Synthesis, crystal structure, spectroscopic and magnetic properties of doubly and triply bridged dinuclear copper(II) compounds containing di-2-pyridylamine as a ligand

The dihydroxo-bridged dinuclear copper(II) compound [Cu₂(dpyam)₂(μ-OH)₂]I₂ (1) and the triply bridged dinuclear copper(II) compounds with a formato bridge [Cu₂(dpyam)₂(μ-O₂CH)(μ-OH)(μ-OMe)](ClO₄) (2) and [Cu₂(dpyam)₂(μ-O₂CH)(μ-OH)(μ-Cl)](ClO₄) · 0.5H₂O (3) (in which dpyam=di-2-pyridylamine) have been synthesized and their crystal structures determined by X-ray crystallographic methods. All three compounds are either centrosymmetric, or have a symmetry plane in the molecule. Compound 1 contains the [Cu₂(dpyam)₂(μ-OH)₂]⁺ unit and iodide anions. Each copper(II) ion is in a slightly tetrahedrally distorted square planar coordination with the square plane consisting of two nitrogen atoms of the dpyam ligand and two bridging hydroxo groups. The Cu-I distances of 3.321 Å are quite long and only involve a weak semi-coordination. Compound 2 contains a triply bridged dinuclear copper(II) species, the coordination environment around each copper(II) ion involves a distorted trigonal-bipyramidal CuN₂O₃ chromophore. In the dinuclear unit of compound 3, the triply bridged copper(II) ions show a distorted trigonal-bipyramidal coordination of the CuN₂O₂Cl chromophore. The Cu-Cu distances are 2.933(2), 3.023(1) and 3.036(1) Å for compounds 1, 2 and 3, respectively.The magnetic susceptibility measurements, measured from 5 to 280 K, revealed a weak antiferromagnetic interaction between the Cu(II) atoms for compound 1 with a singlet-triplet energy gap (J) of −15.3 cm⁻¹, whereas compounds 2 and 3 are ferromagnetic with J=62.5 and 79.1 cm⁻¹, respectively.     

Dinuclear triply bridged copper(II)-carboxylato compounds with different bischelating ligands: Synthesis, crystal structure, spectroscopic and magnetic properties

Three new triply bridged dinuclear copper(II) compounds containing carboxylato bridges, [Cu₂(μ-CH₃COO-κ-O¹,O²)₂(μ-CH₃COO-κ-O¹)(dpyam)₂](BF₄) (1), [Cu₂(μ-CH₂CH₃COO-κ-O¹,O²)(μ-OH)(μ-OH₂)(bpy)₂](ClO₄)₂ (2) and [Cu₂(μ-CH₃COO-κ-O¹,O²)(μ-OH)(μ-OH₂)(phen)₂](ClO₄)₂ (3) (in which dpyam = di-2-pyridylamine, bpy = 2,2-bipyridine, phen = phenanthroline), have been synthesized in order to investigate the magnetic super-exchange pathway between coupled copper(II) centres. All three compounds display a distorted square-pyramidal arrangement around each copper(II) ion with a CuN₂O₃ chromophore. Compound 1 has three acetato bridges, two of which connect each square pyramid at two equatorial sites in a triatomic bridging mode and the third acetato bridge acts at the apical site in the monoatomic bridging mode. The structures of compounds 2 and 3 are mutually similar. In each dinuclear unit, both copper(II) ions are linked at two equatorial positions through a hydroxo bridge and a triatomic carboxylato bridge and at the axial position through a water molecule.The magnetic susceptibility measurements, measured from 5 to 300 K, revealed an antiferromagnetic interaction between the Cu(II) ions in compound 1 and a ferromagnetic interaction for compounds 2 and 3 with singlet-triplet energy gaps (J) of −56, 149 and 120 cm⁻¹, for compounds 1, 2 and 3, respectively.     

