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Miguel Julve - One of the best experts on this subject based on the ideXlab platform.
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iron iii chromium iii and cobalt ii complexes with Squarate synthesis crystal structure and magnetic properties
Inorganica Chimica Acta, 2011Co-Authors: Jose Carranza, Francesc Lloret, Jorunn Sletten, Miguel JulveAbstract:The preparation and variable temperature-magnetic investigation of three Squarate-containing complexes of formula [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ]·2H 2 O ( 1 ) [Cr 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ]·2H 2 O ( 2 ) and [Co(C 4 O 4 )(H 2 O) 4 ] n ( 3 ) [H 2 C 4 O 4 = 3.4-dihydroxycyclobutene-1,2-dione (squaric acid)] together with the crystal structures of 1 and 3 are reported. Complex 1 contains discrete centrosymmetric [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ] diiron(II) units where the iron pairs are joined by a di-μ-hydroxo bridge and two Squarate ligands acting as bridging groups through adjacent oxygen atoms. Two coordinated water molecules in cis position complete the octahedral environment at each iron atom in 1 . The iron–iron distance with the dinuclear unit is 3.0722(6) A and the angle at the hydroxo bridge is 99.99(7)°, values which compare well with the corresponding ones in the isostructural compound 2 (2.998 A and 99.47°) whose structure was reported previously. The crystal structure of 3 contains neutral chains of squarato- O 1 , O 3 -bridged cobalt(II) ions where four coordinated water molecules complete the six-coordination at each cobalt atom. The cobalt–cobalt separation across the Squarate bridge is 8.0595(4) A. A relatively important intramolecular antiferromagnetic coupling occurs in 1 whereas it is very weak in 2 , the exchange pathway being the same [ J = −14.4 ( 1 ) and −0.07 cm −1 ( 2 ), the spin Hamiltonian being defined as H ^ = - J S ^ 1 · S ^ 2 ]. A weak intrachain antiferromagnetic interaction between the high-spin cobalt(II) ions occurs in 3 ( J = −0.30 cm −1 ). The magnitude and nature of these magnetic interactions are discussed in the light of their respective structures and they are compared with those reported for related systems.
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oxalate Squarate and croconate complexes with bis 2 pyrimidylcarbonyl amidatecopper ii synthesis crystal structures and magnetic properties
Inorganica Chimica Acta, 2005Co-Authors: Francesc Lloret, Danielle Cangussu, Humberto O Stumpf, Harry Adams, Jim A Thomas, Miguel JulveAbstract:Abstract The preparation and magnetic properties of three copper(II) compounds of formulae [Cu2(bpcam)2(H2O)2(C2O4)] (1), [Cu2(bpcam)2(H2O)4(C4O4)] · 10 H2O (2) and Cu2(bpcam)2(C5O5)(H2O)3 (3) [bpcam = bis(2-pyrimidyl)amidate, C 2 O 4 2 - = dianion of oxalic acid , C 4 O 4 2 - = dianion of 3 , 4 - dihydroxycyclobut - 3 - ene - 1 , 2 - dione and C 5 O 5 2 - = dianion of 4 , 5 - dihydroxycyclopent - 4 - ene - 1 , 2 , 3 - trione ] are reported. The structures of two of them (1 and 2) have been solved by single crystal X-ray diffraction and consists of centrosymmetric discrete copper(II) dinuclear units bridged by bis-bidentate oxalate (1) and bis-monodentate Squarate (2), with the bpcam group acting as a terminal tridentate ligand. Each copper atom in 1 exhibits a distorted elongated octahedral coordination geometry. Three bpcam nitrogen atoms and one oxalate oxygen define the basal plane while the other oxalate oxygen and a water molecule take up the axial positions. Each copper atom in 2 is in an elongated octahedral surrounding with three bpcam nitrogen atoms and one Squarate oxygen in the equatorial plane and two water molecules in the axial positions. The intramolecular copper–copper separations are 5.677(1) (1) and 7.819(53) A (2). Magnetic susceptibility measurements for 1–3 in the temperature range 1.9–290 K show the occurrence of weak ferromagnetic interactions through oxalato (J = +0.75 cm−1) and squarato (J = +1.26 cm−1), the Hamiltonian being defined by H ˆ = - J S ˆ A · S ˆ B . These values are analyzed and discussed in the light of the available magneto-structural data for analogous systems. The quasi-Curie law observed in 3 (θ = −1.15 K) contrasts with the significant antiferromagnetic interaction through bis-chelating croconate in other structurally characterized croconate-bridged copper(II) complexes and rules out the presence of bridging croconate in this compound.
