Structure and properties of an oxalato-bridged dinickel(II) complex with a tetraazamacrocycle bearing an aminomethyl pendant arm, 5-aminomethyl-5R(S),12R(S)-dimethyl-1,4,8,11-tetraazacyclotetradecane

The oxalato-bridged dinickel(II) complex with the title ligand, [Ni₂(L ^a H)₂(μ-ox)](ClO₄)₂·2H₂O (1), was prepared and its structure was determined by X-ray crystallography, as well as that of the monomeric nickel(II) complex, [Ni(L ^a H)ox]ClO₄·3H₂O (2). In Complexes 1 and 2, the ligand, L ^a , is folded along the N(4)–Ni(1)–N(11) axis. The antiferromagnetic coupling between the two nickel(II) centers in 1 was revealed and the coupling constant, J?=??17.4?cm^?1, and g?=?2.11 were estimated. It was found that the oxalato-bridged dimer 1 was readily converted to the mononuclear cis-nickel(II) complex [NiL ^a (OH₂)](ClO₄)₂ (3a), in basic aqueous solution. In [NiL ^a (CH₃CN)]I₂ (3b), which was derived from 3a, the aminomethyl pendant arm is coordinated to the Ni(II) ion and L ^a is folded along the N(1)–Ni(1)–N(8) axis.     

Dimorphic Modification of the Trinuclear Nickel(II) Complex [Ni3(NCS)6(pdz)6]: Synthesis,Crystal Structure,Thermal, Magnetic and Spectroscopic Properties

Reaction of nickel(II) thiocyanate and pyridazine (pdz) as organic spacer ligand leads to the formation of the ligand‐rich 1:2 (1:2 = metal to ligand ratio) trinuclear nickel(II) complex of composition [Ni₃(NCS)₆(pdz)₆]. Depending on the reaction solvent, different polymorphic modifications are obtained: Reaction in acetonitrile leads to the formation of the new modification 1I and reaction in ethanol leads to the formation of modification 1II reported recently. In their crystal structures discrete [Ni₃(NCS)₆(pdz)₆] units are found, in which each of the Ni²⁺ cations exhibits a NiN₆ distorted octahedral arrangement. The central Ni²⁺ cation is coordinated by four bridging pdz ligands and two thiocyanato anions in trans positions. Both thiocyanato anions exhibit the end‐on bridging mode. The peripheral Ni²⁺ cations are bridged by one thiocyanato anion and by two pdz ligands with the central Ni²⁺ cation. Further they are coordinated by two terminal N‐bonded thiocyanato anions and one terminal N‐bonded pdz ligand. The structure of 1I was determined by X‐ray single crystal structure investigation and emphasized by infrared spectroscopy. Magnetic measurements revealed a quasi Curie behavior with net ferromagnetic interactions for 1I and net antiferromagnetic interactions for 1II . Solvent‐mediated conversion experiments clearly show that modification 1I represents the thermodynamic most stable form at room temperature and that modification 1II is metastable. On thermal decomposition, both modification transform quantitatively in a new ligand‐deficient intermediate. Elemental analysis revealed a 3:4 compound of composition [Ni₃(NCS)₆(pdz)₄]. A structure model supported by IR spectroscopic investigations was assumed, in which three coordination modes of the thiocyanato anion exist, resulting in a 2D polymeric network.     

Dinickel Complexes Bridged by Unusual (N,O,O′)-Coordinated α-Amino Acids: Syntheses,Structural Characterization and Magnetic Properties

Four novel dinickel complexes, coordinated by mixed ligands of tren and racemic amino acids, namely [Ni₂(tren)₂(dl-alaninato)(H₂O)]I₃·2H₂O (1), [Ni₂(tren)₂(dl-leucinato)(H₂O)]I₃·2.5H₂O (2), [Ni₂(tren)₂(dl-phenylalaninato)(H₂O)]I₃·H₂O (3), and {[Ni₂(tren)₂(dl-histinato)](ClO₄)₃·1.5H₂O} _n (4), have been synthesized and structurally characterized by X-ray crystallography, FTIR, u.v. and e.s. spectra. They represent the first series of dinickel(II) complexes bridged by the unusual (N,O,O)-coordinated -amino acids. In complexes (1–3), one of the nickel(II) centers is coordinated by four N-atoms of the tren ligand, one O-atom of the carboxylate group of the amino acidato ligand and one H₂O molecule. The other nickel(II) center is also coordinated by the four N-atoms of the tren ligand, one carboxylic O-atom and the amino N-atom of the amino acidato ligand, resulting in an asymmetric dinuclear core with chromophores of NiN₄O₂ and NiN₅O. In the polymeric {[Ni₂(tren)₂(dl-histinato)](ClO₄)₃·1.5H₂O} _n (4), the imidazole N-atom is also involved in ligation with nickel(II) and both nickel(II) centers have the same chromophore described as NiN₅O. The Ni...Ni distances are in the 5.5199(10)–5.5807(15)Å range. Analyses of the magnetic properties of complexes (1), (3) and (4) show that a weak ferromagnetic interaction exists between the two nickel(II) centers.     

