Azide Bridges Research Articles

Ladders, rings and cubes as structural motifs in three new zinc(II) azide complexes: Synthesis, spectral and structural characterization

Three new zinc(II) azide complexes, namely {[Zn 2(N 3) 4(py-tetrazole) 2](py-tetrazole)} n ( 1), {[Zn 2(N 3) 4(3-OHpy)] · 2H 2O} n ( 2) and [Zn(N 3) 2(pym)] n ( 3), where py-tetrazole = tetrazolo[1,5- a]pyridine, 3-OHpy = 3-hydroxypyridine and pym = pyrimidine, have been synthesized by the hydrothermal methods and structurally characterized. The ligand py-tetrazole was obtained through the interaction of 2-chloropyridine with the azide ion under hydrothermal condition. The structure of 1 consists of a ladder-like arrangement of 1D double chain zinc(II) azide. In the coordination chain, each zinc atom binds di-EO azide bridges connecting another zinc atom in opposite chain, and two EO bridges, one on each side, and the fifth position is occupied by a N atom of py-tetrazole ligand. The structure of 2 features 2D sheets composed of tetranuclear zinc(II) ring and octanuclear zinc(II) ring interconnected by EO azide bridges. The 2D carrying into 3D supramolecular network by the help of several hydrogen bonding interactions. The 3-OHpy molecule acts in the tautomeric keto-form as O, O-bidentate bridging ligand. Complex 3 features distorted octahedral geometry around each zinc center, N, N′-bidentate pyrimidine ligand and EE azido bridges leading to 3D network structure. The IR spectra are measured and discussed. Complex 2 only exhibits photoluminescence properties whereas the other two complexes do not luminesce at room temperature.

Two new 2D μ-azido, μ-oxalato manganese(II) complexes. Synthesis, structure and magnetic properties

By using the oxalate (ox) and azide bridging ligands, the compounds of formulae [Mn 2(N 3) 2(ox)(4-OHpy) 2] n ( 1) (4-OHpy = 4-hydroxypyridine) and [NaMn(ox)(N 3)(H 2O) 4] ( 2) can be prepared. The oxalate ligand is generated by the slow decomposition of l-ascorbic acid. The X-ray diffraction analysis reveals two-dimensional systems: in ( 1), zigzag Mn(II) chains with alternating di-EO-azides (EO = end-on) and di- O, O-pyridone (tautomeric keto-form) bridges are bridged in turn by oxalato anions to form unprecedented two-dimensional honeycomb networks. In ( 2), zigzag Mn(II) chains with oxalate bridges are bridged in turn by double μ 1 , 1 - N 3 - anions to form also unprecedented 2D honeycomb layers. In the structure of 2, the azide group and water molecules are partially disordered. The magnetic susceptibility measurements indicate bulk antiferromagnetic coupling for 1 and 2.

Synthesis, characterization and crystal structures of a pair of azido-bridged polynuclear Schiff base copper(II) complexes with urease inhibitory activity

A pair of azido-bridged Schiff base copper complexes, [CuL1(μ1,3-N3)]n · nClO4(1) and [Cu2(L2)2(μ1,1-N3)2] · 2ClO4(2) (L1 = N,N-diethyl-N′-(1-pyridin-2-ylmethylidene)ethane-1,2-diamine, L2 = N-isopropyl-N′-(1-pyridin-2-ylmethylidene)ethane-1,2-diamine) have been obtained by the same synthetic procedures, but with slightly different Schiff bases. The structures of the complexes have been characterized by IR spectra, elemental analysis, and single crystal X-ray determination. Each Cu atom in the complexes is five-coordinate in a square pyramidal configuration involving the three N atoms of the Schiff base ligand and two N atoms from two bridging azide ligands. The azide ligands adopt end-to-end bridging mode in (1), and end-on bridging mode in (2). The different coordination modes of the azide ligands in the two complexes are assigned to the steric effects of the terminal groups (two ethyl groups for (1) and one isopropyl group for (2)) in the Schiff base ligands. The urease inhibitory activities of the complexes were evaluated. Both of them showed potent inhibition against jack bean urease.

