Azido Bridges Research Articles

A Nanosized {NiII18} Cluster with a 'Flying Saucer' Topology Exhibiting Slow Relaxation of Magnetisation Phenomena at Both 15 K and 1.3 K.

A high-nuclearity {Ni18} complex (1) with a unique 'flying saucer' motif has been prepared from the organic chelate, α-methyl-2-pyridine-methanol (mpmH), in conjunction with bridging azido (N3-) and peroxido (O22-) ligands. Magnetic susceptibility measurements revealed the presence of both ferro- and antiferromagnetic exchange interactions between the metal centres in 1, and the stabilization of spin states with appreciable S values at two different temperature regimes. The end-on bridging azido and alkoxido groups are in all likelyhood the ferromagnetic mediators, while the η3:η3:μ6-bridging peroxides most likely promote the antiparallel alignment of the metals' spin vectors, yielding an overall non-zero spin ground state for the centrosymmetric compound 1. Furthermore, the {Ni18} nanosized cluster behaves as a single-molecule magnet, exhibiting magnetic hysteresis at low temperatures and two relaxation processes at 15 K and 1.3 K, a very rare phenomenon in polynuclear magnetic 3d-metal clusters.

Structures, electrical properties and catecholase-like activity of a series of new copper(II) coordination polymers supported by azido bridges

A series of new copper(II)-azido complexes of 1D polymeric chains of [Cu(L1)(μ1,3-N3)]n (1) and [Cu(L2)(μ1,3-N3)]n (2), and binuclear [Cu(L3)(μ1,1-N3)]2 (3) [HL1 = N-butyl-N-(5-bromosalcylidine)ethane-1,2-diamine, HL2 = N-butyl-N-(5-chlorosalcylidine)ethane-1,2-diamine, HL3 = N-butyl-N-(salcylidine)ethane-1,2-diamine] have been synthesized and characterized. Characterizations of 1–3 have been accomplished by usual physico-chemical techniques such as elemental analysis, FTIR, UV–vis and single crystal X-ray diffraction studies. X-ray diffraction analyses of 1 and 2 reveal that the monomeric units of 1D polymers are interconnected via the μ1,3-azido bridging. The coordination geometry around the copper(II) centers in 1 and 2 can be best described as distorted square pyramidal environments. Complex 3 shows a centrosymmetric structure with two copper(II) centers that are held together by μ1,1-azido bridging in a distorted square pyramidal environment. In the electrical studies of 1–3, both direct current (dc) and alternating current (ac) analyses have been carried out based on the metal-complex (1/2/3)-metal (M-S-M) structures. The sheet resistance of the deposited films and the metal-complex contact resistance are estimated by employing transfer length method (TLM) measurements. The dark current-voltage characteristics of Al-complex (1/2/3)-Al structures are analyzed by considering dual back-to-back Schottky barrier diode structure. The voltage variations of the device current under illumination (400–700 nm) clearly demonstrate the photo-sensitivity of these materials. The catalytic activities of 1–3 have been investigated towards aerial oxidation of 3,5-di-tert-butylcatechol. All three complexes exhibit potential catalytic effectiveness towards oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butyl-o-quinone (3,5-DTBQ) with turnover numbers 14.76, 33.92 and 81.02 h−1 for 1, 2 and 3, respectively.

Jellyfish-type Dinuclear Hafnium Azido Complexes: Synthesis and Reactivity.

Di- and multinuclear hafnium complexes bridged by ligands have been rarely reported. In this article, a novel 3,5-disubstituted pyrazolate-bridged ligand LH5 with two [N2 N]2- -type chelating side arms was designed and synthesized, which supported a series of dinuclear hafnium complexes. Dinuclear hafnium azides [LHf2 (μ-1,1-N3 )2 (N3 )2 ][Na(THF)4 ] 3 and [LHf2 (μ-1,1-N3 )2 (N3 )2 ][Na(2,2,2-Kryptofix)] 4 were further synthesized and structurally characterized, featuring two sets of terminal and bridging azido ligands like jellyfishes. The reactivity of 3 under reduction conditions was conducted, leading to a formation of a tetranuclear hafnium imido complex [L1 Hf2 (μ1 -NH)(N3 ){μ2 -K}]2 5. DFT calculations revealed that the mixed imido azide 5 was generated via an intramolecular C-H insertion from a putative dinuclear HfIV -nitridyl intermediate.