Nickel(II) complexes of polyhydroxybenzaldehyde N4-thiosemicarbazones: synthesis, structural characterization and antimicrobial activities

Nickel(II) complexes with 2,3-dihydroxybenzaldehyde N4-substituted thiosemicarbazone ligands (H₃L¹–H₃L⁴) have been synthesized and characterized with the aim of evaluating the effect of N4 substitution in the thiosemicarbazone moiety on their coordination behavior and biological activities. Two series of nickel(II) complexes with the general formulae [Ni(H₃L)(H₂L)]ClO₄ and [Ni₂(HL)₂] were characterized by analytical and spectral techniques. The molecular structure of one of the complexes, namely, [Ni(H₃L⁴)(H₂L⁴)]ClO₄ was established by single crystal X-ray diffraction studies. The crystal structure of this complex revealed that two H₃L⁴ ligands are coordinated to nickel(II) in different modes; one as a neutral tridentate ONS ligand and the other is as a monoanionic tridentate (ONS^?) ligand. The antimicrobial activities of the compounds were tested against 25 bacterial strains via the disc diffusion method, and their minimum inhibitory concentration (MIC) and minimum microbicidal concentration were evaluated using microdilution methods. With a few exceptions, most of the compounds exhibited low-to-moderate inhibitory activities against the tested bacterial strains. However, the complexes [Ni₂(HL³)₂] (7) and [Ni₂(HL⁴)₂] (8) indicated higher inhibitory activity against Salmonella enterica ATCC 9068 (MIC values 15.7 and <15.7 μg/ml, respectively), compared with gentamicin as the positive control (MIC 25 μg/ml). Complex (7) also inhibited Streptococcus pneumoniae more efficiently (MIC 31.2 μg/ml), compared with gentamicin (MIC > 50 μg/ml). The toxicities of the compounds were tested on brine shrimp (Artemia salina), where no meaningful toxicity level was noted for both the free ligands and the complexes. The cytotoxicities of the compounds on cell viability were determined on MCF7, PC3, A375, and H413 cancer cells in terms of IC₅₀; complexes [Ni(H₃L³)(H₂L³)]ClO₄ (3), [Ni₂(HL³)₂] (7) and [Ni₂(HL⁴)₂] (8) exhibited significant cytotoxicity on the tested cell lines.     

Hydride Reactivity of NiII?X?NiII Entities: Mixed‐Valent Hydrido Complexes and Reversible Metal Reduction

After the lithiation of PYR‐H₂ (PYR^2?=[{NC(Me)C(H)C(Me)NC₆H₃(iPr)₂}₂(C₅H₃N)]^2?), which is the precursor of an expanded β‐diketiminato ligand system with two binding pockets, its reaction with [NiBr₂(dme)] led to a dinuclear nickel(II)–bromide complex, [(PYR)Ni(μ‐Br)NiBr] ( 1 ). The bridging bromide ligand could be selectively exchanged for a thiolate ligand to yield [(PYR)Ni(μ‐SEt)NiBr] ( 3 ). In an attempt to introduce hydride ligands, both compounds were treated with KHBEt₃. This treatment afforded [(PYR)Ni(μ‐H)Ni] ( 2 ), which is a mixed valent Ni^I? μ‐H? Ni^II complex, and [(PYR‐H)Ni(μ‐SEt)Ni] ( 4 ), in which two tricoordinated Ni^I moieties are strongly antiferromagnetically coupled. Compound 4 is the product of an initial salt metathesis, followed by an intramolecular redox process that separates the original hydride ligand into two electrons, which reduce the metal centres, and a proton, which is trapped by one of the binding pockets, thereby converting it into an olefin ligand on one of the Ni^I centres. The addition of a mild acid to complex 4 leads to the elimination of H₂ and the formation of a Ni^IINi^II compound, [(PYR)Ni(μ‐SEt)NiOTf] ( 5 ), so that the original Ni^II(μ‐SEt)Ni^IIX core of compound 3 is restored. All of these compounds were fully characterized, including by X‐ray diffraction, and their molecular structures, as well as their formation processes, are discussed.     

