A systematic study on the thermal decomposition reactions of coordination polymers based on metal(II) selenocyanates and 4,4′-bipyridine: Directed synthesis of a μ-1,3 bridging selenocyanate

Reaction of manganese(II), iron(II), cobalt(II) and nickel(II) selenocyanate with 4,4′-bipyridine (bipy) in water at room temperature leads to the formation of the ligand-rich 1:2 hydrates [{M(bipy)(NCSe)₂(H₂O)₂}·bipy]_n (bipy = 4,4′-bipyridine) with M = Mn (1-Mn), Fe (1-Fe), Co (1-Co) and Ni (1-Ni). In their crystal structures, the metal cations are coordinated by two terminally N-bonded selenocyanato anions, two water molecules, and two bridging bipy ligands in an octahedral coordination mode. These building blocks are connected into linear M-bipy-M chains, which are further linked by hydrogen bonds between the water molecules and non-coordinated bipy ligands into layers. On heating these precursor compounds, they decompose into ligand-rich 1:2 anhydrates [M(NCSe)₂(bipy)₂]_n with M = Mn (2-Mn), Fe (2-Fe), Co (2-Co) and Ni (2-Ni). After water removal the coordination spheres of the metal cations are completed by N-coordination of the bipy ligand which formerly was involved in OH···N hydrogen bonding. On further heating, the manganese(II) compound loses half of its bipy ligands leading to a new ligand-deficient 1:1 intermediate [Mn(NCSe)₂(bipy)]_n (3-Mn) with μ-1,3-bridging selenocyanato anions. In contrast, all other compounds decompose without the formation of ligand-deficient intermediates. These structural changes are accompanied with a dramatic change in their magnetic properties: Whereas all ligand-rich 1:2 compounds 1-M and 2-M (M = metal) show only Curie-Weiss paramagnetism, in the ligand-deficient 1:1 intermediate 3-Mn an antiferromagnetic long-range ordering at T_N = 10.5 K is found. The thermal and magnetic properties are qualitatively compared with those of the related ligand-rich and ligand-deficient selenocyanato and thiocyanato compounds based on bipy, pyrazine and pyrimidine as ligand.     

Coordination chemistry of pyrazolylbis((alkylthio)methyl)borates: Hybrid nitrogen and sulfur donor ligands

The synthesis of iron(II), cobalt(II) and nickel(II) complexes supported by chelating borate ligands containing one pyrazole and two thioethers, phenyl(pyrazolyl)bis((alkylthio)methyl)borates, [Ph(pz)Bt^R], is described. The six-coordinate complexes [Ph(pz)Bt]₂M, M = Fe (1Fe), Co (1Co) and Ni (1Ni), form exclusively the cis isomers as confirmed by X-ray diffraction analyses. Whereas 1Co and 1Ni are high spin, 1Fe exhibits a room temperature magnetic moment, μ_eff = 4.1 μ_B, consistent with spin-crossover behavior. Quantitative analysis of the electronic spectrum of 2Ni leads to a value of D_q = 1086 cm⁻¹, reflective of a ligand field strength somewhat weaker than those imposed by the related tridentate borate ligands Tp or PhTt. Replacement of the methylthioether substituent with the sterically more demanding tert-butylthioether leads to the isolation of [Ph(pz)Bt^tBu]MX, M = Co, X = Cl (2Co); M = Ni, X = Cl (2Ni) or acac (3). The solid state structures of 2Co and 2Ni are chloride-bridged dimers. Additional high-spin cobalt(II) complexes, accessible under distinct preparative conditions, [κ²-Ph(pzH)Bt^tBu] CoCl₂·THF (4) and [κ²-Ph(pz)Bt^tBu]₂Co (5), have been fully characterized.     

