First row divalent transition metal complexes of aryl-appended tris((pyridyl)methyl)amine ligands: syntheses, structures, electrochemistry, and hydroxamate binding properties

Divalent manganese, cobalt, nickel, and zinc complexes of 6-Ph(2)TPA (N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-Ph(2)TPA)Mn(CH(3)OH)(3)](ClO(4))(2) (1), [(6-Ph(2)TPA)Co(CH(3)CN)](ClO(4))(2) (2), [(6-Ph(2)TPA)Ni(CH(3)CN)(CH(3)OH)](ClO(4))(2) (3), [(6-Ph(2)TPA)Zn(CH(3)CN)](ClO(4))(2) (4)) and 6-(Me(2)Ph)(2)TPA (N,N-bis((6-(3,5-dimethyl)phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-(Me(2)Ph)(2)TPA)Ni(CH(3)CN)(2)](ClO(4))(2) (5) and [(6-(Me(2)Ph)(2)TPA)Zn(CH(3)CN)](ClO(4))(2) (6)) have been prepared and characterized. X-ray crystallographic characterization of 1A.CH(3)()OH and 1B.2CH(3)()OH (differing solvates of 1), 2.2CH(3)()CN, 3.CH(3)()OH, 4.2CH(3)()CN, and 6.2.5CH(3)()CN revealed mononuclear cations with one to three coordinated solvent molecules. In 1A.CH(3)()OH and 1B.2CH(3)()OH, one phenyl-substituted pyridyl arm is not coordinated and forms a secondary hydrogen-bonding interaction with a manganese bound methanol molecule. In 2.2CH(3)()CN, 3.CH(3)()OH, 4.2CH(3)()CN, and 6.2.5CH(3)()CN, all pyridyl donors of the 6-Ph(2)TPA and 6-(Me(2)Ph)(2)TPA ligands are coordinated to the divalent metal center. In the cobalt, nickel, and zinc derivatives, CH/pi interactions are found between a bound acetonitrile molecule and the aryl appendages of the 6-Ph(2)TPA and 6-(Me(2)Ph)(2)TPA ligands. (1)H NMR spectra of 4 and 6 in CD(3)NO(2) solution indicate the presence of CH/pi interactions, as an upfield-shifted methyl resonance for a bound acetonitrile molecule is present. Examination of the cyclic voltammetry of 1-3 and 5 revealed no oxidative (M(II)/M(III)) couples. Admixture of equimolar amounts of 6-Ph(2)TPA, M(ClO(4))(2).6H(2)O, and Me(4)NOH.5H(2)O, followed by the addition of an equimolar amount of acetohydroxamic acid, yielded the acetohydroxamate complexes [((6-Ph(2)TPA)Mn)(2)(micro-ONHC(O)CH(3))(2)](ClO(4))(2) (8), [(6-Ph(2)TPA)Co(ONHC(O)CH(3))](ClO(4))(2) (9), [(6-Ph(2)TPA)Ni(ONHC(O)CH(3))](ClO(4))(2) (10), and [(6-Ph(2)TPA)Zn(ONHC(O)CH(3))](ClO(4))(2) (11), all of which were characterized by X-ray crystallography. The Mn(II) complex 8.0.75CH(3)()CN.0.75Et(2)()O exhibits a dinuclear structure with bridging hydroxamate ligands, whereas the Co(II), Ni(II), and Zn(II) derivatives all exhibit mononuclear six-coordinate structures with a chelating hydroxamate ligand.     

Crystal structure and magnetic interactions in nickel(II) dibridged complexes formed by two azide groups or by both phenolate oxygen-azide, -thiocyanate, -carboxylate, or -cyanate groups

Tridentate/tetradentate Schiff base ligands L(1) and L(2), derived from the condensation of o-vanillin or pyridine-2-aldehyde with N,N-dimethylethylenediammine, react with nickel acetate or perchlorate salt and azide, cyanate, or thiocyanate to give rise to a series of dinuclear complexes of formulas [Ni(L(1))(micro(1,1)-N(3))Ni(L(1))(N(3))(OH(2))].H(2)O (1), [[Ni(L(1))(micro(1,1)-NCS)Ni(L(1))(NCS)(OH(2))][Ni(L(1))(micro-CH(3)COO)Ni(L(1))( NCS) (OH(2))]] (2) [[2A][2B]], [Ni(L(1))(micro(1,1)-NCO)Ni(L(1))(NCO)(OH(2))].H(2)O (3), and [Ni(L(2)-OMe)(micro(1,1)-N(3))(N(3))](2) (4), where L(1) = Me(2)N(CH(2))(2)NCHC(6)H(3)(O(-))(OCH(3)) and L(2) = Me(2)N(CH(2))(2)NCHC(6)H(3)N. We have characterized these complexes by analytical, spectroscopic, and variable-temperature magnetic susceptibility measurements. The coordination geometry around all of the Ni(II) centers is a distorted octahedron with bridging azide, thiocyanate/acetate, or cyanate in a micro(1,1) mode and micro(2)-phenolate oxygen ion for 1-3, respectively, or with a double-bridging azide for 4. The magnetic properties of the complexes were studied by magnetic susceptibility (chi(M)) versus temperature measurements. The chi(M) nus T plot reveals that compounds 1 and 4 are strongly ferromagnetically coupled, 3 shows a weak ferromagnetic behavior, and 2 is very weakly antiferromagnetically coupled.     