Novel coordination behavior of a pteridine-benzoylhydrazone ligand (BZLMH): Theoretical calculations, XRD structures and luminescence studies

The XRD structure and the influence of the conformation in the molecular orbitals of the pteridine-benzoylhydrazone ligand (BZLMH = benzoylhydrazone of 6-acetyl-1,3,7-trimethyllumazine, lumazine = (1H,3H)-pteridin-2,4-dione) have been studied. Complexes of BZLMH with nickel(II), zinc(II) and mercury(II) have been prepared and spectroscopically characterized by IR, NMR and fluorescence spectroscopy; also XRD studies have allowed to establish two different coordinative patterns in the complexes [Ni₃(BZLMH)₃(OH)(H₂O)(CH₃CN)₂](ClO₄)₅ · 2H₂O · CH₃CN (2) and [Zn(NO₃)(BZLMH)(H₂O)](NO₃) (3). Compound (2) is a trinuclear hydroxo-centered complex with a central hydroxo group bridging the three nickel(II) ions. The [Ni₃(μ₃-OH)]⁵⁺ core is planar with the benzoylhydrazone ligands coordinated in the bis-bidentate [O(4),N(5)]-[N(61),O(63)] mode. The zinc(II) compound displays a BPT coordination geometry in which the BZLMH ligand acts in a tridentate fashion using N(5), N(61) and O(63) donor atoms. Fluorescence spectroscopic properties of benzoylhydrazone (BZLMH) are studied and the fluorescence band shift and changes in intensity is modulated by complexation with different metal ions (Ni²⁺, Zn²⁺ and Hg²⁺), so the binding is signaled such a possible cause.     

Pentanuclear Nickel(II) Complex with two Vertex-Shared Triaminoguanidine Fragments and Symmetric Capping Ligand

The pentanuclear nickel(II) complex [Ni₅(saltag^Br)₂(tptz)₄] ( Ni5 ) with the tritopic triaminoguanidine-derived Schiff-base ligand H₅saltag^Br (1,2,3-tris[(5-bromosalicylidene)amino]guanidine) and tptz (2,4,6-tris(2-pyridyl)-1,3,5-triazine) as capping ligands is reported. Ni5 crystallizes in the triclinic space group P1 with the central nickel(II) ion linking two triangular arrangements of nickel(II) ions supported by two tritopic triaminoguanidine ligands. The octahedral coordination of the four peripheral nickel(II) ions is complemented by capping tridentate tptz ligands. By variation of the synthesis also the corresponding trinuclear nickel(II) complex [Ni₃(saltag^Br)(tptz)₃]NO₃ ( Ni3 ) is accessible. Magnetic measurements for Ni3 and Ni5 reveal a singlet ground state with antiferromagnetic coupling between the nickel(II) ions, which in the case of Ni5 can only be simulated assuming a two-J exchange coupled spin topology. For both complexes significant zero-field splitting for the nickel(II) ions is evident from the measured magnetic data, which can be verified by theoretical studies revealing a magnetic anisotropy with strong rhombic distortion due to the presence of the tptz co-ligands in both compounds.     

Synthesis, crystal structure and magnetic property of the novel dinuclear nickel(II) complex with 4-(p-methoxyphenyl)-3,5-bis(pyridine-2-yl)-1,2,4-triazole

A novel dinuclear nickel(II) complex, [Ni₂(MOBPT)₂Cl₂(H₂O)₂]Cl₂ · 7H₂O (MOBPT = 4-(p-methoxyphenyl) −3,5-bis(pyridine-2-yl)-1,2,4-triazole), has been synthesized and characterized by elemental analysis, IR and single crystal X-ray diffraction methods. The crystal structure determination shows that the dinuclear Ni₂N₈ unit is almost planer in which each Ni^II ion is coordinated by four nitrogen atoms from MOBPT equatorially and a water molecule and a chloride ion axially in a distorted octahedral geometry. Magnetic measurements reveal a relatively weak antiferromagnetic exchange in the complex.     

