Molecular architectures for trimetallic d/f/d complexes: structural and magnetic properties of a LnNi2 core

A series of cationic, trimetallic d/f/d complexes have been prepared which use a multidentate, macrocyclic amine phenol ligand to coordinate divalent first row d-block transition metal ions (TM) and lanthanides (Ln) ions in close proximity, desirable for magnetic studies. Isolable complexes of the d/f/d cluster compounds with the formula [Ln(TM)2(bcn)2]ClO4.nH2O, where H3bcn is tris-N, N', N'-(2-hydroxybenzyl)-1,4,7-triazacyclononane, TM = Zn(II) and Ni(II) and Ln = La(III), Nd(III), Gd(III), Dy(III), and Yb(III), were synthesized by a one-pot sequential reaction of stoichiometric amounts of H 3bcn with the TM(II) and Ln(III) metal ions. The spontaneously formed cationic complexes were characterized by a variety of analytical techniques including IR, NMR, +ESI-MS, and EA. The [TM(Hbcn)].nH2O and [TM3(bcn)2].nH2O complexes were also synthesized to probe the building blocks of the d/f/d coaggregated species. The solid-state X-ray crystal structures of [GdNi2(bcn)2(CH3CN)2]ClO4.CH3CN and [GdZn2(bcn)2(CH3CN)2]ClO4.CH3CN were determined to be nearly identical with each TM(II) encapsulated in an octahedral geometry by the N3O3 binding pocket of the bcn (3-) ligand. The eight coordinate Gd(III) was bicapped by two [TM(bcn)](-) moieties and coordinated by two solvent molecules. Because of the isostructurality of the [LnZn2(bcn)2]ClO4.nH2O and [LnNi2(bcn)2]ClO4.nH2O complexes, an empirical approach using the LnZn2 magnetic data was utilized to remove first-order anisotropic contributions from the LnNi2 species. Ferromagnetic spin interactions were determined for the [LnNi2(bcn)2]ClO4.nH2O complexes, where Ln = Gd(III), Dy(III), and Yb(III), while an antiferromagnetic exchange was observed for Ln = Nd(III).     

Synthesis and coordination chemistry of organoiridium complexes supported by an anionic tridentate ligand

Treatment of deprotonated N-(dimethylaminoethyl)-2-diphenylphosphinoaniline with bis(cyclooctene)iridium chloride dimer affords a thermally stable iridium(I) olefin complex. Infrared analysis of the corresponding monocarbonyl iridium(I) compound indicates a relatively electron rich metal center. Reaction of the iridium(I) cyclooctene complex with iodomethane effects oxidation of the metal yielding a five-coordinate iridium(III) methyl iodide complex which reversibly coordinates tetrahydrofuran. X-ray crystallography confirms coordination of ether to the iridium(III) methyl iodide complex and NMR spectroscopic experiments establish an equilibrium constant of 1.66(9) M for tetrahydrofuran binding. A five-coordinate iridium(III) dimethyl complex has also been prepared and characterized by X-ray diffraction. Hydrogenolysis of the dialkyl species permits identification of a short-lived classical iridium(III) dihydride complex.     

Synthesis,structural characterizations,spectroscopic and magnetic properties of MnII and MnIII complexes with an unprecedented bridging coordination mode of 2-salicylichydrazono-1,3-dithiolane ligand

Two new complexes [Mn^III(HL)₂(acac)] and [Mn^II(HL)₂]_n have been obtained by reacting manganese(III) acetylacetonate monohydrate or manganese(II) chloride monohydrate with 2-salicylichydrazono-1,3-dithiolane ligand (H₂L). Both compounds have been fully characterized by spectroscopic methods and single crystal X-ray diffraction. In the solid state, the molecular packing are described and discussed in term of weak H-bonds and short contacts. The unprecedented bridging coordination mode of this ligand lead to the first 2-salicylichydrazono-1,3-dithiolane-bridged coordination polymer [Mn^II(HL)₂]_n. The EPR spectrum of this compound was obtained with g ≈ 2.07, corresponding to a manganese ion (+II) in octahedral high-spin coordination sphere. The Mn^II complex exhibit paramagnetic behavior corresponding to quasi-isolated metal centers.     

