Apical Coordination Site Research Articles

A Novel Strategy to Introduce 18F, a Positron Emitting Radionuclide, into a Gallium Nitrate Complex: Synthesis, NMR, X-Ray Crystal Structure, and Preliminary Studies on Radiolabelling with 18F

A hexan-3,4-dione bis(4N-phenylthiosemicarbazone) gallium nitrate complex was synthesised and the structure was confirmed by NMR studies. The complex was prepared using an appropriately substituted dithiosemicarbazone and sodium methoxide in anhydrous methanol. The structure was further confirmed using single crystal X-ray crystallography. The crystal structure of gallium nitrate complex of diphenylthiosemicarbazone comprise a planar configuration of the tetradentate coordinated thiosemicarbazone with the Ga3+ ion, with the nitrate ligand occupying the apical coordination site. The X-ray structure of the gallium fluoride complex of pentan-2,3-dione bis(4N-phenylthiosemicarbazone) has been determined and confirms exchange of the nitrate can be achieved with fluoride. We show facile exchange of 18F, a positron emitter, to form the 18F-gallium complex under mild conditions, thus providing confirmation that such a transformation can be used to introduce 18F directly into nitrate-coordinated complexes of gallium-thiosemicarbozone complexes, a new labelling strategy for the preparation of imaging agents.

Syntheses and Structures of Monomeric and Dimeric Ternary Complexes of Copper(II) with 2,2′‐Bipyridyl and Carboxylate Ligands

The syntheses and crystal structures of Cu(C10H8N2)(C9H7O2)(H2O) (1) and [Cu2(C10H8N2)2(C7H6NO2)3(C7H7NO2)]·Cl·3H2O (2) are described [C10H8N2 = 2,2′‐bipyridine (bipy), C9H7O2– = cinnamate anion (cinn–), C7H6NO2– = p‐amino benzoate anion (paba–), and C7H7NO2 = p‐amino benzoic acid (Hpaba)]. Complex 1 [triclinic, space group P1 (no. 2), a = 12.0357 (7) Å, b = 13.8799 (8) Å, c = 16.3225 (9) Å, α = 84.916 (3)°, β = 88.551 (3)°, γ = 67.877 (3)°, V = 2516.0 (2) Å3, Z = 4] contains two molecules in the asymmetric unit: both feature a distorted square‐pyramidal CuN2O3 chromophore arising from the coordination of a bidentate bipy ligand, two monodentate cinn– anions, and a water molecule to the metal ion. The cation in complex 2 [orthorhombic, space group P212121 (no. 19), a = 13.5061 (10) Å, b = 18.1441 (11) Å, c = 18.9671 (13) Å, V = 4648.1 (5) Å3, Z = 4] is dimeric with square pyramidal CuN2O3 and CuN3O2 metal coordination polyhedra: each metal ion is coordinated by a bidentate bipy ligand and two bridging paba– anions; the apical coordination site of one is occupied by an O‐bonded paba– anion and the other by an N‐bonded Hpaba neutral molecule. The cation in 2 is isomeric with the previously reported [Cu2(C10H8N2)2(C7H6NO2)2(C7H7NO2)2]2+ cation, in which both apical Hpaba molecules are N‐bonded to their metal ions.

Heteronuclear NMR Spectroscopic Investigations of Gallium Complexes of Substituted Thiosemicarbazones Including X-Ray Crystal Structure, a New Halogen Exchange Strategy, and 18F Radiolabelling