Cationic assembly of metal complex aggregates: structural diversity,solution stability,and magnetic properties

The tetradentate imino-carboxylate ligand [L](2)(-) chelates the equatorial sites of Ni(II) to give the complex [Ni(L)(MeOH)(2)] in which a Ni(II) center is bound in an octahedral coordination environment with MeOH ligands occupying the axial sites. Lanthanide (Ln) and Group II metal ions (M) template the aggregation of six [Ni(L)] fragments into the octahedral cage aggregates (M[Ni(L)](6))(x)(+) (1: M = Sr(II); x = 2,2: M = Ba(II); x = 2, 3: M = La(III); x = 3, 4: M = Ce(III); x = 3, 5: M = Pr(III); x = 3, and 6: M = Nd(III); x = 3). In the presence of Group I cations, however, aggregates composed of the alkali metal-oxide cations template various cage compounds. Thus, Na(+) forms the trigonal bipyramidal [Na(5)O](3+) core within a tricapped trigonal prismatic [Ni(L)](9) aggregate to give ((Na(5)O) subset [Ni(L)](9)(MeOH)(3))(BF(4))(2).OH.CH(3)OH, 7. Li(+) and Na(+) together form a mixed Li(+)/Na(+) core comprising distorted trigonal bipyramidal [Na(3)Li(2)O](3+) within an approximately anti-square prismatic [Ni(L)](8) cage in ((Na(3)Li(2)O) subset [Ni(L)](8)(CH(3)OH)(1.3)(BF(4))(0.7))(BF(4))(2.3).(CH(3)OH)(2.75).(C(4)H(10)O)(0.5), 8, while in the presence of Li(+), a tetrahedral [Li(4)O](2+) core within a hexanuclear open cage [Ni(L)](6) in ((Li(4)O) subset [Ni(L)](6)(CH(3)OH)(3))2ClO(4).1.85CH(3)OH, 9, is produced. In the presence of H(2)O, the Cs(+) cation induces the aggregation of the [Ni(L)(H(2)O)(2)] monomer to give the cluster Cs(2)[Ni(L)(H(2)O)(2)](6).2I.4CH(3)OH.5.25H(2)O, 10. Analysis by electronic spectroscopy and mass spectrometry indicates that in solution the trend in stability follows the order 1-6 > 7 > 8 approximately 9. Magnetic susceptibility data indicate that there is net antiferromagnetic exchange between magnetic centers within the cages.     

Nickel(II) complexes of tripodal 4N ligands as catalysts for alkane oxidation using m-CPBA as oxidant: ligand stereoelectronic effects on catalysis

Several mononuclear Ni(II) complexes of the type [Ni(L)(CH(3)CN)(2)](BPh(4))(2) 1-7, where L is a tetradentate tripodal 4N ligand such as N,N-dimethyl-N',N'-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L1), N,N-diethyl-N',N'-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L2), N,N-dimethyl-N'-(1-methyl-1H-imidazol-2-ylmethyl)-N'-(pyrid-2-ylmethyl)ethane-1,2-diamine (L3), N,N-dimethyl-N',N'-bis(1-methyl-1H-imidazol-2-ylmethyl)ethane-1,2-diamine (L4), N,N-dimethyl-N',N'-bis(quinolin-2-ylmethyl)ethane-1,2-diamine (L5), tris(benzimidazol-2-ylmethyl)amine (L6) and tris(pyrid-2-ylmethyl)amine (L7), have been isolated and characterized using CHN analysis, UV-Visible spectroscopy and mass spectrometry. The single-crystal X-ray structures of the complexes [Ni(L1)(CH(3)CN)(H(2)O)](ClO(4))(2) 1a, [Ni(L2)(CH(3)CN)(2)](BPh(4))(2) 2, [Ni(L3)(CH(3)CN)(2)](BPh(4))(2) 3 and [Ni(L4)(CH(3)CN)(2)](BPh(4))(2) 4 have been determined. All these complexes possess a distorted octahedral coordination geometry in which Ni(II) is coordinated to four nitrogen atoms of the tetradentate ligands and two CH(3)CN (2, 3, 4) or one H(2)O and one CH(3)CN (1a) are located in cis positions. The Ni-N(py) bond distances (2.054(2)-2.078(3) ?) in 1a, 2 and 3 are shorter than the Ni-N(amine) bonds (2.127(2)-2.196(3) ?) because of sp(2) and sp(3) hybridizations of the pyridyl and tertiary amine nitrogens respectively. In 3 the Ni-N(im) bond (2.040(5) ?) is shorter than the Ni-N(py) bond (2.074(4) ?) due to the stronger coordination of imidazole compared with the pyridine donor. In dichloromethane/acetonitrile solvent mixture, all the Ni(ii) complexes possess an octahedral coordination geometry, as revealed by the characteristic ligand field bands in the visible region. They efficiently catalyze the hydroxylation of alkanes when m-CPBA is used as oxidant with turnover number (TON) in the range of 340-620 and good alcohol selectivity for cyclohexane (A/K, 5-9). By replacing one of the pyridyl donors in TPA by a weakly coordinating -NMe(2) or -NEt(2) donor nitrogen atom the catalytic activity decreases slightly with no change in the selectivity. In contrast, upon replacing the pyridyl nitrogen donor by the strongly σ-bonding imidazolyl or sterically demanding quinolyl/benzimidazolyl nitrogen donor, both the catalytic activity and selectivity decrease, possibly due to destabilization of the intermediate [(4N)(CH(3)CN)Ni-O˙](+) radical species. Adamantane is selectively (3°/2°, 12-17) oxidized to 1-adamantanol, 2-adamantanol and 2-adamantanone while cumene is selectively oxidized to 2-phenyl-2-propanol. In contrast to cyclohexane oxidation, the incorporation of sterically hindering quinolyl/benzimidazolyl donors around Ni(ii) leads to a high 3°/2° bond selectivity for adamantane oxidation. A linear correlation between the metal-ligand covalency parameter (β) and the turnover number has been observed.     

