End-on Research Articles

A novel 2D copper(II) coordination polymer with bidentate coligands and alternating double EO- and single EE-azido bridges

A novel azido-bridged Cu(II) coordination polymer, [CuL(N 3 ) 2 ] n ( 1 ), ( L = 2-aminomethylpyridine), has been synthesized and structurally characterized. Complex 1 displays a 2D (6, 3) layered structure formed by alternating double EO- and single EE-azido bridges between Cu(II) ions. The complex also reveals an overall weak antiferromagnetic coupling between Cu(II) ions. A novel two-dimensional (2D) copper(II) coordination polymer, [CuL(N 3 ) 2 ] n ( 1 ) (L = 2-aminomethylpyridine), has been synthesized and characterized by elemental analysis, IR, X-ray crystallography and magnetic susceptibility. The complex crystallizes in space group P 2 1 / c with a = 9.940(3), b = 8.057(2), c = 12.310(4) Å, β = 104.119(4)°, V = 956.1(5) Å 3 , Z = 4, with final R = 0.0543. The copper(II) ion in 1 is coordinated through two N atoms of the ligand L and four N atoms from the azido ligands in an elongated octahedron. The polymer consists of (6, 3) layers in which alternate double end-on (EO) and single end-to-end (EE) N 3 - bridging modes are found. The pyridine rings coming from adjacent layers are stacked by π – π interactions. Magnetic measurements reveal a weak antiferromagnetic exchange between copper(II) ions in 1 .

Antiferro- and Ferromagnetic Interactions in Mn(II), Co(II), and Ni(II) Compounds with Mixed Azide−Carboxylate Bridges

A series of transition metal coordination polymers with azide and flexible zwitterionic dicarboxylate ligands was synthesized and structurally and magnetically characterized. These compounds are formulated as [M(2)(L(1))(N(3))(4)] (L(1) = 4,4'-trimethylenedipyridinio-N,N'-diacetate and M = Mn, 1; Co, 2; and Ni, 3) and [ML(2)(N(3))(6)(H(2)O)(2)] (L(2) = 4,4'-dipyridinio-N,N'-diacetate and M = Mn, 4; Co, 5). The isomorphous compounds 1-3 consist of two-dimensional coordination layers in which the anionic uniform chains with mixed triple bridges (two end-on (EO) azides and a syn-syn carboxylate) are cross-linked by the flexible cationic 4,4'-trimethylenedipyridinium spacers, while the isomorphous compounds 4 and 5 consist of alternating chains with triple (two EO azides plus a carboxylate) and double (two end-to-end azides) bridges, the 4,4'-dipyridinium spacers serving as side bridges along the chain. Magnetic studies demonstrated that the triple bridge transmits antiferromagnetic coupling in the Mn(II) compounds (1 and 4) but ferromagnetic coupling in the Co(II) and Ni(II) species (2, 3, and 5). The differences have been discussed in terms of the collaboration or competition between the carboxylate and azide pathways. Compound 4 exhibits alternating antiferromagnetic interactions, while alternating ferromagnetic-ferromagnetic-antiferromagnetic interactions with spin canting are suggested for 5.

The reaction mechanism of the molybdenum hydroxylase xanthine oxidoreductase: evidence against the formation of intermediates having metal-carbon bonds.

ENDOR spectra of the catalytically relevant "very rapid" Mo(V) species generated in the course of the reaction of xanthine oxidoreductase with substrate have been examined by two different groups. While the data themselves are virtually identical, the analysis has been variously interpreted as supporting or refuting the existence of a molybdenum-carbon bond in the signal-giving species. While the basis for this difference in interpretation has now been generally agreed upon - the Mo-C distance in the signal-giving species is now understood to be too long to represent a direct Mo-C bond - independent information concerning the structure of the signal-giving species is highly desirable. Recently, several X-ray crystal structures of catalytically relevant complexes of the enzyme with several substrates and inhibitors have been reported. Taken together, these structures strongly and unambiguously support the interpretation that the intermediate giving rise to the "very rapid" EPR signal, as well as the Mo(IV) intermediate that precedes it in the reaction mechanism, has product coordinated to the active site molybdenum via the catalytically introduced hydroxyl group in a simple "end-on" fashion, with no metal-carbon bond character to the complex. The manner in which product is bound and its orientation within the active site provide important clues as to the specific catalytic roles of active sites in accelerating the reaction rate.