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crystal structures and magnetic properties of the Squarate o1 on bridged dinuclear copper ii complexes cu2 phen 4 c4o4 cf3so3 2 3h2o n 2 and cu2 bipy 4 c4o4 cf3so3 2 6h2o n 3
Inorganica Chimica Acta, 1999Co-Authors: Isabel Castro, Francesc Lloret, Jorunn Sletten, Maria Luisa Calatayud, Miguel JulveAbstract:Abstract Two dinuclear copper(II) complexes of the formula [Cu2(phen)4(C4O4)](CF3SO3)2 · 3H2O (1) and [Cu2(bipy)4(C4O4)](CF3SO3)2 · 6H2O (2) [phen=1,10-phenanthroline, bipy=2,2′-bipyridine and C4O4 2−=dianion of 3,4-dihydroxy-3-cyclobuten-1,2-dione (squaric acid)] have been synthesized and characterized by single-crystal X-ray diffraction. Their structures consist of [Cu2(phen)4(C4O4)]2+ (1) and [Cu2(bipy)4(C4O4)]2+ (2) dinuclear copper(II) cations, uncoordinated CF3SO3 − anions and crystallization water molecules. The copper is in a distorted square pyramidal environment: one Squarate-oxygen atom and three phen- (1) or bipy- (2) nitrogen atoms of two phen (1) or bipy (2) terminal ligands form a distorted square plane around the copper whereas the axial position is occupied by the remaining phen- (1) or bipy- (2) nitrogen atom. The Squarate adopts the μ-1,2- (1) and μ-1,3- (2) bis(monodentate) coordination modes, the intradimer copper–copper separation being 4.912(2) (1) and 7.310(1) (2) A, respectively. Variable temperature magnetic susceptibility measurements reveal the occurrence of significant intramolecular antiferromagnetic coupling, the relevant parameters being J=−26.4 cm−1 and g=2.14 for 1 and J=−8.6 cm−1 and g=2.07 for 2 (J being the exchange parameter in the isotropic spin Hamiltonian Ĥ=−JŜA · ŜB). The influence of both the symmetry of the copper(II) centered magnetic orbitals and the coordination modes of the bridging Squarate on the magnitude of antiferromagnetic coupling in related Squarate-bridged copper(II) complexes is analyzed and discussed.
Luiz Fernando C De Oliveira - One of the best experts on this subject based on the ideXlab platform.
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synthesis vibrational spectroscopy and crystal structures of polymers involving transition metals with Squarate ions and 1 3 bis 4 pyridyl propane
Vibrational Spectroscopy, 2007Co-Authors: Charlane C Correa, Renata Diniz, Bernardo L Rodrigues, Maria Irene Yoshida, Luciano H Chagas, Wagner M Teles, Flavia C Machado, Howell G M Edwards, Luiz Fernando C De OliveiraAbstract:Abstract Two new coordination polymers of general formula [Mn(C 4 O 4 )(BPP) 2 (H 2 O) 2 ] and [Co(C 4 O 4 )(BPP) 2 (H 2 O) 2 ] [where BPP = 1,3-bis(4-pyridyl)propane; C 4 O 4 = Squarate ion] were synthesized and characterized by vibrational spectroscopy (Raman and infrared), X-ray diffraction and thermal analysis. These two compounds are isostructural, containing BPP and Squarate ligands coordinated to the metal sites, as well as two water molecules, in a distorted octahedral geometry. The Squarate ion adopts the 1,3-bis(monodentate) coordination mode binding two metallic sites, extending the chain along the a crystallographic axis; this chain interacts with other adjacent chains by means of hydrogen bonds through the free oxygen atoms of the Squarate ion and also the water molecule, as well as the π-stacking of the pyridine rings of the BPP ligand, giving rise to a two-dimensional arrangement where the unidimensional chains are interdigitated. The vibrational spectra of both compounds are very similar and are supportive of the crystallographic data. In the infrared spectra of both complexes an observed band of medium intensity around 1620 cm −1 and another strong band at 1535 cm −1 , assigned to CC/CN and CO stretching modes, respectively, are indicative of the coordination of BPP and Squarate ions to the metal sites. In the Raman spectra, the strong band at 1769 cm −1 , assigned to the CO stretching mode of uncoordinated carbonyl groups of the Squarate ion, is noteworthy.