Five thiosemicarbazone ligands have been synthesized, and their coordination chemistry with gallium was investigated. The reaction of these thiosemicarbazones with gallium chloride in alcohol solutions in the presence of a base yielded the corresponding penta-coordinated Ga-Cl metal complexes. In contrast, the reaction of gallium nitrate with the ligands in the presence of alkoxides resulted in the formation of the corresponding Ga-alkoxides, rather than the anticipated Ga-nitrate complex. The crystal structures of gallium chloride and gallium methoxide complexes of diphenylthiosemicarbazone comprise a planar configuration of the tetradentate-coordinated thiosemicarbazone with Ga3+ ion, with the chloride or methoxide groups occupying the apical coordination site. The corresponding ethoxido complex was also prepared in an identical fashion, and NMR analysis confirmed structural similarity to the methoxido complex. Facile halogen exchange reactions of the gallium chloride complexes were achieved by treatment with silver nitrate, followed by addition of KF or KI to generate the gallium fluoride and iodide complexes, respectively. This method of exchange using halogenated inorganic salts aids the preparation of group 13 fluorides, which are notoriously insoluble in organic solvents, for complexation with organic ligands. All compounds have been fully characterized by NMR, and the X-ray crystal structures of two of the complexes are reported. Additionally, the positron-emitting isotope 18F was introduced in the structure of the diphenyl gallium thiosemicarbazone complex.

Crystal structures of μ-oxalato-bis-[azido-(hista-mine)-copper(II)] and μ-oxalato-bis-[(dicyan-amido)(hista-mine)-copper(II)

The title compounds, μ-oxalato-κ(4) O (1),O (2):O (1'),O (2')-bis-[[4-(2-amino-eth-yl)-1H-imid-azole-κ(2) N (3),N (4)](azido-κN (1))copper(II)], [Cu2(C2O4)(N3)2(C5H9N3)2], (I), and μ-ox-al-ato-κ(4) O (1),O (2):O (1'),O (2')-bis-[[4-(2-amino-eth-yl)-1H-imidazole-κ(2) N (3),N (4)](dicyanamido-κN (1))copper(II)], [Cu2(C2O4)(C2N3)2(C5H9N3)2], (II), are two oxalate-bridged dinuclear copper complexes. Each Cu(II) ion adopts a five-coordinate square-pyramidal coordination sphere where the basal N2O2 plane is formed by two O atoms of the oxalate ligand and two N atoms of a bidentate chelating histamine mol-ecule. The apical coordination site in compound (I) is occupied by a monodentate azide anion through one of its terminal N atoms. The apical coordination site in compound (II) is occupied by a monodentate dicyanamide anion through one of its terminal N atoms. The mol-ecules in both structures are centrosymmetric. In the crystals of compounds (I) and (II), the dinuclear complexes are linked through N-H⋯X and C-H⋯X (X = N, O) hydrogen bonds where the donors are provided by the histamine ligand and the acceptor atoms are provided by the azide, dicyanamide, and oxalate ligands. In compound (I), the coordinatively unsaturated copper ions inter-act with the histamine ligand via a C-H⋯Cu inter-action. The coordinatively unsaturated copper ions in compound (II) inter-act via a weak N⋯Cu inter-action with the dicyanamide ligand of a neighboring mol-ecule. The side chain of the histamine ligand is disordered over three sets of sites in (II).

Crystal structure of catena-poly[hemi[1,3-bis-(2,6-diisoprop-ylphenyl)imidazolium] [[μ3-acetato-κ(3) O:O:O'-tri-μ2-acetato-κ(6) O:O'-dicopper(II)(Cu-Cu)]-μ-chlorido] di-chloro-methane sesqui-solvate