The coordination chemistry of mono(di-2-pyridylamine) copper(II) complexes with monovalent and divalent oxoanions: crystal structure, spectroscopic and magnetic properties of dinuclear [Cu(L)(μ-H2PO4)(H2PO4)]2 and polynuclear [Cu(L)(μ3-HPO4)]n

The crystal structures of two copper(II) complexes containing the ligand di-2-pyridylamine (dpyam) with monovalent H₂PO₄ ⁻ and divalent HPO₄ ²⁻ oxoanions, [Cu(dpyam)(μ-H₂PO₄-O,O^′)(H₂PO₄)]₂ (1) and [Cu(dpyam)(μ₃-HPO₄-O,O^′,O″)]_n (2), are reported and determined by X-ray crystallography. The dinuclear Cu(II) complex 1 was obtained by the reaction of dpyam with Cu(NO₃)₂ · 3H₂O and KH₂PO₄ in a water-ethanol (45/55) mixture. The molecules are linked into dinuclear units by two bridging didentate dihydrogenphosphate groups (endo/exo) in an equatorial-equatorial configuration giving a slightly distorted square pyramidal stereochemistry. The Cu-Cu contact distance of 5.136(2) Å is unusually large due to the exo/endo binding of the phosphate bridges. Complex 2 is a polymeric copper(II) derivative with helical [Cu(HPO₄)]₃ units surrounded by dpyam ligands and stabilized by intermolecular hydrogen bonds. Two nearest Cu(II) ions are bridged by a tridentate hydrogenphosphate group which is didentately coordinated to one copper(II) ion, and monodentately coordinated to another in an equatorial-equatorial configuration in an unusual bridging coordination mode. Each copper(II) ion in 2 exhibits a tetrahedrally distorted square-based geometry with the third oxygen atom (Cu-O=2.719(3) Å), from the hydrogenphosphate group weakly bound in an approximately axial position giving an extremely tetrahedrally distorted square-based pyramidal CuN₂O₂O^′ chromophore. The magnetic susceptibility measurements (5-300 K) reveals an antiferromagnetic interaction with J values of −2.85(1) and −26.20(2) cm⁻¹ for complexes 1 and 2, respectively. Some magneto-structural trends are discussed, along with their EPR and electronic reflectance spectra and compared with those of related complexes.     

Dinuclear terephthalato-bridged copper(II) complexes: Syntheses, spectral and structural characterization, and magnetic properties

Herein, we report the syntheses, spectral and structural characterization, and magnetic behavior of four new dinuclear terephthalato-bridged copper(II) complexes with formulae [Cu₂(trpn)₂(μ-tp)](ClO₄)₂ · 2H₂O (1), [Cu₂(aepn)₂(μ-tp)(ClO₄)₂] (2), [Cu₂(Medpt)₂(μ-tp)(H₂O)₂](ClO₄)₂ (3) and [Cu₂(Et₂dien)₂(μ-tp)(H₂O)](ClO₄)₂ (4) where tp = terephthalate dianion, trpn = tris(3-aminopropyl)-amin, aepn = N-(2-aminoethyl)-1,3-propanediamine, Medpt = 3,3′-diamino-N-methyldipropylmine and Et₂dien = N,N-diethyldiethylenetriamine. The structures of these complexes consist of two μ-tp bridging Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry of the Cu(II) ions in these compounds may be described as close to square-based pyramid (SP) with severe significant distortion towards trigonal bipyramid (TBP) stereochemistry in 1. The visible spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Cu(II) centers. Also, the solid infrared spectral data for the stretching frequencies of the tp-carboxalato groups, the ν(COO⁻) reveals the existence of bis(monodentate) coordination mode for the bridged terephthalate ligand. The susceptibility measurements at variable temperature over the range 2-300 K are reported. Despite the same bonding mode of the tp bridging ligand, there has been observed slight antiferromagnetic coupling for the compounds 1 and 4 with J values of −0.5 and −2.9 cm³ K mol⁻¹, respectively, and very weak ferromagnetic coupling for 2 and 3 with J values of 0.8 and 10.1 cm³ K mol⁻¹, respectively. The magnetic results are discussed in relation to other related μ-terephthalato dinuclear Cu(II) published compounds.     

Dinuclear nickel(II) and zinc(II) complexes of 2,6-bis[{bis(2-pyridylmethyl)amino}methyl]-4-methylphenol

Reaction of the symmetrical proligand H₂L with metal(II) acetate and a counteranion to promote crystallisation has given the homodinuclear complexes [Zn₂L(OAc)₂](BF₄)]·2MeOH and [Ni₂L(OAc)₂](BF₄)]·2MeOH the crystal structures of which are reported. These show the presence of a triply bridging (μ-cresolato)bis(μ-carboxylato) dimetal core.     