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transition metal complexes with Squarate anion and the pyridyl donor ligand 1 3 bis 4 pyridyl propane bpp synthesis crystal structure and spectroscopic investigation
Polyhedron, 2007Co-Authors: Charlane C Correa, Renata Diniz, Bernardo L Rodrigues, Maria Irene Yoshida, Luciano H Chagas, Wagner M Teles, Flavia C Machado, Luiz Fernando C De OliveiraAbstract:Abstract Synthesis, crystal structure and the vibrational spectra of coordination polymers with 1,3-bis(4-pyridyl)propane (BPP) and Squarate ion ligands and transition metal ions (M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) are described. All compounds are isostructural, and the BPP is not coordinated to metal site since it is in cationic form due to protonation of N atoms from pyridyl rings. The metal is coordinated to two Squarate ions and two water molecules in an octahedral distorted geometry. The two water molecules are involved in medium hydrogen bonds with Squarate ligands and the average of O⋯O distance is 2.679(3) A. Squarate ions adopt the 1,3-bis(monodentate) coordination mode bridging two metal centers giving rise to a 2D arrangement with (4,4) topology. The four-member ring is slightly distorted and the M–M distances are respectively 8.024 and 8.111 A. The cationic form of BPP molecules are located inside of four-member ring cavity, presenting two different orientations, in which one molecule is inverted comparing to another. Vibrational spectra of all compounds are very similar, in agreement to crystal data. In all infrared spectra of the compounds a medium band at 1640 cm−1 is observed, assigned to the in plane deformation mode of NH bond, indicative of the formation of cationic BPP. In the Raman spectra of the investigated compounds is observed a weak band around 1800 cm−1, assigned to the stretching mode of free CO bond, whereas the medium band observed around 1600 cm−1 is tentatively assigned to coordinated CO stretching mode. At last, a very important achievement of this investigation refers to the coordination geometries of all the investigated compounds, which are governed only by the ligands, independently of the different electronic properties of the metal ions.
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vibrational spectroscopy and aromaticity investigation of Squarate salts a theoretical and experimental approach
Journal of Molecular Structure, 2006Co-Authors: Stefanos L Georgopoulos, Renata Diniz, Maria Irene Yoshida, Nivaldo L Speziali, Helio Dos F Santos, Georgia M A Junqueira, Luiz Fernando C De OliveiraAbstract:Abstract Experimental and theoretical investigations of Squarate salts [M2(C4O4)] (M=Li, Na, K and Rb) were performed aiming to correlate the structures, vibrational analysis and aromaticity. Powder X-ray diffraction data show that these compounds are not isostructural, indicating that the metal-Squarate and hydrogen bonds to water molecules interactions play a significant role on the the crystal packing. The infrared and Raman assigments suggest an equalization of the C–C bond lengths with the increasing of the counter-ion size. This result is interpreted as an enhancement in the electronic delocalization and consequently in the degree of aromaticity for salts with larger ions. Quantum mechanical calculations for structures, vibrational spectra and aromaticity index are in agreement with experimental finding, giving insights at molecular level for the role played by distinct complexation modes to the observed properties. Comparison between our results and literature, regarding molecular dynamics in different chemical environments, shows that aromaticity and hydrogen bonds are the most important forces driving the interactions in the solid structures of Squarate ion.