An unusual 3D-topology and dominant ferromagnetic couplings in two Cu(ii)–azide coordination polymers

The coordination polymers [(Cu(N(3))(2))(2)Cu(N(3))(2)(methylpyrazine)(2)](n) 1 and [Cu(4-bromopyridine)(N(3))(2)](n) 2, were prepared from NaN(3), Cu(NO(3))(2).3H(2)O and nitrogen-containing heterocycles. 1 contains a three- and four-connected 3D (4.10(2))(2)(4(2).10(4))-dmd-net based on tetrahedral and trigonal planar nodes, whereas 2 is a sheet-structure formed by a uninodal three-connected 8(2).4 2D-net with additional BrBr (mean 3.903(2) A) and BrN(azide) (3.035(5) A) contacts. Both compounds contain end-on-type azide bridges, and 2 has in addition one end-to-end bridge as well. The corresponding magnetic interactions are J(1,2) = +14.9(6) cm(-1) for the end-on azido interactions in 1 with an additional -1.7 cm(-1) coupling through the pyrazine, and J(1) = 36(6) cm(-1) for the end-on azido interactions and J(2) = 2.5(1) cm(-1) for the orthogonal end-to-end azido interactions found in 2.

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)

Homo‐ and Heterometallic Coordination Oligomers and Polymers Derived from the Preformed Complexes [Cu(bdmpp)(MeCN)2](ClO4)2, [Cu(bdmpp)(N3)2], and [Cu(bdmpp)(N3)(μ‐N3)]2 [bdmpp = 2,6‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)pyridine]: Syntheses, Structures, and Redox Properties

AbstractReactions of three CuII complexes of 2,6‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)pyridine (bdmpp), [Cu(bdmpp)(MeCN)2](ClO4)2 (1), [Cu(bdmpp)(N3)2]·1.5H2O (2·1.5H2O), and [Cu(bdmpp)(N3)(μ‐N3)]2·2MeOH (3·2MeOH), with 4,4′‐bipy, dicyanamide (dca), azide, and MCl2 (M = Cu, Co, Ni) yield a series of homo‐ and heterometallic coordination oligomers and polymers, [{Cu(bdmpp)(ClO4)}2(μ‐4,4′‐bipy)](ClO4)2 (4), {[Cu(bdmpp)(μ‐dca)](ClO4)}n (5), {[Cu(bdmpp)(μ‐N3)](ClO4)·MeCN}n (6), [{Cu(N3)(bdmpp)}2(μ‐N3)2Cu(N3)2] (7), and [{Cu(μ‐N3)(bdmpp)(μ‐N3)M(μ‐N3)(X)}2·eMeCN]n (8: M = Co, X = N3, e = 0; 9: M = Ni, X = Cl; e = 4). Compounds 1–9 have been characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray crystallography. Compound 4 has a centrosymmetric dimeric dication structure in which two [Cu(bdmpp)(ClO4)]+ fragments are bridged by one 4,4′‐bipy. Compounds 5 and 6 have a 1D linear or spiral chain extending along the b axis in which each [Cu(bdmpp)]2+ fragment is linked through bridging dca or azide anions, respectively. Compound 7 has a trinuclear sandwich structure in which two molecules of 2 link a Cu(N3)2 species through two end‐on bridging azide anions. Compounds 8 and 9 have a similar 1D chain structure extending along the c axis in which [Cu(μ‐N3)(bdmpp)(μ‐N3)M(μ‐N3)(X)]2 (M = Co, Ni) molecules are linked by end‐to‐end azide anions (8) or end‐on azide anions (9). In addition, the electrochemical properties of 1–9 in DMF were investigated by cyclic voltammetry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Catena-Poly[[bis(pyridine-κN)nickel(II)]-di-μ-azido-κ4N1:N3-[bis(pyridine-κN)nickel(II)]-di-μ-azido-κ4N1:N1

In the structure of the title compound, [Ni2(N3)4(C5H5N)4]n, neutral chains of NiII atoms are bridged alternately by double end-on and double end-to-end azide bridges. Each NiII center is located on a crystallographic general position and in a slightly distorted octa­hedral coordination environment with two pyridine ligands in the trans positions. Both end-on and end-to-end double azide bridges become equivalent because of the inversion centers lying between each pair of adjacent NiII atoms. In the chain, the Ni⋯Ni separations across the end-on and end-to-end azide bridges are 3.236 (4) and 4.975 (4) A, respectively, and the end-on azide bridging Ni—N—Ni angle is 100.8 (2)°.

