Nickel tetracarbonyl - highly unpleasant, but extremely useful (Credit: Wikimedia commons/ Benjah-bmm27)

For my contribution to Sciencegeist’s toxic blog carnival, I decided to write about a decidedly enigmatic compound. Nickel tetracarbonyl is a transition metal complex but also a foul-smelling (and, given the context of this blog post, naturally highly toxic) gas. These are not generally two molecular properties that coincide. It also forms quite easily when nickel metal comes into contact with carbon monoxide.

Having not personally worked with it, I nevertheless respect and admire nickel tetracarbonyl from afar. However, this is a compound which can provoke intensely personal reactions from people who have had the opportunity to get a little more hands-on. I came across possibly one of the most vivid of these in our Chemistry in its element podcast series when Bernie Bulkin described his initiation into a lab working on metal carbonyl complexes:

‘One of the first things I was given to read when I started was the summary of the toxicological effects of nickel carbonyl.  I learned, with some concern, that at 30ppm it was certainly fatal, and even a significantly lower dose of 3ppm caused death in 50% of a group of test animals.

‘When you breathe it in, it decomposes, giving you a dose of carbon monoxide and depositing some nickel on your lungs. If you survive the first few hours, the nickel causes a form of pneumonia, coughing, breathlessness, extreme fatigue.  This lasts for several days, often resulting in cardiovascular or renal failure and death.  I was relieved to find that the safety precautions in the lab were extremely rigorous.’

The concept of receiving a bolus dose of carbon monoxide – deadly enough in its own right as described in Patrick’s blog yesterday – plus the added spice of nickel-plated lungs, was enough to imprint an instant respect for the compound in my mind.

So why on Earth might we want to make or use this compound, given its extreme potential to cause harm?

Nickel as a metal is industrially important – it is hard, shiny and reasonably resistant to corrosion (except by carbon monoxide of course…). Alloyed into steel or plated over the surface it endows the metal with these useful properties too, so much so that it was used to make coins (before being largely replaced by iron, which is cheaper and doesn’t cause the same kind of skin irritation that some people experience when handling nickel). Some coins, particularly the US five-cent pieces known as ‘nickels’, still contain nickel alloyed with copper or plated on the surface of a steel blank.

Nickel’s hardness and corrosion resistance also makes it ideal as the basis for superalloys used to make jet engine turbine blades. These are generally grown as single crystals of the metal for optimum performance at the high temperatures and force loadings of a working jet engine.

So where does nickel carbonyl fit in?

Nickel is rarely found in ores on its own – it is usually combined with its transition metal neighbours iron and cobalt. In fact, the name nickel comes from colloquial German for ‘devil’ (think of ‘Old Nick’ in English folklore) and cobalt derives from the word for a gremlin or hobgoblin, reflecting their role as annoying impurities in iron ores. So a method for separating the metals would not only deliver the desirable nickel, but improve processes for purifying iron and cobalt as well.

Having discovered nickel carbonyl by accident, Ludwig Mond – a German chemist – found that nickel reacts with carbon monoxide much more quickly than does either iron or cobalt. As a savvy businessman, he realised the potential of this observation and, in the late 19th century, developed it into the Mond process for extracting nickel from mixed ores. Reacting impure nickel with CO releases it as gaseous nickel carbonyl and leaves behind the impurities. The nickel can then be reclaimed by heating the complex until it decomposes. This process is still used when the purest nickel (greater than 99.99% pure) is required.

From a research chemistry point of view, nickel complexes form a variety of useful catalysts. Many of these are prepared from nickel carbonyl in some form, owing to the ease of displacing the carbonyl ligands. However, the chemist aspiring to prepare such catalysts would be well advised to seek out alternative sources of nickel in which someone else has already done the carbonyl substitutions – nickel plated lungs and death by suffocation or pneumonia is certainly not to be recommended…

Phillip Broadwith

                  

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Over at Sciencegeist they’ve throw down the gauntlet and asked bloggers to write about their favourite toxic chemical as part of a carnival of toxins that also play important roles in everyday life. It’s all part of the campaign by chemists and bloggers alike against ‘chemophobia’ – an irrational fear of the chemicals we find all around us in everyday life or even the very word ‘chemical’. Recently there seems to have been a spate of these articles in newspapers with chemical-free labels even popping up in labs where they ought to be choosing their words with a little more care!