(μ‐Oxalato‐O1,O2:O1′,O2′)bis[aqua(diethyl­enetri­amine)nickel(II)] bis(hexafluorophosphate) dihydrate

The title compound, [Ni₂(C₂O₄)(C₄H₁₃N₃)₂(H₂O)₂](PF₆)₂·‐2H₂O, contains a dinuclear oxalato‐bridged nickel(II) complex cation. The structure determination reveals the presence of a centrosymmetric binuclear complex where the oxalate ligand is coordinated in a bis­‐bidentate mode to the Ni atoms. The distorted octahedral environment of each Ni atom is completed by the three N atoms of the diethyl­enetri­amine ligand in a fac arrangement and by one O atom from a water mol­ecule. PF₆^? acts as counter‐anion. A two‐dimensional network of hydrogen bonds links the cations and anions and stabilizes the structure.     

Nickel and zinc complexes with a monodentate heterocycle and tridentate Schiff base ligands: self‐assembly to one‐ and two‐dimensional supramolecular networks via hydrogen bonding

In the complex (morpholine)[2‐hydroxy‐N′‐(5‐nitro‐2‐oxidobenzylidene)benzohydrazidato]nickel(II), [Ni(C₁₄H₉N₃O₅)(C₄H₉NO)], (I), the Ni^II center is in a square‐planar N₂O₂ coordination geometry. The complex bis[μ‐2‐hydroxy‐N′‐(2‐oxidobenzylidene)benzohydrazidato]bis[(morpholine)zinc(II)], [Zn₂(C₁₄H₁₀N₂O₃)₂(C₄H₉NO)₂], (II), consists of a neutral centrosymmetric dimer with a coplanar Zn₂(μ₂‐O)₂ core. The two Zn^II centers are bridged by phenolate O atoms. Each Zn^II center exhibits a distorted square‐pyramidal stereochemistry, in which the four in‐plane donors come from the O,N,O′‐tridentate 2‐hydroxy‐N′‐(2‐oxidobenzylidene)benzohydrazidate(2−) ligand and a symmetry‐related phenolate O atom, and the axial position is coordinated to the N atom from the morpholine molecule. There are intramolecular phenol–hydrazide O—H...N hydrogen bonds present in both (I) and (II). In (I), square‐planar nickel complexes are linked by intermolecular morpholine–morpholine N—H...O hydrogen bonds, leading to a one‐dimensional chain, while in (II) an infinite two‐dimensional network is formed via intermolecular hydrogen bonds between the coordinated morpholine NH groups and the uncoordinated phenolate O atoms.     

Synthesis and Structural Studies of 2-(hydroxyimino)-1-methylpropylideneamino-phenyliminobutan-2-one Oxime, Ligand and its Complexes with Cu(II) and Ni(II)

A new ligand incorporating a dioxime moiety, (2E,3E)-3-[(2-{[(1E,2E)-2-(hydroxyimino)-1-methylpropylidene]amino}phenyl)imino]butan-2-one oxime, (H₂Phmdo) (3) has been prepared by reacting 2,3-butanedionemono-{O-[4-(1-methyl-2-oxo-propylideneaminooxy)-2,3-bis-(1-methyl-2-oxo-propylideneaminooxy-methyl)-but-2-enyl]-oxime} (2) with 1,2-phenylenediamine. Mono-, di- and trinuclear copper(II) and/or nickel(II) complexes of H₂Phmdo were characterized by elemental analyses, magnetic moments, ¹H-n.m.r. and ¹³C-n.m.r., i.r. and mass spectral studies. The mononuclear copper(II) and nickel(II) complexes of H₂Phmdo were found to have a 1:1 metal:ligand ratio. Elemental analyses, stoichiometric and spectroscopic data of the metal complexes indicated that the metal ions are coordinated to the oxime and imine nitrogen atoms (C=N). In the dinuclear complexes, in which the first Cu^(II) or Ni^(II) ion was complexed with nitrogen atoms of the oxime and imine groups, the second Cu^(II) ion is ligated with dianionic oxygen atoms of the oxime groups and are linked to the 1,10-phenanthroline nitrogen atoms. The data support the proposed structure of H₂Phmdo and its complexes.     