Construction of crystal structures of metal(II)-benzoates (M = Mn, Ni, Co, Cu, Zn, and Cd) and 1,2-bis(4-pyridyl)ethane: Effects of metal coordination modes and their catalytic activities

Five polymeric metal(II)-benzoate complexes of formula [Mn(O₂CPh)₂(CH₃OH)₂(bpa)]_n (1-Mn), [Co(O₂CPh)₂(H₂O)(bpa)_1.5]_n (2-Co), [Ni(O₂CPh)₂(H₂O)(bpa)_1.5]_n (3-Ni), [Cu(O₂CPh)₂(CH₃OH)₂(bpa)]_n (4-Cu), and [Cd(O₂CPh)₂(bpa)_1.5]_n (6-Cd) have been synthesized and characterized (bpa = 1,2-bis(4-pyridyl)ethane). They showed two kinds of structures: parallelogram-like two-dimensional sheets for Co, Ni, and Cd, and one-dimensional chains for Mn, Cu, and Zn. Since similar structures provide similar coordination geometries, the structures depend on the coordination geometries of metal ions. The compounds 1-Mn, 2-Co, 4-Cu, 5-Zn, and 6-Cd have catalyzed efficiently the transesterification of a variety of esters, while 3-Ni has displayed a very slow conversion. The reactivity of catalyst 6-Cd containing Cd ion, well known as an inert metal ion for the ligand substitution, was found to be comparable to that of 5-Zn. The reactivities of the compounds used in this study are in the order of 5-Zn > 6-Cd > 1-Mn > 4-Cu > 2-Co ? 3-Ni, indicating that the non-redox metal-containing compounds (5-Zn and 6-Cd) show better activity than the redox-active metal-containing compounds (1-Mn, 4-Cu, 2-Co, and 3-Ni).     

Synthesis, structures and magnetic properties of four new oxamidato-bridged heterobimetallic complexes

Four new heterobimetallic coordination polymers, namely, {[Cu(aeoe)M(H₂O)₃ · 2H₂O]₂}_n (M = Mn(II) (1), Co(II) (2), Ni(II) (3)) and [Cu(aeoe)Ni(H₂O)₃]₂ (4) (H₄aeoe = N′-(2-aminoterephthalic acid)-N′′-(ethylenediamine)oxamidato) have been synthesized and characterized structurally. Complexes 1-3 are allomerism and feature 1-D ladder-like chain structure constructed from neutral tetranuclear complex units through the syn-anti carboxylate bridges, whereas complex 4 is a cyclic neutral tetranuclear complex unit. Their magnetic properties are also investigated based on their structures.     

Hydrogen-bonded supramolecular manganese(II) complexes with network and sheet structures bridged by terephthalate unit

Two 1D complexes [Mn(4- methylpyrazole)₃(H₂O)(tp)]_n (2) and [Mn(4-methylpyrazole)₄(tp)]_n (3) (tp = terephthalate) were synthesized and characterized by means of X-ray analysis and magnetic studies. The molecular structure of 2 reveals that Mn(II) centers with asymmetric coordination surroundings are bridged by crystallographically different tp ligands, forming a 1D chain. The 1D coordination chains are interconnected by hydrogen bonds between free carboxylate oxygen atoms in a chain and hydrogens of pyrazole nitrogen atoms in neighboring chains, leading to a 3D framework. Compound 3 also exhibits a 1D coordination chain which is hydrogen-bonded to adjacent chains, providing a 2D sheet structure. Interestingly, the structures include intra- and interchain hydrogen bonds contributed from N-H groups of the capping 4-methylpyrazole ligands. Magnetic measurements show weak antiferromagnetic interactions with exchange coupling parameters of J = −0.018 cm⁻¹ for 2 and J = −0.062 cm⁻¹ for 3 through the extended tp ligand on the basis of an infinite chain model (H = −J∑S_i · S_i + 1).     

Structural and magnetic characterization of one-dimensional oxalato-bridged metal(II) complexes with 4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole ligand: A supramolecular open-framework

A new family of one-dimensional oxalato-bridged metal(II) complexes with formula {[M(ox)(abpt)]·4H₂O}_n [M^II = Mn (1), Fe (2), Co (3), Zn (4); ox = oxalate dianion; abpt = 4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole] has been synthesized and chemically, structurally and magnetically characterized. The crystal structures of compounds 2-4 have been solved by single crystal X-ray diffraction, whereas complex 1 has been studied by means of X-ray powder diffraction methods. All of them are isomorphous and crystallize in the triclinic space group P. The metal atoms are bridged by bis-bidentate oxalate anions forming zig-zag chains in which bidentate chelating abpt ligands complete the octahedral O₄N₂ donor set. The crystal structures show an open-framework that contains rectangular channels in which easily removable hydrogen bonded ribbons of water molecules are located. The occurrence of antiferromagnetic intrachain interactions for compounds 1-3 was determined by cryomagnetic susceptibility measurements.     