Dinuclear terephthalato-bridged nickel(II) complexes. Structural characterization and magnetic properties

The dinuclear terephthalato-bridged nickel(II) complexes [Ni₂(cyclen)₂(μ-tp)](ClO₄)₂ (1) [Ni₂(trpn)₂(μ-tp)(H₂O)₂](ClO₄)₂ (2) and [Ni₂(3,3,3-tet)₂(μ-tp)(H₂O)₂](ClO₄)₂ · 2H₂O (3), where tp = terephthalate dianion, cyclen = 1,4,7,10-tetraazacyclododecane, trpn = tris(3-aminopropyl)amine and 3,3,3-tet = 1,5,9,13-tetraazatridecane, were synthesized and structurally characterized by X-ray crystallography. Their magnetic susceptibilities were also determined at variable temperatures over the range 2-300 K. The structures of these complexes consist of μ-tp bridging two Ni(II) centers in a bis(bidentate) bonding fashion in 1 and in bis(monodentate) bonding fashion in 2 and 3. The coordination geometry around the Ni(II) ions in these compounds has a distorted octahedral geometry with four nitrogen atoms from the amine ligand (cyclen, trpn or 3,3,3-tet) and two coordinated oxygen atoms supplied by the chelated carboxylate group of the bridged terephthalate ligand in 1, and by one tp-carboxylate-oxygen in 2 and 3. The sixth coordination site in the last two complexes 2 and 3 is achieved via an oxygen atom from a coordinated water molecule. The intradimer Ni…Ni distances in these complexes are 10.740, 11.428 and 11.537 Å for 1, 2 and 3, respectively. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Ni(II) centers. Also, the analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(bidentate) and bis(monodentate) coordination modes for the bridged terephthalate ligand in 1, 2 and 3, respectively. Despite the different coordination modes of the tp bridging ligand in these complexes, they all exhibit very weak antiferromagnetic coupling. The coupling constants J were found to be −2.2, −0.6 and −1.5 cm³ K mol⁻¹ for the complexes 1, 2 and 3, respectively. The structural and magnetic results of 1-3 are discussed in relation to the other related published μ-terephthalato dinuclear Ni(II) compounds.     

Synthesis, crystal structures and magnetic properties of the copper(II) complexes containing isophthalate anion as coligand

Two new dinuclear isophthalato-bridged copper(II) complexes [Cu₂(ntb)₂(μ-ipt)](ClO₄)₂·4CH₃OH·0.33H₂O (1), [Cu₂(bbma)₂(μ-ipt)(NO₃)(CH₃OH)]NO₃·CH₃OH (2) and one mononuclear complex [Cu(bbma)(ipt)(CH₃OH)_0.67(H₂O)_0.33]·2CH₃OH (3) containing tetradentate and tridentate poly-benzimidazole ligands were synthesized, where ntb is tris(2-benzimidazolylmethyl)amine, bbma is bis(benzimidazol-2-yl-methyl)amine and ipt is isophthalate dianion. All of the complexes were characterized by elemental analysis, IR spectra and X-ray crystallography. The structures of complexes 1 and 2 consist of μ-ipt bridging two Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry around the Cu(II) ions of both compounds has a distorted square pyramidal geometry. The Cu···Cu distances are 9.142 and 10.435 Å for 1 and 2, respectively. Complex 3 has a distorted square pyramidal geometry achieved by the three N-atoms of the bbma ligand, one isophthalate-oxygen atom and one oxygen atom from a coordinated methanol molecule. The magnetic susceptibility measurements at variable temperature over the 2-300 K range for complexes 1 and 2 are reported, with J values to be −0.013 and −0.32 cm⁻¹, respectively. The results show that the two complexes exhibit very weak antiferromagnetic interactions between the dinuclear copper(II) centers.     

Squarato-metal(II) complexes. 1: Structural and magnetic characterization of squarato-bridged dinuclear nickel(II) and copper(II) complexes

