The Man Who Taught Metals to Form Unbreakable Bonds
Malcolm H. Chisholm (1945-2015) revolutionized our understanding of how metal atoms bond with each other, creating new materials with extraordinary properties. 1
Imagine being an architect, but instead of designing buildings with steel and concrete, you construct intricate molecular structures where metal atoms link together through powerful, multiple bonds. This was the world of Malcolm Harold Chisholm, a British inorganic chemist whose groundbreaking work transformed our understanding of chemical bonds and created new possibilities in materials science, energy technology, and sustainable chemistry.
For over four decades, Chisholm pioneered the chemistry of metal-metal multiple bonds, particularly focusing on dimolybdenum and ditungsten compounds—essentially creating and characterizing molecular structures that previous generations of chemists could only dream of 1 3 . His work not only answered fundamental questions about how metal atoms interact but also opened doors to practical applications ranging from biodegradable polymers to advanced solar energy conversion 5 .
Pioneered understanding of double, triple, and quadruple bonds between metal atoms
Developed methods to create stable compounds with unprecedented molecular structures
Enabled advances in biodegradable plastics, solar energy, and sustainable chemistry
To appreciate Chisholm's contributions, we first need to understand the revolutionary concept he helped develop: metal-metal multiple bonds. In simple terms, chemists traditionally understood that metal atoms could form single bonds with each other, but Chisholm and his contemporaries discovered that under the right conditions, metals could form much stronger double, triple, and even quadruple bonds 3 .
Think of it this way: if a single bond between two metal atoms is like two people shaking hands, then a multiple bond is like those same people embracing with both arms—creating a far stronger and more intimate connection.
These extraordinary bonds occur primarily among transition metals—elements like molybdenum and tungsten that occupy the central block of the periodic table 1 .
Single Bond
Double Bond
Triple Bond
Quadruple Bond
What made Chisholm's approach so innovative was his use of specific supporting ligands—molecular "sidekicks" attached to the metals that stabilized these otherwise reactive metal-metal bonds. His pioneering work with alkoxy- and amido-supported complexes created stable environments where these multiple bonds could not only form but could be studied in detail and put to practical use 1 .
In 1976, Chisholm and his team published a landmark paper titled "The molybdenum-molybdenum triple bond. 1. Hexakis(dimethylamido)dimolybdenum and Some Homologs: Preparation, Structure, and Properties" in the Journal of the American Chemical Society 1 . This work represented a quantum leap in inorganic chemistry, systematically demonstrating how to create and characterize compounds with metal-metal triple bonds.
| Step | Procedure | Purpose | Key Observation |
|---|---|---|---|
| Preparation | Reacting molybdenum chloride with lithium dimethylamide in an organic solvent | To replace chloride ions with dimethylamido groups around molybdenum atoms | Formation of a deep green solution indicating the desired product |
| Purification | Crystallization from specific organic solvents | To obtain pure, crystal-line material for study | Formation of well-defined crystals suitable for X-ray analysis |
| Structure Analysis | X-ray crystallography | To determine bond lengths and molecular architecture | Confirmation of Mo-Mo distance consistent with triple bond |
| Property Analysis | Magnetic susceptibility and spectroscopic studies | To understand electronic behavior and confirm bond multiplicity | Diamagnetic behavior confirming all electrons are paired |
The results were extraordinary. The team confirmed that the two molybdenum atoms were indeed connected by a triple bond, with a measured bond distance of approximately 2.18 Ångströms—significantly shorter than a single bond would be, directly demonstrating the stronger attraction between the atoms 1 .
| Parameter | Finding | Significance |
|---|---|---|
| Mo-Mo Bond Distance | ~2.18 Å | Consistent with theoretical predictions for triple bond |
| Molecular Geometry | Trigonal prismatic arrangement | Optimal spatial arrangement to support triple bond |
| Magnetic Properties | Diamagnetic | No unpaired electrons, as expected for triple bond |
| Reactivity | Reactive with small unsaturated molecules | Suggested potential for catalytic applications |
| Bond Type | Bond Order | Example Compounds |
|---|---|---|
| Single Bond | 1 | Some early transition metal halides |
| Double Bond | 2 | Mo₂(chp)₄ (chp = 6-chloro-2-pyridonate) |
| Triple Bond | 3 | Mo₂(NMe₂)₆, W₂(NMe₂)₆ |
| Quadruple Bond | 4 | Mo₂(O₂CCH₃)₄ and derivatives |
While Chisholm's fundamental discoveries about metal-metal bonds were remarkable in their own right, their true value emerged through extensive applications that spanned multiple disciplines. His work demonstrated that pursuing fundamental knowledge often leads to unexpected practical benefits.
His research extended to creating metallo-organic polymers that could form liquid crystals—hybrid materials combining the properties of metals and organic compounds with potential applications in displays and electronics 5 .
| Reagent/Equipment | Function in Research | Specific Example |
|---|---|---|
| Metal Chlorides | Starting materials providing the metal atoms | Molybdenum chloride (MoCl₅), Tungsten chloride (WCl₆) |
| Lithium Dialkylamides | Reagents to install supporting ligands | Lithium dimethylamide (LiNMe₂) |
| Schlenk Line | Specialized glassware for handling air-sensitive compounds | Standard equipment for all syntheses |
| X-ray Crystallographer | Determining molecular structures with atomic precision | Critical for confirming metal-metal bond distances |
Malcolm Harold Chisholm's life work demonstrates the power of fundamental scientific curiosity to transform our understanding of the molecular world. Starting with simple questions about how metal atoms interact, he developed an entirely new branch of inorganic chemistry that continues to influence fields as diverse as materials science, sustainable technology, and energy research.
Published landmark paper on molybdenum-molybdenum triple bonds, establishing new synthetic pathways 1
Elected Fellow of the Royal Society in recognition of his contributions to inorganic chemistry
Awarded the Royal Society's Davy Medal and the ACS Award for Distinguished Service in Inorganic Chemistry
Passed away, leaving behind a legacy of groundbreaking research and generations of trained chemists
His pioneering investigation of metal-metal multiple bonds—exemplified by his seminal 1976 synthesis of hexakis(dimethylamido)dimolybdenum—revealed a hidden landscape of molecular architecture where metals form strong, multiple connections that defy traditional chemical expectations. More than just creating novel compounds, Chisholm's work provided the conceptual framework and synthetic tools that continue to enable new discoveries across chemistry and materials science.
As we face global challenges requiring innovative materials and sustainable technologies, the molecular bridges built by Malcolm Chisholm may well provide the foundation for solutions we have only begun to imagine. His legacy reminds us that fundamental curiosity-driven research, pursued with rigor and creativity, often yields the most profound and practical benefits for society.