Studies on three-dimensional coordination polymer [Cd 2(N 2H 4) 2(N 3) 4] n: Crystal structure, thermal decomposition mechanism and explosive properties

A 3D coordination polymer of cadmium(II) hydrazine azide, [Cd 2(N 2H 4) 2(N 3) 4] n , was synthesized and characterized by elemental analysis and Fourier transform infrared (FT-IR) spectrum. Its crystal structure was determined by single crystal X-ray diffraction analysis. The crystal belongs to monoclinic, P2 1/ c space group, a = 12.555(2) Å, b = 11.724(2) Å, c = 7.842(1) Å, β = 94.56(2)° and Z = 4. The crystal contains two crystallographically independent sets of distorted octahedral Cd(II) atoms and dimeric units of Cd 2N 2, Cd 2(NNN) 2, Cd 2(NN) 2 through double μ-1, 1 azide bridges, μ-1, 3 azide bridges and bidentate bridging hydrazine ligands, respectively, and thus generating a 3D network structure. The thermal decomposition mechanism of the complex was studied by using differential scanning calorimetry (DSC), thermogravimetry–derivative thermogravimetry (TG–DTG) and FT-IR techniques. Under nitrogen atmosphere with a heating rate of 10 °C/min, the thermal decomposition of the complex contained two intense exothermic decomposition processes in the range of 150–304 °C in the DSC curve, and the final decomposed residue at 500 °C was Cd. Sensitivity tests revealed that the title complex is very insensitive to external stimuli.

An Antiferromagnetic Mn(II)‐Azido Chain: Synthesis and Characterization

A new polymeric compound, [Mn(N3)2(1)2]n (2) where 1=N(phenyl)isonicotinamide (NPI), has been synthesized and characterized by X‐ray crystallography and low‐temperature magnetic study. Compound 2 consists of a one‐dimensional chain of octahedral Mn(II) bridged by azide anions in end‐to‐end fashion. In this compound, the Mn(II) ions are linked by 4 azide bridging ligands and 2 monodentate ligands 1. Variable temperature magnetic susceptibility measurements in the temperature range 300–4 K reveal the existence of weak antiferromagnetic interactions (J=−14.6 cm−1).

Aqua(azido)(μ-azido)bis{2-[(2-dimethylaminoethylimino)methyl]-6-methoxyphenolato}dicopper(II) monohydrate

The asymmetric unit of the title compound, [Cu2(C12H17N2O2)2(N3)(μ-N3)(H2O)]·H2O, consists of a dinuclear complex mol­ecule and a solvent water mol­ecule. One Cu atom is six-coordinated by the phenol O atom and by one imine and one amine N atoms from one Schiff base ligand, the phenol and ether O atoms of the second Schiff base, together with a terminal N atom of the bridging azide ligand, in an octa­hedral geometry. The coordination environment of the second Cu atom contains a phenol O and imine and amine N atoms from one Schiff base ligand, two further N atoms, one from the bridging and the other from a terminal azide ligand, and a coordinated water mol­ecule, also in an octa­hedral geometry. The crystal structure involves O—H⋯N and O—H⋯O hydrogen bonds.

Synthesis, spectral and structural characterization of three zinc(II) azide complexes with aminopyrazine

The reaction between zinc(II) azide, Zn(N 3) 2 and aminopyrazine (ampyz) afforded the complexes: [Zn(N 3) 2(ampyz) 2] ( 1), [Zn(N 3) 2(ampyz)] n ( 2) and [Zn 3(N 3) 6(ampyz) 2] n ( 3). These complexes are characterized by spectroscopic and crystallographic methods. The IR spectra of these compounds are measured and discussed. The structure of 1 consists of isolated tetrahedral zinc atom surrounded by two mono-dentate N-ampyz and two terminal azido ligands. Complex 2 features a zigzag chain of zinc centers in which each zinc is surrounded by alternate di-EO (end-on) and di-EE (end-to-end) azide bridges, the chain thus contains alternate four-membered Zn 2N 2 and eight-membered Zn 2(NNN) 2 rings. The two ampyz ligands are located in cis-arrangement and each of them further binds another zinc atom giving rise to a 3D network. Complex 3 contains two structurally different zinc atoms; the six-coordinate Zn(1) center links two di-EO azido bridges and two trans ampyz, thus having ZnN 6 chromophore. The five-coordinate Zn(2) center binds two di-EO bridging azido groups and the fifth position is occupied by an N atom from a bridging ampyz molecule. Both zinc centers, therefore participate in the formation of a 1D chain of cyclic Zn 2N 2 units. Each ampyz ligand binds another zinc atom via the second pyrazinic N atom giving another cross-chain and thus the structure consists of 2D sheets. In these three complexes the azido ligands of all types are asymmetric and linear within the experimental error.