The title copper(II) complex, {(C27H37N2)[Cu4(CH3COO)8Cl]·3CH2Cl2}n, is a one-dimensional coordination polymer. The asymmetric unit is composed of a copper(II) tetra­acetate paddle-wheel complex, a Cl− anion situated on a twofold rotation axis, half a 1,3-bis­(2,6-diisoprop­ylphenyl)imidazolium cation (the whole mol­ecule being generated by twofold rotation symmetry) and one and a half of a di­chloro­methane solvent mol­ecule (one being located about a twofold rotation axis). The central metal-organic framework comprises of a tetra­nuclear copper(II) acetate ‘paddle-wheel’ complex which arises from the dimerization of the copper(II) tetra­acetate core comprising of three μ2-bidentate acetate and one μ3-tridentate acetate ligands per binuclear paddle-wheel complex. Both CuII atoms of the binuclear component adopt a distorted square-pyramidal coordination geometry (τ = 0.04), with a Cu⋯Cu separation of 2.6016 (2) Å. The apical coordination site of one CuII atom is occupied by an O atom of a neighbouring acetate bridge [Cu—O = 2.200 (2) Å], while that of the second CuII atom is occupied by a bridging chloride ligand [Cu⋯Cl = 2.4364 (4) Å]. The chloride bridge is slightly bent with respect to the Cu⋯Cu inter­nuclear axis [Cu—Cl—Cu = 167.06 (6)°] and the tetra­nuclear units are located about a twofold rotation axis, forming the one-dimensional polymer that propagates along [101]. Charge neutrality is maintained by the inclusion of the 1,3-bis­(2,6-diisoprop­ylphenyl)imidazolium cation within the crystal lattice. In the crystal, the cation and di­chloro­methane solvent mol­ecules are linked to the coordin­ation polymer by various C—H⋯O and C—H⋯Cl hydrogen bonds. There are no other significant inter­molecular inter­actions present.

Pseudo-polymorphism of Halogen Substituted Tetraaza[14]annulene Complexes

6,8,15,17-tetramethyldibenzo-5,9,14,18-tetraazacyclotetradecinatonickel (II) (tmtaa) bears strain within its 14-membered ring and is known to adopt saddle-shaped structure. As a consequence, tmtaa has an asymmetric apical coordination sites at both sides of the saddle. Our previous study revealed that the chlorine substituted complex, [Ni(tmtaa-4Cl)] shown in Figure (X = Cl), exhibited pseudo-polymorphism with dichloromethane and chloroform. This behaviour is due to the good affinity between halogen substituents and halomethane solvent. In this study, we grew single crystals of [Ni(tmtaa-4Br)] using various halomethane solvent as crystallization solvents and elucidated the role of the solvents related to the generation of pseudo-polymorprhism. We have succeeded in obtaining two kinds of single crystals 1 and 2 from the same vial container using bromoform. From X-ray structural analysis, 1 and 2 formed twist dimer as with previous report, and are found to include bromoform in their crystal structure. Note that these complexes adopted more distorted saddle-shaped structure than normal tmtaa complexes. The Ni-N4 planes were not planar. The difference of 1 and 2 was the degree of distortion around Ni-N4 plane, and 1 was more distorted than 2. The space group of these complexes were Aba2 and C2/c respectively. The interactions that led to the difference in packing of dimers were CH...π interaction in 1 and π...π interaction in 2.

Improved synthesis of a trisphosphine ligand and crystallographic characterization of the ligand and nickel thiocyanate complex

Improved syntheses of o-C6H4(PEt2)(X) (X=F, Br, I) and the trisphosphine PhP[o-C6H4(PEt2)]2 have been developed and are applicable to a wide variety of phosphine substituents. The trisphosphine, PhP(o-Ph–PEt2)2, has been fully characterized spectroscopically and, for the first time, crystallographically. Reaction of the P3 ligand with one equivalent of NiCl2 or Ni(BF4)2 followed by 2.5 equivalents of KNCS produces the monometallic complexes Ni(X)2[κ3-PhP(o-Ph–PEt2)2], (X=Cl or NCS). The nickel thiocyanate complex has been characterized via a crystal structure. The nickel center has a square pyramidal structure with one of the NCS ligands occupying the apical coordination site. The Ni complex crystallizes in the P1¯ space group with an unusual six molecules in the asymmetric unit (Z′=6), and twelve in the unit cell.

