by Introduction
Cobalt oxalate is a chemical compound with formula CoC2O4. It is a red or purple crystalline solid which occurs naturally as the rare mineral cobaltocalcite. This compound finds several uses due to its unique properties which will be discussed in detail in this article.
Structure and Properties
Cobalt oxalate crystallizes in the monoclinic crystal system. The structure consists of Co2+ ions coordinated by two oxalate ions in a distorted octahedral geometry. The oxalate ions link the cobalt centers into chains running along the b-axis of the unit cell through bridging. These chains are further linked by hydrogen bonding interactions between oxalate oxygen and hydrogen atoms of water molecules.
The compound is hygroscopic in nature and readily absorbs moisture from atmosphere. It dissolves well in water forming pink colored solutions. Thermal decomposition starts above 150°C leading to the formation of cobalt(II) oxide. Oxalate can act both as a bidentate ligand coordinating through both carbonyl oxygen atoms or as a monodentate ligand coordinating through a single oxygen. These structural features give rise to its diverse reactivity and applications.
Magnetic Properties
Cobalt oxalate exhibits weak ferromagnetism below 4.2K due to antiferromagnetic interactions between Co2+ ions coupled with spin-orbit interactions. Above this temperature, it shows antiferromagnetic ordering up to the Néel temperature of 22K. The magnetic susceptibility follows the Curie-Weiss law in the paramagnetic region indicating dominant antiferromagnetic interactions between nearest neighbor cobalt centers.
The magnetic behavior arises from the unpaired electrons in the d orbitals of cobalt which have a preferred orientation or spin. The antiferromagnetic order develops as the neighboring spins align antiparallel to cancel out their magnetic moments above 4.2K. Below this temperature, a net spontaneous magnetization occurs due to canting of the ordered spins. These unique magnetic interactions find various applications.
Applications in Catalysis
Due to the presence of redox-active Co2+ centers, cobalt oxalate has found wide application as a heterogeneous catalyst. Some of its important catalytic uses are:
– Oxidation reactions: It is widely used for the aerobic oxidation of alcohols to carbonyl compounds, oxidation of cyclohexane to adipic acid, etc. The oxalate ligands help stabilize the active cobalt oxy species responsible for oxidation.
– Hydrogenation reactions: Finely divided cobalt oxalate catalyzes the hydrogenation and hydroformylation of alkenes under mild conditions. The metal centers exhibit high activity for addition of H2 across carbon-carbon double bonds.
– Carbon-carbon coupling: It shows excellent activity for Ullmann coupling, Suzuki-Miyaura cross-coupling, cyanation, etc involving the formation of carbon-carbon or carbon-heteroatom bonds.
These reactions are important in bulk chemical and fine chemical industries. Compared to molecular catalysts, cobalt oxalate provides advantages of ease of recovery, recyclability and sustained activity on reuse.
Magnetic Storage Applications
Due to the net ferromagnetic ordering below 4.2K, cobalt oxalate has potential for high density magnetic storage applications. Investigations show it can give coercivities exceeding 15 kOe at low temperatures suitable for practical devices.
When doped with small amounts of manganese, the magnetic transitions are significantly improved. Such Cobalt Oxalate compounds provide very high uniaxial magnetic anisotropy useful for information recording. Nanoparticles of these materials enclosed in protective layers are being researched for next generation hard disk drives and non-volatile memory chips.
Other Uses
A few other specialty applications of cobalt oxalate that have been reported include:
– Gas sensors: Thin films show excellent sensitivity and selectivity for detecting toxic and flammable gases like hydrogen sulfide and methane.
– Electrochemical devices: As an electrode material in lithium ion batteries and supercapacitors due to the redox activity of cobalt.
– Pigments and dyes: Imparts attractive pink/purple colors for applications in paints, inks and textiles. The color intensity depends on particle size.
Thus in summary, cobalt oxalate is a technologically important compound with diverse uses in catalysis, magnetism and electrochemical energy due to the versatile coordination chemistry and magnetic behavior of cobalt. Continuous research globally aims to fully unlock its potential across different fields.
This article discussed the structural, magnetic and applications of cobalt oxalate in detail without any recommendations. The compound was shown to find widespread application as a heterogeneous catalyst due to the redox activity of cobalt centers. It also has promising uses in magnetic memory devices leveraging the ferrimagnetic ordering at low temperatures. Overall, cobalt oxalate is a multifaceted material with several current and emerging technological applications.
