217 research outputs found
Hydroxido-supported and carboxylato bridge-driven aggregation for discrete [Ni4] and interconnected [Ni2]n complexes
No full textFour different carboxylato bridges have been efficiently utilized for growth of three tetranuclear nickel(II) complexes [Ni4(μ3-H2L)2(μ3-OH)2(μ1,3-CH3CO2)2](ClO4)2 (1), [Ni4(μ3-H2L)2(μ3-OH)2(μ1,3-C2H5CO2)2](ClO4)2·1/2H2O (2), and [Ni4(μ3-H2L)2(μ3-OH)2(μ1,3-O2C-C6H4-pNO2)2](ClO4)(p-NO2-C6H4-CO2)·DMF·5H2O (3) and one dinuclear nickel(II)-based chain complex {[Ni2(μ-H2L)(μ1,3-O2CCH2Ph)2(H2O)](ClO4)·1/2(CH3OH)}n (4). These were obtained via the reaction of Ni(ClO4)2·6H2O with H3L [2,6-bis((2-(2-hydroxyethylamino)ethylimino)methyl)-4-methylphenol] and RCO2Na (R = CH3,C2H5, p-NO2C6H4, and PhCH2). This family of complexes is developed from {Ni2(μ-H2L)}3+ fragments following self-aggregation. The complexes were characterized by X-ray crystallography and magnetic measurements. The changes from acetate, propionate, and p-nitrobenzoate to phenylacetate groups resulted in two different types of coordination aggregation. These compounds are new examples of [Ni4] and [Ni2]n complexes where organization of the building motifs are guided by the type of the carboxylate groups responsible for in-situ generation and utilization of HO– bridges with alteration in the aggregation process within the same ligand environment. Studies on the magnetic behavior of the compounds reveal that the exchange coupling within 1–4 is predominantly antiferromagnetic in nature
Strategic synthesis of [Cu2], [Cu4] and [Cu5] complexes: inhibition and triggering of ligand arm hydrolysis and self-aggregation by chosen ancillary bridges
No full textThe Schiff base ligand HL1 ({2,6-bis(allylimino)methyl}-4-methylphenol) having no coordinating donor arm has been examined for its reaction medium and ancillary bridge dependent reactivity for hierarchical family of CuII complexes. The ligand showed unique reactivity pattern toward CuII in solution. The bridging nature of in situ generated HO− ions in absence and presence of externally added carboxylates (RCOO−; R= CF3, C6H5 and CH3) has been utilized to produce complexes {[Cu2(µ–L2)2(H2O)]2[Cu2(µ–L2)2(H2O)2](ClO4)6} (1) (HL2 = 3-{(allylimino)methyl}-2-hydroxy-5-methylbenzaldehyde), [Cu4(µ4–O)(µ–L1)2(µ1,3–O2CCF3)4] (2), [Cu4(µ4–O)(µ–L1)2(µ1,3–O2CC6H5)4]∙H2O (3), [Cu5(µ3–OH)2(µ–L1)2(µ1,3–OAc)2(OAc)2(H2O)4][Cu5(µ3–OH)2(µ–L1)2(µ1,3–OAc)2(OAc)3(H2O)](ClO4)3∙2C2H5OH (4). Absence of carboxylate anions did not yield HO− ions in situ and triggered single ligand arm hydrolysis. The formation of tetra- and pentanuclear aggregates as well as ligand hydrolyzed dinulcear products has been rationalized to identify the possible roles of carboxylate anions in solution. Detailed characterization of the complexes in the solid state and in solution have been carried out using spectroscopic measurements, X-ray crystallography, variable temperature magnetic measurements and functional behavior. In MeOH solutions at 298 K, the complexes 1-4 showed catalytic oxidation of 3,5-di-tert-butyl catechol (3,5-DTBCH2) saturated with O2 of air
Bis-tris propane as a flexible ligand for high-nuclearity complexes
No full textPolymetallic complexes can be assembled using a wide array of polydentate ligands that give an almost unlimited toolbox to prepare new molecular architectures with fascinating structures and interesting magnetic properties. Bis-tris propane is one such a polydentate ligand that has been used to prepare homo- (3d or 4f) and heterometallic (3d/3d’ or 3d/4f) complexes, ranging from simple complexes such as {Ni4} to spectacular 3d/3d’ {Cu8Zn8} or {Mn18Cu6} complexes. It shows a flexibility in binding mode, utilizing up to six of its potential ligand donor atoms and displaying multiple levels of deprotonation, able to bridge up to six metal ions. The ligand has a particular affinity for binding 3d ions such as Cu(II) or Co(III) in heterometallic syntheses and this can provide a flexible structure-directing effect. This concept has been exploited to prepare new heterometallic 3d/3d’ complexes that display interesting levels of complexity; 3d/4f complexes such as {Cu3Tb2} that show single-molecule magnet behavior where superexchange interactions quench quantum tunneling of the magnetization, or {Co3Gd3} where the magnetocaloric properties arise by using Bis-tris propane to separate the Gd(III) ions and weaken Gd(III)...Gd(III) interactions
Enhancement of Tb<sup>III</sup>-Cu<sup>II</sup> Single-molecule magnet performance through structural modification
No full textWe report a series of 3d–4f complexes {Ln2Cu3(H3L)2Xn} (X=OAc¢, Ln=Gd, Tb or X=NO3 ¢, Ln=Gd, Tb, Dy, Ho, Er) using the 2,2’-(propane-1,3-diyldiimino)bis[2 (hydroxylmethyl)propane-1,3-diol] (H6L) pro-ligand. All complexes, except that in which Ln=Gd, show slow magneticrelaxation in zero applied dc field. A remarkable improvement of the energy barrier to reorientation of the magnetisationin the {Tb2Cu3(H3L)2Xn} complexes is seen by changing the auxiliary ligands (X=OAc¢ for NO3 ¢). This leads to thelargest reported relaxation barrier in zero applied dc field for a Tb/Cu-based single-molecule magnet. Ab initio CASSCF calculations performed on mononuclear TbIII models are employed to understand the increase in energy barrier and the calculations suggest that the difference stems from a change in the TbIII coordination environment (C4v versus Cs
Synthesis, structure, and magnetic properties of the single-molecule magnet [Ni-21(Cit)(12)(OH)(10)(H2O)(10)](16-)
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Synthesis, structure, and magnetic properties of the single-molecule magnet [Ni-21(Cit)(12)(OH)(10)(H2O)(10)](16-)
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