Template synthesis and X-ray structural characterization of nickel(II) and zinc(II) complexes of tetradentate SNNS ligands formed by condensation of phthalaldehyde with S-methyldithiocarbazate and 4N-methyl-3-thiosemicarbazide

The reaction of phthalaldehyde (1,2-benzenedialdehyde) with S-methyldithiocarbazate does not lead to the formation of the expected open-chain linear Schiff base, phthalaldehyde bis(S-methyldithiocarbazonate) but a cyclic diazine dithiocarbazate is obtained which has been characterized by spectroscopic and X-ray diffraction. However, if the reaction of phthalaldehyde with S-methyldithiocarbazate is carried out in the presence of nickel(II) and zinc(II) acetate salts, stable metal complexes of empirical formula, [M(phthalsme)] (M=Ni, Zn; phthalsme=doubly deprotonated form of the Schiff base, phthalaldehyde bis(S-methyldithiocarbazonate) are obtained. Likewise, the reaction of 4N-methyl-3-thiosemicarbazide with phthaladehyde in the presence of nickel(II) acetate also yields a crystalline nickel(II) complex, [Ni(phthaltsc)] (phthaltsc=doubly deprotonated form of the teradentate phthaladehyde bis(4N-methyl-3-thiosemicarbazone) ligand. The complexes, [Ni(phthalsme)], [Ni(phthaltsc)] and [Zn(phthalsme)(DMF)] have been characterized by a variety of physico-chemical techniques and their structures have been determined by X-ray diffraction. In these complexes, the ligands are coordinated to the metal ion as dinegatively charged tetradentate chelating agents via the two thiolate sulfur atoms and the azomethine nitrogen atoms. The nickel complexes, [Ni(phthalsme)] and [Ni(phthaltsc)] exhibit a distorted square–planar geometry whereas the zinc complex, [Zn(phthalsme)(DMF)] is five-coordinate and square-pyramidal with the dianionic Schiff base occupying the basal plane of the square-pyramid and the oxygen atom of dimethylformamide in the apical coordination site.

Acetonitriledicarbonyl(η5-pentamethylcyclopentadienyl)iron(II) tetrafluoridoborate

In the structure of the title compound, [Fe{η5-C5(CH3)5}(NCCH3)(CO)2]BF4, the arrangement of ligands around the Fe atom is in a pseudo-octa­hedral three-legged piano-stool fashion in which the penta­methyl­cyclo­penta­dienyl (Cp*) ligand occupies three apical coordination sites, while the two carbonyl and one acetonitrile ligands form the basal axes of the coordination. The Fe—N bond length is 1.924 (3) Å and the Fe—Cp* centroid distance is 1.722 Å.

Dicarbonyl(η5-cyclopentadienyl)[2-(phenylsulfanyl)ethyl]iron(II)

The title compound, [Fe(C5H5)(C8H9S)(CO)2], is a three-legged piano-stool iron(II) complex that is characterized by a thio­ethyl-linked phenyl ring and a cyclo­penta­dienyl moiety that occupies the apical coordination site. The two aromatic rings are essentially planar with the same maximum deviation of 0.009 Å. The mean planes of the phenyl and cyclo­penta­dienyl rings bis­ect at an acute angle of 50.08°.

Synthesis and First Studies of the Host–Guest and Substrate Recognition Properties of a Porphyrin‐Tethered Calix[6]arene Ditopic Ligand

AbstractThe synthesis and first host–guest investigations of a (Zn)porphyrin‐tethered calixarene are described. The target compound was obtained by selective copper‐catalyzed alkyne/azide cycloaddition at one position of a tris‐azide‐substituted calixarene using an alkyne‐functionalized (Zn)porphyrin. After the complexation of zinc to the tris‐imidazole site of the modified calixarene, the heteroditopic receptor showed a strong affinity for primary alkylamines, which formed host–guest complexes within the cavity. This process is in competition with the binding of the amine at the apical coordination site of the (Zn)porphyrin. The use of a diamine (primary) with a C12 aliphatic chain led to the formation of a heteroditopic complex, as evidenced by NMR and UV/Vis spectroscopy. This highlights the possibility of generating cooperative interactions between the three “actors” of the complex (calixarene <> guest <> porphyrin), a feature of great interest as it is reminiscent of the interactions governing enzymatic catalysis (recognition pocket <> substrate <> reactive center).