Effects of Pt...Pt bonding, anions, solvate molecules, and hydrogen bonding on the self-association of Chugaev's cation, a platinum complex with a chelating carbene ligand

Five salts, [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)](BPh(4)).CH(3)OH, [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)](PF(6)).CH(2)Cl(2), [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Cl.4H(2)O, [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Br.3.5H(2)O, and [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Cl.0.1H(2)O, have been crystallized and examined by single crystal X-ray diffraction. While the internal structure of the cation is similar in all salts, the interactions between cations vary in the different salts. Yellow [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)](BPh(4)).CH(3)OH and red [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)](PF(6)) form face-to-face dimers with Pt...Pt separations of 3.6617(6) and 3.340(2) A, respectively. In the latter, hydrogen bonding of the chelating ligand to adjacent anions facilitates the close approach of pairs of cations. The salts [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Cl.4H(2)O, [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Br.3.5H(2)O, and [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Cl.0.1H(2)O form columnar structures with Pt...Pt separations that range from 3.2514(5) to 3.5643(6) A. The water molecules and anions surround these columns and form bridges between neighboring columns. The electronic spectra of aqueous solutions of [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Cl.4H(2)O show spectral changes upon increasing concentrations of the platinum complex that are indicative of the formation of a dimer in solution with an equilibrium constant for dimerization of 23(1).     

Syntheses, characterization, and magnetic studies of copper(II) complexes with the ligand N,N,N',N'-tetrakis(2-pyridylmethyl)-1,3-benzenediamine (1,3-tpbd) and its phenol derivative 2,6-bis[bis(2-pyridylmethyl)amino]-p-cresol] (2,6-Htpcd)

The copper(II) complexes [Cu(4)(1,3-tpbd)(2)(H(2)O)(4)(NO(3))(4)](n)(NO(3))(4n)·13nH(2)O (1), [Cu(4)(1,3-tpbd)(2)(AsO(4))(ClO(4))(3)(H(2)O)](ClO(4))(2)·2H(2)O·0.5CH(3)OH (2), [Cu(4)(1,3-tpbd)(2)(PO(4))(ClO(4))(3)(H(2)O)](ClO(4))(2)·2H(2)O·0.5CH(3)OH (3), [Cu(2)(1,3-tpbd){(PhO)(2)PO(2)}(2)](2)(ClO(4))(4) (4), and [Cu(2)(1,3-tpbd){(PhO)PO(3)}(2)(H(2)O)(0.69)(CH(3)CN)(0.31)](2)(BPh(4))(4)·Et(2)O·CH(3)CN (5) [1,3-tpbd = N,N,N',N'-tetrakis(2-pyridylmethyl)-1,3-benzenediamine, BPh(4)(-) = tetraphenylborate] were prepared and structurally characterized. Analyses of the magnetic data of 2, 3, 4, and [Cu(2)(2,6-tpcd)(H(2)O)Cl](ClO(4))(2) (6) [2,6-tpcd = 2,6-bis[bis(2-pyridylmethyl)amino]-p-cresolate] show the occurrence of weak antiferromagnetic interactions between the copper(II) ions, the bis-terdentate 1,3-tpbd/2,6-tpcd, μ(4)-XO(4) (X = As and P) μ(1,2)-OPO and μ-O(phenolate) appearing as poor mediators of exchange interactions in this series of compounds. Simple orbital symmetry considerations based on the structural knowledge account for the small magnitude of the magnetic couplings found in these copper(II) compounds.     

Structures and magnetic properties of an antiferromagnetically coupled polymeric copper(II) complex and ferromagnetically coupled hexanuclear nickel(II) clusters

Reactions between 2,6-diformyl-4-methylphenol (DFMF) and tris(hydroxymethyl) aminomethane (THMAM = H(3)L2) in the presence of copper(II) salts, CuX(2) (X = CH(3)CO(2)(-), BF(4)(-), ClO(4)(-), Cl(-), NO(3)(-)) and Ni(CH(3)CO(2))(2) or Ni(ClO(4))(2)/NaC(6)H(5)CO(2), sodium azide (NaN(3)), and triethylamine (TEA), in one pot self-assemble giving a coordination polymer consisting of repeating pentanuclear copper(II) clusters {[Cu(2)(H(5)L(2-))(μ-N(3))](2)[Cu(N(3))(4)]·2CH(3)OH}(n) (1) and hexanuclear Ni(II) complexes [Ni(6)(H(3)L1(-))(2)(HL2(2-))(2)(μ-N(3))(4)(CH(3)CO(2))(2)]·6C(3)H(7)NO·C(2)H(5)OH (2) and [Ni(6)(H(3)L1(-))(2)(HL2(2-))(2)(μ-N(3))(4)(C(6)H(5)CO(2))(2)]·3C(3)H(7)NO·3H(2)O·CH(3)OH (3). In 1, H(5)L(2-) and in 2 and 3 H(3)L1(-) and HL2(2-) represent doubly deprotonated, singly deprotonated, and doubly deprotonated Schiff-base ligands H(7)L and H(4)L1 and a tripodal ligand H(3)L2, respectively. 1 has a novel double-stranded ladder-like structure in which [Cu(N(3))(4)](2-) anions link single chains comprised of dinuclear cationic subunits [Cu(2)(H(5)L(2-))(μ-N(3))](+), forming a 3D structure of interconnected ladders through H bonding. Nickel(II) clusters 2 and 3 have very similar neutral hexanuclear cores in which six nickel(II) ions are bonded to two H(4)L1, two H(3)L2, four μ-azido, and two μ-CH(3)CO(2)(-)/μ-C(6)H(5)CO(2)(-) ligands. In each structure two terminal dinickel (Ni(2)) units are connected to the central dinickel unit through four doubly bridging end-on (EO) μ-azido and four triply bridging μ(3)-methoxy bridges organizing into hexanuclear units. In each terminal dinuclear unit two nickel centers are bridged through one μ-phenolate oxygen from H(3)L1(-), one μ(3)-methoxy oxygen from HL2(2-), and one μ-CH(3)CO(2)(-) (2)/μ-C(6)H(5)CO(2)(-) (3) ion. Bulk magnetization measurements on 1 show moderately strong antiferromagnetic coupling within the [Cu(2)] building block (J(1) = -113.5 cm(-1)). Bulk magnetization measurements on 2 and 3 demonstrate that the magnetic interactions are completely dominated by ferromagnetic coupling occurring between Ni(II) ions for all bridges with coupling constants (J(1), J(2), and J(3)) ranging from 2.10 to 14.56 cm(-1) (in the ? = -J(1)(?(1)?(2)) - J(1)(?(2)?(3)) - J(2)(?(3)?(4)) - J(1)(?(4)?(5)) - J(1)(?(5)?(6)) - J(2)(?(1)?(6)) - J(3)(?(2)?(6)) - J(3)(?(2)?(5)) - J(3)(?(3)?(5)) convention).     

