The new compound CS4P2Se10 was serendipitously produced in high purity during a high-temperature synthesis done in a nuclear magnetic resonance (NMR) spectrometer. (31)p magic angle spinning (MAS) NMR of the products of the synthesis revealed that the dominant phosphorus-containing product had a chemical shift of -52.8 ppm that Could not be assigned to any known compound. Deep reddish brown well-formed plate-like crystals were isolated from the NMR reaction ampoule and the structure was solved with X-ray diffraction. Cs4P2Se10 has the triclinic space group P-1 with a = 7.3587(11)angstrom, b = 7.4546(11)angstrom, c = 10.1420(15)angstrom, alpha=85.938(2)degrees, beta=88.055(2)degrees, and gamma=85.609(2)degrees and contains the [P2Se10](4-) anion. To our knowledge, this is the first compound containing this anion that is composed of two tetrahedral (PSe4) units connected by a diselenide linkage. It was also possible to form a glass by quenching the melt in ice water, and Cs4P2Se10 was recovered upon annealing. The static P-31 NMR spectrum at 350 degrees C contained a single peak with a -35 ppm chemical shift and a similar to 7 ppm peak width. This study highlights the potential of solid-state and high-temperature NMR for aiding discovery of new compounds and for probing the species that exist at high temperature. (C) 2007 Elsevier Inc. All rights reserved.