Unusual ligand design: A platinum(II) mediated [2+2] photocycloaddition followed by a nickel(II) induced methoxyactivation

The novel dimer of the composition [Pt 2Cl 4(μ-(κP 1:κP 2- o-MeO- trans-dppen)) 2] ( 1) ( o-MeO- trans-dppen = 1,2-(bis( o-methoxyphenyl)phosphanyl)ethylene) has been prepared and characterized by a single crystal X-ray structure analysis, NMR spectroscopy, mass spectrometry and elemental analysis. This latter compound undergoes a [2 +2] photocycloaddition reaction yielding the tetraphosphane all- trans-1,2,3,4-tetrakis(di( o-methoxyphenyl)phosphanyl)cyclobutane ( o-MeO-dppcb). The X-ray structure of the dimeric Ni(II) complex that contains the latter ligand, of the formula [Ni 2Cl 4(μ-(κP 1:κP 2:κP 3:κP 4- o-MeO-dppcb))] ( 2) reveals that the apical coordination sites of both square pyramidal Ni(II) coordination spheres are occupied by methoxy-oxygen atoms of the ligand. As a consequence, this dimeric Ni(II) complex 2 is prone to a thermally induced regio- and diastereoselective metal-assisted methoxy-group cleavage. The stepwise formed new mono- and bis-phenolate complexes [Ni 2Cl 3(μ-(κO 1,κP 1:κP 2:κP 3:κP 4- o-MeO- O-dppcb))] ( 3) and [Ni 2Cl 2(μ-(κO 1,κP 1:κP 2:κO 2,κP 3:κP 4- o-MeO- O,O′-dppcb))] ( 4), respectively, contain the novel chiral tetraphosphane ligands all- trans-1,2,3-tris((di- o-methoxyphenyl)phosphano)-4-(( o-methoxy-phenyl)( o-phenolate)phosphano)cyclobutane ( o-MeO- O-dppcb) and all- trans-1,2-bis((di- o-methoxyphenyl)phosphano)-3,4-bis(( o-methoxyphenyl)( o-phenolate)phosphano)cyclobutane ( o-MeO- O,O′-dppcb). Compounds 3 and 4 have been synthesized independently and are also fully characterized by both single crystal X-ray structure analyses, NMR spectroscopy, mass spectrometry and elemental analyses. The conversion of 2 into 3 and then further into 4 has been followed by a variable-temperature 31P{ 1H} NMR experiment with compound 2 in DMF- d 7, revealing that the cleavage of the second methoxy group is kinetically disfavoured. This is in agreement with the X-ray structure analysis of 3, indicating the lack of any methoxy-oxygen atom coordination that could easily induce a further methoxy-group cleavage. o-MeO- O-dppcb and o-MeO- O,O′-dppcb are rare P-stereogenic tetraphosphine ligands and contribute to the synthetic field of new κ 3- P,P,O-coordinating phosphanylphenolate ligands that are believed to be important for the SHOP process (SHOP, Shell Higher Olefin Process).

Copper(II)–π interaction in cis-[Cu(orotato)(NH 3) 2] and the crystal structure of [Cu(orotato)(H 2O) 4] · H 2O: X-ray, vibrational spectroscopy and density functional study