Structural evolution and zero-field SMM behaviour in ferromagnetically-coupled disk-type Co7 clusters bearing exclusively end-on azido bridges

Concise chemistry leads to a family of heptanuclear CoII-clusters, [Co7(N3)12(CH3CN)12] [Y2(NO3)4(piv)4]·2CH3CN (DC1) (pivH = pivalic acid), [Co7(N3)12(CH3CN)10(NO3)0.4 (Cl)1.6]·4CH3CN (DC2) and [Co7(N3)12(CH3CN)10(NO3)2]·4CH3CN (DC3), in which the metal ions are exclusively bridged by end-on azido ligands to stabilize a beautiful disk-like topology. The resulting clusters exhibit interesting structural transformations and thermodynamically-distinct steady states verified by theoretical calculations. Magnetic studies reveal the first observation of zero-field SMM behaviour in disk-like heptanuclear CoII complexes.

Synthesis, structural characterization and magnetic studies of two Cu(II)-azide based one-dimensional polymeric chains derived from reduced Schiff base ligands

This article describes syntheses, structural characterizations and magnetic studies of two new Cu(II)-azido based coordination polymers. The complexes, [Cu4(L1)2(N3)6]∞ (1) and [Cu4(L2)2(N3)6]∞ (2) have been synthesized by using Cu(ClO4)2·6H2O, reduced Schiff base ligands (HL1−2) and NaN3 in 1:1:2 M ratios. HL1 and HL2 are the condensation products of salicylaldehyde with N-ethyl-1,2-ethylenediamine and N,N-dimethyl-1,3-propanediamine, respectively. Structural analysis shows that both complexes have similar tetrameric Cu(II) building units in which Cu(II) ions are linked by phenoxo oxygen atoms and two different bridging azido linkages (µ1,1-N3− and µ1,1,3-N3−). An azide co-ligand is also attached with one of the Cu centres through terminal mode. The Cu(II) ions occupy distorted penta-coordinated square pyramidal geometry in complexes 1 and 2. Magnetic susceptibility measurements in the range of 300 K–2 K exhibit the presence of antiferromagnetic interactions between Cu(II) centeres of both complexes 1 and 2.

A Cu12 Metallacycle Assembled from Four C3-Symmetric Spin Frustrated Triangular Units

Assembling metallacycles with interesting topological arrangements is a critical task for chemists. We report here a novel dodecanuclear CuII compound, [{Cu3L(µ-N3)}4(Py)14]·2Py (Cu12) (where Py = pyridine and [H6L]Cl = tris(2-hydroxybenzylidine)triaminoguanidinium chloride, respectively), with the topology of a cycle accomplished by four two-connecting approximately flat C3-symmetric guanidine-based ligands. Each ligand affords three tridentate metal-binding cavities and the four node-to-node connections through single azido bridges are provided by pairs of metal centers. A theoretical investigation using CASSCF in addition to DFT calculations showed strong antiferromagnetic coupling within the Cu3-triangles, resulting in spin-frustrated systems. However, these calculations were not able to properly reproduce the very weak antiferromagnetic couplings between the triangle units, highlighting the challenge of describing the magnetic behavior of this compound.

Part‐per‐million catalysis of azide‐alkyne cycloaddition reaction in water using a new ferromagnetic μ1,1‐N3 bridged dinuclear Cu(II) complex

An original copper(II) dimeric compound formulated as [Cu2(μ1,1‐N3)2L2(N3)2].2CHCl3 (1), with L = 2,6‐pyridinedicarboxaldehydebis(p‐iodophenyl‐imine), has been synthesized and characterized. Single crystal X‐ray structural characterization revealed that this complex displays a centrosymmetric dinuclear structure in which the two Cu(II) centers are connected by double symmetric μ1,1 (end‐on, EO) azido bridges, generating distorted octahedral CuN6 coordination geometry. Magnetic susceptibility measurements indicate a ferromagnetic Cu···Cu coupling with J = 26.7 cm−1 (J being the parameter of the exchange Hamiltonian H = −2JS1S2). The catalytic properties of complex 1 have been evaluated in the one‐pot azide‐alkyne cycloaddition reaction in water without any additional reducing agents or bases. As expected, the absence of any catalyst did not lead to product formation, whereas when complex 1 was introduced as catalyst, the reaction led to the desired product with different chemical yields (10–98%), for which the highest one (98%) corresponds to the reaction performed in the presence of 125 ppm of 1 in water at 90 C. These optimized parameters have been then taken into account to extend the initial reaction based on benzyl chloride and simple alkyne to different substituted benzyl chloride and alkyne molecules.

