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Molecular packing and magnetic properties of lithium naphthalocyanine crystals: Hollow channels enabling permeability and paramagnetic sensitivity to molecular oxygen
Periyakaruppan Thangiah Manoharan
Published in
2009
Volume: 19
   
Issue: 24
Pages: 4138 - 4147
Abstract
The synthesis, structural framework, magnetic and oxygen-sensing properties of a lithium naphthalocyanine (LiNc) radical probe are presented. LiNc was synthesized in the form of a microcrystalline powder using a chemical method and characterized by electron paramagnetic resonance (EPR) spectroscopy, magnetic susceptibility, powder X-ray diffraction analysis, and mass spectrometry. X-Ray powder diffraction studies revealed a structural framework that possesses long, hollow channels running parallel to the packing direction. The channels measured approximately 5.0 × 5.4 2 in the two-dimensional plane perpendicular to the length of the channel, enabling diffusion of oxygen molecules (2.9 × 3.9 2) through the channel. The powdered LiNc exhibited a single, sharp EPR line under anoxic conditions, with a peak-to-peak linewidth of 630 mG at room temperature. The linewidth was sensitive to surrounding molecular oxygen, showing a linear increase in pO2 with an oxygen sensitivity of 31.2 mG per mmHg. The LiNc microcrystals can be further prepared as nano-sized crystals without the loss of its high oxygen-sensing properties. The thermal variation of the magnetic properties of LiNc, such as the EPR linewidth, EPR intensity and magnetic susceptibility revealed the existence of two different temperature regimes of magnetic coupling and hence differing columnar packing, both being one-dimensional antiferromagnetic chains but with differing magnitudes of exchange coupling constants. At a temperature of ∼50 K, LiNc crystals undergo a reversible phase transition. The high degree of oxygen-sensitivity of micro- and nano-sized crystals of LiNc, combined with excellent stability, should enable precise and accurate measurements of oxygen concentration in biological systems using EPR spectroscopy. © 2009 The Royal Society of Chemistry.
About the journal
JournalJournal of Materials Chemistry
ISSN09599428
Open AccessYes
Concepts (45)
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    Accurate measurement
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    Anoxic conditions
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    ANTIFERROMAGNETIC CHAIN
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    Chemical method
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    Electron paramagnetic resonance spectroscopy
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    EPR INTENSITY
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    Epr spectroscopy
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    Exchange coupling constants
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    MICROCRYSTALLINE POWDERS
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    MOLECULAR PACKINGS
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    NANO-SIZED CRYSTALS
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    NAPHTHALOCYANINE
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    Oxygen concentrations
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    Oxygen molecule
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    OXYGEN SENSITIVITY
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    OXYGEN-SENSING
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    PEAK LINEWIDTH
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    Powder x ray diffraction
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    REVERSIBLE PHASE TRANSITION
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    Room temperature
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    Structural frameworks
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    Temperature regimes
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    THERMAL VARIATION
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    TWO-DIMENSIONAL PLANES
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    Antiferromagnetic materials
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    Antiferromagnetism
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    Biological systems
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    Crystals
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    Diffraction
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    Electron resonance
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    Electron spin resonance spectroscopy
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    Exchange coupling
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    Linewidth
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    Lithium
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    Magnetic couplings
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    Magnetic susceptibility
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    Mass spectrometry
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    Paramagnetic materials
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    Paramagnetic resonance
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    Paramagnetism
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    Phase transitions
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    Powders
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    Synthesis (chemical)
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    X ray diffraction analysis
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    Molecular oxygen