Alkoxo Bridges Research Articles

Magneto‐Structural and Computational Study of a Tetranuclear Copper Complex Displaying Carbonyl–π Interactions

A tetranuclear copper(II) complex (1) was synthesized using 2-hydroxy-N-(quinolin-8-yl)acetamide ligand. Single-crystal X-ray diffraction studies revealed that the complex consists of a distorted Cu 4 O 4 core in which the four copper(II) ions are linked by alkoxo bridges. X-ray analysis also evidenced intra-molecular noncovalent carbonyl-π interactions. Those interactions that are encountered between lone-pair electrons (of the amide oxygen atoms here) and π* orbitals of aromatic rings,

Alkyl chain length effect on construction of copper(II) complexes with tridentate Schiff base ligand and DNA interaction

Two tridentate Schiff base ligands were synthesized by condensation of equimolar amounts of benzoylacetone and 2-amino-1-ethanol or 3-amino-1-propanol, H2L1 and H2L2, respectively. The reaction of the Schiff base ligands with Cu(CH3COO)2 in methanol leads to (CuL1)4, 1 and (CuL2)2, 2. In the tetranuclear cubane species, the tridentate H2L has both a chelating and a bridging mode, after double deprotonation of the enolic OH groups. The copper(II) centers are five-coordinate with a NO4 donor set from the ligands. The coordination geometry around each copper ion is essentially square pyramidal with one nitrogen and two oxygens from one ligand and two oxygens of adjacent ligands from the next unit of the cubane. In dinuclear 2, H2L2 has chelating and bridging modes after double deprotonation of the enolic OH groups. The dianionic form of the Schiff base coordinates forming a six-membered chelate ring with Cu(II). Two such monomeric CuL2 entities are eventually linked through the alkoxo bridges to produce dinuclear 2. The absorption spectra strongly suggest that 2 interacts with CT-DNA. Both 1 and 2 appear to be more efficient than the parent compound in DNA cleavage.

Tuning of Hula-Hoop Coordination Geometry in a Dy Dimer

The reaction of DyCl3 with hydrazone Schiff base ligands and sodium acetate in the presence of triethylamine (Et3N) as base affords two dysprosium dimers: [Dy2(HL1)2(OAc)2(EtOH)(MeOH)] (1) and [Dy2(L2)2(OAc)2(H2O)2]·2MeOH (2). The DyIII ions in complexes 1 and 2 are linked by alkoxo bridges, and display “hula hoop” coordination geometries. Consequently, these two compounds show distinct magnetic properties. Complex 1 behaves as a field-induced single molecule magnet (SMM), while typical SMM behavior was observed for complex 2. In addition, comparison of the structural parameters among similar Dy2 SMMs with hula hoop-like geometry reveals the significant role played by coordination geometry and magnetic interaction in modulating the relaxation dynamics of SMMs.

Anion and solvent effects on the coordination behavior of N-(2-pyridinylmethylene)benzoylhydrazone with copper(II): synthesis and structural characterization

The Cu(II) complexes [Cu(HL)Cl2], 1; [Cu(HL)(NO3)(H2O)]NO3, 2a; [Cu(L)(NO3)]2·C3H8O, 2b; [Cu(L)(μ1,1–N3)]2, 3; [Cu(L)(Br)]2, 4; [(H2O)CuL(μ-SO4)CuL], 5a; [CuL(μ-SO4)CuL]·H2O, 5b and [Cu(L)(CH3COO)]2, 6, where HL is a benzoylhydrazone tridentate Schiff base, have been synthesized and characterized by elemental analysis, FTIR, and UV–vis. The structures of 2a, 2b, 3, 4, 5a, and 5b have been determined by single-crystal X-ray diffraction analyses. In 2a, the benzoylhydrazone ligand is neutral and coordinates in its keto form and copper(II) has a distorted octahedral geometry. In dinuclear 2b, 3, 4, 5a, and 5b, there are bridging counter anions and the benzoylhydrazone ligand is monoanionic, coordinating in its enol form. In 5a and 5b, the enolic ligand also supplies a bridging alkoxo to the adjacent copper ion. In 5a, one of the two copper ions is five-coordinate in a distorted square pyramidal geometry, while the other copper ion has an additional water bonded to it in a distorted octahedral geometry. In 5b, both copper ions are five-coordinate with distorted square pyramidal geometries.