A new series of dinuclear squarato-bridged nickel(II) and copper(II) complexes [Ni₂(2,3,2-tet)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (1), [Ni₂(aepn)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂ (2), [Cu₂(pmedien)₂(μ_1,3-C₄O₄)(H₂O)₂](ClO₄)₂.4H₂O (3) and [Cu₂(DPA)₂(μ_1,2-C₄O₄)(H₂O)₂](ClO₄)₂ (4) where is the dianion of 3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid), 2,3,2-tet = 1,4,8,11-tetraazaundecane, aepn = N-(2-aminoethyl)-1,3-propanediamine, pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine and DPA = di(2-pyridylmethyl)amine were synthesized and structurally characterized by X-ray crystallography. The spectral and structural characterization as well as the magnetic behaviour of these complexes is reported. In this series, structures consist of the groups as counter ions and the bridging the two M(II) centers in a μ-1,3- (1-3) and in a μ-1,2-bis(monodentate) (4) bonding fashions. The coordination geometry around the Ni(II) ions in 1 and 2 is six-coordinate with distorted octahedral environment achieved by N atoms of the amines and by one or two oxygen atoms from coordinated water molecules, respectively. In the Cu(II) complexes 3 and 4, a distorted square pyramidal geometry is achieved by the three N-atoms of the aepn or DPA and by an oxygen atom from a coordinated water molecule. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the M(II) centers. The complexes show weak antiferromagnetic coupling with ∣J∣ = 1.8-4.2 cm⁻¹ in the μ-1,3- bridged squarato compounds 1-3, and J = −16.1 cm⁻¹ in the corresponding μ-1,2- bridged squarato complex 4. The magnetic properties are discussed in relation to the structural data.     

Synthesis, structures and magnetic properties of nicotinato-copper(II) complexes with polybenzimidazole and polyamine ligands

Four novel nicotinato-copper(II) complexes containing polybenzimidazole and polyamine ligands were synthesized with formula [Cu₂(bbma)₂(nic)₂](ClO₄)₂·CH₃OH·0.5H₂O (1), [Cu₂(dien)₂(nic)₂](ClO₄)₂·2CH₃OH (2), [Cu(ntb)(nic)]ClO₄·H₂O (3) and [Cu(tren)(nic)]BPh₄·CH₃OH·H₂O (4), in which bbma is bis(benzimidazol-2-yl-methyl)amine, dien is diethylenetriamine, ntb is tris(2-benzimidazolylmethyl)amine, tren is tris(2-aminoethyl)amine and nic is nicotinate anion. All of the complexes were characterized by elemental analysis, IR and X-ray diffraction analysis. Complexes 1 and 2 contain centrosymmetric dinuclear entity with the two Cu(II) atoms bridged by two nicotinate anions in an anti-parallel mode. The Cu···Cu separation is 7.109 Å for 1 and 6.979 Å for 2. Complexes 3 and 4 are mononuclear with nicotinate coordinated to Cu(II) ion by the carboxylate O atom in 3 and the pyridine N atom in 4. All of the complexes exhibit abundant hydrogen bonds to form 1D chain for 1, 3, 4 and 2D network for 2. Magnetic susceptibility measurements over the 2-300 K range reveal very weak ferromagnetic interaction between the two Cu(II) ions in 1 and antiferromagnetic interaction in 2 mediated by nicotinate ligand, with J value to be 0.15 and −0.19 cm⁻¹, respectively.     

Dinuclear fumarato- and terephthalato-bridged copper(II) complexes: Structural characterization and magnetic properties

The dinuclear dicarboxylato-bridged copper(II) complexes [Cu₂(TPA)₂(μ-tp)](ClO₄)₂ · H₂O (1), [Cu₂(TPA)₂(μ-fum)](ClO₄)₂ · 2H₂O (2) and [Cu₂(pmedien)₂(μ-fum)(H₂O)₂](ClO₄)₂ (3) (tp = terephthalate dianion, fum = fumarate dianion, TPA = tris(2-pyridylmethyl)amine and pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine) were synthesized and structurally characterized by X-ray crystallography. The structures of the TPA complexes 1 and 2 consist of μ-tp or μ-fum bridging two Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry around the Cu(II) ions in these compounds has a distorted trigonal bipyamidal geometry, TBP with four nitrogen atoms from the TPA ligand and a coordinated oxygen atom supplied by the carboxylate group of the bridged dicarboxylato ligand. Complex 3 has a distorted square pyramidal geometry achieved by the three N-atoms of the pmedien, one fum-carboxylate-oxygen and by an oxygen atom from a coordinated water molecule. The intradimer Cu…Cu distances in these complexes are 11.078(3), 8.663(4) and 9.520(3) Å for 1, 2 and 3, respectively. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Cu(II) centers. Also, analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(mondentate) coordination mode for the bridged dicarboxylato ligands in compounds 1 and 2. The susceptibility measurements at variable temperature over the 2-300 K range are reported. For 1-3, it has been observed slight antiferromagnetic coupling with J values of −0.8, −3.0 and −2.9 cm⁻¹, respectively.     