Reactivity of 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole, structures and magnetic properties of polynuclear and polymeric Mn(ii), Cu(ii) and Cd(ii) complexes

Five new complexes were obtained from solution or hydrothermal reactions of M(OAc)(2) (M = Mn, Cu and Cd) or CuCl(2) with 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole (abpt) and NaN(3) or 1,3,5-benzenetricarboxylic acid (btcH(3)) in different molar ratios. Structural analysis reveals that Cd(abpt) units in [Cd(abpt)(mu(1,1)-N(3))(2)](n) (1) are bridged by double mu(1,1) end-on (EO) azides into 1D zigzag coordination chains. Similar structural motifs, i.e. the chelation of abpt to the metal center and the double bridges of EO azides, are found in [Mn(4)(abpt)(4)(mu(1,1)-N(3))(8)(H(2)O)(2)] (2). The terminal aqua molecules and the monodentate N(3)(-) groups lead to the formation of a tetranuclear complex rather than a polymeric compound. The abpt underwent deamination in the presence of copper ions during the process of coordination and became 3,5-bis(pyridin-2-yl)-1,2,4-triazolate (bpt-H) in 3-5. [Cu(4)(bpt-H)(4)(N(3))(4)].4.5H(2)O (3) is a neutral tetranuclear grid-like complex, in which the azides act as monodentate ligands. A similar [Cu(4)(bpt-H)(4)](4+) grid-like unit was found in [Cu(4)(bpt-H)(4)(mu-btcH)Cl(2)].2H(2)O (4) and a pair of symmetry-related copper atoms are bridged by the mu-btcH(2)(-) coligand in a butterfly-shaped structure. In [Cu(2)(bpt-H)(mu(6)-btc)(H(2)O)](n) (5), the tetranuclear {Cu(4)(mu-bpt-H)(2)(mu(3)-carboxylate)(2)}(4+) units are bridged by mu(6)-btc(3-) ligands in a 2D step-like layer structure. Temperature-dependent magnetic susceptibility measurements reveal that the double mu(1,1)-N(3)(-) bridges in 2 transmit the ferromagnetic interactions between Mn(2+) centers (J(1) = J(2) = +3.09(4) cm(-1), g(Mn(II)) = 2.02(1)), and the mu-(bpt-H)(-) bridges transmit moderate antiferromagnetic interactions in both 3 (J = -12.78(13) cm(-1)) and 4 (J(1) = -14.96(11) cm(-1)). In 4 the antiferromagnetic coupling via the mu-btcH(2-) bridge was found as the second coupling pathway (J(2) = -9.48(7) cm(-1)). The coexistence of ferromagnetic and antiferromagnetic coupling between four Cu(2+) centers occurs in 5 (J(1) = -0.88(3) cm(-1) and J(2) = +5.01(2) cm(-1)). The magneto-structural relationship for tetranuclear copper pyrazolate/triazolate compounds has been discussed.

A new two-dimensional manganese(II) coordination polymer with alternating double end-on and single end-to-end azido bridges: Crystal structure and magnetic properties

A new azido-bridged Mn(II) coordination polymer, [MnL(N 3) 2]n ( 1) (L = (E)-3-(dimethylamino)-1-(pyridin-2-yl)prop-2-en-1-one), has been synthesized and characterized by elemental analysis, IR, single crystal X-ray diffraction and magnetic measurement. X-ray analysis shows that complex 1 is a 2D network with (6, 3) layers, in which double end-on (EO) azido-bridged dimers are linked by single end-to-end (EE) azido bridges. Magnetic susceptibilities of 1 were measured under a magnetic field of 2 KOe applied over the temperature range 300–1.8 K. The analysis of magnetic data indicates that the EO- and EE-azido bridges mediate the ferromagnetic and antiferromagnetic exchange interactions, respectively, with the antiferromagnetic coupling between Mn(II) ions dominating the magnetic properties of 1.