Electronic and magnetic properties of bimetallic ytterbocene complexes: the impact of bridging ligand geometry

Bimetallic ytterbocene complexes with bridging N-heterocylic ligands have been studied extensively in recent years due to their potential applications ranging from molecular wires to single-molecule magnets. Herein, we review our recent results for a series of ytterbocene polypyridyl bimetallic complexes to highlight the versatility and tunability of these systems based on simple changes in bridging ligand geometry. Our work has involved structural, electrochemical, optical, and magnetic measurements with the goal of better understanding the electronic and magnetic communication between the two ytterbium metal centers in this new class of bimetallics.     

Supramolecular and coordination polymer complexes supported by a tripodal tripyridine ligand containing a 1,3,5-triethylbenzene spacer

By By combining a tripodal tripyridine ligand containing a 1,3,5-triethylbenzene spacer (L) with several divalent transition-metal chlorides, we have selectively prepared a capsule-type supramolecular complex, [PdII3(L)2Cl6] x 2H2O, and one-dimensional (1D) coordination polymer complexes, ([CuII(L)Cl2] x C2H5OH)n, ([CoII3(L)2Cl6] x 2CH2Cl2)n, and ([ZnII3(L)2Cl6] x 2H2O)n, with a zigzag polymer chain, a linear polymer chain, and a ladder polymer chain structure, respectively. All the structures were established in detail by single-crystal X-ray diffraction analysis, and the factors inducing the structural differences among the complexes are discussed by taking account of the differences in coordination geometry (square planar vs tetrahedral) as well as metal-ligand binding strength in the complexes.     

Dinuclear nickel complexes with a Ni(2)O(2) core: a structural and magnetic study

The acetylacetonate complexes [Ni(2)L(1)(acac)(MeOH)] x H(2)O, 1 x H(2)O and [Ni(2)L(3)(acac)(MeOH)] x 1.5H(2)O, 2 x 1.5H(2)O (H(3)L(1) = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine and H(3)L(3) = (2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) were prepared and fully characterised. Their crystal structures show that they are dinuclear complexes, extended into chains by hydrogen bond interactions. These compounds were used as starting materials for the isolation of the corresponding [Ni(2)HL(x)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x n MeOH and [Ni(2)HL(x)(O(2)CCH(2)CO(2))(H(2)O)]x nH(2)O dicarboxylate complexes (x = 1, 3; n = 1-3). The crystal structures of [Ni(2)HL(1)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x MeOH, 3 x MeOH, [Ni(2)HL(3)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x 3 MeOH, 4 x 3 MeOH and [Ni(2)HL(1)(O(2)CCH(2)CO(2))(H(2)O)] x 2.5H(2)O x 0.25 MeOH x MeCN, 5 x 2.5H(2)O x 0.25 MeOH x MeCN, were solved. Complexes 3-5 show dinuclear [Ni(2)HL(x)(dicarboxylate)(H(2)O)] units, expanded through hydrogen bonds that involve carboxylate and water ligands, as well as solvate molecules. The variable temperature magnetic susceptibilities of all the complexes show an intramolecular ferromagnetic coupling between the Ni(II) ions, which is attempted to be rationalized by comparison with previous results and in the light of molecular orbital treatment. Magnetisation measurements are in accord with a S = 2 ground state in all cases.     

Tantalum amido and imido complexes supported by tris[(2-indolyl)methyl]amine,a tetradentate trianionic ligand with reduced pi-donor character

Tris[(2-indole)methyl]amine, N(CH2inH)3, may be readily obtained by reaction of methyl 2-bromomethyl-1-indolecarboxylate with NH3 followed by deprotection with NaOMe/MeOH. In its deprotonated form, [N(CH2in)3]3- is an efficient tetradentate trianionic ligand for tantalum, as illustrated by the isolation and structural characterization of [eta 4-N(CH2in)3]Ta(NAr)(NMe2H) (Ar = 2,6-C6H3Pri2), [eta 4-N(CH2in)3]Ta(NMe2)2 and [eta 4-N(CH2in)3]Ta(NMe2)Cl. The [N(CH2in)3]3- ligand has a structural similarity to that of [N(CH2CH2NR)3]3-, but differs electronically from the latter due to its reduced pi-donor capability, a direct result of the nitrogen being a component of the aromatic pi-system of the indolyl fragment.     