The crystal structure of cis-[Cu(orotato)(NH 3) 2] ( 1) has been reinvestigated, and the structure of [Cu(orotato)(H 2O) 4] · H 2O ( 2) has been determined by single crystal X-ray diffraction and vibrational spectroscopic methods. In both complexes, the copper(II) ion is chelated by the deprotonated nitrogen atom (N1) of the uracil ring and the carboxylate oxygen atom of the orotate ligand. The square-planar environment of Cu is completed by two ammonia N atoms in 1, and two water O atoms in 2. Evidence is presented that the coordination sphere in 1 should be described as a (4+1+1)-geometry, where one axial position is occupied by the carbonyl oxygen atom and the other apical coordination site is located at the C C double bond of the neighboring uracilate ring. The non-covalent Cu(II)–π binding force is very important in stabilizing the columnar, polymeric structure of 1. The molecular structure of 2 is an asymmetric elongated octahedron (4+2) with two long Cu–O (water) axial bonds. Theoretical studies have been performed using the density functional unrestricted UB3LYP method. The natural charges on the atoms are derived from natural bond orbital (NBO) analysis. It is suggested that the π-type interaction between the chelated Cu 2+ cation and the aromatic compounds can play a significant role in biological systems, e.g. in the active sites of copper enzymes.

Dioxovanadium(V) complexes with N,N,O-donor monoanionic ligands: Synthesis, structure and properties

Dioxovanadium(V) complexes having the general formula [VO 2(phsalR)] have been synthesized in 52–63% yields by reacting one mole equivalent each of VOSO 4 · 5H 2O, 4-R-2-(pyridin-2-yl-hydrazonomethyl)-phenols (HphsalR, where R = H, OCH 3, Cl, Br and NO 2) and N(C 2H 5) 3 in water–acetonitrile (1:1.3) mixture. The complexes have been characterized by elemental analysis, magnetic susceptibility and spectroscopic (IR, UV–Vis, NMR and EPR) measurements. The physical properties of the complexes are consistent with the +5 oxidation state of the metal ion in them. The X-ray structure of a representative complex, [VO 2(phsal)] (R = H) has been determined. The metal centre in [VO 2(phsal)] is in square-pyramidal N 2O 3 coordination sphere. The monoanionic pyridine-N, imine-N and phenolate-O donor phsal − and one of the two oxo groups form the N,N,O,O basal plane and the other oxo group satisfies the fifth apical coordination site. This square-pyramidal molecules form weakly associated dimeric units due to the participation of the oxo group at the basal plane in the V–O–V bridge formation. The structure of [VO 2(phsal)] 2 can be described as two edge-shared VN 2O 4 octahedra. In the crystal lattice, these dimeric units form infinite one-dimensional chain structure via intermolecular N–H⋯O V hydrogen bonding interaction.

Trinuclear tris-Co(II) and trans-cobaloxime type Co(III) complexes prepared from Co(II) triflate precursor: Synthesis, structure and properties

Three new coordination compounds, [Co 3(DH) 6] · 24H 2O ( I), [Co(DH) 2Tu 2]CF 3SO 3 ( II) and [Co(DH) 2Py 2]CF 3SO 3 ( III) (where DH − = monoanion of dimethylglyoxime, Py = pyridine, Tu = thiourea), were synthesized starting from Co(CF 3SO 3) 2 · 6H 2O as a substrate. The complexes were characterized by X-ray crystallography, spectroscopic methods (IR, UV–Vis, 1H and 13C NMR, MS) and magnetochemistry. Compound I is a neutral, C 3 i symmetrical, trinuclear Co(II) complex with two tris-{Co 2+(μ-DH) 3} units connected to the central Co(II) ion via bridging oxygen atoms, saturating the Co(II) octahedral coordination. In the case of II and III, the complex cations have the usual trans-octahedral configuration with two DH-chelating units in the equatorial plane of the Co(III) ion and the apical coordination sites occupied by two neutral monodentate ligands (Py or Tu).

Design of high-dimensional copper(II) malonate complexes with exo-polydentate N-donor ligands.