New Zn(II) Coordination Polymers Constructed from Amino-Alcohols and Aromatic Dicarboxylic Acids: Synthesis, Structure, Photocatalytic Properties, and Solid-State Conversion to ZnO

Four new coordination polymers have been obtained solvothermally from the reactions of Zn(NO3)2·6H2O with 1,2-, 1,3-, or 1,4-benzedicarboxylic acids in the presence of various amino-alcohols: 1∞[Zn2(Htea)2(1,2-bdc)] (1), 1∞[Zn(H3tris)(1,3-bdc)(CH3OH)] (2), 3∞[Zn5(Htea)2(1,3-bdc)3(H2O)]·2.6H2O (3), and 3∞[Zn3(H2dea)2(1,4-bdc)3] (4) (H3tea = triethanolamine, H3tris = tris(hydroxymethyl)aminomethane, H2dea = diethanolamine, 1,2-H2bdc =1,2-benzenedicarboxylic acid, 1,3-H2bdc =1,3-benzenedicarboxylic acid, and 1,4-H2bdc =1,4-benzenedicarboxylic acid). Their crystal structures, thermogravimetric analyses, solid-state transformation to ZnO and characterization of the resultant zinc oxide particles are reported. Compounds 1 and 2 show three-dimensional (3D) supramolecular architectures, generated from the interconnection of the zigzag (in 1) and respectively the linear (in 2) chains through hydrogen bonding interactions. The crystal structure of 3 revealed the presence of five different types of zinc atoms that are successively linked through carboxilato or alkoxo bridges in a helicoidal chain running along the crystallographic a axis. Both right-handed (P) and left-handed (M) helices are present in the crystal, and they are alternately interconnected by pairs of isophthalato bridges, resulting in channels of hexagonal shape, filled with water molecules. Compound 4 has a 3D structure in which linear centrosymmetric {Zn3(H2dea)2}6+ nodes are joined by terephthalate bridges. Owing to its porous network, compound 3 was tested in two selective reactions: photooxidation of phenol to hydroquinone and aerobic photooxidative condensation of benzylamine to N-benzylidenebenzylamine.

Syntheses and structures of tetranuclear Zn(II) complexes with in situ generated macrocyclic Schiff base ligands: Applications in Zn2+ sensing

Abstract Three novel Zn(II) complexes, [Zn 4 L 1 Cl 4 ]·3H 2 O ( 1 ), [Zn 4 L 2 Cl 4 ]·2DMF ( 2 ) and [Zn 4 L 3 Cl 4 ]·H 2 O ( 3 ), have been synthesized and structurally characterized. In these complexes, interesting 32-membered dodecadentate macrocyclic ligands were generated in situ by ‘2 + 2’ type condensation reactions between a tetraamine and various dialdehydes. All the complexes are isostructurally tetranuclear Zn(II) complexes, containing endogenous alkoxo and phenoxo bridges. Applications of the macrocyclic ligands as Zn 2+ sensors have been investigated. Take H 4 L 1 for example, it exhibits a 4-fold fluorescence enhancement upon the addition of 2 equiv. of Zn 2+ in MeOH.

A synthetic quest for tris(imidazolyl) carboxylates and their metal complexes: active site models for quercetin 2,3-dioxygenases and other non-heme redox metalloenzymes

