Syntheses, structural analyses, and magneto-structural correlations of three polymeric Fe(II) complexes with azide ligand

Three new metal-organic polymeric complexes, [Fe(N-3)(2)(bPP)(2)] (1), [Fe(N-3)(2)(bpe)] (2), and [Fe(N-3)(2)(phen)] (3) [bpp = (1,3-bis(4-pyridyl)-propane), bpe = (1,2-bis(4-pyridyl)-ethane), phen = 1,10-phenanthroline], have been synthesized and characterized by single-crystal X-ray diffraction studies and low-temperature magnetic measurements in the range 300-2 K. Complexes 1 and 2 crystallize in the monoclinic system, space group C2/c, with the following cell parameters: a = 19.355(4) Angstrom, b = 7.076(2) Angstrom, c = 22.549(4) Angstrom, beta = 119.50(3)degrees, Z = 4, and a = 10.007(14) Angstrom, b = 13.789(18) Angstrom, c = 10.377(14) Angstrom, beta = 103.50(1)degrees, Z = 4, respectively. Complex 3 crystallizes in the triclinic system, space group P (1) over bar, with a = 7.155(12) Angstrom, b = 10.066(14) Angstrom, c = 10.508(14) Angstrom, alpha = 109.57(1)degrees, beta = 104.57(1)degrees, gamma = 105.10(1)degrees, and Z = 2. All coordination polymers exhibit octahedral Fe(II) nodes. The structural determination of 1 reveals a parallel interpenetrated structure of 2D layers of (4,4) topology, formed by Fe(II) nodes linked through bpp ligands, while mono-coordinated azide anions are pendant from the corrugated sheet. Complex 2 has a 2D arrangement constructed through 1D double end-to-end azide bridged iron(11) chains interconnected through bpe ligands. Complex 3 shows a polymeric arrangement where the metal ions are interlinked through pairs of end-on and end-to-end azide ligands exhibiting a zigzag arrangement of metals (Fe-Fe-Fe angle of 111.18degrees) and an intermetallic separation of 3.347 Angstrom (through the EO azide) and of 5.229 Angstrom (EE azide). Variable-temperature magnetic susceptibility data suggest that there is no magnetic interaction between the metal centers in 1, whereas in 2 there is an antiferromagnetic interaction through the end-to-end azide bridge. Complex 3 shows ferro- as well as anti-ferromagnetic interactions between the metal centers generated through the alternating end-on and end-to-end azide bridges. Complex I has been modeled using the D parameter (considering distorted octahedral Fe(II) geometry and with any possible J value equal to zero) and complex 2 has been modeled as a one-dimensional system with classical and/or quantum spin where we have used two possible full diagonalization processes: without and with the D parameter, considering the important distortions of the Fe(II) ions. For complex 3, the alternating coupling model impedes a mathematical solution for the modeling as classical spins. With quantum spin, the modeling has been made as in 2.

Host–guest supramolecular interactions in the coordination compounds of 4,4′-azobis(pyridine) with MnX2(X = NCS–, NCNCN–, and PF6–): structural analyses and theoretical study

Three new Mn(II) coordination compounds {[Mn(NCNCN)2(azpy)]·0.5azpy}n (1), {[Mn(NCS)2(azpy)(CH3OH)2]·azpy}n (2), and [Mn(azpy)2(H2O)4][Mn(azpy)(H2O)5]·4PF6·H2O·5.5azpy (3) (where azpy = 4,4'-azobis-(pyridine)) have been synthesized by self-assembly of the primary ligands, dicyanamide, thiocyanate, and hexafluorophosphate, respectively, together with azpy as the secondary spacer. All three complexes were characterized by elemental analyses, IR spectroscopy, thermal analyses, and single crystal X-ray crystallography. The structural analyses reveal that complex 1 forms a two-dimensional (2D) grid sheet motif These sheets assemble to form a microporous framework that incorporates coordination-free azpy by host-guest pi center dot center dot center dot pi. and C-H center dot center dot center dot N hydrogen bonding interactions. Complex 2 features azpy bridged one-dimensional (ID) chains of centrosymmetric [Mn(NCS)(2)(CH3OH)(2)} units which form a 2D porous sheet via a CH3 center dot center dot center dot pi supramolecular interaction. A guest azpy molecule is incorporated within the pores by strong H-bonding interactions. Complex 3 affords a 0-D motif with two monomeric Mn(II) units in the asymmetric unit. There exist pi center dot center dot center dot pi, anion center dot center dot center dot pi, and strong hydrogen bonding interactions between the azpy, water, and the anions. Density functional theory (DFT) calculations, at the M06/6-31+G* level of theory, are used to characterize a great variety of interactions that explicitly show the importance of host-guest supramolecular interactions for the stabilization of coordination compounds and creation of the fascinating three-dimensional (3D) architecture of the title compounds.