Syntheses, crystal structures and characterizations of three new copper(II) azide coordination polymers with 1,2,4-triazole ligands

Three new copper(II) azide coordination polymers with derivatives of 1,2,4-triazole as bridging coligands, namely [Cu 2(admtrz) 2(N 3) 4] n ( 1) (admtrz = 4-amino-3,5-dimethyl-1,2,4-triazole), [Cu(4-abpt)(N 3) 2] n ·2 nH 2O ( 2) (4-abpt = 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole) and [Cu 3(2-ptrz) 2(N 3) 6] n ( 3) (2-ptrz = 4-(2-pyridyl)-1,2,4-triazole), were prepared and characterized by elemental analyses, IR spectra and X-ray structural analyses. Compound 1 has a 1D chain structure in which Cu(II) ions are bridged by end-on (EO) azides and admtrz ligands. This compound contains three kinds of coordination modes for Cu(II) ions, including tetrahedral, square pyramidal and octahedral geometries. Compound 2 displays an interesting 3D framework structure, in which the azide ligands link Cu(II) ions in end-to-end (EE) mode affording a 2D square layer. This 2D layers are further bridged by bent 4-abpt ligands to form an interesting 3D framework. Furthermore, this structure also exhibits an alpha-Po net topology. Compound 3 displays a 1D rectangle-like chain structure linked by azides adopting end-on (EO) and end-to-end (EE) modes and 2-ptrz ligands. The IR and thermal stabilities of these coordination polymers 1–3 have also been studied.

Three Azido-Bridged Mn(II) Complexes Based on Open-Chain Diazine Schiff-base Ligands: Crystal Structures and Magnetic Properties

Three new Mn(II)−azido polymeric complexes [MnL1(N3)2·CH3OH]n (1) (L1 = 1-(2-pyridyl)-1-amino-4-(6-bromo-2-pyridyl)-2,3-diaza-1,3-butadiene), [MnL2(N3)2]n (2a) and [Mn2(L2)2(N3)4]n (2b) (L2 = 1-(2-pyridyl)-1-amino-4-benzyl-2,3-diaza-1,3-butadiene) have been synthesized and crystallographically characterized, and their magnetic properties are studied. Complexes 1 and 2b show similar one-dimensional (1D) coordination polymeric structure, in which Mn(II) ions are alternately bridged by two end-to-end (EE) and two end-on (EO) azido ligands, resulting in zigzag Mn(II)−azido chains. Complex 2a has a 1D structure, and the Mn(II) ions are connected by double EO azido ligands, forming a neutral 1D uniform chain. Standing in their mother liquor for ca. 2 weeks or more, 2a is transformed to 2b completely. The structures of 2a and 2b are characterized, and the quite different magnetic properties based on this transformation of kinetic favored phase to thermodynamic favored phase are discussed. Magnetic analyses revea...

The crystal structures of four azido-bridged Zn(ii) complexes based on open-chain diazine Schiff-base ligands

Four new Zn(II)-azido polymeric complexes with open-chain diazine Schiff-bases as auxiliary bridging ligands have been synthesized and crystallographically characterized. The differences in the constituents of the auxiliary ligands lead to three different types of polymeric structures. Complex 1, [Zn2(L1–H)(N3)3]n (L1 = 1,4-bis(2-pyridyl)-1-amino-4-methyl-2,3-diaza-1,3-butadiene), and complex 2, [Zn2(L2–H)(N3)3·H2O]n (L2 = 1,4-bis(2- pyridyl)-1,4-diamino-2,3-diaza-1,3-butadiene), show a similar one-dimensional (1D) coordination polymeric structure in which the building blocks of tetranuclear rings are interlinked by double end-on (EO) azido bridges, resulting in a “chain of rings” topology. Complex 3, {[Zn17(N3)24(L3–H)2(L3–2H)4(CH3OH)2]·(CH3OH)6·(H2O)3}n (L3 = butanedione monoxime picolinamide hydrazone) has a two-dimensional (2D) structure in which the Zn13 clusters are interlinked by Zn2 binuclear linkers to result in a (4,4) topology. The remaining complex 4, [Zn2(L4–H)(N3)3]n (L4 = 1-(2-pyridyl)-1-amino-4-methyl-4-thiazolyl-2,3-diaza-1,3-butadiene), has a three-dimensional (3D) network with a counterfeit CdSO4 topology, in which the 1D chains similar to those in complexes 1 and 2 are further interlinked by double EO azido bridges.