Canaries provided a CO early warning system for miners

So I’m going to kick off Chemistry World’s contribution to the carnival with carbon monoxide: the silent killer. It’s now pretty much common knowledge that this diatomic molecule can kill, thanks to television images of people committing suicide by gassing themselves with car exhausts (this is much less likely today as catalytic converters mop up and transform much of the CO in exhaust fumes) and public health campaigns highlighting the dangers of the gas in the home. But John Scott Haldane, the father of noted geneticist J B S Haldane, was the first to realise that this colourless, odourless gas was responsible for the deaths of many miners. The CO that killed these miners was the result of incomplete combustion of carbon during coal dust explosions. J S Haldane, belonging to that intrepid class of chemists that is all but extinct now, used himself as a guinea pig to investigate the effects of CO. By exposed himself to potentially lethal doses of the chemical, he discovered the dangers it posed, which led to the introduction of canaries in mines as early warning signals of danger. Good for miners, bad for canaries! You can hear more about J S Haldane in Chemistry World’s podcast on carbon monoxide.

CO’s killing power comes from its affinity for the haemoglobin in red blood cells, binding to it preferentially over oxygen to form carboxyhaemoglobin. People exposed to CO are figuratively drowning in air – there’s plenty of oxygen all around them but their bodies just can’t absorb enough of it. And, in a grisly twist, carboxyhaemoglobin is bright red, giving victims of CO poisoning a hale and hearty rosy hue.

Unsurprisingly, this has led to boilers, and the deadly gas they can produce, becoming inextricably linked in people’s minds with danger – to be guarded against in the home and on holiday. In the US alone, it is estimated that 40,000 people seek medical attention for CO poisoning each year, so it’s clear it’s still a serious problem.

That’s the dark side of CO, but is there a lighter side? Oddly enough, it was discovered in the 1990s that this deadly gas has a memorable and vital physiological function. It acts as a neurotransmitter in certain parts of the brain involved in long-term memory and has functions in many other parts of the body that are only just being understood. CO joins hydrogen sulfide and nitric oxide as another small and toxic gaseous molecule, which is a vital poison that our bodies both produce and need to function properly. As a result, companies like Alfama are now developing drugs that release CO in minute amounts to treat diseases involving inflammation and a range of other conditions. This turnaround in the way CO is now viewed really gives wings to the old axiom ‘the dose makes the poison’.

Patrick Walter

                  

Source:
http://prospect.rsc.org/blogs/cw/?feed=rss2

 It’s a stalwart of the undergraduate lab and can still be found introducing kids to the joys of science in even today’s modest chemistry sets. But potassium permanganate is good for much more than pretty colours and redox titrations… in fact, it could well save your life. Brian Clegg praises our purple pal in this week’s Chemistry in its element podcast.

                  

Source:
http://prospect.rsc.org/blogs/cw/?feed=rss2

A couple of weeks ago Chemistry World ran a story on a cracking paper from a team in Korea. The researchers took inspiration from the way Egyptian stone masons cracked large stone blocks (they inserted a wedge into a hole and then soaked it with water, causing it to expand and crack the stone) to create a technique to make nanoscale cracks in a controlled manner. They did this by etching a guide of notches and grooves into a silicon substrate and then depositing silicon nitride on top. The notches and grooves create a pathway for cracks to propagate along and this technique could be very useful for electronic and microfluidic devices.

© Nature

However, it now turns out that there’s an authorship dispute. The PhD student who said that she did much of the legwork didn’t get a note on the author list, according to this story in the Korea Herald (h/t @naturenano). The leader of the research group, Nam Koo-hyun at Ewha Womans University, Seoul, told the Herald that he made it clear from the start that the PhD student wouldn’t get a credit and that doing experimental work ‘does not qualify one for authorship’. I’m not sure how other PhD students would feel about this! Plenty of people have received a name check for far less than carrying out the experimental work. What do you think the cut off point should be for getting an author credit?

Patrick Walter

                  

Source:
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