Synthetic routes to tris(imidazolyl)carboxylate ligands and representative metal complexes are reported, which provide more accurate active site models for several classes of redox metalloenzymes. In the first route a hydroxypivalate ester is converted in four regioselective steps to an imidazole diester 4; this is then converted to tris(imidazolyl)carboxylic acid ligand 9, featuring regiospecific double addition of an N-protected lithio-imidazole to an imidazole diester 8. Ligand 9 forms a Co(III) complex, (9)(9-H)Co (10), characterized by X-ray diffraction, coordinated via two imidazole units and the carboxylate. A second route was developed, which provides more soluble ligands that are less prone to form oligomeric complexes. It utilizes addition of the Grignard reagent from 4-iodo-2-isopropylimidazole 12 to an imidazole diester 13, producing atropisomeric tris(imidazolyl)carbinol esters 15M. Treatment of 15M with [Cu(CH3CN)4]PF6 gives a trinuclear complex 16 having alkoxide bridges between neighboring Cu atoms. A third route avoids the bridging alkoxo groups by reduction of tris(imidazolyl)carbinol 15M to the tris(imidazolyl)methane ester 17, which is hydrolyzed to the tris(imidazolyl)methane carboxylic acid 11a. This ligand reacts with [Cu(CH3CN)4]PF6 to produce dinuclear complex [(11a-H)2Cu2](PF6)2 (18), whose X-ray crystal structure shows each copper in a distorted square pyramidal geometry with coordination to the three imidazoles and two bridging carboxylate oxygens. Complex 18 is geometrically similar to the active site copper in quercetin 2,3-dioxygenase.

Synthesis, crystal structures and magnetic properties of bis(μ-dialkoxo)-bridged linear trinuclear copper(ii) complexes with aminoalcohol ligands: a theoretical/experimental magneto–structural study

The bis(μ-dialkoxo)-bridged trinuclear copper(II) complexes [Cu(3)(ap)(4)(ClO(4))(2)EtOH] (1), [Cu(3)(ap)(4)(NO(3))(2)] (2), [Cu(3)(ap)(4)Br(2)] (3) and [Cu(3)(ae)(4)(NO(3))(2)] (4) (ae = 2-aminoethanolato and ap = 3-aminopropanolato) have been synthesised via self-assembly from chelating aminoalcohol ligands with the corresponding copper(II) salts. The complexes are characterised by single-crystal X-ray diffraction analyses and variable temperature magnetic measurements. The crystal structures of complexes 1-4 consist of slightly bent linear or linear trinuclear [Cu(3)(aa)(4)](2+) (aa = aminoalcoholato) units to which the perchlorate, nitrate or bromide anions are weakly coordinated. The adjacent trinuclear units of 1-4 are connected together by hydrogen bonds and bridging nitrate or bromide anions resulting in the formation of 2D layers. Magnetic studies of 1, 2 and 4 show that J values vary from -379 to +36.0 cm(-1) as the Cu-O-Cu angle (θ) and the out-of-plane shift of the carbon atom of the bridging alkoxo group (τ) vary from 103.7 to 94.4° and from 0.9 to 35.5°, respectively. Magnetic exchange coupling constants calculated by DFT methods are of the same nature and magnitude as the experimental ones. For complexes 1, 2 and 4, which have complementarity effects between the θ and τ angles (small θ values are associated with large τ values and vice versa), an almost linear relationship between the calculated J values with θ angles could be established, thus supporting that the θ and τ angles are the two key structural factors that determine the magnetic exchange coupling for such a type of compounds. Complex 3 does not obey this linear correlation because of the existence of counter-complementarity effects between these angles (small θ values are associated with small τ values and vice versa). It is of interest that the theoretical calculations for the magnetic exchange interaction between next-nearest neighbours indicate that the usual approximation in experimental studies of neglecting the magnetic coupling between the next-nearest neighbours in linear trinuclear complexes could lead to considerable errors, especially when J(1) and J(2) are of the same order of magnitude as J(3).

Synthesis and Crystal Structure of Bis(μ3-4-Oxapentan-2-onato)-Tetrakis(μ2-4-Oxapentan-2-onato)-Tetra-Magnesium Dichloride Dichloromethane

A new magnesium alkoxide which posses centrosymmetric tetranuclear structure derived from 1-methoxy-2-propanol, a functionalized alcohol containing asymmetric carbon. X-ray analysis of single crystal shows an open dicubane-like structure with triple-bridging alkoxo groups between alternating five- and six-coordinated magnesium atoms. There are six alkoxo bridging groups in which two of them bridge three metal centers and the other four bridge two. All of the etheric-oxygens are coordinated to magnesium and provide a rigid structure. Two chlorine atoms are bonded to five-coordinated magnesium. This compound crystallizes in the monoclinic system with a = 10.040(6) Ǻ, b = 14.004(9) Ǻ, c = 15.344(5) Ǻ, β = 95.55(9)˚, Z = 2 and V = 2147 Ǻ3 in the space group of P21/n.