[N,N′‐Bis­(salicyl­idene)‐2,2‐di­methyl‐1,3‐propane­diaminato]­nickel(II) and [N,N′‐bis­(salicyl­idene)‐2,2‐di­methyl‐1,3‐propane­diaminato]copper(II)

In the title compounds, {2,2′‐[2,2‐di­methyl‐1,3‐propane­diyl­bis­(nitrilo­methyl­idyne)]­diphenolato‐κ⁴N,N′,O,O′}nickel(II), [Ni(C₁₉H₂₀N₂O₂)], and {2,2′‐[2,2‐di­methyl‐1,3‐propane­diyl­bis­(nitrilo­methyl­idyne)]­diphenolato‐κ⁴N,N′,O,O′}copper(II), [Cu(C₁₉H₂₀N₂O₂)], the Ni^II and Cu^II atoms are coordinated by two iminic N and two phenolic O atoms of the N,N′‐bis­(salicyl­idene)‐2,2‐di­methyl‐1,3‐propane­diaminate (SALPD^2?, C₁₇H₁₆N₂O₂^2?) ligand. The geometry of the coordination sphere is planar in the case of the Ni^II complex and distorted towards tetrahedral for the Cu^II complex. Both complexes have a cis configuration imposed by the chelate ligand. The dihedral angles between the N/Ni/O and N/Cu/O coordination planes are 17.20 (6) and 35.13 (7)°, respectively.     

Spin Interactions and Magnetic Anisotropy in a Triangular Nickel(II) Complex with Triaminoguanidine Ligand Framework

The trinuclear nickel(II) complex [Ni₃(saltag^tBu)(bpy)₃(H₂O)₃]Cl (H₅saltag^tBu = 1,2,3-tris[(5-tert-butylsalicylidene)amino]guanidine) was synthesized and characterized by experimental as well as theoretical methods. The complex salt crystallizes with three molecules of dimethylformamide (dmf) and water as [Ni₃(saltag^tBu)(bpy)₃(H₂O)₃]Cl · 3dmf · 3H₂O ( 1 ) in the trigonal space group P3 , with the complex located on a threefold rotation axis, which is consistent with the molecular C₃ symmetry of the complex cation. Magnetic measurements reveal an antiferromagnetic coupling (J = –35.9 cm^–1) between the nickel(II) ions leading to a diamagnetic ground state for the trinuclear complex cation. Theoretical investigations based on broken-symmetry DFT confirm the antiferromagnetic exchange within the complex cation of 1 . Additional single-ion CASSCF ab initio studies reveal that magnetic anisotropy is present in the system. The experimental and theoretical results for 1 are compared with those of a structurally similar nickel(II) complex that is based on the bromo-substituted derivative of the triaminoguanidine ligand. The differences in their magnetic properties can be attributed to the stronger elongation of the pseudo-octahedral coordination sphere at the nickel(II) centers in case of 1 . The analysis of the magnetic properties of 1 clearly shows that for such exchange coupled systems reliable parameters for the magnetic anisotropy cannot be extracted from experimental data alone.     

X-ray powder structure of a new two-dimensional nickel(II) coordination polymer with pyrazine-2,3,5,6-tetracarboxylic acid

The new nickel(II) coordination polymer poly­[di­aqua­nickel(II)-μ-(pyrazine-2,3,5,6-tetra­carboxyl­ato)-tetra­aqua­nickel(II)], {[{Ni(C₈N₂O₈)(H₂O)₂}Ni(H₂O)₄]}_n, has been synthesized and characterized both spectroscopically and crystallographically, by X-ray powder diffraction analysis. In this two-dimensional coordination polymer, Ni^II ions are bridged by pyrazine-2,3,5,6-tetra­carboxyl­ic acid, coordinating in a bis-bidentate manner, so forming one-dimensional polymeric chains. The chains are linked by a second Ni^II ion, via an O atom of the coordinated carboxyl­ate group, resulting in the formation of a two-dimensional layer-like polymer. The remaining coordination sites of the two independent octahedral Ni^II ions are occupied by water mol­ecules. The layers are connected via hydrogen bonds involving all six coordinated water mol­ecules.     