Di-μ-azido-κ4N:N-bis[(azido-κN)(2,9-dimethyl-1,10-phenanthroline-κ2N,N′)nickel(II)

The title complex, [Ni2(N3)4(C14H12N2)2], is a centrosymmetric dimer in which each NiII atom is coordinated by five N atoms (two from a 2,9-dimethyl-1,10-phenanthroline ligand, two from the bridging azide group and one from the terminal azide) in a slightly distorted square-pyramidal geometry. The Ni⋯Ni distance is 3.2532 (9) A. In the crystal structure, mol­ecules are linked into one-dimensional chains by C—H⋯N hydrogen bonds and π–π stacking inter­actions [π-π interaction distance = 3.6215 (16) A].

Synthesis, crystal structure and magnetic characterization of a dinuclear Mn(II) complex with double end-on azide ligands

A new dinuclear manganese(II) complex [MnL(N 3) 2] 2 · 2CH 3OH 1 has been synthesized and characterized crystallographically and magnetically. L is a tridentate Schiff base ligand which is derived from the reaction of pyridine-2-carbaldehyde and 2-aminoethylbenzimidazole. In the complex 1, each Mn(II) ion is coordinated by one L, one terminal azide ligand and symmetrical double end-on bridging azide ligands. The intermolecular hydrogen bonds extend the structure into a two-dimensional layer. Magnetic determination of 1 indicates that ferromagnetic exchange interaction between the two manganese(II) ions exist in this complex through the double end-on azide bridges.

Four [Cd(L) 2(N 3) 2] n 1D systems with different azide bridging sequences: Synthesis, spectral and structural characterization

Four new cadmium(II) complexes: [Cd(4-Etpy) 2(N 3) 2] n ( 1) (4-Etpy = 4-ethylpyridine), [Cd(3-acpy) 2(N 3) 2] n ( 2) (3-acpy = 3-acetylpyridine), [Cd(4-OHMepy) 2(N 3) 2] n ( 3), (4-OHMepy = 4-hydroxymethylpyridine) and [Cd(3-OHMepy) 2(N 3) 2] n ( 4), (3-OHMepy = 3-hydroxymethylpyridine), are synthesized and structurally characterized. The IR spectra of the complexes are measured and discussed. The single crystal X-ray diffraction revealed that all of these four complexes exhibit 1D [Cd 2(N 3) 2] n chains, six-coordinate cadmium centers and trans arrangement of the two pyridines. In the structure of 1, the azide groups in the double bridges are alternately in the μ-1,3 and μ-1,1 modes between neighboring cadmium atoms, whereas in 2 the chain is formed only from double μ-1,1 azide bridges. In the structure of 3, the double azido bridges show the unprecedented –Cd-(μ-1,1-N 3) 2–Cd-(μ-1,1-N 3) 2–Cd-(μ-1,1-N 3) 2–Cd-(μ-1,3-N 3) 2–Cd– sequence. In the structure of 4, each pair of cadmium centers is simultaneously bridged by two different azides: μ-1,1 and μ-1,3 bridges. In the chain of polyhedra these μ-1,1 and μ-1,3 azido bridges are trans to each other. In all of the four complexes the μ-1,1 azides are asymmetric whereas the μ-1,3 azido ligands are more symmetric, and the azides of both types are almost linear within the experimental error.

Catena-Poly[[(N,N-dimethylethane-1,2-diamine)copper(II)]-di-μ1,1-azido-[(N,N-dimethylethane-1,2-diamine)copper(II)]-di-μ1,3-azido

In the title compound, [Cu2(N3)4(C4H12N2)2]n, an azide-bridged polynuclear copper(II) complex, each Cu atom is coordinated by two N atoms of N,N-dimethyl­ethane-1,2-diamine and four N atoms from four azide bridges in an octa­hedral geometry. The [Cu(C4H12N2)] units are linked by bridging azide ligands, forming chains running along the b axis. The azide ligands form two types of bridges, μ1,1 and μ1,3, which give alternating four- and eight-membered rings in the polymeric chain, both of which are centrosymmetric.