Genetic diversity at the Dhn3 locus in Turkish Hordeum spontaneum populations with comparative structural analyses

We analysed Hordeum spontaneum accessions from 21 different locations to understand the genetic diversity of HsDhn3 alleles and effects of single base mutations on the intrinsically disordered structure of the resulting polypeptide (HsDHN3). HsDHN3 was found to be YSK2-type with a low-frequency 6-aa deletion in the beginning of Exon 1. There is relatively high diversity in the intron region of HsDhn3 compared to the two exon regions. We have found subtle differences in K segments led to changes in amino acids chemical properties. Predictions for protein interaction profiles suggest the presence of a protein-binding site in HsDHN3 that coincides with the K1 segment. Comparison of DHN3 to closely related cereals showed that all of them contain a nuclear localization signal sequence flanking to the K1 segment and a novel conserved region located between the S and K1 segments [E(D/T)DGMGGR]. We found that H. vulgare, H. spontaneum, and Triticum urartu DHN3s have a greater number of phosphorylation sites for protein kinase C than other cereal species, which may be related to stress adaptation. Our results show that the nature and extent of mutations in the conserved segments of K1 and K2 are likely to be key factors in protection of cells.

A unique example of structural and magnetic diversity in four interconvertible copper(II)−azide complexes with the same Schiff base ligand: a monomer, a dimer, a chain, and a layer

Four new Cu(II)-azido complexes of formula [CuL(N-3)] (1), [CuL(N-3)](2) (2), [Cu7L2(N-3)(12)](n) (3), and [Cu2L(dmen)-(N-3)(3)](n) (4) (dmen = N,N-dimethylethylenediamine) have been synthesized using the same tridentate Schiff base ligand HL (2-[1-(2-dimethylaminoethylimino)ethyl]phenol, the condensation product of dmen and 2-hydroxyacetophenone). The four compounds have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Complex 1 is mononuclear, whereas 2 is a single mu-1,1 azido-bridged dinuclear compound. The polymeric compound 3 possesses a 2D structure in which the Cu(II) ions are linked by phenoxo oxygen atoms and two different azide bridges (mu-1,1 and mu-1,1,3). The structure of complex 4 is a double helix in which two mu-1,3-azido-bridged alternating one-dimensional helical chains of CuL(N-3) and Cu(dmen)(N-3)(2) are joined together by weak mu-1,1 azido bridges and H-bonds. The complexes interconvert in solution and can be obtained in pure form by carefully controlling the conditions. The magnetic properties of compounds 1 and 2 show the presence of very weak antiferromagnetic exchange interactions mediated by a ligand pi overlap (J = -1.77) and by an asymmetric 1,1-N-3 bridge (J = -1.97 cm(-1)), respectively. Compound 3 presents, from the magnetic point of view, a decorated chain structure with both ferro- and antiferromagnetic interactions. Compound 4 is an alternating helicoidal chain with two weak antiferromagnetic exchange interactions (J -1.35 and -2.64 cm(-1)).

