Å, c = 27.709(2) Å, α = 90°, β = 90°, γ = 120°, R₁ = 0.0647. The interactions of the complexes and the ligand with calf thymus DNA had been investigated using UV-Vis spectra, fluorescent spectra, CD (circular dichroism) spectra, CV (cyclic voltammetry) and viscosity measurements. These compounds were tested against MFC (mouse forestomach carcinoma) cell lines. The complex 1 showed significant cytotoxic activity against MFC cell lines. The cleavage reaction on plasmid DNA has been monitored by agarose gel electrophoresis. Results suggest that the two complexes bound to DNA via a groove binding mode and the complexes can cleave pBR322 DNA.     

New template reactions of salicylaldehyde S-methyl-isothiosemicarbazone with 2-formylpyridine promoted by Ni(II) or Cu(II) metal ions

The template reaction between salicylaldehyde S-methyl-isothiosemicarbazone and 2-formylpyridine in presence of nickel(II) or copper(II) salts yields two new coordination compounds with general formula [NiL¹]₂(1) and [CuL²]₂(2) (L¹ = the dianionic (N¹-salicylidene)(N⁴-(hydroxy(pyridin-2-yl)methyl) S-methyl-isothiosemicarbazide) ligand and L² = the doubly deprotonated (N¹-salicylidene)(N⁴-(picolinoyl) S-methyl-isothiosemicarbazide) ligand). In the complex 1, the formed L¹ ligand appears as result of an addition reaction of the precursors, while for 2 a redox mechanism is implicated in the formation of L². Despite the fact that the initial organic precursors are the same, the resulting ligands obtained in the template reaction are different. In 1, the Ni(II) metal ion adopts a square-planar geometry and the [NiL¹] units are forming dimerized chains through weak Ni···Ni interactions (3.336 and 3.632 Å). In 2, the Cu(II) metal ions adopt a square-pyramidal geometry and form dinuclear species through weak Cu···O (phenoxo) interactions. The magnetic susceptibility measurements of the complexes reveal the diamagnetic nature of 1 as expected for a square planar Ni(II) complex and a paramagnetic behavior for 2 with weak intra-dimer antiferromagnetic interaction (J/k_B = −2.1(1) K).     

Nickel(II)dicyanamide complexes containing a diamine as end-capping ligand: Composition tailored architectures and magnetic properties

One 0D monomer trans-[Ni(pn)₂(dca)₂] (1), one neutral 2D polymer [Ni(pn)(dca)₂]_n (2) and one polycationic 1D polymer [Ni(pn)₂(dca)]_n(PF₆)_n (3) (pn = 1,3-propanediamine; dca = dicyanamide) have been synthesized and X-ray crystallographically characterized. 1 has terminal trans-Ni(dca)₂ unit, 2 contains both double bridged Ni-(NCNCN)₂-Ni and single bridged Ni-(NCNCN)-Ni units in alternate fashion and 3 consists of single Ni-(NCNCN)-Ni bridge by covalent bonds. The nickel(II) centers are six-coordinated with distorted octahedral geometry. Multiple lateral N-H···N, C-H···N, N-H···F and C-H···F hydrogen bondings promote dimensionality. Variable-temperature magnetic measurements indicate weak antiferromagnetic interactions through μ_1,5 bridge(s).     

Nickel and copper complexes based on tridentate nitrogen donor ligand 2,6-bis-(1-phenyliminoethyl) pyridine: Synthesis, spectral and structural characterization

The reaction of CuCl₂ · 2H₂O with 2,6-bis(1-phenyliminoethyl)pyridine (referred hereafter as L) in 1:1 molar ratio in methanol or acetronitrile at room temperature afforded distorted trigonal-bipyramidal complex [Cu(κ³-L)Cl₂]. On the other hand, the reaction of NiCl₂ · 6H₂O with 2 equivalents of L gave an octahedral complex [Ni(κ³-L)₂]²⁺, which was isolated as [Ni(κ³-L)₂][BF₄]₂ using NH₄BF₄. The complexes have been characterized by elemental analyses, FAB-MS, IR, EPR and electronic spectral studies. Molecular structures of both the [Cu(κ³-L)Cl₂] (1) and [Ni(κ³-L)₂](BF₄)₂ (2) have been determined by single crystal X-ray analyses. Weak interaction studies on 1 and 2 revealed stabilisation of the crystal packing by inter and intra-molecular C-H?X (X = F, Cl, π) interactions. In complex 2 ortho C-H bond from phenyl rings leads to unexpected C-H?π interaction with nickel α,α′-diimine chelate ring. This provides structural support for metalloaromaticity in the chelate ring of complex 2.     

Solvent roles in metal ion coordination: the NiCl2O-solvates, NiCl2 · 4MeOH, NiCl2 · 2MeOH · 0.5dioxan and NiCl2 · 2H2O · 2dioxan

Low-temperature, single crystal X-ray structural characterisations of trans-[NiCl₂(HOMe)₄], trans-O-[Ni(MeOH)₂(μ-Cl)_(2/2)2]_(∞∣∞) · 0.5dioxan and trans-trans-[Ni(H₂O)₂Cl₂(O-dioxan-O)_(2/2)]_(∞∣∞) · dioxan are recorded, offering intriguing insights into O-donor/Ni(II) relativities. All nickel atoms in all structures are located on crystallographic inversion centres, the last two compounds being one-dimensional polymers.     

Two dumbbell-like polyoxometalates constructed from capped molybdovanadate and transition metal complexes

Self assembly of NaVO₃, Na₂MoO₄·2H₂O and NiCl₂·6H₂O with the assistance of organic liginds under hydrothermal conditions results in two molybdovanadates [Ni(enMe)₂]₄{[Ni(enMe)₂(H₂O)]₂[Ni(enMe)₂][(V^VMo^VI₈V₄^IVO₄₀)(V^IVO)₂]₂}·10H₂O (1) and [Ni(enMe)₂]₅{[Ni(enMe)₂]₂[(V^VMo^VI₄Mo^V₄V₄^IVO₄₀)(V^IVO)₄]₂}·2H₂O (2), (enMe = 1,2-diaminopropane), which have been characterized by single crystal X-ray diffraction analysis, IR spectroscopy, and elemental analysis. Both of the two compounds exhibit dumbbell-like structures constructed from capped polyoxomolybdovanadates and [Ni(enMe)₂]²⁺ complexes. Polyoxoxanion 1 is composed of two bicapped Keggin-type anions [(V^VMo₈V₄^IVO₄₀)(V^IVO)₂]⁷⁻, one [Ni(enMe)₂]²⁺ bridging fragment and two decorated nickel(II) complexes. Polyxoxanion 2 consists of two tetracapped molybdenum-vanadium polyoxoanions [(V^VMo^VI₄Mo^V₄V₄^IVO₄₀)(V^IVO)₄]⁷⁻, one [Ni(enMe)₂]²⁺ bridging fragment and a nickel(II) decorated fragment. Polyxoxanions 1 and 2 are further linked to form three-dimensional supramolecular networks through extensive hydrogen bonding interactions. In addition, photocatalysis properties of these two compounds have been investigated.