The effect of ligand charge on the coordination geometry of an Fe(III)ion: five- and six-coordinate Fe(III) complexes of tris(2-benzimidazolylmethyl)amine

By using the tripodal tetradentate ligand tris(2-benzimidazolylmethyl)amine (H(3)ntb), which can have several charge states depending on the number of secondary amine protons, mononuclear octahedral and dinuclear trigonal bipyramidal Fe(III) complexes were prepared. The reaction of mononuclear octahedral [Fe(III)(H(3)ntb)Cl(2)]ClO(4), 1, with 3 equiv of sec-butylamine in methanol led to the formation of mononuclear cis-dimethoxo octahedral Fe(III)(H(2)ntb)(OMe)(2), 2. One equivalent of the sec-butylamine was used to generate the monoanionic H(2)ntb(-) ligand where one of the three amines in the benzimidazolyl groups was deprotonated. The remaining 2 equiv were used to generate two methoxides that were coordinated to the octahedral Fe(III) ion in a cis fashion as demonstrated by the chlorides in 1. Reaction of 1 with excess (7 equiv) sec-butylamine generated the doubly deprotonated dianionic Hntb(2-) that stabilized the dinuclear mu-oxo Fe(III)(2)O(Hntb)(2), 3, adopting a five-coordinate trigonal bipyramidal geometry. The magnetic data for 3 are consistent with the antiferromagnetically coupled Fe(III) (S = 5/2) sites with the coupling constant J = -127 cm(-1).     

Tuning tetranuclear manganese-oxo core electronic properties: adamantane-shaped complexes synthesized by ligand exchange

A series of adamantane-shaped [Mn4O6]4+ aggregates has been prepared. Ligand substitution reactions of [Mn4O6(bpea)4](ClO4)4 (1) with tridentate amine and iminodicarboxylate ligands in acetonitrile affords derivative clusters [Mn4O6(tacn)4](ClO4)4 (4), [Mn4O6(bpea)2(dien)2](ClO4)4)(5), [Mn4O6(Medien)4](ClO4)4 (6), [Mn4O6(tach)4](ClO4)4 (7), [Mn4O6(bpea)2(me-ida)2] (8), [Mn4O6(bpea)2(bz-ida)2] (9), [Mn4O6(bpea)2((t)bu-ida)2] (10), and [Mn4O6(bpea)2((c)pent-ida)2] (11) generally on the order of 10 min with retention of core nuclearity and oxidation state. Of these complexes, only 4 had been synthesized previously. Characterization of two members of this series by X-ray crystallography reveals that compound 7 crystallizes as [Mn4O6(tach)4](ClO4)4 x 3CH3CN x 4.5H2O in the cubic space group Fmm and compound 11 crystallizes as [Mn4O6(bpea)2((c)pent-ida)2].7MeOH in the monoclinic space group C2/c. The unique substitution chemistry of 1 with iminodicarboxylate ligands afforded asymmetrically ligated complexes 8-11, the mixed ligand nature of which is most likely unachievable using self-assembly synthetic methods. A special feature of the iminodicarboxylate ligand complexes 8-11 is the substantial site differentiation of the oxo bridges of the [Mn4O6]4+ cores. While there are four site-differentiated oxo bridges in 8, the solution structural symmetry of 8H+ reveals essentially a single protonation isomer, in contrast to the observation of two protonation isomers for 1H+, one for each of the site-differentiated oxo bridges in 1. Magnetic susceptibility measurements on 4, 7, 8, and 9 indicate that each complex is overall ferromagnetically coupled, and variable-field magnetization data for 7 and 9 are consistent with an S = 6 ground state. Electrochemical analysis demonstrates that ligand substitution of bpea affords accessibility to the Mn(V)(Mn(IV))3 oxidation state.     

Quantum-chemical modeling of metal coordination compounds with photoswitchable magnetic properties controlled by ligand rearrangements

The complexation of chromenes with transition metal ions was studied using the B3LYP*/6-311++G(d,p) method. We are the first to show that transformation of the spin state of a transition metal complex through an LD LISC mechanism can be achieved by means of configurational isomerization of the metal-chelate coordination site induced by ligand rearrangement.     