Complexes of NiX2 (X=Cl− and NO3−) with a NNO donor Schiff base: anion dependent structural variations and spectroscopic behaviour

Two new nickel(11) complexes, [NiLL'(H2O)(2)Cl] (1) and [{NiLL'(H2O)](2)(mu-H)]NO3·H2O(2), have been synthesized using a tridentate Schiff base ligand, HL, 2-[(2-dimethylamino-ethylimino)-methyl]-phenol, along with Cl- or NO3(-) as an anionic co-ligand or counter anion (where L'H = salicylaldehyde). Both complexes have been characterized by X-ray crystallography. The structural analyses reveal that complex 1 is mononuclear whereas 2 is a hydrogen-bridged dinuclear complex. The Ni(II) ions possess a distorted octahedral geometry in both structures. Both complexes show negative solvatochromic behaviour with increasing donor number (DN) of the solvent. In more coordinating solvents, like DMSO or methanol, the colour of the solutions is green, whereas in less coordinating solvents, like dichloromethane (DCM) or acetonitrile, it is red.

Structural and magnetic studies of Schiff base complexes of nickel(ii) nitrite: change in crystalline state, ligand rearrangement and a very rare μ-nitrito-1κO:2κN:3κO′ bridging mode

Four new nickel(II) complexes, [Ni2L2(NO2)2]·CH2Cl2·C2H5OH, 2H2O (1), [Ni2L2(DMF)2(m-NO2)]ClO4·DMF (2a), [Ni2L2(DMF)2(m-NO2)]ClO4 (2b) and [Ni3L¢2(m3-NO2)2(CH2Cl2)]n·1.5H2O (3) where HL = 2-[(3-amino-propylimino)-methyl]-phenol, H2L¢ = 2-({3-[(2-hydroxy-benzylidene)-amino]-propylimino}-methyl)-phenol and DMF = N,N-dimethylformamide, have been synthesized starting with the precursor complex [NiL2]·2H2O, nickel(II) perchlorate and sodium nitrite and characterized structurally and magnetically. The structural analyses reveal that in all the complexes, NiII ions possess a distorted octahedral geometry. Complex 1 is a dinuclear di-m2-phenoxo bridged species in which nitrite ion acts as chelating co-ligand. Complexes 2a and 2b also consist of dinuclear entities, but in these two compounds a cis-(m-nitrito-1kO:2kN) bridge is present in addition to the di-m2-phenoxo bridge. The molecular structures of 2a and 2b are equivalent; they differ only in that 2a contains an additional solvated DMF molecule. Complex 3 is formed by ligand rearrangement and is a one-dimensional polymer in which double phenoxo as well as m-nitrito-1kO:2kN bridged trinuclear units are linked through a very rare m3-nitrito-1kO:2kN:3kO¢ bridge. Analysis of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the nickel(II) ions in four complexes, with exchange parameters J of -5.26, -11.45, -10.66 and -5.99 cm-1 for 1, 2a, 2b and 3, respectively

Anion-directed synthesis of metal-organic frameworks based on 2-picolinate Cu(II) complexes: a ferromagnetic alternating chain and two unprecedented ferromagnetic fish backbone chains

Three new polynuclear copper(II) complexes of 2-picolinic acid (Hpic), {[Cu-2(pic)(3)(H2O)]ClO4}(n) (1), {[Cu-2(pic)(3)(H2O)]BF4}(n) (2), and [Cu-2(pic)3(H2O)(2)(NO3)](n) (3), have been synthesized by reaction of the "metalloligand" [Cu-(pic)(2)] with the corresponding copper(II) salts. The compounds are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. Compounds 1 and 2 are isomorphous and crystallize in the triclinic system with space group P (1) over bar, while 3 crystallizes in the monoclinic system with space group P2(1)/n. The structural analyses reveal that complexes 1 and 2 are constructed by "fish backbone" chains through syn-anti (equatorial-equatorial) carboxylate bridges, which are linked to one another by syn-anti (equatorial-axial) carboxylate bridges, giving rise to a rectangular grid-like two-dimensional net. Complex 3 is formed by alternating chains of syn-anti carboxylate-bridged copper(II) atoms, which are linked together by strong H bonds involving coordinated nitrate ions and water molecules and uncoordinated oxygen atoms from carboxylate groups. The different coordination ability of the anions along with their involvement in the H-bonding network seems to be responsible for the difference in the final polymeric structures. Variable-temperature (2-300 K) magnetic susceptibility measurement shows the presence of weak ferromagnetic coupling for all three complexes that have been fitted with a fish backbone model developed for 1 and 2 (J = 1.74 and 0.99 cm(-1); J' = 0.19 and 0.25 cm(-1), respectively) and an alternating chain model for 3 (J = 1.19 cm(-1) and J' = 1.19 cm(-1)).

