Goniometer helps solve 'blue waters' mystery

The enigma of why aqueous molybdenum solutions are blue may have been solved, with the discovery of a unique 'blackberry' arrangement that may represent a new stable solute state

A BI-200SM goniometer with BI-9000AT autocorrelator from Brookhaven Instruments has recently helped researchers at the Brookhaven National Laboratory (no relation - Ed) in New York solve the enigma of why aqueous molybdenum solutions are blue.

Dr Tianbo Liu in the Department of Physics explained: "Molybdenum and oxygen can combine to form a wide variety of structures and some polyoxomolybdate (POM) molecules are the biggest inorganic molecules known, achieving similar sizes to proteins.

The electronic state of the POMs is responsible for imparting a blue color to the surrounding solution, as the giant POMs cluster together rather than existing as single ions.

Because of the size of the POMs, we realised we could use light scattering to find out the actual structure of the complexes and we subsequently discovered a unique blackberry arrangement that we believe represents a new, stable solute state.

It has changed our understanding of the solution behavior of inorganic molecules when they reach nanometer sizes.

"This project could not have been completed without the goniometer.

We found there were only two suppliers with instruments capable of doing everything we wanted, and we decided on Brookhaven Instruments because its customer support was local and the goniometer was reasonably priced.

I have found the BI-200SM to be a very stable instrument that allows me to determine the angular dependence of the scattered intensity very accurately and measure intensities at very low scattering angles.

I also think the digital correlator is very good, " concluded Dr Liu.

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