Sigma-organyl complexes of ruthenium and osmium supported by a mixed-donor ligand

A series of vinyl, aryl, acetylide and silyl complexes [Ru(R)(kappa2-MI)(CO)(PPh3)2] (R = CH=CH2, CH=CHPh, CH=CHC6H4CH3-4, CH=CH(t)Bu, CH=2OH, C(C triple bond CPh)=CHPh, C6H5, C triple bond CPh, SiMe2OEt; MI = 1-methylimidazole-2-thiolate) were prepared from either [Ru(R)Cl(CO)(PPh3)2] or [Ru(R)Cl(CO)(BTD)(PPh3)2](BTD = 2,1,3-benzothiadiazole) by reaction with the nitrogen-sulfur mixed-donor ligand, 1-methyl-2-mercaptoimidazole (HMI), in the presence of base. In the same manner, [Os(CH=CHPh)(kappa2-MI)(CO)(PPh3)2] was prepared from [Os(CH=CHPh)(CO)Cl(BTD)(PPh3)2]. The in situ hydroruthenation of 1-ethynylcyclohexan-1-ol by [RuH(CO)Cl(BTD)(PPh3)2] and subsequent addition of the HMI ligand and excess sodium methoxide yielded the dehydrated 1,3-dienyl complex [Ru(CH=CHC6H9)(kappa2-MI)(CO)(PPh3)2]. Dehydration of the complex [Ru(CH=CHCPh2OH)(kappa2-MI)(CO)(PPh3)2] with HBF4 yielded the vinyl carbene [Ru(=CHCH=CPh2)(kappa2-MI)(CO)(PPh3)2]BF4. The hydride complexes [MH(kappa2-MI)(CO)(PPh3)2](M = Ru, Os) were obtained from the reaction of HMI and KOH with [RuHCl(CO)(PPh3)3] and [OsHCl(CO)(BTD)(PPh3)2], respectively. Reaction of [Ru(CH=CHC6H4CH3-4)(kappa2-MI)(CO)(PPh3)2] with excess HC triple bond CPh leads to isolation of the acetylide complex [Ru(C triple bond CPh)(kappa2-MI)(CO)(PPh3)2], which is also accessible by direct reaction of [Ru(C triple bond CPh)Cl(CO)(BTD)(PPh3)2] with 1-methyl-2-mercaptoimidazole and NaOMe. The thiocarbonyl complex [Ru(CPh = CHPh)Cl(CS)(PPh3)2] reacted with HMI and NaOMe without migration to yield [Ru(CPh= CHPh)(kappa2-MI)(CS)(PPh3)2], while treatment of [Ru(CH=CHPh)Cl(CO)2(PPh3)2] with HMI yielded the monodentate acyl product [Ru{eta(1)-C(=O)CH=CHPh}(kappa2-MI)(CO)(PPh3)2]. The single-crystal X-ray structures of five complexes bearing vinyl, aryl, acetylide and dienyl functionality are reported.     

Solid-state and solution properties of cationic lanthanide complexes of a new neutral heptadentate N4O3 tripodal ligand

The synthesis of the potentially heptadentate ligand tris[6-((2-N,N-diethylcarbamoyl)pyridyl)methyl]amine, tpaam, containing three pyridinecarboxamide arms connected to a central nitrogen is described. Lanthanide complexes of this ligand are prepared and characterized. The crystallographic structure of the complexes of three lanthanide ions (La, Nd, Lu) is determined. The lanthanide(III) complexes of tpaam crystallize as monomeric species (in the presence of chloride or iodide counterions) in which the ligand tpaam acts as a N4O3 donor. The crystal structures presented here show that the Ln[bond]O and Ln[bond]N(pyridyl) distances in the complexes of tpaam are similar to those found for the tpaa complexes (H(3)tpaa = alpha,alpha',alpha' '-nitrilotri(6-methyl-2-pyridinecarboxylic acid) despite the difference in charge. A lengthening of the Ln[bond]N(apical) distance is observed in the tpaam complexes compared to the tpa (tris[(2-pyridyl)methyl]amine) complexes which is more marked for larger lanthanides than for smaller ones. The solution structures of the tpaam complexes were analyzed across the 4f series and compared to the solution structures of the lanthanide complexes of the tetradentate ligand tpa. Proton NMR studies are in agreement with the presence of C(3)(v) symmetric solution species for both ligands. For the larger lanthanides, the cation moves away from the apical nitrogen compared to the position occupied in tpa complexes, whereas for the smaller lanthanides, the metal ion is located in a similar position for the two ligands. Quite surprisingly, the formation constant of the Eu(tpaam)Cl(3) complex in D(2)O at 298 K (log beta(110) = 2.34(4)) is very similar to the one reported for Eu(tpa)Cl(3) (log beta(110) = 2.49(4) at 298 K in D(2)O) indicating that the addition of three amide groups to the ligand tpa does not lead to any increase in stability of the lanthanide complexes of tpaam compared to those of tpa.     