Four novel Co(II) and Mn(II) coordination polymers with triazolyl derivate: Syntheses, crystal structures and magnetic properties

Four novel coordination polymers, one-dimensional chains [M(PTE)₂(N₃)₂]_n (M = Mn for 1 and Co for 2), and two-dimensional layers [M(PTE)₂(dca)₂]_n (M = Mn for 3 and Co for 4) (PTE = 1-(2,4-difluorophenyl-2-(1H-1,2,4-triazol-1-yl)ethanone, dca = dicyanamide anion, N(CN)₂⁻), have been synthesized under mild ambient conditions and structurally characterized by single crystal X-ray diffraction. In all four crystal structures, the metal atoms adopt octahedral coordination geometry with six nitrogen atoms from two monodentate PTE ligands and four azido (or dca) bridging ligands. The crystal structures of 1 and 2 are isostructural 1-D polymeric chains, alternatively linked by double end-on and double end-to-end azido bridges. However, the bent dca ligands as bidentate μ₂-1,5 bridging ligands interlink the octahedral metal units to lead to 2-D (4,4) grid networks in 3 and 4. Temperature-dependent magnetic measurements in 2-300 K have been performed for these four polymers, and suggest alternative ferro- and antiferromagnetic couplings for end-on and end-to-end azido bridges in 1, and the dominant ferromagnetic coupling in 2, respectively. Both polymers 3 and 4 show weak antiferromagnetic exchanges through the μ₂-1,5-dca bridges. The effects of auxiliary coligands on the structure and the nature of these magnetic exchanges are discussed in the light of the crystal structures in detail.     

Ni(II) coordination compounds based on mixed phthalate and aromatic amine ligands: synthesis, crystal structures and magnetic properties

Three new coordination compounds, [Ni(Pht)(Py)₂(H₂O)₃] (1), [Ni(Pht)(β- Pic)₂(H₂O)₃] · H₂O (2) and [Ni(Pht)(1-MeIm)₂(H₂O)₃] (3) (where Pht²⁻ = dianion of o-phthalic acid; Py = pyridine, β-Pic = 3-methylpyridine, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy and thermogravimetric analysis. Crystallographic studies 1-3 reveal that each Ni(II) center has a distorted octahedral geometry being coordinated by two nitrogen atoms of aromatic amines, one oxygen atom from a carboxylate group of a phthalate ligand and three water molecules. Pht²⁻ anions act as monodentate ligands, while the remaining uncoordinated carboxylate oxygen atoms participate in the formation of hydrogen bonding. The uncoordinated oxygen atoms form hydrogen bonds with the coordinated water molecules from adjacent complexes creating a centrosymmetric dimer unit. Further, these dimer units are connected by O-H?O hydrogen bonds in double-chains. Depending on the nature of aromatic amines, the arrangement of these double-chains differs. The double-chains are held together only by van der Waals interactions in 1. In contrast, in 2 these chains form layers by π-π interactions between antiparallel molecules of β-Pic as well as by π-π interactions between β-Pic and Pht aromatic rings. In complex 3, the double-chains are knitted together via C-H?O hydrogen bonds between the methyl group of 1-MeIm and the coordinated carboxylate oxygen atom of Pht, as well as π-π contacts involving antiparallel 1-MeIm cycles. The thermal dependence of the magnetic susceptibilities for compounds 1 and 2 shows a weak antiferromagnetic interaction between the two Ni²⁺ ions of the hydrogen bonded dimers. For compound 3, a ferromagnetic interaction could be observed. Modeling the experimental data with MAGPACK resulted in: g = 2.22, |D| = 4.11 cm⁻¹ and J = −0.29 cm⁻¹ for compound 1, g = 2.215, |D| = 3.85 cm⁻¹ and J = −0.1 cm⁻¹ for compound 2 and g = 2.23, |D| = 4.6 cm⁻¹ and J = 0.22 cm⁻¹ for compound 3.     

Synthesis, structure, sorption and magnetic properties of Ni(II) and Cu(II) complexes with thiosemicarbazone of 2-hydroxybenzaldehyde, bridged by 4,4′-bipyridine

(ML)₂(bipy) complexes (LH₂ = thiosemicarbazone of 2-hydroxybenzaldehyde, bipy = 4,4′-bipyridine, M = Ni(II), 1, or Cu(II), 2) were synthesized and characterized by X-ray crystallography. Compound 1 possessed porous structure due to peculiarities of crystal packing, whereas 2 formed infinite zig-zag chains with dense non-porous packing. It was shown that 1 absorbed 0.013 cm³/g of methanol vapor in two steps. Complex 1 was diamagnetic; for 2, the dependency of χ versus T could be interpreted by Bleaney-Bowers expression in 20-300 K temperature range (J = −6.8 cm⁻¹, g = 2.07).     