Synthesis, crystal and molecular structures of 1D and 2D supramers of copper(II) with N,N′-{bis(pyridin-2-yl) benzylidene}butane-1,4-diamine

Reaction of copper(II) perchlorate with N,N′-{bis(pyridin-2-yl)benzylidene}butane-1,4-diamine (bpbd) yielded monoclinic crystals of bluish green [Cu(bpbd)(ClO4)]ClO4 (1), and a similar reaction in presence of azide anion, N3− formed monoclinic crystals of dark green [Cu(bpbd)(N3)]2ClO4 (2). Crystal data for 1: space group P21/c, Z=4, a=17.3968(4) A, b=9.3182(2) A, c=17.6794(4) A, β=102.149(1)°. The geometry around Cu(II) centre is distorted square pyramidal with axial site occupied by O atom of perchlorate and in plane Cu is bonded to four N atoms of the organic ligand. The intermolecular C–H...π stacking in 1 forms a zigzag chain (1D) supramer. Crystal data for 2: space group C2/c, Z=4, a=22.3109(4) A, b=17.7832(3) A, c=14.3389(2) A, β=92.553(1)°. In dinuclear 2, Cu(II) has tetragonally distorted octahedral geometry coordinated by four N atoms of bpbd, with the fifth and sixth positions occupied by N atoms of two end-on bridging azides. The π...π interaction leads to a two dimensional (2D) sheet within which the counter anions are embedded. Both the compounds 1 and 2 show simple paramagnetism. Cyclic voltammetry and fluorescence spectra are also reported.

Metal complexes formed by metal-assisted solvolysis of di-pyridylketone azine: structures and magnetic properties

A series of metal complexes were achieved from the metal-assisted solvolysis reaction of di-pyridylketone azine (dpka). The tetranuclear nickel cluster , [Ni(2)[dpk(O)(OH)][dpk(O)(OCH(3))](N(3))(2)](2), is centrosymmetric with a central core described as an edge-shared triangle core. Neighboring Ni(II) ions are alternately bridged by (micro(2)-N(3), micro(3)-O) and (micro(2)-O, micro(3)-O) double bridges. Complex , [Cu(4)[dpk(O)(OCH(3))](4)(N(3))(2)](CuCl(2))(2) contains a tetranuclear cluster and two identical [CuCl(2)]M(-) anions. The tetranuclear structure has two crystallographically imposed twofold axes, in which the four copper ions are arranged to be rhombic shape. The neighboring copper(ii) ions along the lateral are bridged by single micro(2)-O from the ligand dpk(O)(OCH(3)) and the short diagonal copper ions are bridged by two symmetric end-on azides. In dinuclear Cu(ii) complex [Cu(2)[dpka(OCH(2)CH(3))]Cl(2)](ClO(4)) (3), the metal centers are coordinated in a planar configuration and bridged by a -N-N- bridge. It is also observed that the Cl atom coordinated to one Cu(II) center is also weakly coordinated to another inversion related Cu(II) to generate a centrosymmetric dimer. The metal centers in one-dimensional polymeric Cu(ii) complex [Cu(2)[dpka(OCH(3))](N(3))(2)(ClO(4))](n) (4), however, are bridged by a -N-N- bridge and an end-to-end azide bridge, alternately. Magnetic susceptibility measurements indicate that shows ferromagnetic interaction within the tetranuclear cluster, and that displays moderately strong antiferromagnetic interaction (J = -56.7 cm(-1)) for the bis(micro-N(3)) bridge. For compound , it shows strong antiferromagnetic coupling (J = -286 cm(-1)) between the intradinuclear Cu(II) ions mediated by the single N-N bridge and negligible magnetic interactions between the adjacent dinuclear Cu(II) ions mediated by the single end-to-end azide bridge. The mechanism of the metal-assisted solvolysis reaction was also discussed.