A zipper-like double chain coordination polymer constructed from a novel pseudo-macrocyclic binuclear Cu(II) complex

Abstract A novel coordination polymer [Cu2(HL)(CH3OH)(ClO4)]n(ClO4)n (1) has been synthesized from a multihydoxy Schiff base ligand, 1,3-bis(salicylidene iminoethylamino)-2-propanol (H3L). Single crystal X-ray diffraction analyses reveal that the coordination polymer is comprised of binuclear units, wherein the copper centers are bridged by a single alkoxo group, with a large bridging angle of 135.06°. By the linkage of an intramolecular hydrogen bond, an interesting pseudo-macrocyclic structure is formed. The binuclear moieties are assembled into a 1-D chain by the linkage of axially coordinated ClO4− anions, and the 1-D chains are further connected via intermolecular C-H⋅⋅⋅π stacking interactions, affording a zipper-like double chain supramolecular structure. Variable-temperature magnetic data measurements and analyses show the existence of strong antiferromagnetic interaction between the copper centers within the binuclear unit, mediated by the single alkoxo bridge with a − 2J value of 545 cm− 1.

Self assembly of asymmetric tetranuclear Cu(II) [2 × 2] grid-like complexes and of a dinuclear Ni(II) complex from pyridyl-phenol Schiff base ligands

Self assembly of N-salicylidene 2-aminopyridine ( L1H) with Cu(NO 3) 2·3H 2O affords [Cu 4( L1) 4(NO 3) 3(CH 3OH)][Cu( L1)(NO 3) 2](2-aminopyridinium)(NO 3)·5CH 3OH ( 1) which is composed of an asymmetric [2 × 2] grid-like cationic complex that co-crystallizes with a Cu(II) mononuclear anion. This remarkable tetranuclear unit presents three penta-coordinated and one hexa-coordinated Cu(II) sites. This quadruple helicate structure reveals strong anti-ferromagnetic coupling ( J = −340(2) cm −1) between Cu(II) ions through a double alkoxo bridge. Reacting L1H with Cu(NO 3) 2·3H 2O in slightly different conditions affords however a more symmetric tetranuclear grid-like complex: [Cu 4( L1) 4(NO 3) 2(OH) 2](2-aminopyridinium)(OH)·CH 3OH) ( 2). A dinuclear Ni(II) complex, [Ni 2( L2) 2( L2H) 2(NCS) 2(CH 3OH) 2]·2CH 3OH ( 3), obtained with another related donor ligand ( L2H = N-salicylidene 3-aminomethylpyridine) was also prepared .

A new mixed-valence hexanuclear cobalt complex, [Co4IICo2III(dea)2(Hdea)4)(piv)4](ClO4)2·H2O: Synthesis, crystal structure and magnetic properties

A new Co II /Co III hexanuclear complex, [Co 4 II Co 2 III (dea) 2 (Hdea) 4 )(piv) 4 ](ClO 4 ) 2 ·H 2 O 1 , has been obtained by reacting cobalt(II) perchlorate, diethanolamine, and pivalic acid (H 2 dea = diethanolamine and piv = pivalato anion). The cobalt ions are held together by four μ 3 and four μ 2 alkoxo bridges as well as by four syn – syn carboxylato groups. The hexanuclear motif contains four Co(II) and two Co(III) ions. The {Co II 4 Co III 2 (μ 2 -O) 4 (μ 3 -O) 4 } core can be described as a four face-sharing monovacant and bivacant distorted heterocubane units. The cobalt(III) ions are hexacoordinated. Two of the cobalt(II) are hexacoordinated, while the two others are pentacoordinated with a bipyramidal stereochemistry. The magnetic properties of 1 have been investigated in the temperature range 1.9–300 K. Compound 1 exhibits an overall antiferromagnetic behaviour with a ground singlet spin state.