The power of NMR: the beginnings

Observed by physicists in the 1930s, the nuclear magnetic resonance effect has been exploited by chemists in structural analyses for decades.

Facile strategies for the synthesis and crystallization of linear trinuclear nickel(II)-Schiff base, complexes with carboxylate bridges: Tuning of coordination geometry and magnetic properties

Three new linear trinuclear nickel(II) complexes, [Ni-3(salpen)(2)(OAc)(2)(H2O)(2)]center dot 4H(2)O (1) (OAc = acetate, CH3COO-), [Ni-3(salpen)(2)(OBz)(2)] (2) (OBz=benzoate, PhCOO-) and [Ni-3(salpen)(2)(OCn)(2)(CH3CN)(2)] (4) (OCn = cinnamate, PhCH=CHCOO-), H(2)salpen = tetradentate ligand, N,N'-bis(salicylidene)-1,3-pentanediamine have been synthesized and characterized structurally and magnetically. The choice of solvent for growing single crystal was made by inspecting the morphology of the initially obtained solids with the help of SEM study. The magnetic properties of a closely related complex, [Ni-3(salpen)(2)(OPh)(2)(EtOH)] (3) (OPh = phenyl acetate, PhCH2COO-) whose structure and solution properties have been reported recently, has also been studied here. The structural analyses reveal that both phenoxo and carboxylate bridging are present in all the complexes and the three Ni(II) atoms remain in linear disposition. Although the Schiff base ligand and the syn-syn bridging bidentate mode of the carboxylate group remain the same in complexes 1-4, the change of alkyl/aryl group of the carboxylates brings about systematic variations between six- and five-coordination in the geometry of the terminal Ni(II) centres of the trinuclear units. The steric demand as well as hydrophobic nature of the alkyl/aryl group of the carboxylate is found to play a crucial role in the tuning of the geometry. Variable-temperature (2-300 K) magnetic susceptibility measurements show that complexes 1-4 are antiferromagnetically coupled (J = -3.2(1), -4.6(1). -3.2(1) and -2.8(1) cm(-1) in 1-4, respectively). Calculations of the zero-field splitting parameter indicate that the values of D for complexes 1-4 are in the high range (D = +9.1(2), +14.2(2), +9.8(2) and +8.6(1) cm(-1) for 1-4, respectively). The highest D value of +14.2(2) and +9.8(2) cm(-1) for complexes 2 and 3, respectively, are consistent with the pentacoordinated geometry of the two terminal nickel(II) ions in 2 and one terminal nickel(II) ion in 3. (C) 2009 Elsevier Ltd. All rights reserved.

Use of a reduced Schiff-Base ligand to prepare novel chloro-bridged chains of rare Cu(II) trinuclear complexes with mixed azido/oxo and chloro/oxo bridges

Two mixed bridged one-dimensional (1D) polynuclear complexes, [Cu3L2(mu(1,1)-N-3)(2)(mu-Cl)Cl](n) (1) and {[Cu3L2(mu-Cl)(3)Cl]center dot 0.46CH(3)OH}(n), (2), have been synthesized using the tridentate reduced Schiff-base ligand HL (2-[(2-dimethylamino-ethylamino)-methyl]-phenol). The complexes have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. In both complexes the basic trinuclear angular units are joined together by weak chloro bridges to form a 1D chain. The trinuclear structure of 1 is composed of two terminal square planar [Cu(L)(mu(1,1)-N-3)] units connected by a central Cu(II) atom through bridging nitrogen atoms of end-on azido ligands and the phenoxo oxygen atom of the tridentate ligand. These four coordinating atoms along with a chloride ion form a distorted trigonal bipyramidal geometry around the central Cu(II). The structure of 2 is similar; the only difference being a Cl bridge replacing the mu(1,1)-N-3 bridge in the trinuclear unit. The magnetic properties of both trinuclear complexes can be very well reproduced with a simple linear symmetrical trimer model (H = JS(i)S(i+1)) with only one intracluster exchange coupling (J) including a weak intertrimer interaction (.j) reproduced with the molecular field approximation. This model provides very satisfactory fits for both complexes in the whole temperature range with the following parameters: g = 2.136(3), J = 93.9(3) cm(-1) and zj= -0.90(3) cm(-1) (z = 2) for 1 and g = 2.073(7), J = -44.9(4) cm(-1) and zJ = -1.26(6) cm(-1) (z = 2) for 2.