Doubly Bridged Dinuclear Cadmium(II)azido Schiff Base Complexes: Synthesis, X-Ray Structure and Luminescence Properties of [Cd(L)(N3)]2(Y)2 [L = Schiff Bases, Y = ClO4 −, PF6 −

Three new Schiff bases, \(N,N'\)-(bis(pyridin-2-yl)alkylidene)butane-1,4-diamine [(py)(R)C=N-(CH\(_{2}\))\(_{4}\hbox{-}\)N=C(R)(py), L: py = pyridine; R = H, \(N,N^\prime\)-(bis(pyridin-2-yl)formylidene)butane-1,4-diamine (bpfd); R = Me, \(N,\!N^\prime\)-(bis(pyridin-2-yl)methylidene)butane-1,4-diamine (bpmd); R = C\(_{6}\rm{H}_{5}\), \(N,N^\prime\)-(bis(pyridin-2-yl)bezylidene)butane-1,4-diamine (bpbd)] were prepared and used to synthesize six dinuclear cadmium(II)azido complexes of type [Cd(L)(N\(_{3}\))]\(_{2}\)(Y)\(_{2}\) [L = bpfd, Y = ClO\(_{4}\) (1a); L = bpfd, Y = PF\(_{6}{^-}\) (1b); L = bpmd, Y = ClO\(_{4}{^-}\) (2a); L = bpmd, Y = PF\(_{6}{^-}\) (2b); L = bpbd, Y = ClO\(_{4}{^-}\) (3a); and L = bpbd, Y = PF\(_{6}{^-}\) (3b)]. Two representative members of the series, 3a and 3b, have been characterized by single crystal X-ray diffraction measurements. Structural study reveals that each cadmium center in both dinuclear compounds is located in a distorted octahedral coordination environment surrounded by six nitrogen atoms—four (N1, N2, N3, N4) from tetradentate ligand, and the fifth and sixth positions occupied by nitrogen atoms (N5, N5*) of doubly end-on bridging azides. The complexes display intraligand 1\((\pi\hbox{--}\pi^{*})\) fluorescence and intraligand 3\((\pi\hbox{--}\pi^{*})\) phosphorescence in glassy solutions (MeOH at 77 K).

Weak Ferromagnetism and Dynamic Magnetic Behavior in a Single End‐to‐End Azide‐Bridged Nickel(II) Chain

An isolated 1D NiII chain containing single end-to-end azide bridges has been constructed (see figure). The non-centrosymmetric character of the three-atom single-bridge leads to a weak ferromagnetic behavior. Surprisingly, it shows a strong frequency dependence of AC susceptibility and magnetic hysteresis loops even at 10 K. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2089/2006/c0253_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

An Unprecedented Asymmetric End-On Azido-Bridged Copper(II) Imino Nitroxide Complex: Structure, Magnetic Properties, and Density Functional Theory Analysis

The dinuclear copper(II) complex [Cu2(mu(1,1)-N3)2(im-2py)2(N3)2] [im-2py = 2-(2-pyridyl)-4,4,5,5-tetramethylimidazolinyl-1-oxy] has been prepared and structurally characterized. The crystal structure consists of a dinuclear unit in which the Cu(II) ions are bridged by two azido ions in a end-on asymmetric fashion and the imino nitroxide radicals are chelating by the two imino N atoms. Accordingly, the magnetic susceptibility data were analyzed considering a linear spin-coupling scheme rad(1)-Cu(2)-Cu(3)-rad(4) (with Si = 1/2, i = 1-4), where the Heisenberg spin Hamiltonian assumes the general form -2Sigma(i)<(j)S(i)S(j). Considering only first-neighbor spin-coupling constants (J13 = J24 = J14 = 0), magnetic susceptibility measurements show that the copper(II) imino nitroxide rad-Cu-(Cu-rad)(rad-Cu)-Cu-rad exchange coupling is ferromagnetic and large (J12 = J34 = J1 > +190 cm(-1)), as is expected for copper imino nitroxide species, and the copper-copper (rad)-Cu-Cu-(rad) coupling through the asymmetric double end-on azide bridges appeared antiferromagnetic and rather large [J23 = J2 = -43(2) cm(-1)]. By contrast, a density functional theory analysis of the system through the computation of broken-symmetry-state energies resulted in J2 approximately 0 cm(-1). This apparent paradox is resolved by introducing a second-neighbor rad-(Cu)-Cu-(rad)(rad)-Cu-(Cu)-rad spin-coupling constant J13 = J24 = J3, which turns out to be antiferromagnetic both experimentally (when J2 is set equal to zero) and computationally.