Syntheses, structures and magnetic properties of three 1-D chain metal-nitroxide coordination polymers bridged by e,e-trans-1,4-cyclohexanedicarboxylate

Three new one-dimensional (1-D) chain metal-nitroxide complexes of the formula [M(NIT4Py)₂(e,e-trans-1,4-chdc)(H₂O)₂]_n (M = Co(II) 1, Ni(II) 2 and Zn(II) 3; NIT4Py = 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and 1,4-chdc = 1,4-cyclohexanedicarboxylate dianion) have been synthesized and characterized structurally as well as magnetically. The X-ray crystal structure analyses of complexes 1, 2 and 3 reveal that they are isostructural. Three complexes all crystallize in neutral 1-D chains where metal-nitroxide units [M(NIT4Py)₂(H₂O)₂] are linked by the linear 1,4-cyclohexanedicarboxylate dianion. The 1,4-chdc completes the segregation and only possesses the e,e-trans-conformation, although there are both cis- and trans-isomers in the raw material. The magnetic measurements show that complexes 1 and 2 both exhibit weak antiferromagnetic interactions between the metal ions and the nitroxides.     

Five-coordinate cobalt(II) complexes of tris(2-pyridylmethyl)amine (TPA): Synthesis, structural and magnetic characterization of a terephthalato-bridged dinuclear cobalt(II) complex

The cobalt(II) complexes [Co(TPA)Cl]ClO₄ (1), [Co(TPA)Br]ClO₄ (2), [Co(TPA)(H₂O)]Cl(ClO₄) (3) and [Co₂(TPA)₂(μ-tp)](ClO₄)₂ · 2H₂O (4) (TPA = tris(2-methylpyridyl)amine and tp = terephthalate dianion) were synthesized and structurally characterized by UV-vis and IR spectroscopy. The molecular structures of complexes 1 and 4 were determined by X-ray crystallography and their magnetic properties were measured over the temperature range 2-300 K. The coordination geometry around the central Co(II) in these compounds has a distorted trigonal bipyamidal geometry with four nitrogen atoms from the TPA ligand and the fifth coordination site is occupied by Cl⁻ ion in 1, Br⁻ ion in 2, coordinated oxygen atom from H₂O in 3 and by an oxygen atom supplied by the carboxylate group of the bridged terephthalato ligand in 4. The visible spectra of the complexes 1-3 in MeOH show strong distortion toward tetrahedral geometry. For complex 4, analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(monodentate) coordination mode for the bridged tp. X-ray data for 1 and 4 show that the former is mononuclear while the latter is dinuclear. The electronic spectrum of 4 in MeOH is in complete agreement with the assigned X-ray geometry around the Co(II) centers. The magnetic behavior of the mononuclear complex 1 is indicative of a high-spin compound with zero-field splitting. The best fit was obtained with ∣D∣ = 7.3 cm⁻¹, g = 2.25. The dinuclear complex 4 exhibits weak antiferromagnetic coupling with a coupling constant J = −0.8 cm⁻¹. The magnetic properties and the structural parameters of 4 are discussed in relation to the other related μ-terephthalato dinuclear Co(II) compounds. The geometry of the coordination sphere around 4 is unique - the CSD compilation listing only one other compound with such a geometry around the dinuclear Co(II) complex and its composition is far different from that in 4. However, they share a common feature of having a weakly antiferromagnetic coupling between Co(II) centers.     