Insertion of a hydroxido bridge into a diphenoxido dinuclear copper(II) complex: drastic change of the magnetic property from strong antiferromagnetic to ferromagnetic and enhancement in the catecholase activity

A diphenoxido-bridged dinuclear copper(II) complex, [Cu2L2(ClO4)(2)] (1), has been synthesized using a tridentate reduced Schiff base ligand, 2-[[2-(diethylamino)-ethylamino]methyl]phenol (HL). The addition of triethylamine to the methanolic solution of this complex produced a novel triple bridged (double phenoxido and single hydroxido) dinuclear copper(II) complex, [Cu2L2(OH)]ClO4 (2). Both complexes 1 and 2 were characterized by X-ray structural analyses, variable-temperature magnetic susceptibility measurements, and spectroscopic methods. In 1, the two phenoxido bridges are equatorial-equatorial and the species shows strong antiferromagnetic coupling with J = -615.6(6.1) cm(-1). The inclusion of the equatorial-equatorial hydroxido bridge in 2 changes the Cu center dot center dot center dot Cu distance from 3.018 angstrom (avg.) to 2.798 angstrom (avg.), the positions of the phenoxido bridges to axial-equatorial, and the magnetic coupling to ferromagnetic with J = 50.1(1.4) cm(-1). Using 3,5-di-tert-butylcatechol as the substrate, the catecholase activity of the complexes has been studied in a methanol solution; compound 2 shows higher catecholase activity (k(cat) = 233.4 h(-1)) than compound 1 (k(cat) = 93.6 h(-1)). Both complexes generate identical species in solution, and they are interconvertible simply by changing the pH of their solutions. The higher catecholase activity of 2 seems to be due to the presence of the OH group, which increases the pH of its solution.

Synthesis, crystal structures, magnetic properties and catecholase activity of double phenoxido-bridged penta-coordinated dinuclear nickel(II) complexes derived from reduced Schiff-base ligands: mechanistic inference of catecholase activity

Three double phenoxido-bridged dinuclear nickel(II) complexes, namely [Ni-2(L-1)(2)(NCS)(2)] (1), [Ni-2(L-2)(2)(NCS)(2)] (2), and [Ni-2(L-3)(2)(NCS)(2)] (3) have been synthesized using the reduced tridentate Schiff-base ligands 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL1), 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL2), and 2-[1-(3-dimethylarnino-propylamino)-ethyl]-phenol (HL3), respectively. The coordination compounds have been characterized by X-ray structural analyses, magnetic-susceptibility measurements, and various spectroscopic methods. In all complexes, the nickel(II) ions are penta-coordinated in a square-pyramidal environment, which is severely distorted in the case of 1 (Addison parameter tau = 0.47) and 3 (tau = 0.29), while it is almost perfect for 2 (tau = 0.03). This arrangement leads to relatively strong antiferromagnetic interactions between the Ni(II) (S = 1) metal centers as mediated by double phenoxido bridges (with J values of -23.32 (1), -35.45 (2), and -34.02 (3) cm(3) K mol(-1), in the convention H = -2JS(1)S(2)). The catalytic activity of these Ni compounds has been investigated for the aerial oxidation of 3,5-di-tert-butylcatechol. Kinetic data analysis following Michaelis-Menten treatment reveals that the catecholase activity of the complexes is influenced by the flexibility of the ligand and also by the geometry around the metal ion. Electrospray ionization mass spectroscopy (ESI-MS) studies (in the positive mode) have been performed for all the coordination compounds in the presence of 3,5-DTBC to characterize potential complex-substrate intermediates. The mass-spectrometry data, corroborated by electron paramagnetic resonance (EPR) measurements, suggest that the metal centers are involved in the catecholase activity exhibited by the complexes.