Two polymeric malonato-bridged copper(II) complexes of formulas [(H(2)bpe)[Cu(mal)2]]n.4nH2O (1) and [Cu(4")(mal)(4)(bpe)(3)]n.6nH(2)O (2) [mal = malonate dianion; bpe = 1,2-bis(4-pyridyl)ethylene] have been synthesized and characterized by X-ray diffraction. Complex 1 crystallizes in triclinic space group P(-)1, Z = 1, with unit cell parameters a = 4.8831(10) A, b = 9.585(2) A, c = 11.813(2) A, alpha = 77.29(3) degrees, beta = 82.18(3) degrees, and gamma = 84.92(3) degrees, whereas complex 2 crystallizes in the monoclinic space group P2(1)/n, Z = 4, with unit cell parameters a = 13.462(3) A, b = 10.275(5) A, c = 19.579(4) A, and beta = 105.21(3) degrees. The structure of 1 consists of anionic malonato-bridged uniform copper(II) chains which are connected through hydrogen bonds involving malonate-oxygen atoms, noncoordinated water molecules, and H(2)bpe(2+) cations. The intrachain copper-copper separation through carboxylate-malonate bridge in the anti-syn conformation is 4.8831(10) A. Complex 2 possesses a three-dimensional structure made up of neutral corrugated malonated-bridged copper(II) layers linked through bis-monodentate bpe molecules. The copper(II) atoms within each layer are bridged by a double mu-oxo and four carboxylato-malonate bridges with copper-copper separations of 3.4095(7) A (through oxo) and 4.9488(11)-6.5268(13) A (through carboxylato). The shortest interlayer copper-copper separation across bridging bpe is 13.434(3) A. Variable-temperature magnetic measurements (2-290 K) show an overall ferromagnetic behavior for both compounds. The magnetic pathway of complex 1 is through a single carboxylate-malonate bridge connecting apical and equatorial positions of adjacent copper(II) atoms, and the value of the magnetic coupling (J) for 1 through a numerical expression for a ferromagnetic uniform chain of interacting local doublets is J = +0.049(1) cm(-1). The values for the magnetic couplings through the main intralayer exchange pathways in 2 which correspond to carboxylate-malonate bridges connecting equatorial-equatorial (J(1)) and equatorial-apical (J(2)) coordination sites and to the double mu-oxo bridge linking equatorial-apical (J(5)) positions have been determined through a simplified model. The three magnetic couplings are weak, two of them being ferromagnetic (J(1) = +23(1) cm(-1) and J(2) = +6.5(1) cm(-1)) and the other one antiferromagnetic [zJ' = -1.0(1) cm(-1)]. The values of the magnetic couplings in 1 and 2 compare well with those previously reported for similar malonato-bridged copper(II) complexes of different dimensionalities.

Synthesis, characterization, and acid–base properties of (N–N)PtIV(CH3)2(OH)2 − x(OCH3)x(x = 0, 1) complexes

(N–N)PtIV(CH3)2(OH)2 − x(OCH3)x (x = 0, 1; N–N = bipy, 4,4′-(CH3)2bipy, 4,4′-tBu2bipy, ArNC(CH3)–C(CH3)NAr (Ar = 3,5-(CF3)2C6H3, 3,5-(CH3)2C6H3, 2,6-(CH3)2C6H3) complexes have been prepared by oxidation of the appropriate (N–N)PtII(CH3)2 complexes using H2O2/H2O. In methanol, the hydroxo–methoxy complexes are formed (x = 1), whereas in acetone, the dihydroxo complexes are formed (x = 0). A single-crystal X-ray structure determination establishes the structure of (4,4′-(CH3)2bipy)PtIV(CH3)2(OH)2 as a dihydroxo compound with octahedral geometry, with the hydroxo ligands occupying apical coordination sites. The acidities of the protonated bipy hydroxo complexes, (4,4′-R2bipy)PtIV(CH3)2(OH)(OH2)+ cations, were determined in methanol. The acidities closely matched that of Cl2CHCOOH (pKa = 6.38 in CH3OH).

