Ricardo Baggio

Crystal structures and luminescent properties of terbium(III) carboxylates

Abstract Single crystals of three terbium(III) carboxylates of formulae [Tb2(CH3COO)6(H2O)4]·4H2O (1), [Tb2(CF3COO)6(H2O)6] (2) and [Tb(Hoda)3]·H2oda·H2O (3) (H2oda=2,2′-oxydiacetic acid) were obtained and their structures determined by X-ray crystallography. Compounds 1 and 2 are dimeric, in the former the terbium atoms are bound by two tridentate carboxylates in the μ2-bridging mode, whereas in the latter the bridging is fourfold with all carboxylates in the syn–syn coordination mode. Compound 3 is mononuclear containing three tridentate Hoda anions, and consecutive units are linked by a network of H-bonds involving the interstitial molecules. The luminescence spectra of the carboxylates were analyzed in the solid state and in aqueous solution. Comparison of the emission lifetimes in H2O and D2O allowed the determination of the average value for q, the number of coordinated water molecules, being 9.2 for 1 and 2 and 3.6 for 3, respectively. The quenching effect of Cu(II) on the luminescence of the terbium(III) carboxylates was evaluated through the emission decay constants. From the addition of Cu(II) to an aqueous solution of 3, single crystals of polymeric [{Cu3Tb2(oda)6(H2O)6}·12H2O]n (4) were isolated with completely quenched luminescence. Compound 4 exhibits an overall antiferromagnetic interaction.

Molecular structure and magnetic properties of [Gd(LH4)(NO3)2(H2O)]NO3(H2O)2, [Sm(LH4)(NO3)2(H2O)]NO3 (H2O)1.5(CH3OH)0.5 and [Cu2(LH2)(H2O)2](NO3)2 complexes (LH4: Schiff base ligand derived from 4-methyl-2,6-diformylphenol and 1,3-diaminopropanol)

Abstract Novel lanthanide(III) complexes (Ln=Gd (1), Sm (2), La (3)) of the macrocyclic ligand LH4 have been prepared and characterized. The binuclear copper(II) complex (Cu2(LH2)(H2O)2)(NO3)2 (4), has been obtained by transmetalation of complex 3 with Cu(CF3COO)2. The macrocyclic Schiff base ligand (LH4) is formed by the condensation of two molecules of 4-methyl-2,6-diformylphenol with two molecules of 1,3-diaminopropanol in the presence of the lanthanide ions. The alcohol group of the macrocycle does not coordinate to the copper(II) centers of the binuclear complex. However, one of the secondary alcohol groups of the ligand coordinates in an asymmetric mode to the lanthanide ion in the corresponding three complexes. The X-ray crystal structures of (Gd(LH4)(NO3)2(H2O))(NO3)(H2O)2 (1), (Sm(LH4)(NO3)2(H2O))(NO3)(H2O)1.5(CH3OH)0.5 (2), and (Cu2(LH2)(H2O)2)(NO3)2 (4) have been determined. Magnetic susceptibility measurements in the 5–300 K range were obtained for these complexes.

Synthesis and characterization of zinc(II) oxydiacetate (oda) complexes. Crystal structures of [{Zn(oda)·0.3H2O}n], [Zn(oda)(bipy)(H2O)]·2.5H2O and [Zn(oda)(phen)(H2O)]·1.5H2O (bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline)

Three novel zinc(II) oxydiacetate (oda) compounds [{Zn(oda)·0.3H2O}n]1, [Zn(oda)(bipy)(H2O)]·2.5H2 O 2(bipy = 2,2′-bipyridine) and [Zn(oda)(phen)(H2O)]·1.5H2O 3(phen = 1,10-phenanthroline) have been synthesized and their structures determined by single-crystal X-ray diffraction methods. Compound 1 consists of polymeric sheets formed by ZnO5 units bridged by carboxylate groups in anti-syn conformation along the z axis; 2 and 3 are mononuclear with the zinc atoms in distorted octahedral ZnN2O4 co-ordination geometries. Thermal decomposition of the compounds under an oxygen atmosphere affords ZnO at ca. 500 °C.