Nickel(II) Chain with Alternating End-On/End-to-End Single Azido Bridges: A Combined Structural, Magnetic, and Theoretical Study

The reaction of a tridentate Schiff base LH (L-: 1,1,1-trifluoro-7-(dimethylamino)-4-methyl-5-aza-3-hepten-2-onato) with a Ni(II) salt in the presence of azide salt has led to a new alternating end-on (EO)/end-to-end (EE) azido-bridged Ni(II) chain of formula {[Ni2(micro1,1-N3)(micro1,3-N3)(L)2(MeOH)2]}n. Its originality lies in the presence of single EE and EO coordination modes for the azide. It crystallizes in the C2/c space group, a=21.570(7) A, b=10.79(1) A, c=16.154(5) A, beta=120.81(2) degrees, Z=4. The chain can be viewed as {Ni2(N3)(L)2(MeOH)2}+ dimeric units linked to each other in a zigzag pattern by the other azide. Magnetic susceptibility and magnetization measurements have been performed and revealed that the chain can magnetically be depicted as isolated {Ni2(N3)} units exhibiting antiferromagnetic interaction (JAF approximately -37 cm(-1)). Ab initio calculations confirmed the efficient magnetic coupling through the EE bridge and vanishingly small EO {Ni2(micro1,1-N3)} interactions.

Synthesis and Magnetic Study of μ1,1‐Azido‐Bridged Dinuclear Manganese(II) Complexes Based on Tripyridyl Ligands

AbstractThree azido‐bridged MnII complexes of formulas [Mn2(N3)4(ttp)2] (1), [Mn2(N3)4(ttp‐N3)2] (2) and [Mn2(N3)4(ttp‐N3)2]3[MnIII(ttp‐N3)(N3)3]2 (3), where ttp and ttp‐N3 represent 4′‐p‐tolyl‐2,2′:6′,2″‐terpyridine and 4′‐p‐azidomethylphenyl‐2,2′:6′,2″‐terpyridine, were synthesized and characterized by single‐crystal X‐ray diffraction analysis and magnetic studies. The Mn ions in complexes 1 and 2 are coordinated by three N atoms of the ttp or ttp‐N3 ligands, and they are connected by double end‐on (EO) azide ligands; this forms a dinuclear MnII system with Mn–N–Mn bridging angles of 103.5 and 103.1°. The Br atoms of the –CH2Br ligands were replaced by azido groups during the formation of complexes 2 and 3. The structure of complex 3 comprises two structurally similar MnII dimers with double end‐on bridging azide groups and one mononuclear MnIII structure. The bridging Mn–N–Mn angles in 3 are 104.2, 105.1, and 106.73°. Magnetic studies indicate the presence of intramolecular ferromagnetic superexchange. The strength of ferromagnetic coupling within the Mn2 cores in 1–3 is dependent on the Mn–N–Mn bridging angles. The magnetic coupling constants for intermolecular exchange are 2.46(4), 2.25(2), and 1.92(4) cm–1 for 1, 2, and 3, respectively, on the basis ofHamiltonian Ĥ = –2JŜ1Ŝ2.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Structural diversity of four novel cadmium coordination polymers constructed by 1,4-bis(imidazol-1-yl)butane and anion ligands