Synthesis and structural studies of dimolybdenum(V), palladium(II) and dicopper(I) complexes that contain mixed pyridyl-iso-propylphosphine ligands

The reaction of Mo₂(μ-O₂CCH₃)₄ with 2-pyridyl(diisopropylphosphino)methane (NP) affords the dimolybdenum(V) complex Mo₂(μ-O)₂O₂Cl₂(η²-NP)₂ (1). Complexes of the related 2-pyridylbis(diisopropylphosphino)methane ligand (NP²) have been isolated, namely, a mixed bromo/chloro complex of composition PdBr_1.09Cl_0.91(η²-NP²) (2) and the dicopper(I) complex [Cu₂(μ-η³-NP²)₂](BF₄)₂ (3). The structures of 1, 2 and 3 have been established by X-ray crystallography.     

A novel tetranuclear hydrogenphosphate-bridged Cu(II) cluster. Synthesis, structure, spectroscopy and magnetism of [Cu4(dpyam)4(μ4,η-HPO4)2(μ-X)2]X2(H2O)6 (X = Cl, Br)

Two novel tetranuclear compounds with an unprecedented mode of a hydrogenphosphato bridge, [Cu₄(dpyam)₄(μ₄,η³-HPO₄)₂(μ-X)₂]²⁺ (in which dpyam = di-2-pyridylamine and X = Cl (1), Br (2)) have been synthesised and characterised structurally and magnetically. The Cu(II) ions in the structures each display a square-pyramidal geometry, with two tridentate hydrogenphosphato groups bridging four copper atoms in a μ₄,η³ coordination mode which is rarely found in hydrogenphosphate metal compounds. Each (different) pair of Cu(II) ions is additionally bridged by halide ions, with relatively long Cu-X distances (2.551(3)-2.604(3) Å for 1 and 2.707(1)-2.766(2) Å for 2) and subsequently also a small Cu-X-Cu angle (65.7(1)° and 65.1(1)° for 1 and 61.6(1)° and 62.4(1) for 2) and a large Cu-X-Cu angle (95.5(1)° and 96.5(1)° for 1 and 91.1(1)° and 92.6(1)° for 2). Cu?Cu distances in the tetranuclear units varies from 2.802(3) to 5.232(3) Å for 1 and from 2.834(1) to5.233(1) Å in 2. The lattice structures are stabilised by extensive intermolecular hydrogen bonds. The magnetic susceptibility measurements down to 5 K revealed a weak ferromagnetic interaction between the outer pairs of Cu(II) ions which vary from 22 to 46 cm⁻¹ in 1 and 12 to 33 cm⁻¹ in 2 and a moderately strong antiferromagnetic interaction between the inner Cu(II) ions of −79 cm⁻¹ in 1 and −83 cm⁻¹ in 2, via the Cu-O-P-O-Cu pathway.     

Imidazole derivatives of binuclear copper (II) and nickel (II) complexes incorporating bis(1,4,7-triazacyclononan-1-yl) ligands

A series of new binuclear copper (II) and nickel (II) complexes of the macrocyclic ligands bis(1,4,7-triazacyclononan-1-yl)butane (L^but) and bis(1,4,7-triazacyclononan-1-yl)-m-xylene (L^mx) have been synthesized: [Cu₂L^butBr₄] (1), [Cu₂L^but(imidazole)₂Br₂](ClO₄)₂ (2), [Cu₂L^mx(μ-OH)(imidazole)₂](ClO₄)₃ (3), [Cu₂L^but(imidazole)₄](ClO₄)₄ · H₂O (4), [Cu₂L^mx(imidazole)₄](ClO₄)₄ (5), [Ni₂ L^but(H₂O)₆](ClO₄)₄ · 2H₂O (6), [Ni₂L^but(imidazole)₆](ClO₄)₄ · 2H₂O (7) and [Ni₂L^mx (imidazole)₄(H₂O)₂](ClO₄)₄ · 3H₂O (8). Complexes 1, 2, 7 and 8 have been characterized by single crystal X-ray studies. In each of the complexes, the two tridentate 1,4,7-triazacyclononane rings of the ligand facially coordinate to separate metal centres. The distorted square-pyramidal coordination sphere of the copper (II) centres is completed by bromide anions in the case of 1 and/or monodentate imidazole ligands in complexes 2, 4 and 5. Complex 3 has been formulated as a monohydroxo-bridged complex featuring two terminal imidazole ligands. Complexes 6-8 feature distorted octahedral nickel (II) centres with water and/or monodentate imidazole ligands occupying the remaining coordination sites. Within the crystal structures, the ligands adopt trans conformations, with the two metal binding compartments widely separated, perhaps as a consequence of electrostatic repulsion between the cationic metal centres. The imidazole-bearing complexes may be viewed as simple models for the coordinative interaction of the binuclear complexes of bis (tacn) ligands with protein molecules bearing multiple surface-exposed histidine residues.     