A novel nickel(II) coordination polymer incorporating 1,4‐phenylene­diacetic acid and 1,10‐phenanthroline

The title nickel(II) coordination polymer, viz. poly[[bis­(1,10‐phenanthroline)tris­(μ₃‐1,4‐phenyl­enediacetato)trinickel(II)] dihydrate], {[Ni₃(C₁₀H₈O₄)₃(C₁₂H₈N₂)₂]·2H₂O}_n, consists of linear trinuclear building blocks with two crystallographically unique Ni atoms. One Ni^II atom and the geometric centre of one 1,4‐phenyl­enediacetate ligand in the trinuclear unit both lie on inversion centres, while the other unique Ni^II atom lies near the inversion centre, together with another 1,4‐phenyl­enediacetate ligand. Each pair of adjacent trinuclear units is bridged by 1,4‐phenyl­enediacetate ligands, forming two kinds of infinite chains along the a and b axes, respectively. These two kinds of chains crosslink to yield a two‐dimensional network in the ab plane. The two‐dimensional sheets further stack along the c axis viaπ–π stacking inter­actions and hydrogen bonds, forming a three‐dimensional supramolecular structure.     

A hybrid imidazolylidene/imidazolium nickel NHC complex: an isolated intermediate

Macrocyclic ligand systems with a variety of (different) donor sites oftentimes give rise to very exciting and unexpected multinuclear metal complexes. We report herein the structure of a trinuclear mixed imidazolylidene/imidazolium nickel N‐heterocyclic carbene (NHC) complex, namely di‐μ‐chlorido‐bis{μ‐calix[2]imidazolium[2]imidazolylidene[2]pyrazolate}trinickel(II) tetrakis(hexafluoridophosphate) acetonitrile tetrasolvate, [Ni₃(C₂₄H₂₄N₁₂)₂Cl₂](PF₆)₄·4CH₃CN or [Ni₃(L ^Me)₂Cl₂](PF₆)₄·4CH₃CN, that can be understood as a trapped reaction intermediate during the synthesis of the respective [Ni₂L ^Me](PF₆)₂ product. The structure not only contains protonated next to deprotonated imidazole heterocycles, but also Ni²⁺ ions with fundamentally different coordination modes within one molecule. Two of the three metal atoms are coordinated in a square‐pyramidal fashion by half a ligand molecule and one chloride ligand, whereas the third Ni²⁺ ion is bound octahedrally by four pyrazolate moieties and two chloride anions.     

Metal complexes of mercaptoamines—I. Synthesis and crystal and molecular structure of tetrakis (3-amino-1-propanethiolato) trinickel(II)chloride

The reaction of nickel(II)chloride with γ-mercapto-propylamine in ethanolic solution gives the complex [Ni₃(MPA)₄]Cl₂(MPA=NH₂-(CH₂)₃-S). The complexes [Ni₃(MPA)₄]X₂(X=Br, I, ClO₄) can be synthesized from the chloride complex by addition of the sodium salt in aqueous solution. The crystal structure consists of discrete divalent trinuclear cations and chloride anions. Each sulphur atom of the ligand acts as a bridge between two nickel atoms, and the nitrogen atoms complete the coordination around the terminal nickel atoms. The geometry around the metal atoms is square-planar. The electronic and IR spectra of the complexes [Ni₃(MPA)₄]X₂(X=Br, I, ClO₄) indicate that all these compounds are composed of the [Ni₃(MPA)₄]²⁺ and X^? ions.     

Hydrogen Bonds as Structural Directive towards Unusual Polynuclear Complexes: Synthesis,Structure, and Magnetic Properties of Copper(II) and Nickel(II) Complexes with a 2-Aminoglucose Ligand