Synthesis and crystal structure of a distorted face sharing double cubane like tetranuclear NiII-Cu2II-NiII compound derived from a reduced di-Schiff base ligand

One new tetranuclear face sharing distorted double cubane like hetero-metallic Ni II 2 Cu 2 II compound has been synthesized using a [NiL R ] “metalloligand”, where H 2 L R = N,N'-bis(2-hydroxybenzyl)-1,3-propanediamine. The compound has been characterized by elemental analysis, spectroscopic methods and single crystal XRD. In the compound, in addition to the m 2 -phenoxido bridges, the two terminal Ni II atoms are linked to each of the central Cu II ion by means of an end-on bridging azido ( m 1,1 -N 3 ) ion separately, resulting a tetranuclear cubane like structure.

An Azido-Bridged Dysprosium Chain Complex Showing Zero-field Slow Magnetic Relaxation.

A one-dimensional (1D) azido-bridged dysprosium coordination polymer featuring a zig-zag chain structure constructed from a halogen-functionalized quinoline derivative and N3 - ligands was structurally and magnetically characterized. Magnetic studies revealed that the chain complex exhibits zero-field slow magnetic relaxation and a significant butterfly-like hysteresis loop, originating from highly magnetic anisotropy of the Dy3+ ions in a D4d symmetry. This compound represents the first azido-bridged lanthanide chain showing zero-field slow magnetic relaxation behavior. These results highlight that the combination of high symmetric Ln3+ ions with the versatile azido bridging ligand provides an effective approach for the design and construction of advanced lanthanides molecular magnets.

Combining benzotriazoles and azides in copper(II) chemistry: synthesis, structural and spectroscopic characterization of a 1-D corrugated tape [Cu(N3)2(1-Mebta)]n coordination polymer (1-Mebta = 1-methylbenzotriazole)

The tertiary CuII/N3 –/1-Mebta reaction scheme, where 1-Mebta is 1-methylbenzotriazole, led to the coordination complex [Cu(N3)2(1-Mebta)]n (1), which has an unusual 1-D corrugated tape polymeric structure built by μ-1,1 and μ3-1,1,1 end-on bridging azido groups, and terminally bound 1-Mebta ligands. Solid-state IR and UV-Vis spectra of 1 are discussed in terms of its structure. The combined results demonstrate the flexibility of both the azido and 1-Mebta groups upon coordination with 3d-metal ions, and their usefulness in the synthesis of azido-rich Cu(II) coordination polymers.

Strong Coupling and Slow Relaxation of the Magnetization for an Air-Stable [Co4] Square with Both Tetrazine Radicals and Azido Bridges.

Introducing both tetrazine radical and azido bridges afforded two air-stable square complexes [MII4(bpztz•-)4(N3)4] (MII = Zn2+, 1; Co2+, 2; bpztz = 3,6-bis(3,5-dimethylpyrazolyl)-1,2,4,5-tetrazine), where the metal ions are cobridged by μ1,1-azido bridges and tetrazine radicals. Magnetic studies revealed strong antiferromagnetic metal-radical interaction with a coupling constant of -64.7 cm-1 in the 2J formalism in 2. Remarkably, 2 exhibits slow relaxation of magnetization with an effective barrier for spin reverse of 96 K at zero applied field.