Structural analysis and magnetic properties of the copper(II) dicyanamide complexes [Cu2(dmphen)2(dca)4], [Cu(dmphen)(dca)(NO3)]n and [Cu(4,4-dmbpy)(H2O)(dca)2] (dca=dicyanamide; dmphen=2,9-dimethyl-1,10-phenanthroline; 4,4-dmbpy=4,4-dimethyl-2,2-bipyridine)

The preparation, crystal structures and magnetic properties of three copper(II) compounds of formulae [Cu₂(dmphen)₂(dca)₄] (1), [Cu(dmphen)(dca)(NO₃)]_n (2) and [Cu(4,4^′-dmbpy)(H₂O)(dca)₂] (3) (dmphen=2,9-dimethyl-1,10-phenanthroline, dca=dicyanamide and 4,4^′-dmbpy=4,4^′-dimethyl-2,2^′-bipyridine) are reported. The structure of 1 consists of discrete copper(II) dinuclear units with double end-to-end dca bridges whereas that of 2 is made up of neutral uniform copper(II) chains with a single symmetrical end-to-end dca bridge. Each copper atom in 1 and 2 is in a distorted square pyramidal environment: two (1) or one (2) nitrile-nitrogen atoms from bridging dca groups, one of the nitrogen atoms of the dmphen molecule (1 and 2) and either one nitrile-nitrogen from a terminal dca ligand (1) or a nitrate-oxygen atom (2) build the equatorial plane whereas the second nitrogen atom of the heterocyclic dmphen fills the axial position (1 and 2). The copper-copper separations through double (1) and single (2) end-to-end dca bridges are 7.1337(7) (1) and 7.6617(7) (2). Compound 3 is a mononuclear copper(II) complex whose structure contains two neutral and crystallographically independent [Cu(4,4^′-dmbpy)(H₂O)(dca)₂] molecules which are packed in two different layer arrangements running parallel to the bc-plane and alternating along the a-axis. The copper atoms in both molecules have slightly distorted square pyramidal surroundings with the two nitrogen atoms of the 4,4^′-dmbpy ligand and two dca nitrile-nitrogen atoms in the basal plane and a water oxygen in the apical position. A semi co-ordinated dca nitrile-nitrogen from a neighbour unit [2.952(6) Å for Cu(2)-N] is in trans position to the apical water molecule in one of the two molecules, this feature representing part of the difference in supramolecular connections in the alternating layers referred to above. Magnetic susceptibility measurements for 1-3 in the temperature range 1.9-290 K reveal the occurrence of weak antiferromagnetic interactions through double [J=−3.3 cm⁻¹ (1), ] and single [J=−0.57 cm⁻¹ (2), ] dca bridges and across intermolecular contacts [θ=−0.07 K (3)].     

X-ray structure and spectroscopic characterization of divalent dinuclear cobalt complexes containing carboxylate- and phosphodiester- auxiliary bridges

Two dinuclear spin-coupled divalent cobalt complexes, [Co₂(P1-O)(μ₂-OAc)](ClO₄)₂, (1) and [Co₂(P1-O)(μ₂-BNPP)](ClO₄)₂, (2) containing μ-1,3 acetate (OAc) and bis(4-nitrophenyl)phosphate (BNPP) auxiliary bridges, respectively, were synthesized by the reaction of a classic dinucleating ligand, P1-OH with cobalt(II) perchlorate in presence of acetic acid/bis(4-nitrophenyl)phosphate. They were characterized by single crystal X-ray diffraction, to show a trigonal bipyramidal geometry around each cobalt center and the intervening bridging atoms that are responsible for spin-transfer between the two divalent cobalt centers; the alkoxo oxygen donor occupies an equatorial position, and the auxiliary ligand oxygens (OAc/BNPP) occupy the axial positions. Solution state magnetic moment measurement together with UV-Vis/NIR spectra revealed a high-spin ground state (S = 3/2) for Co(II) in these compounds. Complexes 1 and 2 show interesting ¹H NMR spectral features of resonances with relatively narrower linewidths in conjunction with a sizable chemical shift dispersion of −5 and 265 ppm. Complex 2 containing the bis(4-nitrophenyl)phosphate auxiliary bridge showed narrower spectral window than complex 1 that has the acetate auxiliary bridge.     