Structural and spectroscopic comparison of five-coordinate cobalt(II) and nickel(II) thiolato complexes with the related four-coordinate complexes

Five-coordinate thiolato complexes, [L1M(SMeIm)] (M = Co and Ni) (L1 = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate anion and HSMeIm = 2-mercapto-1-methylimidazole), were synthesized. These complexes were compared with the corresponding Cu(II) and Zn(II) complexes with the same ligands and were also compared with the related four-coordinate complexes [L1M(SC₆F₅)] (HSC₆F₅ = pentafluorobenzenthiol). All the complexes were characterized by X-ray crystallography and UV-Vis absorption, IR, ¹H NMR, and other spectroscopic techniques. All five-coordinate thiolato complexes, [L1M(SMeIm)] (M = Co, Ni, and Cu), form a distorted square pyramidal structure with a high spin state, and only [L1Zn(SMeIm)] takes a four-coordinate structure with a distorted tetrahedral configuration. The N21-M-S bond angles of the obtained five-coordinate complexes were proportional to the corresponding d value, which comes from between the equatorial basal plane with N4S ligand donor sets and metal ion. These observations and M-S bond distances affect on UV-Vis and far-IR spectral behavior.     

Synthesis, structures and magnetic properties of oxamido-bridged trinuclear Cu-M-Cu macrocyclic complexes (M = Mn(II) and Co(II))

Two oxamido-bridged trinuclear complexes of formula {[(LCu)(EtOH)]₂Mn(EtOH)₂}(ClO₄)₂ (1) and {[(LCu)(EtOH)]₂Co(EtOH)₂}(ClO₄)₂ · 2H₂O (2) (H₂L = 2,3-dioxo-5,6:13,14-dichlorobenzo-7,12-diphenyl-1,4,8,11-tetraazacyclo-pentadeca-7,11-diene) have been synthesized and structurally characterized. The central ions of complexes 1-2 (Mn(II), Co(II)) are all bridged by macrocyclic oxamido groups. Their magnetic properties were studied by susceptibility versus temperature measurement, the best fitting of the experimental data led to J = −16.91 cm⁻¹ for 1 and J = −27.73 cm⁻¹ for 2.     

Third-order NLO properties of the DMF solutions of 3-D network and 2-D layered organic-metal polymers with (4, 4) grid units

Reactions of 1,1′-(1,4-butanediyl)bis-1H-benzimidazole (bbbm) with Cd(II), Ni(II), or Co(II) afford three organic-metal polymers: {[Cd(bbbm)(SO₄)(H₂O)₂]CH₃OH}_n (1), {[Ni(bbbm)₂(H₂O)₂](NO₃)₂ · 2CH₃OH · 6H₂O}_n (2) and {[Co(bbbm)₂(H₂O)₂](NO₃)₂ · 2CH₃OH · 6H₂O}_n (3). In 1, bbbm and coordinate to Cd(II) simultaneously leading to a 3-D structure. In 2 and 3, each bridging bbbm ligand links two Ni(II) or Co(II) ions forming the 2-D layered structure with (4, 4) grid units. Each (4, 4) grid unit is a 44-membered ring and constructed by four bbbm ligands acting as four sides and four Ni(II) or Co(II) ions representing four corners. Their third-order nonlinear optical (NLO) properties in DMF solution have been studied by Z-scan technique. The results show that the DMF solution of 2 possesses both the large third-order NLO absorptive and strong refractive behaviors; and 3’s shows large NLO absorptive effect and weak NLO refractive behavior. A reasonably good fit between the experimental data and the theoretical curve suggests that the experimentally obtained NLO effects are effective third-order in nature.     

Synthesis, structure, and catalytic ethylene oligomerization of nickel(II) and cobalt(II) complexes with symmetrical and unsymmetrical 2,9-diaryl-1,10-phenanthroline ligands

A series of nickel(II) and cobalt(II) complexes, NiX₂L (X = Cl, Br; 1-6) and CoCl₂L (7-9), with 2,9-diaryl-1,10-phenanthroline ligands (L¹-L³) have been synthesized and characterized by elemental analysis, UV-Vis, IR spectroscopy, and X-ray crystal structural study (for 1, 4-7, 9). The solid-state structures of 1, 5-7 and 9 show four-coordinate, slightly flattened tetrahedral geometry at the Ni(II) or Co(II) center, while 4 is five-coordinated (square-pyramidal), containing a THF molecule as an auxiliary ligand. The title complexes (1-9) display good catalytic activities in ethylene oligomerization when activated with methylaluminoxane (MAO). While the Co(II) precatalysts produce primarily C₄ isomers, the Ni(II) complexes give ethylene dimers and trimers at normal pressure. The activities and yields of linear α-olefins increase with increasing ethylene pressure for the Ni(II) complexes, leading to more high-molar-mass products (C₈-C₁₈). Complex 6 displays the best catalytic activity among the complexes studied (up to 1518 kg/mol[Ni] h at 10 atm).     