Di- and tetra-nuclear copper(II), nickel(II), and cobalt(II) complexes of four bis-tetradentate triazole-based ligands: synthesis, structure, and magnetic properties

Four bis-tetradentate N(4)-substituted-3,5-{bis[bis-N-(2-pyridinemethyl)]aminomethyl}-4H-1,2,4-triazole ligands, L(Tz1)-L(Tz4), differing only in the triazole N(4) substituent R (where R is amino, pyrrolyl, phenyl, or 4-tertbutylphenyl, respectively) have been synthesized, characterized, and reacted with M(II)(BF(4))(2)·6H(2)O (M(II) = Cu, Ni or Co) and Co(SCN)(2). Experiments using all 16 possible combinations of metal salt and L(TzR) were carried out: 14 pure complexes were obtained, 11 of which are dinuclear, while the other three are tetranuclear. The dinuclear complexes include two copper(II) complexes, [Cu(II)(2)(L(Tz2))(H(2)O)(4)](BF(4))(4) (2), [Cu(II)(2)(L(Tz4))(BF(4))(2)](BF(4))(2) (4); two nickel(II) complexes, [Ni(II)(2)(L(Tz1))(H(2)O)(3)(CH(3)CN)](BF(4))(4)·0.5(CH(3)CN) (5) and [Ni(II)(2)(L(Tz4))(H(2)O)(4)](BF(4))(4)·H(2)O (8); and seven cobalt(II) complexes, [Co(II)(2)(L(Tz1))(μ-BF(4))](BF(4))(3)·H(2)O (9), [Co(II)(2)(L(Tz2))(μ-BF(4))](BF(4))(3)·2H(2)O (10), [Co(II)(2)(L(Tz3))(H(2)O)(2)](BF(4))(4) (11), [Co(II)(2)(L(Tz4))(μ-BF(4))](BF(4))(3)·3H(2)O (12), [Co(II)(2)(L(Tz1))(SCN)(4)]·3H(2)O (13), [Co(II)(2)(L(Tz2))(SCN)(4)]·2H(2)O (14), and [Co(II)(2)(L(Tz3))(SCN)(4)]·H(2)O (15). The tetranuclear complexes are [Cu(II)(4)(L(Tz1))(2)(H(2)O)(2)(BF(4))(2)](BF(4))(6) (1), [Cu(II)(4)(L(Tz3))(2)(H(2)O)(2)(μ-F)(2)](BF(4))(6)·0.5H(2)O (3), and [Ni(II)(4)(L(Tz3))(2)(H(2)O)(4)(μ-F(2))](BF(4))(6)·6.5H(2)O (7). Single crystal X-ray structure determinations revealed different solvent content from that found by microanalysis of the bulk sample after drying under a vacuum and confirmed that 5', 8', 9', 11', 12', and 15' are dinuclear while 1' and 7' are tetranuclear. As expected, magnetic measurements showed that weak antiferromagnetic intracomplex interactions are present in 1, 2, 4, 7, and 8, stabilizing a singlet spin ground state. All seven of the dinuclear cobalt(II) complexes, 9-15, have similar magnetic behavior and remain in the [HS-HS] state between 300 and 1.8 K.     