Magnetism and structure in chains of copper dinuclear paddlewheel units.

An anhydrous copper carboxylate compound of formula [Cu(trans-2-butenoate)(2)](n) has been characterized. X-ray analysis reveals a structure built by paddlewheel units bridged by pairs of Cu...O axial bonds to give infinite chains arranged in a new topological motif. Susceptibility measurements in the 10-300 K temperature range, and isothermal magnetization curves at 2, 5, 10, and 50 K with fields up to 5 T, were obtained. Electron Paramagnetic Resonance (EPR) spectra of powder samples were measured at 33.9 GHz at 300 K, and at 9.60 GHz at temperatures in the range 90 <or= T <or= 350 K. Fitting the susceptibility data to a chain model of alternating paddlewheel and [Cu(mu-O)(2)Cu] dinuclear units yielded exchange interactions J(1) = -330.6(1) cm(-1) and J(2) = 5.9(2) cm(-1). The EPR spectra reflect the usual antiferromagnetic dinuclear behavior, with zero field splitting parameters of the excited spin triplet, D = -0.329(3) cm(-1) and E approximately 0, plus a central peak not expected for isolated dinuclear units. We interpret this peak as arising from the stochastic spin dynamics of the chain introduced by exchange couplings between spins in neighbor dinuclear units, which averages out the zero field splitting. Interactions of the units with the rest of the chain acting as a spin bath give rise to a quantum transition between localized dinuclear states and states of the spin chain. This effect competes with the condensation of the antiferromagnetic dinuclear units into the singlet ground state, producing a characteristic temperature dependence of the shape of the powder EPR spectra. We interpret these features in terms of basic theories of magnetic resonance in coupled spin systems applied to the chain array of dinuclear units.

A discrete dinuclear Cu(II)–Gd(III) complex derived from a Schiff base ligand, [CuGd(ems)(NO3)3H2O]Cu(ems) (ems: N,N′-ethylene-bis-5-methoxy salicylaldiimine)

Abstract A Cu(II)–Gd(III) heteronuclear complex with N,N′-ethylene-bis-5-methoxy salicylaldiimine (ems) as ligand has been synthesized. The complex crystallizes in the monoclinic system C2/c space group. The structure consists of two different discrete molecules: a mononuclear unit containing a single Cu(II) center, and a dinuclear one containing both a nine coordinated Gd(III) plus a four coordinated Cu(II) cation [CuGd(H2O)(NO3)(ems)]. The complex was characterized by magnetic susceptibility and electron paramagnetic resonance. The Cu(II)–Gd(III) complex presents a ferromagnetic interaction (J=1.88 cm−1); its effective magnetic moment was found to increase with decreasing temperature. Both electronic and structural parameters are shown to influence the magnitude of the magnetic interaction.

New homobinuclear carboxylate-bridged gadolinium(III) complexes

Abstract Two novel gadolinium(III) trans-2-butenoate dimeric compounds [Gd2(O2CCHCHCH3)6(H2O)4]·2H2O (1) and [Gd2(O2CCHCHCH3)6(phen)2]·2H2O (2) have been synthesized via hydrothermal routes. Compound 1 consists of two independent dimers in the unit cell, one is doubly bridged (η2:η1:μ2) and the other quadruply bridged (two η1:η1:μ2 and two η2:η1:μ2). Compound 2 is dimeric with a quadruply bridged core (two η1:η1:μ2 and two η2:η1:μ2). Magnetic measurements for 2 show that there is a weak antiferromagnetic intramolecular Gd⋯Gd interaction.