Supramolecular assembly driven by hydrogen-bonding and π-π stacking interactions based on copper(II)-terpyridyl complexes

Six 2D and 3D supramolecular complexes [Cu(L1)(O₂CCH₃)₂] · H₂O (1), [Cu₂(L2)₂(μ₂-O₂CCH₃)₂](BF₄)₂ (2), [Cu₂(L1)₂(BDC)(NO₃)₂] · 0.5H₂O (3) [Cu₂(L2)₂(BDC)(NO₃)₂] (4), [Cu₂(L3)₂(BDC)(NO₃)₂] · 0.5H₂O (5) and [Cu₂(L2)₂(BDC)(H₂O)₂](BDC) · 8H₂O (6) (L1 = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine, L2 = 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine, L3 = 4′-phenyl-2,2′:6′,2″-terpyridine, BDC = 1,4-benzenedicarboxylate), have been prepared and structurally characterized by X-ray diffraction crystallography. In complexes 1, 3, and 4, 1D channels are formed through C-H?O and C-H?N hydrogen-bonding interactions, and further linked into 3D structure via C-H?O and O-H?O interactions. Complex 2 is a 2D layer constructed from intermolecular C-H?F and π-π stacking interactions. In the structure of 6, the BDC²⁻ ions and solvent water molecules form a novel 2D layer containing left- and right-handed helical chains via hydrogen-bonds, and an unusual discrete water octamer is formed within the layer. In 2, 4, 6 and [Ag₂(L2)₂](PF₆)₂ (7) the bonding types of pendent pyridines of L2 depending on the twist about central pyridines are involved in intramolecular (2 and 4), intermolecular (6) or coordination bonds (7) in-twist-order of 5.8°, 3.7°, 28.2° and 38.0°, respectively. Differently, the pendent pyridines of L1 in 1 and 3 form intermolecular hydrogen bonds despite of distinct corresponding twist angles of 25.1° (1) and 42.6°(3). Meanwhile, π-π stacking interactions are present in 1-6 and responsible for the stabilization of these complexes.     

Chlorido-bridged polymeric and dinuclear copper(II) complexes with tridentate Schiff base: Synthesis, crystal structure and magnetic properties

Two copper(II) complexes, [Cu(qsal)Cl](DMF) (1) and [Cu₂(qsalBr)₂Cl₂](DMF) (2), with tridentate Schiff base ligands, 8-(salicylideneamino)quinoline (Hqsal) and 8-(5-bromo-salicylideneamino)quinoline (HqsalBr), respectively, were synthesised and structurally characterized. Each copper(II) ion in the two complexes is in a distorted square pyramidal N₂OCl₂ environment. Complex 1 exists as a polymeric species via equatorial-apical chloride bridges, whereas 2 is a di-chlorido-bridged dinuclear complex, where each bridging chloride simultaneously occupies an in-plane coordination site on one copper(II) ion and an apical site on the other copper(II) ion. Variable-temperature magnetical susceptibility measurements on the two complexes in the temperature range 2-300 K indicate the occurrence of intrachain ferromagnetic (J = +6.58 cm⁻¹) and intramolecular antiferromagnetical (J = −6.91 cm⁻¹) interactions.     

Polynuclear nickel (II) and copper (II) complexes of hexaazamacrocycles incorporating pairs of diethylenetriamine subunits separated by aromatic spacers