The reaction of benzyl 2-amino-4,6-O-benzylidene-2-deoxy-α-D -glucopyranoside (HL) with the metal salts Cu(ClO₄)₂ ⋅ 6 H₂O and Ni(NO₃)₂ ⋅ 6 H₂O affords via self-assembly a tetranuclear μ₄-hydroxido bridged copper(II) complex [(μ₄-OH)Cu₄(L)₄(MeOH)₃(H₂O)](ClO₄)₃ ( 1 ) and a trinuclear alcoholate bridged nickel(II) complex [Ni₃(L)₅(HL)]NO₃ ( 2 ), respectively. Both complexes crystallize in the acentric space group P2₁. The X-ray crystal structure reveals the rare (μ₄-OH)Cu₄O₄ core for complex 1 which is μ₂-alcoholate bridged. The copper(II) ions possess a distorted square-pyramidal geometry with an [NO₄] donor set. The core is stabilized by hydrogen bonding between the coordinating amino group of the glucose backbone and the benzylidene protected oxygen atom O4 of a neighboring {Cu(L)} fragment as hydrogen-bond acceptor. For complex 2 an [N₄O₂] donor set is observed at the nickel(II) ions with a distorted octahedral geometry. The trinuclear isosceles Ni₃ core is bridged by μ₃-alcoholate O3 oxygen atoms of two glucose ligands. The two short edges are capped by μ₂-alcoholate O3 oxygen atoms of the two ligands coordinated at the nickel(II) ion at the vertex of these two edges. Along the elongated edge of the triangle a strong hydrogen bond (244 pm) between the O3 oxygen atoms of ligands coordinating at the two relevant nickel(II) ions is observed. The coordinating amino groups of the these two glucose ligands are involved in additional hydrogen bonds with O4 oxygen atoms of adjacent ligands further stabilizing the trinuclear core. The carbohydrate backbones in all cases adopt the stable ⁴C₁ chair conformation and exhibit the rare chitosan-like trans-2,3-chelation. Temperature dependent magnetic measurements indicate an overall antiferromagnetic behavior for complex 1 with J₁=−260 and J₂=−205 cm⁻¹ (g=2.122). Compound 2 is the first ferromagnetically coupled trinuclear nickel(II) complex with J_A=16.4 and J_B=11.0 cm⁻¹ (g_1,2=2.183, g₃=2.247). For the high-spin nickel(II) centers a zero-field splitting of D_1,2=3.7 cm⁻¹ and D₃=1.8 cm⁻¹ is observed. The S=3 ground state of complex 2 is consistent with magnetization measurements at low temperatures.     

Synthesis,Structure and Properties of an Oxalato-Bridged Dinuclear Nickel(II) Complex

A new dinuclear nickel(II) compound, [Ni₂(TPA)2(μ-C₂O₄)](H₂O)_0.75(ClO₄)₂ [TPA = tris(2-pyridylmethyl) amine], was synthesized and characterized by electronic spectroscopy and X-ray methods. In the complex, the oxalate ion acts as a bis-bidentate ligand and the two Ni(II) ions are six coordinated with a distorted octahedral structure. The complex crystallizes in the triclinic space group P_i , with a = 13.203(4), b = 16.574(5), c = 21.802(6) Å, α = 78.644(5), β = 80.299(5), γ = 72.446(5)°, V = 4429 ų, Z = 2; R ₁ = 0.0615, wR ₂ = 0.1639. In the temperature range 4-300 K, magnetic measurements show that the exchange interaction between the two metal ions is antiferromagnetic with J = ? 18.74 cm^?1, g = 2.10.     

Magnetic Exchange Interactions in Dinuclear Copper(II) and Nickel(II) Complexes with μ‐Oxalato Bridges. The Structure of μ‐Oxalato(O,O′, O″, O‴)‐bis{[1, 8‐di(2‐pyridyl)‐3, 6‐dithiaoctane‐N,N′, S,S′]nickel(II)} Dinitrate Dihydrate

A copper(II) and two nickel(II) dinuclear oxalato‐bridged compounds of formulae [{Cu(bpdto)}₂(μ‐ox)](ClO₄)₂ ( 1 ), [{Ni(bpdto)]₂(μ‐ox)](ClO₄)₂( 2 ), and [{Ni(bpdto)}₂(μ‐ox)](NO₃)₂·2H₂O ( 3 ), where bpdto = 1, 8‐bis(2‐pyridyl)‐3, 6‐dithiaoctane and ox = oxalate = C₂O₄^2— anion, have been synthesized and characterized. The crystal structure of 3 was determined by single‐crystal X‐ray analysis. It is a dinuclear complex with i symmetry in which the oxalate ligand is coordinated in bis(didentate) fashion to the inversion centre‐related nickel atoms. The distorted octahedral environment of each nickel atom is completed by two sulphur atoms in the equatorial plane and by two pyridyl nitrogen atoms in axial positions. Magnetic susceptibility measurements over the range 5 — 299K, show antiferromagnetic interactions that are weak in 1 (J = —12.8 cm^—1) and strong in 2 and 3 (J = —37.8 and —40.9 cm^—1, respectively), which in the case of 3 is in keeping with the observed structural parameters.