Molecule-Based Magnets: Ferro- and Antiferromagnetic Interactions in Nickel(II) Cyclohexasiloxanolate Sandwich Complexes

Ferromagnetic exchange-coupling interactions mediated by siloxanolate ligands have been detected in the two nickel(II) nanoscale clusters Na2[(PhSiO2)6Na4Ni4(OH)2(O2SiPh)6]. 16Bu(n)OH (1) and Na2[(PhSiO2)6Ni6(O2SiPh)6Cl].12CH3OH. H2O (2), which qualify as interesting precursors for new molecule-based magnetic materials. Complex 1 has an S = 4 spin ground state, whereas complex 2 has an S = 0 spin ground state. due to the presence of additional antiferromagnetic interactions through the encapsulated mu(6)-chloride ion

[(salen)Al]-Mediated, Controlled and Stereoselective Ring-Opening Polymerization of Lactide in Solution and without Solvent: Synthesis of Highly Isotactic Polylactide Stereocopolymers from Racemic d,l-Lactide

Easily accessible [(salen)(iPrO)Al] exerts excellent molecular-weight and stereochemical control in lactide polymerization either in solution or in the absence of solvent. The R,R initiator shows a marked preference for L-lactide over D-lactide. Stereoblock copolylactides with high melting points can be prepared directly from d,l-lactides by using a racemic initiator

SILOXANE CLUSTERS OF HIGHER VALENCE TRANSITION-METALS - REDOX PROPERTIES

Cyclic voltammetric behaviour of polymetallic complexes of hexaphenylcyclohexasiloxane-hexaol with Ni, Mn and dodecaphenyl-cyclododecasiloxane-dodecaol with Cu was studied. The complexes react electrochemically as a unit assembly of the complexed metals

Molecule-based Magnets: Ferro- and Antiferromagnetic Interactions in Copper(II)-polyorganosiloxanolate Clusters

The magnetic behavior of the clusters [(PhSiO2)6Cu6(O2SiPh)6]\ub76EtOH (1), Na4[(PhSiO2)12Cu4]\ub78BuOH (2), and K4[(C2H2SiO2)12Cu4]\ub76BuOH (3) was studied by combined magnetic susceptibility measurements and variable-temp. EPR techniques (9.25 and 245 GHz). The six Cu(II) ions in the core of 1, which approaches 6/mmm symmetry, are ferromagnetically coupled as a result of the geometry at the bridging siloxanolate O atoms (Cu-O-Cu = 91.5-94.6\ub0; J = -42 cm-1). The ground S = 3 spin state is split in zero field mainly due to anisotropic exchange contributions (D = 0.30 cm-1). Notably, both the magnitude and the sign of the zero-field splitting parameter were detd. from HF-EPR spectra. Large antiferromagnetic Cu-Cu interactions (J 3c 200 cm-1) and an S = 0 ground state were detected in the tetranuclear clusters 2 and 3 as a consequence of the larger Cu-O-Cu angles. The results are relevant to the search for new mol.-based magnetic materials

Synthesis of macrocyclic tris-cis-tris-trans- dodeca[(phenyl)(hydroxy)]cyclododecasiloxane in carbonic acid solution

The possibility to synthesize stereoregular tris-cis-tris-trans- dodeca[(phenyl)(hydroxy)]cyclododecasiloxane (tris-cis-tris-trans-[PhSi(O)OH]12) in an inorganic liquid medium – aqueous carbonic acid solution – was shown. The interaction of polyhedral phenylcoppersodiumsiloxane, {[(C6H5Si(O)O−]12(Cu2+)4(Na+)4}*(L)m (L = Bun OH, H2O), with carbonic acid can be considered as a new ‘green’ method to obtain functional organosiloxane macrocycles. In contrast to the known methods, no organic solvents were used during the reaction. The identification of the structure of the end compound was performed by means of NMR and Infrared spectroscopy as well as X-ray crystallography