A ferromagnetic methoxido-bridged Mn(III) dimer and a spin-canted metamagnetic μ1,3-azido-bridged chain

Two new Mn(III) complexes of formulas [MnL1(N-3)(OMe)](2) (1) and [MnL2(N-3)(2)](n) (2) have been synthesized by using two tridentate NNO-donor Schiff base ligands HL1{(2-[(3-methylaminoethylimino)-methyl]-phenol)} and HL2 {(2-[1-(2-dimethylaminoethylimino)methyl]-phenol)}, respectively. Substitution of the H atom on the secondary amine group of the N-methyldiamine fragment of the Schiff base by a methyl group leads to a drastic structural change from a methoxido-bridged dimer (1) to a single mu(1,3)-azido-bridged 1D helical polymer (2). Both complexes were characterized by single-crystal X-ray structural analyses and variable-temperature magnetic susceptibility measurements. The magnetic properties of compound I show the presence of weak ferromagnetic exchange interactions mediated by double methoiddo bridges (J = 0.95 cm(-1)). Compound 2 shows the existence of a weak antiferromangetic coupling along the chain (J = -8.5 cm(-1)) through the single mu(1,3)-N-3 bridge with a spin canting that leads to a long-range antiferromagnetic order at T-c approximate to 9.3 K and a canting leading to a weak ferromagnetic long-range order at T-c approximate to 8.5 K. It also exibits metamagnetic behavior at low temperatures with a critical field of ca.1.2 T due to the weak antiferromagnetic interchain interactions that appear in the canted ordered phase.

Synthesis, crystal structures and magnetic properties of two bis(μ-phenoxido)dicopper(II) complexes derived from reduced Schiff base ligands

Two phenoxido bridged dinuclear Cu(II) complexes, [Cu-2(L-1)(2)(NCNCN)(2)] (1) and [Cu-2(L-2)(2)(NCNCN)(2)]center dot 2H(2)O (2) have been synthesized using the tridentate reduced Schiff-base ligands 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL1) and 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL2), respectively. The complexes have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Both the complexes present a diphenoxido bridging Cu2O2 core. The geometries around metal atoms are intermediate between trigonal bipyramid and square pyramid with the Addison parameters (tau) = 0.57 and 0.49 for 1 and 2, respectively. Within the core the Cu-O-Cu angles are 99.15 degrees and 103.51 degrees and average Cu-O bond distances are 2.036 and 1.978 angstrom for compounds 1 and 2, respectively. These differences have marked effect on the magnetic properties of two compounds. Although both are antiferromagnetically coupled, the coupling constants (J = -184.3 and -478.4 cm (1) for 1 and 2, respectively) differ appreciably.

Synthesis, crystal structure, and magnetic properties of a very rare double μ-1,1-azido- and a μ-1,1-(OMe)-bridged FeIII dimer containing a N,N,O-donor tridentate Schiff base ligand

Two new Fe-III complexes, [Fe2L2(mu-OMe)(2)(NCS)(2)] (1) and [Fe2L2(mu-N-3)(2)(N-3)(2)] (2), have been synthesized using a N,N,O-donor tridentate Schiff base ligand HL {2-[(2-dimethylaminoethylimino)methyl]phenol}, the condensation product of salicylaldehyde and N,N-dimethyl-1,2-diaminoethane. The complexes were characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Both crystal structures are centrosymmetric dimers containing two Fe-III atoms, which are bridged in compound 1 by two methoxy anions and in compound 2 by two mu-1,1-azides. The chelating tridentate Schiff base and a terminal thiocyanato (for 1) or azido (for 2) group complete the hexacoordination of the distorted octahedral environment of each iron center. The magnetic properties of compound 1 show the presence of antiferromagnetic exchange interactions mediated by double methoxy bridges (J = -29.45 cm(-1)). Compound 2 shows the presence of very weak ferromagnetic exchange interactions mediated by double mu-1,1-N-3 bridges (J = 1.08 cm(-1)).