Download Barium Introduction

Element of the Day
Barium
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Ba
At. # 56
At. Wt. 137.327 (7)
[Xe]6s2
Ox. St. +2
MP = 1000 K
BP = 2143 K
298 K solid state
• 1808 - Sir Humphry
Davy, England
• Soft metallic
• Silvery/white
• Green flame
• Easily oxidized
(water, alcohol)
Uses of Barium
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White pigment in paints
Glass
Carbonate form - rat poison
Sulfate form - X-ray diagnostics (insoluble)
Barite form - oil well drilling fluids; rubber
Nitrate & Chlorate forms - fireworks
Ba(SbF6)25XeF2: First Xenon(II)
Compound with Barium.
Synthesis, Vibrational Spectra, and
Crystal Structure
Inorganic Chemistry 2002, 41, 5521-5524
Department of Inorganic Chemistry and
Technology, Jozef Stefan Institute,
Slovenia
Presented by Jocelyn Carswell - 02/12/02
Introduction
• Metal (II) fluorides of alkaline earths react
with Lewis acids in anhydrous HF
• Product has “naked” metal center
surrounded by weakly interacting AF6anions to coordinate weak ligands in solvent
(A = As, Sb)
• Good starting point for new coordination
compounds from various ligand donors
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• Use moderately strong ligand donor XeF2
• Previously two alkaline earth compounds
with XeF2 bound to metal center were
isolated (Ca, Sr)
• This paper - first xenon (II) compound of
barium; first xenon (II) compound in
hexafluoroantimonates (V) of alkaline earth
series
• Ba(SbF6)25XeF2 mentioned previously but
no mention of synthesis or structure
• Preparation of Ba(SbF6)2:
– BaF2 into PFA trap, SbF5 sublimated into trap,
aHF condensed into trap
– Reaction time: 5 minutes
– Cool to room temperature, remove excess aHF
and SbF5
– Product is white solid
– Product verification by total F content: 37.5%
Experimental
• All volatile materials dealt with under
vacuum in Teflon PFA or FEP vessels for
minimal chemical interference
• Nonvolatile materials sensitive to moisture
used in drybox of Argon atmosphere;
subsequent reactions in PFA/FEP vessels to
minimize moisture absorption (< 1 ppm
water vapour)
• Synthesis of Ba(SbF6)25XeF2:
– Ba(SbF6)2 in PFA trap, aHF condensed into
trap
– Clear, colourless solution formed
– Sublimation of XeF2 into solution
– Warm to room temperature, removal of excess
aHF and XeF2
– White solid formed after 24 hours
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Crystal Structure
• Preparation of Single Crystals:
– White solid in one leg of two legged PFA
reaction vessel, aHF condensed into solution
– Solution kept at 291 K, other leg cooled with
water to 283 K
– Slow transfer of aHF out of solution deposits
colourless single crystals
• Product Analysis
Elemental Analysis
• Free and total fluoride ions determined by
fluoride ion selective electrode
• Barium determined by titration with EDTA
• Antimony determined by redox titration
• Mass percentages were calculated
• Theoretical values and experimental values
within 0.1%
• Formula unit two alternating
layers
• Layer 1 - heavy
atom center of
symmetry
• Ba ions nearly
rhombic net
array
• In rhombic plane,
Ba ion - center of F
rectangle
• Sb species centered
in edge of rhombus;
linked to two Ba
ions via F bridging
• XeF2 centered in
rhombus,
perpendicular to
plane of the layer
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• Xe in plane interacts with 12 F
ligands
• Layer 2 - XeF2
molecules
• Layer 2 holds
structure together
via F ligand
coordination
• Note: Ba from
Layer 1 is above Xe
in Layer 2,
repeating structure
• R: 521 cm-1 F ligands
on Xe2
• R: 510 cm-1 F ligands
on other Xe (same
vibration)
• R: 653, 592, 581 cm-1
distorted SbF6octahedral formation
• IR: 673, 636 cm-1
octahedral formation
of Sb complex
• IR: XeF2 vibrations
IR and Raman Spectroscopy
• FT-IR spectrometer
• Powder sample between silver chloride
plates in brass cell (IR analysis)
• Solid sample in PFA reaction vessel
(Raman analysis)
Conclusions
• Synthesis:
– hexafluorometalate anions are poor Lewis base
solvents, so even aHF (a poor Lewis base
solvent) ensures solvation of cations
– addition of XeF2 (stronger Lewis base) gives
environment where Ba ions cannot withdraw F
ligands from Xe and must instead coordinate
them (effective competition between Sb and Xe
molecules based on energy provision)
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Conclusions
• Structure:
– degrees of Lewis basicity witnessed in Ba-F
bond distance comparison for Xe and Sb
molecules
– Xe1 interacts with other Xe molecules, similar
to semi-ionic solid
– Xe2 are well anchored with little vibration
witnessed due to Xe1 interactions
– Xe2 ligands are pulled into Layer 1
– Space group symmetry is C2/m
Reference
• Turicnik, Benkic, Zemva. Ba(SbF6)25XeF2:
First Xenon(II) Compound with Barium.
Synthesis, Vibrational Spectra, and Crystal
Structure. Inorg. Chem. 2002, 41, 55215524.
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