Ferromagnetic CuII4, CoII4, and NiII6 Azido Complexes Derived from Metal-Assisted Methanolysis of Di-2,6-(2-pyridylcarbonyl)pyridine

Reaction of copper(II) perchlorate with di-2,6-(2-pyridylcarbonyl)pyridine (pyCOpyCOpy, dpcp) in the presence of sodium azide yields complex [Cu(4)(N(3))(2){pyC(OMe)(O)pyC(OMe)(O)py}(2)(MeOH)(2)](ClO(4)) x 2 MeOH (1 x 2 MeOH), which crystallizes in the monoclinic P2(1)/c space group. Similar reaction of cobalt(II) nitrate yields complex [Co(4)(N(3))(2)(NO(3))(2){pyC(OMe)(O)pyC(OMe)(O)py}(2)] x 0.5 MeOH (2 x 0.5 MeOH) which crystallizes in the monoclinic I2/m space group. Reaction of nickel(II) perchlorate yields complex [Ni(6)(CO(3))(N(3))(6){pyCOpyC(O)(OMe)py}(3)(MeOH)(2)(H(2)O)][Ni(6)(CO(3))(N(3))(6){pyCOpyC(O)(OMe)py}(3) (MeOH)(3)](ClO(4))(2) x 1.8 MeOH (3 x 1.8 MeOH), which crystallizes in the triclinic P1 space group, as a mixed salt of two similar Ni(II)(6) cations, differing only in one terminally coordinated solvate molecule. The cation of 1 consists of four Cu(II) ions in a rhombic topology, while complex 2 consists of four Co(II) ions in a defective double cubane topology. Each of the two cations in 3 contains six Ni(II) ions in a cyclic topology, adopting a chair conformation. In 1 and 2 the ligand has undergone complete methanolysis and full deprotonation, yielding its dianionic bis-gem-diol form. In 3 it has undergone only partial methanolysis. All complexes exhibit ferromagnetic intramolecular interactions. Ferromagnetism in 1 is caused by the structural constraints imposed by the {pyC(OMe)(O)pyC(OMe)(O)py}(2-) ligand on the Cu(II) ions, while in the case of 2 and 3 it is the result of the combined effect of the end-on azido and alkoxo bridges of dpcp, which form M-N(azido)-M and M-O(alkoxo)-M angles between 90-105 degrees. The magnetic susceptibility data of 1 and 3 were analyzed with appropriate spin Hamiltonian models (H =- 2J(ij)S(i)S(j) formalism). For 1, a solution considering J = +26.8 cm(-1) along the periphery of the rhombus was found. In 3 it was found that alternating exchange couplings of J = +6.1 cm(-1) and J' = +27 cm(-1) were operative along the periphery of the ring.

Ferro- and anti-ferromagnetically coupled tetracopper(II) 2 × 2 homoleptic rectangular grids supported by both μ-O and μ-(N-N) bridges derived from a new pyrazole based polydentate Schiff base ligand–magneto-structural correlations and DFT calculation