Family of carboxylate- and nitrate-diphenoxo triply bridged dinuclear Ni(II)Ln(III) complexes (Ln = Eu, Gd, Tb, Ho, Er, Y): synthesis, experimental and theoretical magneto-structural studies, and single-molecule magnet behavior

Seven acetate-diphenoxo triply bridged M(II)-Ln(III) complexes (M(II) = Ni(II) and Ln(III) = Gd, Tb, Ho, Er, and Y; M(II) = Zn(II) and Ln(III) = Ho(III) and Er(III)) of formula [M(μ-L)(μ-OAc)Ln(NO(3))(2)], one nitrate-diphenoxo triply bridged Ni(II)-Tb(III) complex, [Ni(μ-L)(μ-NO(3))Tb(NO(3))(2)]·2CH(3)OH, and two diphenoxo doubly bridged Ni(II)-Ln(III) complexes (Ln(III) = Eu, Gd) of formula [Ni(H(2)O)(μ-L)Ln(NO(3))(3)]·2CH(3)OH have been prepared in one pot reaction from the compartmental ligand N,N',N"-trimethyl-N,N"-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H(2)L). Moreover, Ni(II)-Ln(III) complexes bearing benzoate or 9-anthracenecarboxylate bridging groups of formula [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN have also been successfully synthesized. In acetate-diphenoxo triply bridged complexes, the acetate bridging group forces the structure to be folded with an average hinge angle in the M(μ-O(2))Ln bridging fragment of ~22°, whereas nitrate-diphenoxo doubly bridged complexes and diphenoxo-doubly bridged complexes exhibit more planar structures with hinge angles of ~13° and ~2°, respectively. All Ni(II)-Ln(III) complexes exhibit ferromagnetic interactions between Ni(II) and Ln(III) ions and, in the case of the Gd(III) complexes, the J(NiGd) coupling increases weakly but significantly with the planarity of the M-(O)(2)-Gd bridging fragment and with the increase of the Ni-O-Gd angle. Density functional theory (DFT) theoretical calculations on the Ni(II)Gd(III) complexes and model compounds support these magneto-structural correlations as well as the experimental J(NiGd) values, which were found to be ~1.38 and ~2.1 cm(-1) for the folded [Ni(μ-L)(μ-OAc)Gd(NO(3))(2)] and planar [Ni(H(2)O)(μ-L)Gd(NO(3))(3)]·2CH(3)OH complexes, respectively. The Ni(II)Dy(III) complexes exhibit slow relaxation of the magnetization with Δ/k(B) energy barriers under 1000 Oe applied magnetic fields of 9.2 and 10.1 K for [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN, respectively.     

A new two-dimensional molybdenum(V) nickel phosphate built up of [H18(Mo16O32)Ni16(PO4)26(OH)6(H2O)8]18- wheels

The new molybdenum(V) nickel phosphate Na(6)Ni(6)[(Mo(2)O(4))(8)Ni(16)(H(2)PO(4))(4)(HPO(4))(10)(PO(4))(12)(OH)(6)(H(2)O)(8)].66H(2)O (1) was synthesized hydrothermally. The structure (orthorhombic, space group Cccm; a = 23.999(4), b = 36.595(6), c = 20.445(4) A) was solved from single-crystal data. The framework structure of 1 consists of anionic inorganic sheets formed by the linkages of large polyoxomolybdate rings via nickel(II) octahedra. Charge-compensating sodium atoms are interleaved between the sheets. Magnetic studies of compound 1 revealed that among the 22 nickel(II) centers, 10 are interacting. The chi(M)T = f(T) curve can be fitted using the dinuclear expression appropriate to the HDVV isotropic exchange Hamiltonian H = -2JS(1).S(2), with S(1) = S(2) = 1 and J = -24.1 cm(-)(1), showing that nickel is antiferromagnetically coupled within Ni(2) pairs.     

Ni(P(Ph)2N(C6H4X)2)2]2+ complexes as electrocatalysts for H2 production: effect of substituents, acids, and water on catalytic rates

A series of mononuclear nickel(II) bis(diphosphine) complexes [Ni(P(Ph)(2)N(C6H4X)(2))(2)](BF(4))(2) (P(Ph)(2)N(C6H4X)(2) = 1,5-di(para-X-phenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane; X = OMe, Me, CH(2)P(O)(OEt)(2), Br, and CF(3)) have been synthesized and characterized. X-ray diffraction studies reveal that [Ni(P(Ph)(2)N(C6H4Me)(2))(2)](BF(4))(2) and [Ni(P(Ph)(2)N(C6H4OMe)(2))(2)](BF(4))(2) are tetracoordinate with distorted square planar geometries. The Ni(II/I) and Ni(I/0) redox couples of each complex are electrochemically reversible in acetonitrile with potentials that are increasingly cathodic as the electron-donating character of X is increased. Each of these complexes is an efficient electrocatalyst for hydrogen production at the potential of the Ni(II/I) couple. The catalytic rates generally increase as the electron-donating character of X is decreased, and this electronic effect results in the favorable but unusual situation of obtaining higher catalytic rates as overpotentials are decreased. Catalytic studies using acids with a range of pK(a) values reveal that turnover frequencies do not correlate with substrate acid pK(a) values but are highly dependent on the acid structure, with this effect being related to substrate size. Addition of water is shown to dramatically increase catalytic rates for all catalysts. With [Ni(P(Ph)(2)N(C6H4CH2P(O)(OEt)2)(2))(2)](BF(4))(2) using [(DMF)H](+)OTf(-) as the acid and with added water, a turnover frequency of 1850 s(-1) was obtained.     