The reaction of the flexible bis(imidazole) ligand 1,4-bis(imidazol-1-yl)butane (bimb) with corresponding Cd(II) salts (NCS −, dicyanamide (dca), N 3 - , ClO 4 - ) yields four new coordination polymers, from 1D to 3D networks, namely [Cd(bimb) 2(NCS) 2] n ( 1), [Cd(bimb)(dca) 2] n ( 2), [Cd(bimb)(N 3) 2] n ( 3) and {[Cd(bimb) 3](ClO 4) 2} n ( 4). In 1, each Cd(II) atom links two Cd(II) atoms by double bimb ligands and extends to form an one-dimensional chain structure containing the Cd 2(bimb) 2 22-membered metallocycle. In 2, double μ 1,5-dca bridges connect the Cd(II) atoms to form the zigzag [Cd(dca) 2] n chains and extend through bimb long bridges in four different directions alternatively to construct a novel three-dimensional network. In 3, double end-to-end (EE) and double end-on (EO) azide short bridges alternatively link Cd(II) atoms to form the [Cd(N 3) 2] n chains containing both eight- and four-membered metallocycles which further extend via bimb long bridges in four different directions alternatively to result a three-dimensional network. Compound 4 comprises two equivalent, mutually interpenetrating three-dimensional networks.

Two chain complexes of [(CH 3) 2NH 2] [M(N 3) 2(HCOO)] (M=Fe and Co) studied by first-principle electronic-structure calculation

The electronic structures of two ferromagnetic polynuclear complexes, where the anionic [M(N 3) 2(HCOO) −] n chains with a 3-fold bridge of two end-on (EO) azido and one sys– syn formato ligands are isolated by the cations of [(CH 3) 2NH 2] +, have been studied using the full-potential linearized augmented plane wave method based on the density functional theory (DFT). The result shows that spin populations in these two complexes are mainly distributed on the octahedron by four nitrogen atoms and two oxygen atoms of two formats at apical sites that surround the metal ions (M=Fe and Co). There are large and positive spin populations on metal ions, small and positive spin populations on the oxygen and nitrogen atoms of the anionic [M(N 3) 2(HCOO) −] n chains. Ferromagnetic coupling through the two EO-azido bridges in these two complexes has been mainly attributed to the spin delocalization, also with weak spin polarization effect.

Zn(II), Cd(II) and Hg(II) complexes of 8-aminoquinoline.: Structure, spectra and photoluminescence property

The reaction of 8-aminoquinoline (8-aq) with M(NO 3) 2 and M(ClO 4) 2 (where M = Zn, Cd and Hg) has synthesized complexes of the composition [M(8-aq) 2(H 2O) 2](X) 2 (X = NO 3, ClO 4) whereas MCl 2 has isolated M(8-aq)Cl 2 type non-ionic compounds. The reaction of M(OAc) 2, 8-aq and NaN 3/NH 4CNS in a 1:1:2 mole ratio has separated polynuclear complexes of the composition [M(8-aq)(Y) 2] n (Y = N 3, NCS). The complexes have been characterized by spectroscopic data and have been structurally confirmed by single crystal X-ray diffraction study in some representative cases. The X-ray structure of [Zn(8-aq) 2(H 2O) 2](NO 3) 2 shows C–H– π, and π– π interactions and forms a H-bonded sheet (with interactions between the oxygen of NO 3 and C(9)–H of 8-aq/coordinated H 2O). A novel one-dimensional cadmium(II) azido complex, [Cd(8-aq)(N 3) 2]n ( 9), in which the azido takes on an end-on (EO) bridging mode, has been synthesized and characterized. The presence of π– π interactions result in a supramolecular two-dimensional behaviour for the structure. The complexes are photoluminescent at room temperature.

Spin-canting in a 1D chain Mn(II) complex with alternating double end-on and double end-to-end azido bridging ligands

A new one-dimensional (1D) azido-bridged manganese(II) complex, [Mn(dpq)(N 3) 2] n [dpq = dipyrido-(3,2-d:2′,3′-f)-quinoxaline] ( 1), was synthesized and characterized. Crystal structure study reveals that 1 contains a 1D manganese(II) chain bridged by alternating double end-to-end (EE) and double end-on (EO) azido ligands. The strong interchain π–π stacking interaction extends the structure into a 2D supramolecular array. The analysis of magnetic data indicates that the EO- and EE-azido bridges mediate the ferromagnetic and antiferromagnetic interactions, respectively. Interestingly, complex 1 exhibits a weak ferromagnetic property below 6 K probably due to spin canting.