The pyrazole derived Schiff base polytopic ligand 5-methyl-N'-[1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazide (PzCAP), prepared by the reaction between 5-methylpyrazole-3-carbohydrazide and 2-acetyl pyridine, has two potentially bridging functional groups [mu-O and mu-(N-N)] and consequently can exhibit different coordination conformations. Two tetranuclear homoleptic copper(II) 2 x 2 rectangular grid-complexes [Cu(4)(PzCAP)(4)(NO(3))(2)] (NO(3))(2).8H(2)O (1) and [Cu(4)(PzCAP)(4)(ClO(4))(2)] (ClO(4))(2) (2) were formed by a strict self-assembly process employing metal and ligand under 1:1 mol proportion. Each pair of the ligand molecules in the two complexes are arranged in roughly parallel fashion but under different conformations. The ligand PzCAP contains terminal pyridine and pyrazole residues bound to a central flexible diazine subunit (N-N). The rectangular Cu(II) 2 x 2 grid complexes having [Cu(4)(mu-N-N)(2)(mu-O)(2)] core involve a mixture of two diazine (Cu-N-N-Cu approximately 160 degrees ) and two alkoxo (Cu-O-Cu approximately 138 degrees ) bridges along the length and breadth respectively. In the [Cu(4)(mu-N-N)(2)(mu-O)(2)] core in , out of the four Cu(II) centers, all are hexa-coordinated but there are two penta-coordinated and two hexa-coordinated Cu(II) centers in the same core of . Each complex having the central [Cu(4)(mu-N-N)(2)(mu-O)(2)] core, exhibits quite different magnetic interactions among the metal centers. The paramagnetic Cu(II) centers bridged through the diazine fragment are involved in anti-ferromagnetic interaction while a dominant ferromagnetic interaction prevails between the alkoxo-bridged Cu(II) centers. The [Cu(4)(mu-N-N)(2)(mu-O)(2)] cluster in shows both ferromagnetic and anti-ferromagnetic interaction (J(1) = -0.80 cm(-1) and J(2) = +3.49 cm(-1)), a very unusual characteristic in this system while the same cluster in exhibits dominant anti-ferromagnetic coupling (J(1) = -89.1 cm(-1) and J(2) = +5.5 cm(-1)) through the trans Cu-(N-N)-Cu bridging arrangement, typical for systems of this sort. Both the complexes and have been characterized structurally, magnetically and spectroscopically. The exchange pathways parameters (J(1) and J(2)) have also been evaluated from density functional theoretical calculations to corroborate the bridging signatures with experimental findings.

Structure and magnetic property of a mixed-valence nonanuclear cobalt compound with a square-pyramidal CoII5 core

A novel cobalt compound [Co(9)(HL)(4)(L)(4)Cl(2)] x (EtOH)(2)(H(2)O)(2) (H(3)L = (E)-2-2((1,3-dihydroxy-2-methylpropan-2-ylimino)methyl) phenol) has been solvothermally synthesized and structurally characterized. The compound crystallised in the space group C2/c with a = 32.624(2) A, b = 9.4814(4) A, c = 33.395(2) A, beta = 109.339(5) degrees and V = 9746.8(9) A(3). The crystal structure is a mixed-valence nonanuclear Co(II/III) oligomer, which contains a square-pyramidal Co(II)(5) core formed through mu(4)-Cl and mu(3)-alkoxo bridges and the pentanuclear Co(II)(5) core is surrounded by four peripheral Co(III) ions at the square-pyramidal base plane through mu(2)-alkoxo bridges. Magnetic properties of the compound can be considered as the magnetism of the Co(II)(5) core, and the superexchange interactions between Co(II) ions within the core were calculated with three Co(II)-Co(II) superexchange parameters by using MAGPACK software package to give J(1) = + 11.1 cm(-1), J(2) = -6.50 cm(-1), J(3) = -3.25 cm(-1), D = + 6.0 cm(-1) and g = 2.30.

Synthesis, molecular and supramolecular structure, spectroscopy and electrochemistry of a dialkoxo-bridged diuranyl(VI) compound

