Bis(1-hydroxy-1H-pyridine-2-thionato-O,S)copper
[CAS# 14915-37-8]

Identification

• Classification: Pharmaceutical intermediate >> Heterocyclic compound intermediate >> Pyridine compound >> Pyridine derivative
• Name: Bis(1-hydroxy-1H-pyridine-2-thionato-O,S)copper
• Synonyms: copper bis(1-oxidopyridine-2-thione)
• Molecular Formula: 2(C₅H₄NOS).Cu
• Molecular Weight: 315.86
• CAS Registry Number: 14915-37-8
• EC Number: 238-984-0
• SMILES: C1=CC(=S)N(C=C1)[O-].C1=CC(=S)N(C=C1)[O-].[Cu+2]

Safety Data

• Hazard Symbols: GHS05;GHS06;GHS07;GHS09 Danger
• Risk Statements: H302-H315-H318-H330-H400
• Safety Statements: P260-P264-P264+P265-P270-P271-P273-P280-P284-P301+P317-P302+P352-P304+P340-P305+P354+P338-P316-P317-P320-P321-P330-P332+P317-P362+P364-P391-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Serious eye damage	Eye Dam.	1	H318
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	1	H330
Acute toxicity	Acute Tox.	2	H330
Specific target organ toxicity - single exposure	STOT SE	3	H335
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410

Discovery and Applications

Bis(1-hydroxy-1H-pyridine-2-thionato-O,S)copper is a copper complex formed from two bidentate 1-hydroxy-1H-pyridine-2-thionate ligands coordinated to a central copper ion through oxygen and sulfur donor atoms. The ligand is derived from 2-mercaptopyridine N-oxide, which can exist in tautomeric equilibrium between thiol and thione forms. Upon deprotonation, it acts as an O,S-chelating ligand, binding metal ions through the oxygen of the N-oxide group and the sulfur atom at the 2-position. The resulting complex is commonly isolated as a stable, colored solid and has been extensively characterized in coordination chemistry.

Systematic investigation of pyridine N-oxides and their sulfur analogues developed during the mid-20th century as part of broader research into heterocyclic ligands capable of forming stable chelate complexes. The ability of 1-hydroxy-2-pyridinethione derivatives to coordinate metals through two adjacent donor atoms was demonstrated through analytical and spectroscopic studies. Copper complexes of such ligands attracted particular attention because copper readily forms stable chelates with mixed oxygen and sulfur donors. Structural analysis using techniques such as infrared spectroscopy, electronic absorption spectroscopy, and X-ray crystallography confirmed the bidentate coordination mode and the formation of five-membered chelate rings.

The copper center in bis(1-hydroxy-1H-pyridine-2-thionato-O,S)copper is typically in the +2 oxidation state. Coordination by two monoanionic ligands provides a four-coordinate environment, often described as approximately square planar or distorted tetrahedral depending on solid-state packing and specific experimental conditions. Crystallographic studies have established that each ligand binds through the deprotonated oxygen and sulfur atoms, forming two chelate rings around the metal ion. The delocalized electronic structure of the ligand contributes to the stability of the complex.

One of the most widely documented applications of copper complexes of 1-hydroxy-2-pyridinethione derivatives is in the field of antifouling and antimicrobial materials. Related metal complexes have been used as biocidal agents in coatings and wood preservation formulations. Their activity has been evaluated in standardized laboratory tests against fungi and bacteria, and their performance has been correlated with controlled release of the active species from treated surfaces. The stability of the chelate complex influences both durability and efficacy in such applications.

In addition to practical uses, bis(1-hydroxy-1H-pyridine-2-thionato-O,S)copper has served as a model compound in coordination chemistry. Studies of its electronic spectra have provided insight into ligand-to-metal charge transfer transitions and d–d transitions characteristic of copper(II) complexes. Magnetic susceptibility measurements have confirmed the presence of an unpaired electron consistent with a d⁹ electronic configuration. These experimental observations align with established ligand field theory for copper(II) complexes in four-coordinate geometries.

The ligand framework has also been examined for its ability to stabilize different metal ions beyond copper. Comparative investigations with zinc, iron, and other transition metals have highlighted how donor atom identity and chelate ring formation influence complex stability constants. Such work has contributed to the broader understanding of structure–property relationships in O,S-donor ligand systems.

From a synthetic perspective, preparation of bis(1-hydroxy-1H-pyridine-2-thionato-O,S)copper typically involves reaction of a soluble copper(II) salt with the deprotonated ligand in aqueous or alcoholic solution. The complex often precipitates as a colored solid that can be purified by recrystallization. Elemental analysis and spectroscopic characterization confirm stoichiometry and coordination mode.

The discovery and characterization of this copper chelate illustrate the development of mixed-donor ligand chemistry and its practical implications. By combining oxygen and sulfur coordination in a rigid heterocyclic framework, the ligand forms stable complexes whose structural and functional properties have been validated through extensive experimental study.

References

2001. Bis[1-hydroxypyridine-2(1H)-thionato-S,O]copper(II). Acta Crystallographica Section C: Crystal Structure Communications.
DOI: 10.1107/s0108270101012306