A Rare Angular Trinuclear Mixed Valence Cobalt(III-II-III) Complex With Azido Bridges And Salpn-Type Schiff-Base Ligand: Synthesis, Crystal Structure And DFT Study

We describe herein a novel angular trinuclear Co(III)–Co(II)–Co(III) mixed-valence Schiff base complex of formula [{(μ-L)(μ-N3)CoIII(N3)}2CoII(H2O)2]⋅MeOH⋅1.5H2O (1), obtained by aerial oxidation of [CoIIL] (2) precursor, where H2L = N,N′-bis(5-bromosalicylidene)-1,3-diaminopropane. The crystal structure of complex 1 reveals that the two terminal cobalt(III) ions are connected to the central cobalt(II) ion through single phenoxo- and single end-on azido bridges giving rise to this unique bent configuration to the (Co3}-core. The oxidation states and geometries around the cobalt atoms in the complexes are confirmed by spectroscopic studies and magnetic moment measurements, which are strongly supported by NBO analysis. It is found that the quartet spin state of the title complex has the lowest energy, both for the X-ray and optimized geometries. The HOMO/LUMO gap values calculated in implicit methanol indicate high stability of complex 1 in solution. The substantial value for the hydrogen bond energy is considered as a major contributing factor to the stabilization of complex 1. We have provided insight in the electronic structural features, including charge and spin distribution, of complex 2 based on the theoretical investigations of the optimized structure. Detailed study on facile synthesis enables us to propose a tentative mechanism of the reaction pathway.

Synthesis, crystal structure, and urease inhibition of an end-on azido-bridged dinuclear copper(II) complex with an oxidized tridentate Schiff base ligand

An end-on azido-bridged dinuclear copper(II) complex, [Cu2L2(μ1,1-N3)2], where L is the deprotonated form of N-(2-hydroxy-4-methoxybenzylidene)picolinamide (HL), has been prepared by the reaction of 5-methoxy-2-[(pyridin-2-ylmethylimino)methyl]phenol (HL′) with copper bromide and sodium azide in methanol. The structure of the complex was characterized by elemental analysis, IR and UV–vis spectra, and single crystal X-ray diffraction. The complex possesses crystallographic inversion symmetry, with the two Cu ions (3.36 Å) bridged by two end-on azido bridges. Each Cu ion is in a square pyramidal coordination. The original ligand HL′ was unexpectedly oxidized to HL under mild conditions during preparation of the complex. The complex has excellent urease inhibitory activity.

One-Pot Self-Assembly of Dinuclear, Tetranuclear, and H-Bonding-Directed Polynuclear Cobalt(II), Cobalt(III), and Mixed-Valence Co(II)/Co(III) Complexes of Schiff Base Ligands with Incomplete Double Cubane Core.

The reaction of 2,6-diformyl-4-methylphenol (DFMF) with 1-amino-2-propanol (AP) and tris(hydroxymethyl)aminomethane (THMAM) was investigated in the presence of Cobalt(II) salts, (X = ClO4−, CH3CO2−, Cl−, NO3−), sodium azide (NaN3), and triethylamine (TEA). In one pot, the variation in Cobalt(II) salt results in the self-assembly of dinuclear, tetranuclear, and H-bonding-directed polynuclear coordination complexes of Cobalt(III), Cobalt(II), and mixed-valence CoIICoIII: [Co2III(H2L−1)2(AP−1)(N3)](ClO4)2 (1), [Co4(H2L−1)2(µ3-1,1,1-N3)2(µ-1,1-N3)2Cl2(CH3OH)2]·4CH3OH (2), [Co2IICo2III(HL−2)2(µ-CH3CO2)2(µ3-OH)2](NO3)2·2CH3CH2OH (3), and [Co2IICo2III (H2L12−)2(THMAM−1)2](NO3)4 (4). In 1, two cobalt(III) ions are connected via three single atom bridges; two from deprotonated ethanolic oxygen atoms in the side arms of the ligands and one from the1-amino-2-propanol moiety forming a dinuclear unit with a very short (2.5430(11) Å) Co-Co intermetallic separation with a coordination number of 7, a rare feature for cobalt(III). In 2, two cobalt(II) ions in a dinuclear unit are bridged through phenoxide O and μ3-1,1,1-N3 azido bridges, and the two dinuclear units are interconnected by two μ-1,1-N3 and two μ3-1,1,1-N3 azido bridges generating tetranuclear cationic [Co4(H2L−1)2(µ3-1,1,1-N3)2(µ-1,1-N3)2Cl2(CH3OH)2]2+ units with an incomplete double cubane core, which grow into polynuclear 1D-single chains along the a-axis through H-bonding. In 3, HL2− holds mixed-valent Co(II)/Co(III) ions in a dinuclear unit bridged via phenoxide O, μ-1,3-CH3CO2−, and μ3-OH− bridges, and the dinuclear units are interconnected through two deprotonated ethanolic O in the side arms of the ligands and two μ3-OH− bridges generating cationic tetranuclear [Co2IICo2III(HL−2)2(µ-CH3CO2)2(µ3-OH)2]2+ units with an incomplete double cubane core. In 4, H2L1−2 holds mixed-valent Co(II)/Co(III) ions in dinuclear units which dimerize through two ethanolic O (μ-RO−) in the side arms of the ligands and two ethanolic O (μ3-RO−) of THMAM bridges producing centrosymmetric cationic tetranuclear [Co2IICo2III (H2L1−2)2(THMAM−1)2]4+ units which grow into 2D-sheets along the bc-axis through a network of H-bonding. Bulk magnetization measurements on 2 demonstrate that the magnetic interactions are completely dominated by an overall ferromagnetic coupling occurring between Co(II) ions.