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intermolecular interaction studies in ammonium Squarate crystal structure and vibrational spectra
Journal of Molecular Structure, 2005Co-Authors: Stefanos L Georgopoulos, Renata Diniz, Bernardo L Rodrigues, Maria Irene Yoshida, Luiz Fernando C De OliveiraAbstract:Abstract Ammonium Squarate salt [(NH 4 ) 2 C 4 O 4 ] crystallizes in the monoclinic space group P2 1 /c. The crystal presents the Squarate ions displayed in layers parallel to a crystallographic axis and forming hydrogen bonds interactions with NH 4 + cations, localized between Squarate anions layers. The Squarate anion presents similar CC and CO bond distances which indicate a degree of electronic delocalization in the rings. A π-stacking interaction is observed between Squarate rings separated by interplanar distance and centroid ring distance of respectively 3.41 and 3.71 A. The electron delocalization was also observed in the vibrational spectra. The infrared spectrum shows a narrow band around 1530 cm −1 , assigned to a coupled stretching mode of CO and CC groups, indicating the high symmetry of the Squarate ion. The Raman spectrum also shows this effect in the 1000 to 1200 cm −1 region (related to CC stretching mode), where it is expected a decrease of the number of bands if compared to Squarate ion in aqueous solution, where the symmetry is actually D 4 h ; in the (NH 4 ) 2 C 4 O 4 Raman spectrum just one strong band is observed at 1120 cm −1 . All the vibrational results indicate the symmetry is very close to the one observed for the solvated ion in aqueous solution; once again the vibrational analysis appears as an important tool in recognizing the oxocarbon ion geometry in the solid state.
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crystal structure and raman spectra of rubidium hydrogen Squarate
Journal of Molecular Structure, 2005Co-Authors: Stefanos L Georgopoulos, Renata Diniz, Bernardo L Rodrigues, Luiz Fernando C De OliveiraAbstract:Abstract Rubidium hydrogen Squarate (RbHC 4 O 4 , RbHSQ) crystallized in monoclinic space group P 2 1 / c . This compound form a short asymmetric intermolecular hydrogen bond whose O–O distance is 2.482(4) A. The hydrogen Squarate anions are forming head-to-tail infinite chain hydrogen-bonding motifs. A long interplanar separation (4.15 A) indicates that a weak π interaction occurs between hydrogen Squarate anions in RbHSQ. The hydrogen bond and cation–anion interactions are the predominant driving forces in the crystal packing. The Raman spectrum of RbHSQ shows an average behaviour between squaric acid and Squarate dianion, however, the vibrational modes at ca. 1800 cm −1 (CO stretching mode) and in the region 1500–1700 cm −1 (CO+CC stretching modes) are the most affected by the presence of strong hydrogen bonding interactions.
Leo A Paquette - One of the best experts on this subject based on the ideXlab platform.
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a highly abbreviated synthesis of pentalenene by means of the Squarate ester cascade
Organic Letters, 2002Co-Authors: Leo A Paquette, Feng GengAbstract:The sequential addition of 5-methylcyclopentyllithium and propynyllithium to diisopropyl Squarate results in the efficient formation of a functionalized angular triquinane having two of its five-membered rings substituted precisely as in the target sesquiterpene. Only seven additional steps are then required to access pentalenene.
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applications of the Squarate ester cascade to the expeditious synthesis of hypnophilin coriolin and ceratopicanol
Journal of the American Chemical Society, 2002Co-Authors: Leo A Paquette, Feng GengAbstract:The first applications of the Squarate ester cascade to natural products synthesis have been realized. Only 10 laboratory steps mediate the conversion of diisopropyl Squarate to (±)-hypnophilin (8). Key reactions include a combination of chlorination, reduction, dehydration, and oxidation maneuvers in the proper sequence. A penultimate precursor to 8 has previously been converted into coriolin (9), thereby allowing a formal synthesis of racemic 9 also to be claimed. A rather different strategy was employed to arrive at (±)-ceratopicanol (10). Of the seven steps involved, three consisted of the use of lithium in liquid ammonia. The three divergent synthetic objectives realized in these experiments involved (a) generation of an extended enolate anion and its regioselective C-methylation at the γ-carbon; (b) unprecedented reductive cleavage of a β-isopropoxy group in a 2,3-diisopropoxy-2-cyclopentenone setting; and (c) conventional conversion of an α-alkoxy ketone to the parent carbonyl system. Thus, the app...
