| Summary: | This study was initiated in order to synthesize, and where appropriate, to investigate the
magnetic properties of selected main group and transition metal cationic complexes, all
stabilized by weakly basic fluoro anions derived either from the Brönsted superacids HSO₃F and
HSO₃CF₃,or the Lewis acids SbF₅and AsF₅.
Of the preparative reactions, the solvolysis of metal(ll) fluorosulfates in excess SbF₅
according to:
[scientific formula – please see full abstract) with M=Ni, Pd, Cu, Ag or Sn, is found to be a useful synthetic route to the corresponding
divalent hexafluoro antimonates. The products, as their precursors, are characterized as CdCl₁₂-
type layered polymeric compounds. Relevant vibrational (Raman and IR), electronic and
¹¹⁹Sn-Mössbauer spectra as well as magnetic susceptibility measurements and X-ray powder
data are reported. Several compounds prepared by this method display unusual features:
Pd(SbF₆)₂ is, like its fluorosulfate precursor, paramagnetic with the Pd²+ ion in a ³A₂g ground
state. Ag(SbF₆)₂,unlike its paramagnetic blue valence isomer, is diamagnetic and nearly white
in color, and is formulated as the mixed valency complex Ag(I)[Ag(III)(SbF₆)₄]. The
Cu(SbF₆)₂ compound also contains, in addition to Cu²+ ions, small quantities of Cu(I) and
Cu(Ill) ions. Both Ni(SbF₆)₂ and Pd(SbF₆)₂ exhibit temperature dependent low magnetic
moments, indicative of antiferromagnetic exchange. Pd(SbF₆)₂ also displays very weak ferro
magnetism below -lOK.
The Sn(SbF₆)₂ product from the above synthesis, and its precursor Sn(SO₃F)₂,react with
excess 1,3,5-trimethylbenzene(mesitylene or mes) to give the it-arene adducts Sn(SbF₆)₂ 2mes
and Sn(SO₃F)₂ mesin high yield. The adducts are characterized by elemental analysis and
infrared spectra. The adduct formation is followed by ¹¹⁹Sn Mössbauer spectroscopy. It is
found that only tin(ll) compounds with large, weakly nucleophilic anions are capable of forming
mesitylene complexes, while SnCl₂,SnF₂,and stannocene do not give any indication of adduct
formation under similar reaction conditions.
The divalent fluorosulfates Ni(SO₃F)₂,Pd(SO₃F)₂ and Ag(SO₃F)₂,precursors to the
M(SbF₆)₂ compounds, and the mixed valency Pd(II)[Pd(IV)(SO₃F)₆],as well as their
corresponding trifluoromethylsulfate derivatives Ni(SO₃CF₃)₂, Pd(SO₃CF₃)₂ and
Ag(SO₃CF₃)₂,investigated for their magnetic behavior by susceptibility studies down to -4
K,
show significant magnetic exchange, and except in Ag(SO₃CF₃)₂,the onset of magnetic
exchange becomes observable at low temperatures. The fluorosulfates are found to exhibit
strong ferromagnetism below -11 K, whereas the trifluoromethylsulfates behave as anti
ferromagnets with the spin interactions noted over a wider temperature range. The maximum
magnetic susceptibilities of Ni(SO₃F)₂,Pd(SO₃F)₂ and Ag(SO₃F)₂ indicate saturation
magnetization, and hence for these compounds field dependent maximum magnetic moments
are obtained in the temperature range -5 to 10.5 K. Maxima in the susceptibility vs. tempera
ture plots are noted for the antiferromagnets Pd(SO₃CF₃)₂ and Ag(SO₃CF₃)₂ at -4 and -13 K
respectively. Unlike in the corresponding divalent antiferromagnetic fluorides, no spin canting
is detected in the trifluoromethylsulfates at lower temperatures.
Magnetic susceptibility measurements to -4 K are also carried out for the main group
molecular cations withinO2[AsF6],Br2[Sb3F16]andI2[Sb2F1i] The data are interpreted
utilizing previous results from photoelectron spectroscopy, known crystal structures, magnetic
studies on the superoxide ion and the ozonide ion, and in the case of Oj[AsF6],previous ESR
studies.
The magnetic properties of the three materials are quite different. Br2[Sb3F16]obeys Curie-
Weiss law between 80 and 4 K. The magnetic moment decreases slightly from 2.04 B at room
temperature to 1.93 B at 4 K. I2[Sb2F11]exhibits relatively strong antiferromagnetic
coupling with a maximum in XM observed at -54 K. The magnetic moment (corrected for TIP)
decreases from 1.92 B at 124 K to 0.41 B at 4 K. Experimental susceptibilities for this
compound over the temperature range 300-4 K have been compared to values calculated using
three different theoretical models for extended chains of antiferromagnetically coupled
paramagnetic species.02+[AsF6]exhibits Curie-Weiss behavior over the temperature range
60-2 K. The magnetic moment, uncorrected for TIP, varies from 1.63 B at 80 K to 1.17 I.LB at 2
K, and the presence of weak antiferromagnetic coupling in this material is suggested. === Science, Faculty of === Chemistry, Department of === Graduate
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