Two azido-bridged [2×2] cobalt(ii) grids featuring single-molecule magnet behaviour.

The self-assembly of Co(ii) salts, pyridazine derivatives and azides afforded two azido-bridged [2×2] grid-type complexes {[(L)4CoII4(N3)4][BPh4]4}·sol (1, L = 3,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (pzdz) and sol = 4CH3CN·3CHCl3·2CH3OH and 2, L = 3,6-di(pyridin-2-yl)pyridazine (pydz) and sol = 4CH3CN). Upon comparison with other related grid-like complexes, the incorporation of end-on azido-bridges resulted in overall intramolecular ferromagnetic couplings, and thus endowed complexes 1 and 2 single molecule magnet behaviour with field-induced slow magnetic relaxation.

Magnetic Properties of End-to-End Azide-Bridged Tetranuclear Mixed-Valence Cobalt(III)/Cobalt(II) Complexes with Reduced Schiff Base Blocking Ligands and DFT Study.

Two tetranuclear mixed-valence cobalt(III/II) complexes having the general formula [(μ1,3-N3){CoII(Ln)(μ-O2CC6H4NO2)CoIII(N3)}2]PF6 (where H2L1 and H2L2 are two reduced Schiff base ligands) have been synthesized and characterized. The structures of both complexes show cobalt(II) and cobalt(III) centers with a distorted octahedral geometry with cobalt(III) and cobalt(II) centers located at the inner N2O2 and outer O4 cavities of the reduced Schiff base ligands, respectively. The oxidation states of both cobalt centers have been confirmed by bond valence sum (BVS) calculations. The magnetic properties show that both compounds behave as cobalt(II) dimers connected through an end-to-end azido bridging ligand and show moderate antiferromagnetic Co(II)–Co(II) couplings of −11.0 and −14.4 cm–1 for 1 and 2, respectively, as also corroborated by DFT calculations, Jtheo = −13.07 cm–1 for 1 and −12.49 cm–1 for 2. The calculated spin densities of both complexes at the cobalt(II) centers are −2.75 and +2.75, respectively, clearly supporting that they are the magnetic centers.

Macrocyclic copper(II) complexes containing diazacyclam-based ligand: spectral, structural and docking studies

The macrocyclic copper complex, [Cu(ACE)(NO3)2] (ACE = 1,3,6,10,12,15-hexaazatricyclo[13.3.1.16,10]eicosane), was synthesized by template condensation from a mixture of N1-(2-aminoethyl)-1,3-diaminopropane, formaldehyde and copper(II) nitrate. Replacement of the nitrate with thiocyanato and azido ligands gives [Cu(ACE)NSC]NSC (2) and the 1D-coordination polymer, [Cu(ACE)(μ-N3)]n[N3]n (3), respectively. Complex 1, [Cu(ACE)(NO3)]NO3, is an intermediate product in which one of the nitrate ions is separated from its parent molecule. The formation of 1 allowed us to conclude that the mechanism of ion exchange in the parent molecule is similar to SN1. These complexes have been characterized by FT-IR spectroscopy and X-ray crystallography. In the crystal structures of 1 and 2, the copper(II) ion has a distorted square pyramidal geometry in which the N4-donor ACE ligand lies on the equatorial plane and other ligand occupies the axial position. The copper(II) ion in 3 has an octahedral geometry, coordinating to one ACE ligand in the equatorial plane and two N-donor bridging azido groups in the axial positions. In all structures, owing to the Jahn-Teller effect, the coordinated bond length of the axial position is longer than the equatorial ones. The ability of the ACE ligand and its complexes 1 and 2, along with their analogues, to interact with 10 selected biomacromolecules (BRAF kinase, CatB, DNA gyrase, HDAC7, rHA, RNR, TrxR, TS, Top II and B-DNA) was investigated by docking calculations and compared with that of doxorubicin.