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three component coupling via the Squarate ester cascade as a concise route to the bioactive triquinane sesquiterpene hypnophilin
Organic Letters, 2002Co-Authors: Feng Geng, Jian Liu, Leo A PaquetteAbstract:A Squarate ester cascade is used to provide in one step, via the coupling of three reactants, a highly oxygenated linear triquinane product. The latter is transformed in nine steps into hypnophilin. The access route involves a combination of chlorination, reduction, dehydration, and oxidation maneuvers in the proper sequence.
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delineating the possibilities for intramolecular interception of the Squarate ester cascade through the use of metalated enecarbamates
Canadian Journal of Chemistry, 2000Co-Authors: Jinsung Tae, Leo A PaquetteAbstract:Highly functionalized and annulated 2,4-cyclooctadienones are formed in a stereoselective manner by sequential treatment of Squarate esters with a lithiated enecarbamate (six-membered ring or larger) and a cycloalkenyl- or 1-alkenyllithium reagent. The mechanistic details of this multistep process are presented. Particular attention is drawn to the step that involves intramolecular nucleophilic attack by a proximal oxido anion at the carbamate carbonyl and results in redirection of the cascade. This step is thwarted when five-membered cyclic enecarbamates are employed because of the excessive buildup of ring strain in the associated transition state.Key words: Squarate esters, enecarbamates, conrotatory ring opening, intramolecular acylation, alkenyllithium reagents.
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cascade rearrangements following twofold addition of alkenyl anions to Squarate esters
ChemInform, 1998Co-Authors: Leo A PaquetteAbstract:The double 1,2-addition of alkenyl, cycloalkenyl, and alkynyllithium reagents to Squarate esters constitutes a very expedient method for rapidly increasing structural complexity with formation of polycyclic end products. The simple one-pot process is amenable to regioselective operation, stereochemical control, self-immolative chirality transfer, 1,5-asymmetric induction, and chemical modulation.
Francesc Lloret - One of the best experts on this subject based on the ideXlab platform.
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iron iii chromium iii and cobalt ii complexes with Squarate synthesis crystal structure and magnetic properties
Inorganica Chimica Acta, 2011Co-Authors: Jose Carranza, Francesc Lloret, Jorunn Sletten, Miguel JulveAbstract:The preparation and variable temperature-magnetic investigation of three Squarate-containing complexes of formula [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ]·2H 2 O ( 1 ) [Cr 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ]·2H 2 O ( 2 ) and [Co(C 4 O 4 )(H 2 O) 4 ] n ( 3 ) [H 2 C 4 O 4 = 3.4-dihydroxycyclobutene-1,2-dione (squaric acid)] together with the crystal structures of 1 and 3 are reported. Complex 1 contains discrete centrosymmetric [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ] diiron(II) units where the iron pairs are joined by a di-μ-hydroxo bridge and two Squarate ligands acting as bridging groups through adjacent oxygen atoms. Two coordinated water molecules in cis position complete the octahedral environment at each iron atom in 1 . The iron–iron distance with the dinuclear unit is 3.0722(6) A and the angle at the hydroxo bridge is 99.99(7)°, values which compare well with the corresponding ones in the isostructural compound 2 (2.998 A and 99.47°) whose structure was reported previously. The crystal structure of 3 contains neutral chains of squarato- O 1 , O 3 -bridged cobalt(II) ions where four coordinated water molecules complete the six-coordination at each cobalt atom. The cobalt–cobalt separation across the Squarate bridge is 8.0595(4) A. A relatively important intramolecular antiferromagnetic coupling occurs in 1 whereas it is very weak in 2 , the exchange pathway being the same [ J = −14.4 ( 1 ) and −0.07 cm −1 ( 2 ), the spin Hamiltonian being defined as H ^ = - J S ^ 1 · S ^ 2 ]. A weak intrachain antiferromagnetic interaction between the high-spin cobalt(II) ions occurs in 3 ( J = −0.30 cm −1 ). The magnitude and nature of these magnetic interactions are discussed in the light of their respective structures and they are compared with those reported for related systems.