The synthesis, molecular and supramolecular structure, spectroscopy and electrochemistry of a dialkoxo-bridged diuranyl(VI) compound [(UO 2) 2(L) 2(dimethylformamide) 2] ( 1) derived from the Schiff base ligand H 2L, obtained on condensation of 3-methoxysalicylaldehyde with 2-aminoethanol, have been described. The compound has been characterized by IR, UV–Vis, NMR and mass spectra, as well as by single crystal X-ray structure determination. The title compound crystallizes in the monoclinic P2 1/ n space group with the following unit cell parameters a = 10.5713(2) Å, b = 11.9895(2) Å, c = 12.9372(2) Å, β = 102.773(3)° and Z = 2. The structure of 1 reveals that it is a dialkoxo-bridged dinuclear compound of uranium(VI) containing two deprotonated ligands, [L] 2−, two dimethylformamide (dmf) molecules and two UO 2 2+ centers. The coordination geometry around the uranium(VI) center is distorted pentagonal bipyramidal; two uranyl oxygens occupy the axial positions, while the basal pentagonal plane is defined by a phenoxo oxygen, two bridging alkoxo oxygens, one imine nitrogen, and one dmf oxygen. Three C–H⋯O type hydrogen bonds involving one uranyl oxygen, two dmf hydrogens and the imine hydrogen link the dinuclear units into a two-dimensional network. The ESI-MS spectrum of 1 in dimethylsulfoxide exhibits two peaks at m/ z = 464.17 and 927.26, which are assignable to [(UO 2) 2L 2H] + (60%) and [(UO 2) 2LH] + (100%) cations, respectively. Cyclic voltammetric measurements of 1 reveal that the uranium(VI) center is reduced quasireversibly at E 1/2 = −1112 mV with Δ E P = 97 mV.

Contributions to the Structural Chemistry of 2‐Amino Alcoholate Derivatives of Titanium and Zirconium Alkoxides and Their Partial Hydrolysis Products

AbstractThe structures of Ti2(OiPr)6(OCHMeCH2NH2)2 and Ti2(OiPr)6(OCH2CHMeNH2)2, obtained by reaction of Ti(OiPr)4 with the corresponding amino alcohols, were investigated to elucidate the structural influence of the organic substituents at the amino alcohol. A methyl group at the OH‐substituted carbon atom results in a larger distortion of the structure than a methyl group at the NH2‐substituted carbon. The disubstituted compound Ti2(OiPr)4(OCH2CH2NH2)4 was formed, when NaTi(OiPr)5 was reacted the amino ethanol. While one OCH2CH2NH2 ligand is chelating, the oxygen atom of the second bridges the titanium atoms, and the NH2 group is dangling. The structures of the partial hydrolysis products Ti4O4(OiPr)4(OCHPhCHMeNHMe)4 and Ti8O6(OEt)12(OCH2CH2NH2)8 were also investigated. The former contains an incomplete double‐cube Ti4O4 cluster core, the latter is made of two Ti4O3(OEt)6(OCH2CH2NH2)4 sub‐units, with a nearly planar Ti4(μ2‐O)2(μ3‐O)(μ2‐OEt)2 ring system, connected by two OEt bridges. Zr(OCH2CH2NH2)4 is a mononuclear compound with four chelating amino alcoholate ligands. The structure of Zr6(OBu)18(OCH2CH2NH2)6 is assembled from two Zr2(OBu)5(OCH2CH2NH2)3 and two Zr(OBu)4 sub‐units, which are associated by alkoxo bridges. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Self-Assembled Copper(II) Coordination Polymers Derived from Aminopolyalcohols and Benzenepolycarboxylates: Structural and Magnetic Properties

The new copper(II) or copper(II)/sodium(I) 1D coordination polymers [Cu2(Hmdea)2(mu-H2O)(mu2-tpa)]n.2nH2O (1), [Cu2(H2tipa)2(mu2-ipa)]n.4nH2O (2), [Cu2(H2tea)2Na(H2O)2(mu2-tma)]n.6nH2O (3), [Cu2(H2tea)2(mu2-ipa)]n.nH2O (4a), and [Cu2(H2tea)2{mu3-Na(H2O)3}(mu3-ipa)]n(NO3)n.0.5nH2O (4b) have been prepared in aqueous medium by self-assembly from copper(II) nitrate, aminopolyalcohols [methyldiethanolamine (H2mdea), triisopropanolamine (H3tipa), and triethanolamine (H3tea)] as main chelating ligands and benzenepolycarboxylic acids [terephthalic (H2tpa), isophthalic (H2ipa), and trimesic (H3tma) acid] as spacers. They have been characterized by IR spectroscopy, elemental and single-crystal X-ray diffraction analyses, the latter indicating the formation of unusual multinuclear metal cores interconnected by various benzenepolycarboxylate spacers, leading to distinct wavelike, zigzag, or linear 1D polymeric metal-organic chains. These are further extended to 2D or 3D hydrogen-bonded supramolecular networks via extensive interactions with the intercalated crystallization water molecules. The latter are associated, also with aqua ligands, by hydrogen bonds resulting in acyclic (H2O)3 clusters in 1, (H2O)8 clusters in 2, infinite 1D water chains in 3, and disordered water-nitrate associates in 4b, all playing a key role in the structure stabilization and its extension to further dimensions. Variable-temperature magnetic susceptibility measurements have shown that 1-4 exhibit a moderately strong ferromagnetic coupling through the alkoxo bridge. The small Cu-O-Cu bridging angle and the large out-of-plane displacement of the carbon atom of the alkoxo group accounts for this behavior. The magnetic data have been analyzed by means of a dinuclear and a 1D chain model, and the magnetic parameters have been determined. The magnetic exchange coupling in 3, to our knowledge, is the highest found in alkoxo-bridged copper(II) complexes.