Spin distribution and electronic structure of the ferromagnetic half-metal [Mn(bipy)(N 3) 2]: Ab initio study

Ab initio calculations have been performed to study the electronic structure and the alternating ferromagnetic–antiferromagnetic interactions of the manganese(II)-azido one-dimensional compound: [Mn(bipy)(N 3) 2] (bipy=2,2′-bipyridine). The density of states, the total energy and the spin magnetic moment were calculated. The calculations predict that the compound [Mn(bipy)(N 3) 2] is a ferromagnetic half-metal and the spin magnetic moment is 4.000 μ B per molecule. At the same time, it has a metallic antiferromagnetic metastable state. Based on the spin distribution obtained from ab initio calculations, we found that the spin populations are strongly positive on the Mn 2+ ions. For the end-on (EO) azido groups, the magnetic moments are mainly distributed on the two terminal N1 and N3 atoms, weakly positive on the central N2 atoms. While for the end-to-end (EE) azido groups, the magnetic moments of the terminal N6 atoms are larger and that of the other terminal N4 atoms are smaller. The analysis of the spin populations shows that the ferromagnetic coupling through the azido groups is resulted from a spin delocalization mechanism together with the spin polarization effect. The results of our calculation are in good agreement with the experiment.

One-dimensional copper(II) complex containing alternate single and double end-on azide ligands: Crystal structure and magnetic characterization

A novel one-dimensional azido-bridged coordination polymer of formula [Cu2(L)2(H2O)(N3)4]n (1) has been synthesized and characterized crystallographically and magnetically, where L is 5-methylpyrimidin-2-amine. Complex 1 consists of 1D chain in which the Cu(II) ions with a square pyramidal geometry are alternately bridged by asymmetric single and symmetric double end-on (EO) azido ligands. Magnetic analysis reveals that the dominating ferromagnetic interaction is mediated by the symmetric double azido bridge with the exchange parameter J=55.17cm−1.

Synthesis, crystal structure, and properties of copper(II) and manganese(II) complexes with azide and 3,4-di(2′-pyridyl)-1,2,5-oxadiazole

Two transition metal complexes with azide and 3,4-di(2′-pyridyl)-1,2,5-oxadiazole (dpo), [Cu2(dpo)2(N3)4] (1), and [Mn(dpo)2(N3)2] (2), have been synthesized and characterized by single-crystal X-ray diffraction. The Cu(II) complex is binuclear with double end-on (EO) azido bridges, in which each Cu(II) ion assumes a distorted square pyramidal geometry, and each EO azido bridge adopts a quasi-symmetric fashion. In contrast, the Mn(II) complex is mononuclear, in which the Mn(II) ion is ligated by two dpo ligands and two terminal azide ions, with a distorted octahedron geometry. Magnetic studies on the Cu(II) complex revealed that the double EO azido bridge mediates ferromagnetic coupling with J=12.8 cm−1.

Separate Pathways for O Acetylation of Polymeric and Monomeric Sialic Acids and Identification of Sialyl O -Acetyl Esterase in Escherichia coli K1

O acetylation at carbon positions 7 or 9 of the sialic acid residues in the polysialic acid capsule of Escherichia coli K1 is catalyzed by a phase-variable contingency locus, neuO, carried by the K1-specific prophage, CUS-3. Here we describe a novel method for analyzing polymeric sialic acid O acetylation that involves the release of surface sialic acids by endo-N-acetylneuraminidase digestion, followed by fluorescent labeling and detection of quinoxalinone derivatives by chromatography. The results indicated that NeuO is responsible for the majority of capsule modification that takes place in vivo. However, a minor neuO-independent O acetylation pathway was detected that is dependent on the bifunctional polypeptide encoded by neuD. This pathway involves O acetylation of monomeric sialic acid and is regulated by another bifunctional enzyme, NeuA, which includes N-terminal synthetase and C-terminal sialyl O-esterase domains. A homologue of the NeuA C-terminal domain (Pm1710) in Pasteurella multocida was also shown to be an esterase, suggesting that it functions in the catabolism of acetylated environmental sialic acids. Our combined results indicate a previously unexpected complexity in the synthesis and catabolism of microbial sialic and polysialic acids. These findings are key to understanding the biological functions of modified sialic acids in E. coli K1 and other species and may provide new targets for drug or vaccine development.