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oxalate Squarate and croconate complexes with bis 2 pyrimidylcarbonyl amidatecopper ii synthesis crystal structures and magnetic properties
Inorganica Chimica Acta, 2005Co-Authors: Francesc Lloret, Danielle Cangussu, Humberto O Stumpf, Harry Adams, Jim A Thomas, Miguel JulveAbstract:Abstract The preparation and magnetic properties of three copper(II) compounds of formulae [Cu2(bpcam)2(H2O)2(C2O4)] (1), [Cu2(bpcam)2(H2O)4(C4O4)] · 10 H2O (2) and Cu2(bpcam)2(C5O5)(H2O)3 (3) [bpcam = bis(2-pyrimidyl)amidate, C 2 O 4 2 - = dianion of oxalic acid , C 4 O 4 2 - = dianion of 3 , 4 - dihydroxycyclobut - 3 - ene - 1 , 2 - dione and C 5 O 5 2 - = dianion of 4 , 5 - dihydroxycyclopent - 4 - ene - 1 , 2 , 3 - trione ] are reported. The structures of two of them (1 and 2) have been solved by single crystal X-ray diffraction and consists of centrosymmetric discrete copper(II) dinuclear units bridged by bis-bidentate oxalate (1) and bis-monodentate Squarate (2), with the bpcam group acting as a terminal tridentate ligand. Each copper atom in 1 exhibits a distorted elongated octahedral coordination geometry. Three bpcam nitrogen atoms and one oxalate oxygen define the basal plane while the other oxalate oxygen and a water molecule take up the axial positions. Each copper atom in 2 is in an elongated octahedral surrounding with three bpcam nitrogen atoms and one Squarate oxygen in the equatorial plane and two water molecules in the axial positions. The intramolecular copper–copper separations are 5.677(1) (1) and 7.819(53) A (2). Magnetic susceptibility measurements for 1–3 in the temperature range 1.9–290 K show the occurrence of weak ferromagnetic interactions through oxalato (J = +0.75 cm−1) and squarato (J = +1.26 cm−1), the Hamiltonian being defined by H ˆ = - J S ˆ A · S ˆ B . These values are analyzed and discussed in the light of the available magneto-structural data for analogous systems. The quasi-Curie law observed in 3 (θ = −1.15 K) contrasts with the significant antiferromagnetic interaction through bis-chelating croconate in other structurally characterized croconate-bridged copper(II) complexes and rules out the presence of bridging croconate in this compound.
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crystal structures and magnetic properties of the Squarate o1 on bridged dinuclear copper ii complexes cu2 phen 4 c4o4 cf3so3 2 3h2o n 2 and cu2 bipy 4 c4o4 cf3so3 2 6h2o n 3
Inorganica Chimica Acta, 1999Co-Authors: Isabel Castro, Francesc Lloret, Jorunn Sletten, Maria Luisa Calatayud, Miguel JulveAbstract:Abstract Two dinuclear copper(II) complexes of the formula [Cu2(phen)4(C4O4)](CF3SO3)2 · 3H2O (1) and [Cu2(bipy)4(C4O4)](CF3SO3)2 · 6H2O (2) [phen=1,10-phenanthroline, bipy=2,2′-bipyridine and C4O4 2−=dianion of 3,4-dihydroxy-3-cyclobuten-1,2-dione (squaric acid)] have been synthesized and characterized by single-crystal X-ray diffraction. Their structures consist of [Cu2(phen)4(C4O4)]2+ (1) and [Cu2(bipy)4(C4O4)]2+ (2) dinuclear copper(II) cations, uncoordinated CF3SO3 − anions and crystallization water molecules. The copper is in a distorted square pyramidal environment: one Squarate-oxygen atom and three phen- (1) or bipy- (2) nitrogen atoms of two phen (1) or bipy (2) terminal ligands form a distorted square plane around the copper whereas the axial position is occupied by the remaining phen- (1) or bipy- (2) nitrogen atom. The Squarate adopts the μ-1,2- (1) and μ-1,3- (2) bis(monodentate) coordination modes, the intradimer copper–copper separation being 4.912(2) (1) and 7.310(1) (2) A, respectively. Variable temperature magnetic susceptibility measurements reveal the occurrence of significant intramolecular antiferromagnetic coupling, the relevant parameters being J=−26.4 cm−1 and g=2.14 for 1 and J=−8.6 cm−1 and g=2.07 for 2 (J being the exchange parameter in the isotropic spin Hamiltonian Ĥ=−JŜA · ŜB). The influence of both the symmetry of the copper(II) centered magnetic orbitals and the coordination modes of the bridging Squarate on the magnitude of antiferromagnetic coupling in related Squarate-bridged copper(II) complexes is analyzed and discussed.