Copper(II)-activated transformation of azomethine to imidate: synthetic and structural studies

The Schiff base 2-pyridine–carboxaldehyde 4-dimethylaminobenzoylhydrazone (HL, 1) was prepared by reacting 2-pyridine–carboxaldehyde and 4-dimethylaminobenzoylhydrazine in a 1:1 molar ratio in methanol. Reaction of HL ( 1) with Cu(O 2CCH 3) 2·H 2O (in a 1:1 molar ratio) in methanol afforded a dinuclear copper(II) complex, [Cu 2(μ-O 2CCH 3) 2L′ 2]·2H 2O ( 2). The azomethine functionality (CHN) of 1 is converted to imidate (C(OMe)N) in the complexed ligand L′ −. Molecular structures of both 1 and 2 were determined by X-ray crystallographic studies. The dinuclear molecule of 2 is centrosymmetric and contains two monoatomic bridging acetate groups. Each copper(II) centre is in a square-pyramidal N 2O 3 coordination sphere. The ligand, L′ − coordinates the metal ion via the pyridine-N, the imidate-N, and the deprotonated amide-O atoms. One of the acetate oxygen atoms completes the N 2O 2 square-plane. The oxygen of the symmetry-related acetate fills the apical coordination site. Structural parameters are consistent with both copper ions being in a +2 oxidation state. The room temperature magnetic moment is 1.89 μ B (per Cu). In powder phase the complex displays an axial EPR spectrum at 298 K. The complex is nonconducting in methanol solution. The electronic spectrum shows a ligand field absorption at 680 nm and charge transfer bands in the range 426–215 nm.

Structures and Magnetic Properties of [o- and p-MePyNN+]2[Cu(ox)2] (MePyNN+ = Nitronyl Nitroxyl Radical Cation)

Abstract Reactions of [o-MePyNN+]PF6 and [p-MePyNN+]PF6 with [n-Bu4N]2[Cu(ox)2] in acetonitrile yielded dark-blue crystals of [o-MePyNN+]2[Cu(ox)2]·2CH3OH (1) and [p-MePyNN+]2[Cu(ox)2]·2H2O (2), respectively, where [o-MePyNN+] or [p-MePyNN+] represents the 2-(2 or 4-N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazo-1-oxyl 3-oxide radical cation. X-ray structural analyses showed that the crystals of 1 and 2 are isomorphous. The coordination geometry of the Cu2+ ions in 1 and 2 is an elongated octahedron, and the equatorial and apical coordination sites of the Cu2+ ions are occupied by two oxalato groups and two radial cations, respectively. Magnetic susceptibility measurements for 1 and 2 revealed that the copper and radical centers are ferromagnetically coupled with J = +8.2(1) and +7.8(1) cm-1 (H = -2J∑SCu·Srad), respectively.

A dimeric pervanadyl (VO2+) complex with a tridentate Schiff base ligand

A di(μ-oxo)-bridged dinuclear complex, [VO2(pamh)]2 was isolated by reacting bis(acetylacetonato)vanadium(IV) and the Schiff base, N-(anisoyl)-N′-(picolinylidene)-hydrazine (Hpamh) in acetonitrile. The complex crystallizes in the space group \(P\bar 1 \) ;1; (#2) on crystallographic inversion center. Crystal data: a = 8.2202(12) A, b = 9.8389(19) A, c = 10.1907(17) A, α = 68.245(15)°, β = 74.47(2)°, γ = 66.710(19)°, V = 696.0(2) A3, and Z = 1. The physical properties of the complex and the structural parameters are consistent with the +5 oxidation state of the metal ions. The monomeric VO2(pamh) unit is square-pyramidal. The planar mononegative ligand (pamh−) coordinates the metal ion via the pyridine-N, the imine-N, and the amide-O atoms. One of the oxo groups completes the NNOO basal plane and also participates in the Vndash;Ondash ;V bridge formation. The other oxo group satisfies the fifth apical coordination site. The molecular structure of the dimeric complex, [VO2(pamh)]2 can be described as two edge-shared distorted VO4N2 octahedra.