Coordination mode of some polypyridyl ligands towards the platinum(II) complexes [Pt(dppf)(H2O)2](CF3SO3)2 (dppf=1,1′-bis(diphenylphosphino)ferrocene) and [Pt(Me2SO)2Cl2]. Crystal structure of the seven-membered chelate ring complex [Pt(dpq)Cl2] (dpq=2,3-di(2-pyridyl)quinoxaline)

Abstract A series of novel platinum(II) complexes were isolated through the reaction of the polypyridyl ligands 2,3,7,8-tetra(2-pyridyl)pyrazino[2,3-g]quinoxaline (tpq), 2,3-di(2-pyridyl)pyrazine (dpp), 2,3-di(2-pyridyl)quinoxaline (dpq) and 6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline (ddpq) with the heterobimetallic complex [Pt(dppf)(H2O)2](CF3SO3)2 or with the dimethyl sulfoxide complex [Pt(Me2SO)2Cl2]. The di-platinum complex [{Pt(dppf)}2(tpq)](CF3SO3)4 and the mono-platinum compounds [Pt(dppf)(L)](CF3SO3)2 (L=dpp, ddpq) and [Pt(L)Cl2] (L=dpq, ddpq) were synthesized. As shown by 1H NMR spectroscopy, in these complexes the bridging tpq and the mononucleating ligands dpp, dpq and ddpq present an uncommon bidentate chelate mode; they are bonded to the Pt(II) centres only by the means of their pyridyl nitrogen atoms. This behaviour was corroborated through the X-ray crystallographic study of the [Pt(dpq)Cl2] derivative. The redox properties of the three new dppf-based complexes, in dichloromethane solution, show in all cases that they undergo ferrocene-based (dppf) oxidations and that the primary cathodic processes are tpq-centered in the tpq complex and platinum(II)-centered in the dpp and ddpq complexes.

SYNTHESIS AND X-RAY CRYSTAL DETERMINATION OF FOUR NOVEL LANTHANIDE(III) OXYDIACETATE COMPLEXES

Abstract Four newlanthanide oxydiacetates [{Y(Hoda)3}·H2oda·H2O] (1), [{Y2(oda)3(H2O)4·2H2O}n] (2), [{LaGd(oda)3(H2O)3·6H2O}n] (3) and [{LaY (oda)3(H2O)3·6H2O}n] (4) (oda = O2CCH2OCH2CO2) have been synthesized and their structures determined by singlecrystal X-ray methods. Compound 1 is monometallic with distorted YO9 units formed via coordination of three tridentate Hoda ligands. Compound 2 consists of polymeric sheets of YO9 units formed via coordination of three tridentate oda ligands bridged through carboxylate groups to YO8 units. Compounds 3 and 4 are isomorphous heterobimetallic three-dimensional networks of LnO9 units (Ln Gd or Y) formed via coordination of three tridentate oda ligands bridged to the larger radius La (III) in LaO9 units through carboxylate groups.

A new simplifying approach to molecular geometry description : the vectorial bond-valence model

A method to describe, analyze and even predict the coordination geometries of metal complexes is proposed, based on previous well established concepts such as bond valence and valence-shell electron-pair repulsion (VSEPR). The idea behind the method is the generalization of the scalar bond-valence concept into a vector quantity, the bond-valence vector (BVV), with the innovation that the multidentate ligands are represented by their resultant BVVs. Complex n-ligand coordination spheres (frequently indescribable at the atomic level) reduce to much simpler ones when analyzed in BVV space, with the bonus of a better applicability of the VSEPR predictions. The geometrical implications of the BVV description are analyzed for the cases of n=2 and 3 (n=number of ligands), and the validity of its predictions, checked for a large number of metal complexes.

X-ray study on the nickel(II)-oxydiacetic system and its 1,10-phenanthroline and 2,2′:6′,2′′ terpyridine complexes

Abstract Three new metal–organic coordination complexes have been prepared and their crystal structures determined: [Ni(oda)(H2O)3]·1.5H2O, [Ni(oda)(phen)(H2O)]·1.5H2O and [Ni(oda)(terpy)]·2H2O (oda=oxydiacetate, phen=1,10-phenanthroline, terpy=2,2′:6′,2′′ terpyridine). The oxydiacetate ligand is tridentate in these compounds, being hinged in the first and nearly planar in the other two. Hydrogen-bonding and π–π interaction is extensive in the solids.