title: CaBe2Ge2 type phosphides REIr2P2 (RE = La-Nd, Sm) and arsenides REIr2As2 (RE = La-Nd): synthesis, structure, and solid state NMR spectroscopy.
abstract: The phosphides REIr(2)P(2) (RE = La-Nd, Sm) and arsenides REIr(2)As(2) (RE = La-Nd) were synthesized by a ceramic route via precursor compounds REIr(2) with phosphorus and arsenic, respectively. Well-shaped single crystals were obtained from lead and bismuth fluxes, respectively. The nine pnictides crystallize with the tetragonal CaBe(2)Ge(2) type structure, space group P4/nmm. The structures of CeIr(2)P(2), SmIr(2)P(2), LaIr(2)As(2) and CeIr(2)As(2) were refined from single crystal X-ray diffractometer data. The structures are composed of three-dimensional [Ir(2)P(2)] and [Ir(2)As(2)] networks in which the rare earth atoms fill cavities of coordination number 16 (8 P + 8 Ir). The phosphorus and arsenic atoms have tetrahedral and square pyramidal iridium coordination. Temperature dependent magnetic susceptibility measurements show intermediate cerium valence for CeIr(2)P(2). The rare-earth and phosphorus local environments in LaIr(2)P(2) are characterized further by (139)La and (31)P single and double resonance solid state nuclear magnetic resonance (NMR) spectroscopy. Strong (31)P Knight shifts and extremely short spin-lattice relaxation times indicate that the bonding character of the phosphide species is strongly metallic. The two crystallographically distinct phosphorus sites are well-resolved in the (31)P magic-angle spinning (MAS) spectrum and also differ significantly with respect to their effective magnetic shielding anisotropies. Unambiguous site assignments are accomplished on the basis of homonuclear (31)P-(31)P magnetic dipole-dipole interactions, which can be measured in a site-resolved fashion in this compound using static (31)P spin echo decay spectroscopy. The highly symmetric La environment in LaIr(2)P(2) is characterized by a sharp (139)La MAS-NMR spectrum, revealing rather weak nuclear electric quadrupole coupling. Furthermore, a second local environment is detected, which is characterized by stronger quadrupolar coupling and similar dipolar coupling strength with (31)P as the regular site, according to (139)La{(31)P} rotational echo double resonance (REDOR) NMR results. On the basis of these data we attribute this site to a La species next to a phosphorus vacancy. From the signal area of this resonance we deduce a composition LaIr(2)P(1.90).
authors.affiliation: Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Pfannenschmidt
authors.forename: Frederik
authors.initials: F
authors.lastname: Behrends
authors.forename: Hannes
authors.initials: H
authors.lastname: Lincke
authors.forename: Matthias
authors.initials: M
authors.lastname: Eul
authors.forename: Konrad
authors.initials: K
authors.lastname: Schäfer
authors.forename: Hellmut
authors.initials: H
authors.lastname: Eckert
authors.forename: Rainer
authors.initials: R
authors.lastname: Pöttgen