K. Prassides – författare

Mixed valency is one of various names used to describe compounds which contain ions of the same element in two different formal states of oxidation. The existence of mixed valency systems goes far back into the geological evolutionary history of the earth and other planets, while a plethora of mixed valency minerals has attracted attention since antiquity. Indeed, control of the oxidation states of Fe in its oxides (FeO, Fe304' Fe203) was elegantly used in vase painting by the ancient Greeks to produce the characteristic black and red Attic ceramics (Z. Goffer, "Archaeological Chemistry", Wiley, New York, 1980). It was, however, only 25 years ago that two reviews of mixed valency appeared in the literature almost simultaneously, signalling the first attempt to treat mixed valency systems as a separate class of compounds whose properties can be correlated with the molecular and the electronic structure of their members. Then mixed valency phenomena attracted the interest of disparate classes of scientists, ranging from synthetic chemists to solid state physicists and from biologists to geologists. This activity culminated with the NATO ASI meeting in Oxford in 1979. The 1980's saw again a continuing upsurge of interest in mixed valency. Its presence is a necessary factor in the search for highly conducting materials, including molecular metals and superconductors. The highly celebrated high T c ceramic superconducting oxides are indeed mixed valency compounds.

In September 1985, in an attempt to simulate the chemistry in a carbon star, Harry Kroto, Bob Curl and Richard Smalley set up a mass spectrometry experiment to study the plasma produced by focusing a pulsed laser on solid graphite. Serendipitously, a dominant 720 amu mass peak corresponding to a C60 species was revealed in the time-of-flight mass spectrum of the resulting carbon clusters. It was proposed that this C60 cluster had the closed cage structure of a truncated icosahedron (a soccerball) and was named Buckminsterfullerene because geodesic dome concepts, pioneered by the architect Buckminster Fuller, played an important part in arriving at this solution. The signal for a C70 species (840 amu) , proposed to have the ellipsoidal shape of a rugbyball, was also prominent in the early experiments. Five years later, the seminal work of the Sussex! Rice collaboration was triumphantly confirmed as Wolfgang Krlitschmer and Donald Huffman succeeded in producing, and separating, bulk crystalline samples of fullerene material from arc-processed (in an inert gas atmosphere) carbon deposits. From then onwards, fullerene research continued, and still proceeds, at an exhilarating pace. The materials excited the imagination of many diverse classes of scientists, resulting in a truly interdisciplinary field. Many of our old, seemingly well-founded, preconceptions in carbon science had to be radically altered or totally abandoned, as a new round world of chemistry, physics and materials science began to unfold.

Mixed valency is one of various names used to describe compounds which contain ions of the same element in two different formal states of oxidation. The existence of mixed valency systems goes far back into the geological evolutionary history of the earth and other planets, while a plethora of mixed valency minerals has attracted attention since antiquity. Indeed, control of the oxidation states of Fe in its oxides (FeO, Fe304' Fe203) was elegantly used in vase painting by the ancient Greeks to produce the characteristic black and red Attic ceramics (Z. Goffer, "Archaeological Chemistry", Wiley, New York, 1980). It was, however, only 25 years ago that two reviews of mixed valency appeared in the literature almost simultaneously, signalling the first attempt to treat mixed valency systems as a separate class of compounds whose properties can be correlated with the molecular and the electronic structure of their members. Then mixed valency phenomena attracted the interest of disparate classes of scientists, ranging from synthetic chemists to solid state physicists and from biologists to geologists. This activity culminated with the NATO ASI meeting in Oxford in 1979. The 1980's saw again a continuing upsurge of interest in mixed valency. Its presence is a necessary factor in the search for highly conducting materials, including molecular metals and superconductors. The highly celebrated high T c ceramic superconducting oxides are indeed mixed valency compounds.

In September 1985, in an attempt to simulate the chemistry in a carbon star, Harry Kroto, Bob Curl and Richard Smalley set up a mass spectrometry experiment to study the plasma produced by focusing a pulsed laser on solid graphite. Serendipitously, a dominant 720 amu mass peak corresponding to a C60 species was revealed in the time-of-flight mass spectrum of the resulting carbon clusters. It was proposed that this C60 cluster had the closed cage structure of a truncated icosahedron (a soccerball) and was named Buckminsterfullerene because geodesic dome concepts, pioneered by the architect Buckminster Fuller, played an important part in arriving at this solution. The signal for a C70 species (840 amu) , proposed to have the ellipsoidal shape of a rugbyball, was also prominent in the early experiments. Five years later, the seminal work of the Sussex! Rice collaboration was triumphantly confirmed as Wolfgang Krlitschmer and Donald Huffman succeeded in producing, and separating, bulk crystalline samples of fullerene material from arc-processed (in an inert gas atmosphere) carbon deposits. From then onwards, fullerene research continued, and still proceeds, at an exhilarating pace. The materials excited the imagination of many diverse classes of scientists, resulting in a truly interdisciplinary field. Many of our old, seemingly well-founded, preconceptions in carbon science had to be radically altered or totally abandoned, as a new round world of chemistry, physics and materials science began to unfold.