Coaggregation of paramagnetic d- and f-block metal ions with a podand-framework amine phenol ligand

This report covers initial studies in the coaggregation of nickel (Ni2+) and lanthanide (Ln3+) metal ions to form complexes with interesting structural and magnetic properties. The tripodal amine phenol ligand H3tam (1,1,1-tris(((2-hydroxybenzyl)amino)methyl)ethane) is shown to be particularly accommodating with respect to the geometric constraints of both transition and lanthanide metal ions, forming isolable complexes with both of these ion types. In the solid-state structure of [Ni(H2tam)(CH3CN)]PF6.2.5CH3CN.0.5CH3OH (1), the Ni(II) center has a distorted octahedral geometry, with an N3O2 donor set from the [H2tam]- ligand and a coordinated solvent (acetonitrile) occupying the sixth site. The reaction of stoichiometric amounts of H3tam with the Ni(II) ion in the presence of lanthanide(III) ions provides [LnNi2(tam)2]+ cationic complexes which contain coaggregated metal ions. These complexes are isolable and have been characterized by a variety of analytical techniques, with mass spectrometry proving to be particularly diagnostic. The solid-state structures of [LaNi2(tam)2(CH3OH)1/2(CH3CH2OH)1/2(H2O)]ClO4.0.5CH3OH.0.5CH3CH2OH.4H2O (2), [DyNi2(tam)2(CH3OH)(H2O)]ClO4.CH3OH. H2O(6), and [YbNi2(tam)2(H2O)]ClO4.2.58H2O(9) have been determined. Each complex contains two octahedral Ni(II) ions, each of which is encapsulated by the ligand tam3- in an N3O3 coordination sphere; each [Ni(tam)]-unit caps the lanthanide(III) ion via bridging phenoxy oxygen donor atoms. In 2, La3+ is eight-coordinated, while in 6, Dy(III) is seven- (to "weakly eight-") coordinated, and Yb(III) in 9 has a six-coordination environment. The complexes are symmetrically different, 2 possessing C2 symmetry and 6 and 9 having C1 symmetry. Magnetic studies of 2, 6, and 9 indicate that antiferromagnetic exchange coupling between the Ni(II) and Ln(III) ions increases with decreasing ionic radius of Ln(III).     

Metalloantimalarials: targeting of P. falciparum strains with novel iron(III) and gallium(III) complexes of an amine phenol ligand

Emergence of chloroquine (CQ)-resistant Plasmodium falciparum strains necessitates discovery of potent and inexpensive antimalarial drugs. The high cost of new drugs negatively impacts their access and distribution in the regions of the world with scarce economic resources. While exploring structure-activity relationships, using gallium(III) as a surrogate marker for iron(III), we found cationic, and moderately hydrophobic, compounds, [[1,12-bis(2-hydroxy-3-ethyl-benzyl)-1,5,8,12-tetraazadodecane]metal(III)](+) (metal = Fe(III) and Ga(III); [Fe-3-Eadd](+), 3; [Ga-3-Eadd](+), 4), that possessed antimalarial activity. Crystal structure analyses revealed octahedral geometry for these complexes. The RP-HPLC analysis, after incubation in PBS or HEPES buffer (pH 7.4) at 37 degrees C for 3 days, detected only parental compounds thereby providing evidence for stability under physiological conditions. Both 3 and 4 demonstrated promising half-maximum inhibitory concentration (IC(50)) values of approximately 80 and 86 nM in the CQ-sensitive HB-3 line, respectively. However, both 3 and 4 were found to possess elevated IC(50) values of 2.5 and 0.8 microM, respectively, in the CQ-resistant Dd2 line, thus displaying preferential cytotoxicity toward the CQ-sensitive HB3 line. In cultured parasites, 3 and 4 targeted hemozoin formation. Thus, these compounds acted similarly to chloroquine with regard to action and resistance, despite the lack of structural similarity to quinolines. Finally, similarity in coordination chemistry, stability, and antimalarial cytotoxicity profiles indicated that gallium(III) ion can serve as a template for iron(III) in structure elucidation of active molecules in solution.     