Weak Metamagnetic-like 1D Manganese(II) Complex with a Double μ1,1-Azido Bridge: A Structure and Magnetic Study

The azido-bridged manganese complex of formula [Mn(tptz)(mu(1,1)-N3)2]n [1; tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine] has been synthesized and characterized by single-crystal X-ray diffraction analysis and a low-temperature magnetic study. The complex 1 crystallizes in the orthorhombic space group Pbcn, with a = 17.911(5) A, b = 15.804(5) A, c = 6.6538(18) A, and Z = 4. The Mn atoms are coordinated by three N atoms of the tptz ligands and connected to each other by double end-on (EO) azide ligands, forming a neutral 1D chain. The adjacent 1D chains are connected by face-to-face pi-pi-stacking interactions and C-H...pi interactions of pyridine rings of the tptz ligands, which leads to the formation of a supramolecular 2D sheet structure. Temperature- and field-dependent magnetic analyses reveal dominant intrachain ferromagnetic interactions with EO azide-bridge and weak interchain antiferromagnetic interactions with overall metamagnetic behavior having 3D magnetic ordering at 2.7 K. The critical field is approximately 80 G, at which the interlayer antiferromagnetic ground-state switches to a ferromagnetic state.

Facile synthesis of Cu(II) complexes of monocondensed N,N,N donor Schiff base ligands: Crystal structure, spectroscopic and magnetic properties

Four new copper(II) complexes, [(CuL 1N 3) 2](ClO 4) 2 ( 1), [(CuL 2N 3) 2](ClO 4) 2 ( 2), [CuL 3(N 3)(ClO 4)] n ( 3) and [CuL 4(μ-1,1-N 3)(μ-1,3-N 3)(ClO 4)] n ( 4) where L 1 = N 1-pyridin-2-yl-methylene-propane-1,3-diamine, L 2 = N 1-(1-pyridin-2-yl-ethylidene)propane-1,3-diamine, L 3 = N 1-(1-pyridin-2-yl-ethylidene)ethane-1,2-diamine and L 4 = N 1-(1-pyridin-2-yl-ethylidene)propane-1,2-diamine are four tridentate N,N,N donor Schiff base ligands, have been derived and structurally characterized by X-ray crystallography. Compounds 1 and 2 consist of double basal–apical end-on (EO) azide bridged dinuclear Cu II complexes with square-pyramidal geometry. In complex 3 the square planar mononuclear [CuL 3(N 3)] units are linked by weakly coordinated perchlorate ions in the axial positions of Cu II to form a one-dimensional chain. Two such chains are connected by hydrogen bonds involving perchlorate ions and azide groups. Compound 4 consists of 1-D chains in which the Cu II ions with a square-pyramidal geometry are alternately bridged by single EO and end-to-end (EE) azido ligands, both adopting a basal–apical disposition. Variable temperature (300–2 K) magnetic susceptibility measurements and magnetization measurements at 2 K have been performed. The results reveal that complexes 1 and 2 are antiferromagnetically coupled through azido bridges ( J = −12.18 ± 0.09 and −4.43 ± 0.1 cm −1 for 1 and 2, respectively). Complex 3 shows two different magnetic interactions through the two kinds of hydrogen bonds; one is antiferromagnetic ( J 1 = −9.69 ± 0.03 cm −1) and the other is ferromagnetic ( J 2 = 1.00 ± 0.01 cm −1). From a magnetic point of view complex 4 is a ferromagnetic dinuclear complex ( J = 1.91 ± 0.01 cm −1) coupled through the EO bridge only. The coupling through the EE bridge is practically nil as the N(azido)–Cu II (axial) distance (2.643 Å) is too long.