Importance of Orbital Complementarity in Spin Coupling through Two Different Bridging Groups in Dicopper(II) Complexes of Endogenous Alkoxo Bridging Ligand with Exogenous Carboxylate: Ab-initio and Semi-Empirical Calculations

The influence of overlap interactions between the bridging ligands and the metal d orbitals on the super-exchange coupling constant are studied by means of ab-initio restricted Hartree-Fock molecular orbital calculations. The interaction between the magnetic d orbitals and the HOMOs of the carboxylate oxygen atoms are investigated in homologous asymmetrically dibridged dicopper(II) complexes which have significantly different - 2J values (the energy separation between the spin-triplet and spin-singlet states). In order to determine the nature of the fronter orbitals, extended Hückel molecular orbital (EHMO) calculations are also reported. The differences in the magnitude of the coupling constants and magnetic behaviour are rationalized in terms of the bridging ligand orbital complementary / countercomplementary concept.

Tuning Anisotropy Barriers in a Family of Tetrairon(III) Single-Molecule Magnets with anS= 5 Ground State

Tetrairon(III) Single-Molecule Magnets (SMMs) with a propeller-like structure exhibit tuneable magnetic anisotropy barriers in both height and shape. The clusters [Fe4(L1)2(dpm)6] (1), [Fe4(L2)2(dpm)6] (2), [Fe4(L3)2(dpm)6].Et2O (3.Et2O), and [Fe4(OEt)3(L4)(dpm)6] (4) have been prepared by reaction of [Fe4(OMe)6(dpm)6] (5) with tripodal ligands R-C(CH2OH)3 (H3L1, R = Me; H3L2, R = CH2Br; H3L3, R = Ph; H3L4, R = tBu; Hdpm = dipivaloylmethane). The iron(III) ions exhibit a centered-triangular topology and are linked by six alkoxo bridges, which propagate antiferromagnetic interactions resulting in an S = 5 ground spin state. Single crystals of 4 reproducibly contain at least two geometric isomers. From high-frequency EPR studies, the axial zero-field splitting parameter (D) is invariably negative, as found in 5 (D = -0.21 cm(-1)) and amounts to -0.445 cm(-1) in 1, -0.432 cm(-1) in 2, -0.42 cm(-1) in 3.Et2O, and -0.27 cm(-1) in 4 (dominant isomer). The anisotropy barrier Ueff determined by AC magnetic susceptibility measurements is Ueff/kB = 17.0 K in 1, 16.6 K in 2, 15.6 K in 3.Et2O, 5.95 K in 4, and 3.5 K in 5. Both |D| and U(eff) are found to increase with increasing helical pitch of the Fe(O2Fe)3 core. The fourth-order longitudinal anisotropy parameter B4(0), which affects the shape of the anisotropy barrier, concomitantly changes from positive in 1 ("compressed parabola") to negative in 5 ("stretched parabola"). With the aid of spin Hamiltonian calculations the observed trends have been attributed to fine modulation of single-ion anisotropies induced by a change of helical pitch.