Effect of flexibility of organic dicarboxylates anions on the four 3D metal-organic frameworks constructed from flexible benzimidazolyl-based ligand

Four new polymeric frameworks, [Co(bbbi)(L1)] (1), [Cu(bbbi)(L1)] (2), [Co(bbbi)(L2)] (3) and [Ni(bbbi)(L2)] (4), (bbbi = 1,1-(1,4-butanediyl)bis-1H-benzimidazole, H₂L1 = 5-nitroisophthalic acid and H₂L2 = itaconic acid) have been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. Complexes 1 and 2 are isomorphous, and they can be described as CsCl-type net utilizing bimetal cores as eight-connected nodes, the bridging bbbi ligands and L1 serve as spacers to yield a unique eight-connected net with 4²⁴6⁴ topology. Complexes 3 and 4 are isomorphous. It is interesting that 3D frameworks containing meso-helical chains (left- and right helical chains) have been observed in 3 and 4, in which meso-helical chains are alternately linked by bbbi ligands coordinating to Co1(Ni1) cations with the zigzag shaped conformation to generate a 3D binodal (4,4)-connected net with {5³·6·8²}{5²·6⁴} topology structure. The bbbi ligands adopt three conformations, namely, the completely “M” shaped conformation in 1 and 2, the zigzag shaped conformation and “Ω” shaped conformation in 3 and 4. The influence of carboxylate anions with different flexibility on the construction of different network topology in the self-assembly process has been discussed. Moreover, the thermal stabilities and the voltammetric behavior of complexes 1-4 have been reported.     

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 and structural characterisation of four saccharinate - Metal complexes with 2,2′:6,2″-terpyridine (terpy) as a co-ligand

Four saccharinate complexes of divalent transition metals with 2,2′:6,2″-terpyridine (terpy) as a co-ligand have been synthesised, and characterised by elemental analysis and single crystal X-ray diffraction at low temperature. The complexes [M(terpy)(sac)(H₂O)₂] sac · H₂O (1, M = Mn; 2, M = Co; 3, M = Ni) are isostructural, crystallising in space group Pbca. The metal ions have approximately octahedral coordination, with the two coordinated water molecules occupying cis-positions. These water molecules are hydrogen-bonded to the oxygen atom in the free water molecule. The copper(II) ion in the anhydrous complex [Cu(terpy)(sac)₂] 4 is five-coordinate; the compound crystallises in the space group P2(1)/c.     

Manganese(II) coordination polymers with bis(5-tetrazolyl)methane: Synthesis, structure and magnetic properties

Two new Mn(II) coordination polymers with bis(5-tetrazolyl)methane (H₂btm), [Mn(btm)(phen)(H₂O)] · H₂O (1) and [Mn(btm)(2,2′-bpy)] · 1.5H₂O (2), have been synthesized and their structures determined by X-ray diffraction. In complex 1, the btm ligands assume the μ₂-1,1′:4 coordination mode and interlink Mn(II) ions into infinite one-dimensional chains. The chains are assembled into a three-dimensional architecture via hydrogen bonds and π-π interactions. For 2, Mn(II) ions are connected by btm ligands in the μ₃-1,1′:2:3′ mode to produce two-dimensional (6,3) coordination network. Magnetic investigations revealed that interactions through the btm bridges in both 1 and 2 are antiferromagnetic.     

Metal(II)-organic coordination polymers with two distinct atropisomeric building units from an axially prochiral inner salt through interchain C-H?X hydrogen bonds (X = O, Cl; metal = cobalt, nickel)

Two isostructural photoluminescent metal-organic coordination polymers, namely, [M(H-mpypdc)(Cl)(H₂O)₃]_n (mpypdc = 2,6-dimethyl-4-(pyridin-4-yl)pyridine-3,5-dicarboxylate; M = Co (2) and Ni (3)), were synthesized from H₂mpypdc (1), and characterized by single crystal X-ray analyses. New ligand 1 is an inner salt. In the metal-organic coordination polymeric chains, two distinct S- and R-atropisomeric units are generated from the axially prochiral 1 through C-H?X (X = O, Cl) hydrogen bonds. There have interesting 2D supramolecular networks [M(Cl)(H₂O)₂]_n in the crystal structures of title compounds. The photoluminescence of new compounds are also investigated in solid state at ambient temperature.