Structural and magnetic studies of Schiff base complexes of nickel(II) nitrite: change in crystalline state, ligand rearrangement and a very rare μ-nitrito-1κO:2κN:3κO' bridging mode

Four new nickel(II) complexes, [Ni(2)L(2)(NO(2))(2)]·CH(2)Cl(2)·C(2)H(5)OH, 2H(2)O (1), [Ni(2)L(2)(DMF)(2)(μ-NO(2))]ClO(4)·DMF (2a), [Ni(2)L(2)(DMF)(2)(μ-NO(2))]ClO(4) (2b) and [Ni(3)L'(2)(μ(3)-NO(2))(2)(CH(2)Cl(2))](n)·1.5H(2)O (3) where HL = 2-[(3-amino-propylimino)-methyl]-phenol, H(2)L(') = 2-({3-[(2-hydroxy-benzylidene)-amino]-propylimino}-methyl)-phenol and DMF = N,N-dimethylformamide, have been synthesized starting with the precursor complex [NiL(2)]·2H(2)O, nickel(ii) perchlorate and sodium nitrite and characterized structurally and magnetically. The structural analyses reveal that in all the complexes, Ni(II) ions possess a distorted octahedral geometry. Complex 1 is a dinuclear di-μ(2)-phenoxo bridged species in which nitrite ion acts as chelating co-ligand. Complexes 2a and 2b also consist of dinuclear entities, but in these two compounds a cis-(μ-nitrito-1κO:2κN) bridge is present in addition to the di-μ(2)-phenoxo bridge. The molecular structures of 2a and 2b are equivalent; they differ only in that 2a contains an additional solvated DMF molecule. Complex 3 is formed by ligand rearrangement and is a one-dimensional polymer in which double phenoxo as well as μ-nitrito-1κO:2κN bridged trinuclear units are linked through a very rare μ(3)-nitrito-1κO:2κN:3κO' bridge. Analysis of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the nickel(ii) ions in four complexes, with exchange parameters J of -5.26, -11.45, -10.66 and -5.99 cm(-1) for 1, 2a, 2b and 3, respectively.     

Photochemical behavior of azobenzene-conjugated CoII, CoIII, and FeII bis(terpyridine) complexes

Azobenzene-conjugated mononuclear and dinuclear terpyridyl complexes of Co(II), Co(III), and Fe(II) were synthesized, and their photoisomerization behavior was investigated. Co(II) and Co(III) complexes, [tpyCo(tpy-AB)]X(n) and [(Cotpy)(2)(tpy-AB-tpy)]X(n) (tpy-AB = C(15)N(3)H(10)-C(6)H(4)-N=NC(6)H(5), tpy-AB-tpy = C(15)N(3)H(10)-C(6)H(4)-N=NC(6)H(4)-C(15)N(3)H(10), X = PF(6) or BPh(4)), exhibit trans-to-cis photoisomerization by irradiation at 366 nm, and this behavior is dependent on solvents and counterions. For the Co(II) complexes, BPh(4) salts undergo cis-to-trans isomerization in propylene carbonate by both photoirradiation with visible light (435 nm) and heat, indicating that reversible trans-cis isomerization has occurred. [Co(tpy-AB)(2)](BPh(4))(2) shows a two-step trans-to-cis isomerization process. The trans-cis isomerization behavior of Co(III) complexes was observed only in the solvents with a low donor number such as 1,2-dichloroethane. Fe(II) complexes, [tpyFe(tpy-AB)]X(n) (X = PF(6) or BPh(4)), exhibit slight trans-to-cis photoisomerization due to the energy transfer from the azobenzene moiety to Fe(tpy)(2) moieties.     

Synthesis, structure, and reactivity of dinuclear nickel amino-thiophenolate complexes bearing bridging VO2(OH)2- and VO2(OR)2- coligands

A series of novel mixed ligand dinickel complexes of the type [Ni(II)(2)L(μ-L')](+), where L' is a tetrahedral oxo-alkoxo vanadate (L' = [O(2)V(V)(OR)(2)](-), R = H or alkyl) and L a macrocyclic N(6)S(2) supporting ligand, have been prepared, and their esterification reactivity has been studied. The orthovanadate complex [Ni(2)L(μ-O(2)V(OH)(2))](+) (2), prepared by reaction between [Ni(2)L(μ-Cl)]ClO(4) with Na(3)VO(4) and a phase transfer reagent in CH(3)CN, reacts smoothly with MeOH and EtOH forming the vanadate diesters [Ni(2)L(μ-O(2)V(OMe)(2))](+) (3) and [Ni(2)L(μ-O(2)V(OEt)(2))](+) (4). The dialkyl orthovanadate esters in 3 and 4 are readily transesterified with mono- and difunctional alcohols. Complex 3 can also be generated from 4 by transesterification with MeOH. Complexes 3 and 4 react with diols (ethylene glycol, propylene glycol and diethylene glycol) as well to afford the complexes [Ni(2)L(μ-O(2)V(OH)(OCH(2)CH(2)OH))](+) (5), [Ni(2)L(μ-O(2)V(OCH(2))(2)CH(2))](+) (6), and [Ni(2)L(μ-O(2)V(OCH(2)CH(2))(2)O)] (7). The crystal structures of the tetraphenylborate salts of complexes 3-7 reveal in each case four-coordinate O(2)V(V)(OR)(2)(-) groups bonded in a μ(1,3)-bridging mode to generate trinuclear complexes with a central N(3)Ni(μ-S)(2)(μ(1,3)-O(2)V(OR)(2))NiN(3) core. The stabilization of the four-coordinate V(V)O(2)(OR)(2)(-) moieties is a consequence of both the two-point coordinative fixation to and the steric protection of the bowl-shape binding pocket of the [Ni(2)L](2+) fragment. Cyclic voltammetry experiments reveal that the encapsulated vanadate esters are not reduced in a potential window of -2.0 to +2.5 V vs SCE. The spins of the nickel(II) (S(i) = 1 ions) in 3 are weakly ferromagnetically coupled (J = +23 cm(-1), (H = -2JS(1)S(2))) to produce an S = 2 ground state.     