Charlane C Correa - One of the best experts on this subject based on the ideXlab platform.
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synthesis vibrational spectroscopy and crystal structures of polymers involving transition metals with Squarate ions and 1 3 bis 4 pyridyl propane
Vibrational Spectroscopy, 2007Co-Authors: Charlane C Correa, Renata Diniz, Bernardo L Rodrigues, Maria Irene Yoshida, Luciano H Chagas, Wagner M Teles, Flavia C Machado, Howell G M Edwards, Luiz Fernando C De OliveiraAbstract:Abstract Two new coordination polymers of general formula [Mn(C 4 O 4 )(BPP) 2 (H 2 O) 2 ] and [Co(C 4 O 4 )(BPP) 2 (H 2 O) 2 ] [where BPP = 1,3-bis(4-pyridyl)propane; C 4 O 4 = Squarate ion] were synthesized and characterized by vibrational spectroscopy (Raman and infrared), X-ray diffraction and thermal analysis. These two compounds are isostructural, containing BPP and Squarate ligands coordinated to the metal sites, as well as two water molecules, in a distorted octahedral geometry. The Squarate ion adopts the 1,3-bis(monodentate) coordination mode binding two metallic sites, extending the chain along the a crystallographic axis; this chain interacts with other adjacent chains by means of hydrogen bonds through the free oxygen atoms of the Squarate ion and also the water molecule, as well as the π-stacking of the pyridine rings of the BPP ligand, giving rise to a two-dimensional arrangement where the unidimensional chains are interdigitated. The vibrational spectra of both compounds are very similar and are supportive of the crystallographic data. In the infrared spectra of both complexes an observed band of medium intensity around 1620 cm −1 and another strong band at 1535 cm −1 , assigned to CC/CN and CO stretching modes, respectively, are indicative of the coordination of BPP and Squarate ions to the metal sites. In the Raman spectra, the strong band at 1769 cm −1 , assigned to the CO stretching mode of uncoordinated carbonyl groups of the Squarate ion, is noteworthy.
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transition metal complexes with Squarate anion and the pyridyl donor ligand 1 3 bis 4 pyridyl propane bpp synthesis crystal structure and spectroscopic investigation
Polyhedron, 2007Co-Authors: Charlane C Correa, Renata Diniz, Bernardo L Rodrigues, Maria Irene Yoshida, Luciano H Chagas, Wagner M Teles, Flavia C Machado, Luiz Fernando C De OliveiraAbstract:Abstract Synthesis, crystal structure and the vibrational spectra of coordination polymers with 1,3-bis(4-pyridyl)propane (BPP) and Squarate ion ligands and transition metal ions (M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) are described. All compounds are isostructural, and the BPP is not coordinated to metal site since it is in cationic form due to protonation of N atoms from pyridyl rings. The metal is coordinated to two Squarate ions and two water molecules in an octahedral distorted geometry. The two water molecules are involved in medium hydrogen bonds with Squarate ligands and the average of O⋯O distance is 2.679(3) A. Squarate ions adopt the 1,3-bis(monodentate) coordination mode bridging two metal centers giving rise to a 2D arrangement with (4,4) topology. The four-member ring is slightly distorted and the M–M distances are respectively 8.024 and 8.111 A. The cationic form of BPP molecules are located inside of four-member ring cavity, presenting two different orientations, in which one molecule is inverted comparing to another. Vibrational spectra of all compounds are very similar, in agreement to crystal data. In all infrared spectra of the compounds a medium band at 1640 cm−1 is observed, assigned to the in plane deformation mode of NH bond, indicative of the formation of cationic BPP. In the Raman spectra of the investigated compounds is observed a weak band around 1800 cm−1, assigned to the stretching mode of free CO bond, whereas the medium band observed around 1600 cm−1 is tentatively assigned to coordinated CO stretching mode. At last, a very important achievement of this investigation refers to the coordination geometries of all the investigated compounds, which are governed only by the ligands, independently of the different electronic properties of the metal ions.
