title: NaCeP(2)Se(6), Cu(0.4)Ce(1.2)P(2)Se(6), Ce(4)(P(2)Se(6))(3), and the incommensurately modulated AgCeP(2)Se(6): new selenophosphates featuring the ethane-like [P(2)Se(6)](4-) anion.
abstract: NaCeP(2)Se(6), Cu(0.4)Ce(1.2)P(2)Se(6), and AgCeP(2)Se(6) were prepared from nearly stoichiometric proportions of the starting materials plus extra selenium at 750-850 degrees C. Ce(1.33)P(2)Se(6) (or Ce(4)(P(2)Se(6))(3)) was obtained from the same reaction that produced Cu(0.4)Ce(1.2)P(2)Se(6). The structure of all four compounds was determined by single-crystal X-ray diffraction. NaCeP(2)Se(6), Cu(0.4)Ce(1.2)P(2)Se(6), and Ce(1.33)P(2)Se(6) crystallize in the monoclinic space group, P2(1)/c, with a = 12.1422(2), b = 7.6982(1), c = 11.7399(2) A, beta = 111.545(1) degrees and Z = 4 for NaCeP(2)Se(6); a = 12.040(1), b = 7.6418(8), c = 11.700(1) A, beta = 111.269(2) degrees and Z = 4 for Cu(0.4)Ce(1.2)P(2)Se(6); and a = 6.8057(5), b = 22.969(2), c = 11.7226(8) A, beta = 124.096(1) degrees and Z = 6 for Ce(1.33)P(2)Se(6). NaCeP(2)Se(6) has a two-dimensional character and is isostructural to the KLnP(2)Q(6) family of compounds, where Ln = La, Ce, and Pr for Q = Se and Ln = La for Q = S. The structure consists of [CeP(2)Se(6)](n)(n-) layers which are separated by Na(+) cations. Each layer contains CeSe(9) distorted, tricapped trigonal prisms and [P(2)Se(6)](4-) ethane-like anions. Cu(0.4)Ce(1.2)P(2)Se(6) possesses a similar structure; however, substitution of the alkali metal by copper and cerium atoms renders the structure three dimensional. Ce(1.33)P(2)Se(6) is the pure lanthanide member of this structure type. In this three-dimensional structure, there are three cerium metal sites which are partially occupied. The structure of AgCeP(2)Se(6) was solved in the superspace group P2(1)/c(alpha0gamma) and represents an incommensurately modulated version of the KLnP(2)Q(6) structure type, with a = 9.971(5), b = 7.482(3), c = 11.757(4) A, beta = 145.630(9) degrees, q = 0.3121(18)a + 0.4116(19)c, and Z = 2. The structures of the compounds reported here and those of the KLnP(2)Q(6) family are highly related to the monoclinic-II, M(II)PQ(3) structure type (where M = Pb, Sn, Ca, and Sr for Q = S and M = Pb and Sn for Q = Se). Optical and vibrational spectroscopic characterization is also reported.
authors.affiliation: Department of Chemistry and Center for Fundamental Materials Research, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Aitken
authors.forename: Michel
authors.initials: M
authors.lastname: Evain
authors.forename: Lykourgos
authors.initials: L
authors.lastname: Iordanidis
authors.forename: Mercouri G
authors.initials: MG
authors.lastname: Kanatzidis