The first coordination complexes of selenones: a structural comparison with complexes of sulfones

Reactivity of the two classes of very weak donors R(2)XO(2) (X = S, R = Me (1) and Ph (2); X = Se, R = Me (3) and Ph (4)) have been studied. Coordination properties of sulfones and selenones in solution and in the gas phase have been compared for the first time using a model bidentate metal complex, [Rh(2)(O(2)CCF(3))(4)]. Two coordination modes, bridging mu(2)-O,O' and terminal eta(1)-O, have been detected. These types of binding were realized in two series of sulfone and selenone metal complexes, polymeric mono-adducts [Rh(2)(O(2)CCF(3))(4).(R(2)XO(2))]( infinity ) (X = S, R = Me (1a); R = Ph (2a); X = Se, R = Ph (4a)) and discrete bis-adducts [Rh(2)(O(2)CCF(3))(4).(R(2)XO(2))(2)] (X = S, R = Ph (2b); X = Se, R = Me (3b)). The compositions and structures of new compounds have been confirmed by NMR and IR spectroscopy, chemical analyses, and X-ray diffraction studies. Compounds 3b and 4a are the first crystallographically characterized metal complexes having selenone ligands coordinated to the metal centers. Preparation and X-ray study of analogous metal complexes of sulfone and selenone ligands allow, for the first time, tracking the structural changes induced by metal coordination. In addition, the X-ray structure of dimethyl selenone, Me(2)SeO(2) (3), an analogue of Me(2)SO(2), has been determined. Geometries of coordinated sulfone and selenones ligands have been compared with those of the corresponding "free" molecules.     

Binuclear copper(II) complexes with N4O3 coordinating heptadentate ligand: synthesis, structure, magnetic properties, density-functional theory study, and catecholase activity

The N4O3 coordinating heptadentate ligand afforded binuclear complex [Cu 2(H 2L)(mu-OH)](ClO4)2 (1) and [Cu2(L)(H2O)2]PF6 (2). In complex 1, two copper ions are held together by mu-phenoxo and mu-hydroxo bridges, whereas in complex 2, the copper centers are connected only by a mu-phenoxo bridge. In 1, both the Cu(II) centers have square pyramidal geometry (tau=0.01-0.205), whereas in the case of 2, one Cu(II) center has square pyramidal (tau=0.2517) and other one has square based pyramidal distorted trigonal bipyramidal (tau=0.54) geometry. Complexes 1 and 2 show an strong intramolecular and very weak antiferromagnetic interaction, respectively. Density-functional theory calculations were performed to establish the magneto structural correlation between the two paramagnetic copper(II) centers. Both of the complexes display a couple of one-electron reductive responses near -0.80 and -1.10 V. The complexes show significant catalytic activity at pH 8.5 on the oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC) to 3,5-di- tert-butylquinone (3,5-DTBQ), and the activity measured in terms of kcat=29-37 h(-1).     

Transition metal dinitrogen complexes supported by a versatile monoanionic [N2P2] ligand

By adjusting to the steric and electronic requirements of differing metal centers, the new multidentate monoanionic ligand [N(2)P(2)] has demonstrated a unique ability to stabilize a range of transition metal-dinitrogen complexes in a variety of oxidation states and coordination geometries.     

Microwave assisted synthesis and magnetic properties of octanuclear and enneanuclear Ni(II) complexes: an unprecedented coordination mode for the NO(2)(-) ligand

Octanuclear and enneanuclear Ni(II) complexes have been synthesized using a microwave reactor. The octanuclear complex Ni(8) presents a new triply bridging coordination mode for the NO(2)(-) ligand.     

Mononuclear and binuclear iron(III) complexes incorporating N4O3 coordinating heptadentate ligand: Synthesis,structure and magnetic properties

The N₄O₃ coordinating heptadentate ligand afforded the mononuclear [Fe^III(HL)][BPh₄] (1) and binuclear [Fe₂^IIIL(OAc)₂][BPh₄] (2) complexes. In complex 1, the ligand binds in a trianionic N₂O₃ fashion whereas in the case of 2 the ligand binds in the trianionic N₄O₃ form in which the iron ions are held together by μ-phenoxo and bis μ-acetato bridges. In 1, the Fe(III) center has a trigonal bipyramidal geometry (τ = 0.84) whereas in 2 both the Fe(III) centers have a distorted octahedral geometry. Complex 2 shows an intramolecular weak antiferromagnetic interaction. Gas phase geometry optimizations have been performed using density functional theory without any symmetry constraints. The gas phase optimized structures agree well with the X-ray structure.