Ferromagnetic interaction in mu1,3-cyanamido-derived copper(II) cryptates

The reaction of dinuclear copper(II) cryptates with calcium cyanamide, CaNCN, and sodium dicyanamide, Na[N(CN)(2)] results in dinuclear compounds of formulae [Cu(2)(HNCN)(R3Bm)](ClO(4))(3) (1), [Cu(2)(dca)(R3Bm)](ClO(4))(3)4H(2)O (2), and [Cu(2)(NCNCONH(2))(R3Bm)](CF(3)SO(3))(3) (3), in which R3Bm=N[(CH(2))(2)NHCH(2)(C(6)H(4)-m)CH(2)NH(CH(2))(2)](3)N and dca=dicyanamido ligand (NCNCN(-)). The X-ray diffraction analysis reveals for both 1 and 3 a dinuclear entity in which the copper atoms are bridged by means of the -NCN- unit. The molar magnetic susceptibility measurements of 1-3 in the 2-300 K range indicate ferromagnetic coupling. The calculated J values, by using theoretical methods based on density functional theory (DFT) are in excellent agreement with the experimental data. Catalytic hydration of a nitrile to an amide functional group is assumed responsible for the formation of 3 from a mu(1,3)-dicyanamido ligand.     

Copper perchlorate and tetrafluoridoborate compounds with the ligand 1,4,5-triazanaphthalene. Gradual transformation of mononuclear Cu(II) compounds via polynuclear mixed-valence Cu(II)/Cu(I) species to dinuclear Cu(I); syntheses, characterizations and X-ray structures

When the ligand 1,4,5-triazanaphthalene (abbreviated as tan) is reacted with Cu(II) BF(4)(-) and ClO(4)(-) salts, a variety of mononuclear compounds has been found, all with the [Cu(tan)(4)] unit and varying amounts of weakly coordinating axial ligands and lattice solvents. Reproducible compounds formed include two purple compounds, analyzing as [Cu(tan)(4)](ClO(4))(2)(CH(3)OH)(2)(H(2)O) (1) and [Cu(tan)(4)](BF(4))(2)(CH(3)OH)(1.5)(H(2)O) (3), and two blue compounds, analyzing as [Cu(tan)(4)](ClO(4))(2)(H(2)O)(2) (2) and [Cu(tan)(4)](2)(BF(4))(2)(H(2)O)(2) (4). Upon standing at room temperature, red-coloured, mixed-valence dinuclear-based 3D coordination polymers are formed by conversion of the purple/blue products, of which [Cu(2)(tan)(4)](n)(BF(4))(3n) (5) and the isomorphic methanol-water adduct [Cu(tan)(4)](n)(BF(4))(3n)(CH(3)OH)(n)(H(2)O)(5n) (5A) are presented in this paper. In addition a fully reduced dinuclear Cu(I) compound of formula [Cu(2)(tan)(3)(ClO(4))(2)] (7) has been observed, and structurally characterized, as a rare three-blade propeller structure, with a Cu-Cu distance of 2.504 ?.     

Ni5, Ni8, and Ni10 clusters with 2,6-diacetylpyridine-dioxime as a ligand

In the present work, novel coordination possibilities for the system dapdoH(2)/Ni(II) (dapdoH(2) = 2,6-diacetylpyridine-dioxime) have been explored. Depending on the starting reagents and solution conditions, several clusters with nuclearities ranging from Ni(5) to Ni(10) were achieved and structurally characterized, namely, [Ni(5)(R-COO)(2)(dapdo)(2)(dapdoH)(2)(N(CN)(2))(2)(MeOH)(2)] in which R-COO(-) = benzoate (1) or 3-chlorobenzoate (2), [Ni(8)(dapdo)(4)(NO(3))(4)(OH)(4)(MeOH)(4)] (3), and [Ni(10)(dapdo)(8)(N(CN)(2))(2)(MeO)(MeOH)](NO(3)) (4). For the first time, pentadentate coordination for the dapdo(2-) ligand has been established. All compounds show a combination of square-planar and octahedrally coordinated nickel atoms. According to the Ni(2)(sp)Ni(3)(Oh) (1 and 2), Ni(4)(sp)Ni(4)(Oh) (3), and Ni(4)(sp)Ni(6)(Oh) (4) environments, these systems magnetically behave as trimer, tetramer, and hexanuclear clusters, respectively. dc magnetic measurements in the 2-300 K range of temperature reveal antiferromagnetic coupling for all compounds, and the correlation of the superexchange interaction with the torsion angles involving the oximato bridges is experimentally confirmed.     

Synthesis and characterization of novel 99gTc(V) and Re(V) complexes with water-soluble tetraaza diamido dipyridino ligands: single-crystal X-ray structural investigations of mono- and dinuclear complexes

Rhenium and technetium are known for their useful applications in nuclear medicine with similar properties. In this study, new diamido dipyridino (N(4)) water-soluble ligands (2-C(5)H(4)NCH(2)NHCO)(2)CH(2), 1 (L(1)H2), (2-C(5)H(4)NNHNHCO)(2)CH(2), 2, and [2-C(5)H(4)N(+)(O)(-)CH(2)NHCO](2)CH(2), 3, were synthesized. Reaction of L(1)H2 with ReOCl(3)(PPh(3))(2) resulted in the novel six-coordinated rhenium(V) complex, trans-ReO(L(1))(OEt), 4. The complex was characterized by spectroscopic methods, and its X-ray crystallographic analysis revealed that rhenium is coordinated to four nitrogen atoms of the ligand and to two oxygen atoms from the deprotonated ethanol and the oxo group respectively in a distorted octahedral geometry. In solution, complex 4 was transformed to a new complex 5, which was proved to be the dinuclear complex mu-oxo [ReO(L(1))](2)O. Reaction of 1 with [n-Bu(4)N][ReOCl(4)] resulted in the neutral complex 6, trans-[ReO(L(1))]Cl. Similarly, when ligand 1 was reacted with [n-Bu(4)N][(99g)TcOCl(4)], the neutral trans-[(99)TcO(L(1))]Cl complex 7 was formed, which upon dissolution transformed into a cationic complex 8, trans-[(99)TcO(L(1))(OH(2))](+)Cl(-). The single-crystal X-ray structure of 8 reveals that the coordination sphere about technetium is a distorted octahedron with four nitrogen atoms in the equitorial plane, while doubly bonded oxygen and coordinated water occupy the apical positions. Further dissolution of 8 resulted in the formation of dinuclear mu-oxo [TcO(L(1))](2)O, 9. This study shows that Tc and Re have similar metal core structures in solution for diamido dipyridino systems, besides similarity in geometrical structure, proved by the X-ray structures on the same ligands.     

