Structural and magnetic investigations on new molecular quantum rings

Abstract

We report on a comparative investigation of the structural and magnetic properties of three oxygen-bridged polynuclear (N ¼ 6, 8, 10) Cu(II) cyclomethylsiloxanolate complexes, Cu 6 [(MeSiO 2 ) 6 ] 2 $6DMF (1), {Cu 8 [(MeSiO 2 ) 8 ] 2 $8DMF}$EtOH (2) and {Cu 10 [(MeSiO 2 ) 10 ] 2 $10DMF}$6DMF (3). All three molecular complexes have a planar ring-shaped configuration of the copper S ¼ 1/2 spins. The analysis of the magnetic data, with particular emphasis placed on the high-temperature behaviour, together with the structural information enables us to correlate the evolution of the exchange coupling J between the magnetic S ¼ 1/2 centers of the quantum ring as a function of the number N of magnetic sites to the structural changes of the molecular crystals.

Synthesis, Structure and Magnetic Properties of a Novel Hexanuclear Copper Methylsiloxane Complex

“…For the family of the ring-shaped polynuclear Cu II cyclomethylsiloxanolate complexes, the critical bonding angle of the oxygen bridge Cu-O-Cu for a transition between ferromagnetic and antiferromagnetic exchange is approximately 96°. [10] Yet, it seems plausible that the highest bonding angles of about 94°(see Table 1) might be close enough to the critical angle that the corresponding exchange coupling is significantly reduced compared to the other two. Our results thus seem to suggest that the magnetic properties of quantum rings are very susceptible to small structural infringements of symmetry, which at once effectively split the ring as a whole into a system with simpler blocks: poorly cooperating trimers or dimers.…”

“…The first terms are given by Equation (2) (2) where J av = (J 1 + J 2 + J 3 )/3 is the average exchange interaction within the ring. [10,15] In Equations (2)- (4), N is the number of spins and k B is the Boltzmann constant. For uniform exchange couplings J 1 = J 2 = J 3 , we have compared this high-temperature approximation with results of a complete numerical diagonalization for spin S = 1/2 rings with N = 6 and concluded that this is in satisfactory agreement with the exact solution for temperatures above 3/2·J av .…”

“…Preliminary results of this work have been published in ref. [10] , in which the high-temperature susceptibility of this complex has been analyzed and an initial comparative investigation of the structural and magnetic properties has been carried out.…”

A novel flower basket-shaped organosilyl derivative based on trivacant tungstosilicate: [(C4H9)4N]3H[α-A-SiW9O34(CH3SiO)6]·3H2O

“…In addition, it should be noted that, similarly to the known sandwich-like complexes [Cu 6 {(MeSiO 2 )6 } 2 ]·6DMF[32,33], both of which consists of a hexa-number ring formed methylsiloxane.As we know, the previously reported organosilyl derivatives based on POMs are limited and mainly domainated by di-, tri-and tetrasubstituted species. The first disubstituted organosilyl derivative based on monovacant POMs [α-SiW11 O 39 {O(SiR) 2 }] 4− contains a dimeric μ-oxo-bridged (RSi) 2 O group occupying the vacant site of [α-SiW 11 O 39 ] 8− , in which each {RSi\} group links to two {WO 6 } units of [α-SiW 11 O 39 ] 8− backbone through Si\O\W bridge [7].…”

Alkali-Metal-Directed Hydrolytic Condensation of 3-Mercaptopropyltrimethoxysilane

“…It was found that properties of metal cations can influence the structure of the formed moieties since they work as template centers and structural elements helping to bind siloxane bonds into cyclic organosiloxanolate fragments [20][21][22][23][24][25][26][27][28][29][30][31][32]. While transition or rare-earth metal cations lead to the formation of varied-size (n=4 [20], 5 [21], 6, 8, 12 [22][23][24]) cyclic species, sodium and potassium cations enable the synthesis of small cyclosiloxanes containing three [25][26][27][28] or four [29][30][31] silicon atoms. Reaction parameters (the amount of water, type of organosilane and solvent) also can affect the ring size of cyclic products [32].…”