Structures of Pd(CN)₂ and Pt(CN)₂: Intrinsically Nanocrystalline Materials?

Abstract

Analysis and modeling of X-ray and neutron Bragg and total diffraction data show that the compounds referred to in the literature as "Pd(CN)(2)" and "Pt(CN)(2)" are nanocrystalline materials containing small sheets of vertex-sharing square-planar M(CN)(4) units, layered in a disordered manner with an intersheet separation of ~3.44 Å at 300 K. The small size of the crystallites means that the sheets' edges form a significant fraction of each material. The Pd(CN)(2) nanocrystallites studied using total neutron diffraction are terminated by water and the Pt(CN)(2) nanocrystallites by ammonia, in place of half of the terminal cyanide groups, thus maintaining charge neutrality. The neutron samples contain sheets of approximate dimensions 30 Å × 30 Å. For sheets of the size we describe, our structural models predict compositions of Pd(CN)(2)·xH(2)O and Pt(CN)(2)·yNH(3) (x ≈ y ≈ 0.29). These values are in good agreement with those obtained from total neutron diffraction and thermal analysis, and are also supported by infrared and Raman spectroscopy measurements. It is also possible to prepare related compounds Pd(CN)(2)·pNH(3) and Pt(CN)(2)·qH(2)O, in which the terminating groups are exchanged. Additional samples showing sheet sizes in the range ~10 Å × 10 Å (y ~ 0.67) to ~80 Å × 80 Å (p = q ~ 0.12), as determined by X-ray diffraction, have been prepared. The related mixed-metal phase, Pd(1/2)Pt(1/2)(CN)(2)·qH(2)O (q ~ 0.50), is also nanocrystalline (sheet size ~15 Å × 15 Å). In all cases, the interiors of the sheets are isostructural with those found in Ni(CN)(2). Removal of the final traces of water or ammonia by heating results in decomposition of the compounds to Pd and Pt metal, or in the case of the mixed-metal cyanide, the alloy, Pd(1/2)Pt(1/2), making it impossible to prepare the simple cyanides, Pd(CN)(2), Pt(CN)(2), or Pd(1/2)Pt(1/2)(CN)(2), by this method.

Study of sorption of platinum and palladium cyanometallate complexes as the key to understanding the mechanism of binding the [Au(CN)2]− anion with carbon adsorbents

“…In particular, for K 2 6 ] synthesized and used in the present work ν(C≡N) is 2192 cm -1 that agrees well with the published data [17,31] for this compound. A similar shift of ν(C≡N) bands into the near-infrared region is also observed, when bridging bonds Pt II -C≡N-Сu II [28] or Pt II -C≡N-Pt II are formed [32]. These data suggest that cyanide ligands forming a part of predominating adsorbate are terminal and enter into the composition of a platinum(II) complex.…”

CuNi(CN)4: a two-dimensional cyanide framework containing CuIIin a square-planar environment

“…both the metal and cyanide groups are perfectly ordered with Cu(II) coordinated to the nitrogen end of the cyanide group and Ni(II) to the carbon end. The layered structure of this new mixed-metal cyanide is related to those of Ni(CN) 2 , which forms more extended sheets [1,2], and Pd(CN) 2 ·xNH 3 and Pt(CN) 2 ·xH 2 O, which form nanosheets [3]. The overall appearance of the powder X-ray diffraction pattern, including the unusual peak shapes of the observed Bragg reflections, has been successfully explained using models incorporating stacking disorder between next nearest neighbour layers.…”

Characterization of palladium species after γ-irradiation of a TBP–alkane–Pd(NO3)2system

“…63 Usually in an X-ray powder diffraction pattern, peak intensity and resolution (full-width half maximum) are related to the crystallinity state of the materials (crystallite size and micro-deformation of the crystal lattice). In Fig.…”

“…3 for the sake of illustration in the case of Pd(CN) 2 -$0.29H 2 O). 63 The differences observed between the lattice Fig. 1 Formation of two precipitates (F S,1 and F S,2 ) after g-irradiation at 500 kGy with 60 Co source of the biphasic system.…”

“…The reaction between 25 C and 110 C, and between 110 C and 350 C can be attributed to water vaporization 63 and release of organic functions, 67,68 respectively. The weight loss between 350 C and 650 C may correspond to the release of (CN) 2(g) .…”