A series of Ni(II) and Cu(II) complexes of the hexaaza macrocycles, 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1^11,15]triaconta-1(29),11(30),12,14,25,27-hexaene (L¹) and 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2^11,14]triaconta-1(26),11(29),12,14(30),24(28),25-hexaene (L²), have been prepared and the crystal structures determined for [Ni₂L¹(O₂CCH₃)₂(H₂O)₂](ClO₄)₂ (1), [Ni₂L²(DMF)₆](ClO₄)₄ · 2H₂O (2), {[Cu₂L²Br(O₂CCH₃)](ClO₄)₂}_n (3), [Cu₂L²(μ-CO₃)(H₂O)₂]₂(ClO₄)₄ · 8H₂O (4), [Cu₂L²(O₂CCH₃)₂](BF₄)₂ (5), and [Cu₂L¹(μ-imidazolate)Br]₂Br₄ · 6H₂O (6). In these complexes, two metal centers are bound per ligand; in 1 and 3-6, the N₃ subunits of L¹ or L² coordinate meridionally to the metal centers, whilst in 2, each N₃ subunit in L² adopts a facial mode of coordination. The binuclear cations in 1 and 2 have chair-like conformations, with the distorted octahedral Ni(II) coordination spheres completed by terminal water and a bidentate acetate ligand in 1 and three DMF ligands in 2. The Cu(II) centers in 3-6 generally reside in square planar environments, although a weakly binding ligand enters the coordination sphere in some cases, generating a distorted square pyramidal geometry. The binuclear [Cu₂L²]⁴⁺ units in 3, 4 and 5 adopt similar bowl-shaped conformations, stabilized by H-bonding interactions between pairs of amine groups from L² and a perchlorate or tetrafluoroborate anion. In 3, the binuclear units are linked through acetate groups, bridging in a syn-anti fashion, to produce a zig-zag polymeric chain structure, whilst 4 incorporates a tetrameric cation consisting of two binuclear units linked via a pair of carbonate bridges. Compound 6 features an imidazolate bridge between the two Cu(II) centers bound by L¹. Pairs of [Cu₂L¹(μ-imidazolate)]³⁺ units are then weakly linked through a pair of bromide anions.     

Synthesis and characterization of imidazolate-bridged polynuclear copper complexes

Copper(II) complexes of N4-donor ligands containing imidazole moieties, 4-[bis(1-methylimidazole-2-yl-methyl)aminomethyl]imidazole (Him-im₂) and 4-[bis(1-methylimidazole-2-yl-methyl)aminoethyl]imidazole (Hhis-im₂), were prepared, and [Cu(Him-im₂)Cl]ClO₄ (1) and [Cu(Hhis-im₂)Cl]ClO₄ (2) were structurally characterized by the X-ray diffraction method. Complexes 1 and 2 have a mononuclear structure with a coordinated chloride ion. The geometry of the Cu(II) center in 1 was found to be 5-coordinate trigonal-bipyramidal, whereas that of 2 was square-pyramidal. Complexes 1 and 2 showed different absorption and EPR spectra in MeOH, indicating that these compounds in solution maintain the structures revealed in the solid state. On the other hand, the reaction of Him-im₂ with Cu(ClO₄)₂ · 6H₂O under basic conditions gave a tetranuclear Cu(II) complex, [Cu₄(im-im₂)₄](ClO₄)₄ (3), whereas using the ligand Hhis-im₂ gave two kinds of polynuclear complexes [Cu₄(his-im₂)₄](ClO₄)₄ (4) and [Cu₆(his-im₂)₆](ClO₄)₆ (5) exhibiting discretely different structures. X-ray crystal structure analysis of the polynuclear complexes revealed their cyclic structures bridged by the imidazolate moiety. The geometry difference of the Cu(II) centers between 1 and 2 is thus concluded to determine the structures of tetranuclear complexes 3 and 4, respectively. Temperature dependent magnetic susceptibility measurements of complexes 3, 4, and 5 have shown an antiferromagnetic exchange interaction with a coupling constant of J = −32.5, −27.1 and −22.8 cm⁻¹, respectively.     

Lewis acidity of platinum(II)-based Baeyer-Villiger catalysts: An electrochemical approach

The electrochemical behavior of the Pt(II)-based Baeyer-Villiger catalysts of the general formulae [Pt(μ-OH)(P^∩P)]₂(BF₄)₂ (P^∩P = dppe (1a), 2Fdppe (1 b), 4Fdppe (1c), dfppe (1d), dmpe (1e), depe (1f), dippe (1g), dtbpe (1h)) and [Pt(OH₂)₂(P^∩P)](OTf)₂ (P^∩P = dppe (2a), 2Fdppe (2b), 4Fdppe (2c), dfppe (2d)) is reported. They exhibit irreversible reduction processes whose potentials reflect the Lewis acidity of the metal centres, showing (for the aromatic diphosphine complexes) overall relations with the number of fluorine atoms, with J_Pt-P, with the ν(CN) coordination shift of a ligand isocyanide probe and with the catalytic activity. Single-crystal X-ray diffraction analyses were carried out for [Pt(μ-OH)(4Fdppe)]₂(BF₄)₂ (1c) and [Pt(μ-OH) (dippe)]₂(BF₄)₂ (1g).