Reactions of a platinum(III) dimeric complex with alkynes in water: novel approach to alpha-aminoketone, alpha-iminoketone, and alpha,beta-diimine via ketonyl-Pt(III) dinuclear complexes

Reaction of the platinum(III) dimeric complex [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(NO(3))(2)](NO(3))(2) (1), prepared in situ by the oxidation of the platinum blue complex [Pt(4)(NH(3))(8)((CH(3))(3)CCONH)(4)](NO(3))(5) (2) with Na(2)S(2)O(8), with terminal alkynes CH[triple bond]CR (R = (CH(2))(n)CH(3) (n = 2-5), (CH(2))(n)CH(2)OH (n = 0-2), CH(2)OCH(3), and Ph), in water gave a series of ketonyl-Pt(III) dinuclear complexes [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(2)COR)](NO(3))(3) (3, R = (CH(2))(2)CH(3); 4, R = (CH(2))(3)CH(3); 5, R = (CH(2))(4)CH(3); 6, R = (CH(2))(5)CH(3); 7, R = CH(2)OH; 8, R = CH(2)CH(2)OH; 9, R = (CH(2))(2)CH(2)OH; 10, R = CH(2)OCH(3); 11, R = Ph). Internal alkyne 2-butyne reacted with 1 to form the complex [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(CH(3))COCH(3))](NO(3))(3) (12). These reactions show that Pt(III) reacts with alkynes to give various ketonyl complexes. Coordination of the triple bond to the Pt(III) atom at the axial position, followed by nucleophilic attack of water and hydrogen shift from the enol to keto form, would be the mechanism. The structures of complexes 3.H(2)O, 7.0.5C(3)H(4)O, 9, 10, and 12 have been confirmed by X-ray diffraction analysis. A competitive reaction between equimolar 1-pentyne and 1-pentene toward 1 produced complex 3 and [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(2)CH(OH)CH(2)CH(2)CH(3))](NO(3))(3) (14) at a molar ratio of 9:1, suggesting that alkyne is more reactive than alkene. The ketonyl-Pt(III) dinuclear complexes are susceptible to nucleophiles, such as amines, and the reactions with secondary and tertiary amines give the corresponding alpha-amino-substituted ketones and the reduced Pt(II) complex quantitatively. In the reactions with primary amines, the once formed alpha-amino-substituted ketones were further converted to the iminoketones and diimines. The nucleophilic attack at the ketonyl group of the Pt(III) complexes provides a convenient means for the preparation of alpha-aminoketones, alpha-iminoketones, and diimines from the corresponding alkynes and amines.     

Structures and magnetism of {Ni2Na2}, {Ni4} and {Ni6(II)Ni(III)} 2-hydroxy-3-alkoxy-benzaldehyde clusters

Three polynuclear complexes, [NiNa(μ(1,1,1)-N(3))(μ-hmb)(2)(DMF)](2), (1), [Ni(4)(μ(3)-OMe)(4)(heb)(4)(MeOH)(1.05)(H(2)O)(2.95)], (2) and [Ni(III)(OH)(6)(hmb)(6)Ni(II)(6)]·(ClO(4))(3) (3) (Hhmb = 2-hydroxy-3-methoxy-benzaldehyde; Hheb = 2-hydroxy-3-ethoxy-benzaldehyde), were prepared by reaction of the appropriate ligand with nickel(II) perchloride hexahydrate under solvothermal conditions. All compounds were characterized by elemental analysis, IR spectroscopy and X-ray single-crystal diffraction. Compound 1 exhibits a centrosymmetric heterotetranuclear cluster which represents the first nickel complex to possess two connected face-sharing cubes structure {Ni(2)Na(2)N(2)O(4)}. Compound 2 has a tetranuclear Ni cluster with a cubane topology in which the Ni(II) and the oxygen atoms from the methanol ligands occupying alternate vertices of the cube. Compound 3 consisits of a mixed-valence [Ni(III)(OH)(6)(hmb)(6)Ni(II)(6)](3+) subunits and it represents the first nickel {Ni(II)(6)Ni(III)} complex to possess a planar hexagonal disc-like structure. The results show that the minor ligand modifications or solvent change have a key role in the structural control of the self-assembly process. Magnetic properties of 1-3 in the 300-2 K have been discussed. The {Ni(2)Na(2)} (1) and {Ni(4)} (2) core display dominant ferromagnetic interactions from the nature of the binding modes through μ(3)-N(3)(-) or μ(3)-OCH(3)(-), while {Ni(II)(6)Ni(III)} core (3) displays dominant anti-ferromagnetic interactions from the nature of the binding modes through μ(3)-OH(-).