An Azido-Cyanide Mixed-Bridged [Fe4Ni4] Single-Molecule Magnet.

Taking advantages of both azide and cyanide bridges in magnetism and synthesis, an azido-cyanide mixed-bridged octanuclear [FeIII4NiII4] SMM of [{(enbzpy)Ni2(μ1,1-N3)2·(DMF)}{Tp*Fe(CN)3}2]2·2DMF·14H2O (1) was explored and characterized, which exhibits slow relaxation of the magnetization and an S = 6 ground state benefit from the end-on azido bridges.

Different reactivity patterns for [M(trien)]2+/3+ (M = NiII and CoIII) toward azido ions: Cationic charge dependence and different mode of ligand enfolding for 1D chain formation

Linear and flexible N4 ligand trien (N′-{2-(2-aminoethylamino)-ethyl}-ethane-1,2-diamine) has been used to show octahderal coordination around NiII ions and cis coordination from two ancillary bridges from azide ions. Room temperature reaction of trien with Ni(NO3)·6H2O and NaN3 has led to an end-to-end (EE) azido bridged one-dimensional NiII based helical coordination chain of formula [NiII(μ-N3)2 (trien)]n (NO3)·H2O {1n·(NO3)·H2O}. Propagation of the chain in one dimension in a helical fashion is continued from the azido bridges in cis directions. Comparative reaction protocol using Co(NO3)2·6H2O on the other hand provided a discrete mononuclear octahedral cobalt (III) complex cis-[CoIII(N3)2 (trien)](NO3)·2H2O {2·(NO3)·2H2O} due to different type of ligand wrapping having only terminal coordination from azide ions.

Syntheses, crystal structures and photo physical aspects of azido-bridged tetranuclear cadmium (II) complexes: DFT/TD-DFT, thermal, antibacterial and anti-biofilm properties

In this work we have reported two novel tetranuclear Cd(II) complexes viz. [Cd4 (LOMe)2 (μ1,1-N3)3 (μ1,3-N3)]n (1) and [Cd4 (LOEt)2 (μ1,1-N3)3(OAc)]2 (2) where (H2LOMe) and (H2LOEt) are two important less explored salen-type Schiff base ligands. Both of the complexes have been characterized by using routine spectroscopic techniques, elemental analyses (C, H and N), X-ray powder diffraction pattern (PXRD) and thermal analysis by TGA along with single x-ray crystallography. The complete structural study discloses that in both cases the fully deprotonated ligand [LOMe]2- or [LOEt]2- utilized all potential coordination sites to accommodate four Cd(II) ions. Complex 1 is a one-dimensional polymer with azide (N3) linkage having both (μ1,1 end on) and (μ1,3 end-to-end) azido bridging but complex 2 is a discrete octanuclear ensamble where two [Cd4(O)4(N)2]2+ units bridged to each other showing μ1,1 end on end on azide bridging. Exploration of photo physical properties in DMSO solvent reveals that Cd(II) complexes enhance appreciably the fluorescence behavior over free Schiff base ligands (H2LOMe) and (H2LOEt). DFT calculations performed at B3LYP/def2-TZVP level of theory reveal both the energetics and composition of FMOs in these complexes and also show electrophilic and nucleophilic areas via molecular electrostatic maps [ESP] concept. The antibacterial, membrane damage assay and anti-biofilm properties of complexes 1 and 2 were investigated very carefully against some important Gram-positive and Gram-negative bacterial strains.