New Cyclosiloxanolate Cluster Complexes of Transition Metals

New cyclosiloxanolate transition metal cluster complex derivs. were prepd. PhSiO2K reacted with NiX2 (X2 = Cl2 or acac) to give K2{[η6-(PhSiO2)6]2[μ3-(OH)]2Ni4K4}, a mixed Group 1-group 10 metal complex. PhSiO2Na reacted with Ni(NH3)6I2 to give Na{[η6-(PhSiO2)6]2Ni6(μ6-I)} as the 1st example of encapsulated I- ion in siloxanolate complexes. The macrocyclic Na4{[η12-(PhSiO2)12]Cu4} complex reacted with η6-(1,3,5-C7H8)Cr(CO)3 to give the heterobimetallic adduct Na4{[η12-(PhSiO2)12]Cu4}[Cr(CO)3]3 as one of the rare examples of heterobimetallic complexes with different oxidn. nos. of the metals. The Cu deriv. {[η6-(PhSiO2)6]2Cu6(BuOH)5} reacted in MeOH/CHCl3 (1:6) with Et4NCN to give hexanuclear {[η6-(PhSiO2)6]2Cu6(η2-C3H5N2O2)2}, contg. 2-amino-2-oxoethanimidic acid Me ester monoanion ligands, product of an unexpected C-C coupling reaction. This latter complex was characterized also by x-ray diffraction crystal and mol. structure detn

Rational design of large-spin clusters based on the hexacopper(II) siloxanolate core

The hexacopper(II) siloxanolate cage [Cu6{(PhSiO2)6}2(BuOH)5]·3BuOH was synthesized by reaction between CuCl2 and potassium phenylsiloxanolate in n-butanol, and characterized by single-crystal x-ray diffraction, magnetic measurements and high-frequency EPR (HF-EPR). The complex exhibits a torus-like structure featuring a layer of six copper(II) ions sandwiched between two cyclic (PhSiO2)66- ligands and surrounded by BuOH mols. Two different mols. are obsd. in the crystal structure of [Cu6{(PhSiO2)6}2(BuOH)5]·3BuOH. One mol. has all six copper atoms bonded to BuOH ligands and the other has only four of the six copper atoms bonded to BuOH ligands. The magnetic properties were characterized by moderate ferromagnetic exchange interactions between the S = 1/2 copper(II) centers to give an S = 3 ground spin state. Variable temp. HF-EPR spectra evidence a hard-axis magnetic anisotropy with gpar = 2.063, gperp = 2.225 and D = 0.31 cm-1. The cage is very sol. in org. solvents and, upon exchange of the labile BuOH ligands, it functions as a high-spin hexatopic receptor for monodentate units. Reaction with the trigonal bipyramidal copper(II) mononuclear [Cu(tmpa)CN]+ in CHCl3/MeOH soln. (tmpa = tris(2-pyridylmethyl)amine) affords the decacopper(II) complex [Cu6{(PhSiO2)6}2{NCCu(tmpa)}4](PF6)4, whose x-ray structure and magnetic behavior are presented

Heterobimetallic cyclosiloxanolate sandwich clusters: Na{[η6-cyclo(PhSiO2)6]2[Fe(OR)]2Ni4(μ6-Cl)} (R = H, Me)

The heterobimetallic cyclosiloxanolate sandwich clusters Na{[η6-cyclo(PhSiO2)6]2[Fe(OR)]2Ni4(μ6-Cl)} (R = H, Me) (1) were prepd. from Na2{[(PhSiO2)6]2Na4Ni4(OH)2} as solvates. The new clusters 1 were characterized by spectra (UV-visible, IR, 1H-NMR), cyclic voltammetry, cond., magnetic susceptibility, and single-crystal x-ray diffraction for 1·10MeOH (R = Me)

Bimetallic Cyclooligosiloxanolate Complexes of Copper and Nickel

The bimetallic cyclosiloxanolate cluster complexes Na[(PhSiO2)6Cu4Ni2(μ6-Cl)(PhSiO2)6] (1) and Na[(PhSiO2)6Cu3Ni3(μ6-Cl)(PhSiO2)6] (2) were prepd. by Na+ and Ni2+ ion exchange from in situ generated Na2{[(PhSiO2)6]2Na4Ni4(OH)2}. Complexes 1 and 2 were characterized by anal., spectroscopic and electrochem. methods as well as complex 2 by single-crystal x-ray diffraction (2·7DMSO·H2O: orthorhombic, space group P212121, R = 0.076). The x-ray structure shows a sandwich-type array comprising two superimposed cyclosiloxanolate rings and an M6Cl unit in between. For the 1st time the regioselectivity of the metal ion exchange could be deduced from the x-ray structural parameters