Azidoaurates of the Alkali Metals

Abstract

Synthesis, crystal structure as well as IR-and Ramanspectroscopic properties of the new ternary azidoaurates(III) A[Au(N 3 ) 4 ] (A ϭ K, Rb, Cs) are reported. The translucent orangered compounds were prepared by reaction of the respective binary azides with HAuCl 4 in aqueous solutions at room temperature. The crystal structures determined by single crystal X-ray diffraction methods are monoclinic 1671 and provide the first examples for azidoaurates with mono-atomic cations. The unusual reduction of the lattice parameter a with increasing cation size in the isotypic series is discussed in detail. IRand Raman-spectroscopic measurements show strongly covalent gold-nitrogen contacts, a bonding situation which is further supported by quantum chemical calculations and ELF-analyses. prepare binary alloys, e.g. NaAu 2 [9]. In this study, the influence of cation size on the crystal structure, the shape of the azidoaurate anions, and the spectroscopic properties have been investigated in detail. Experimental SectionDue to the potentially explosive nature of the compounds under investigation, all handlings were carried out under extreme caution. It was especially important to prevent shock, heat, and intense radiation, as well as handling the products with metallic objects. Binary azides, KN 3 , RbN 3 , and CsN 3 , were synthesized from NaN 3 (Roth, 99.9 %, recrystallized in water) and the corresponding carbonates A 2 CO 3 (A ϭ K, Rb, Cs, all Alfa, 99.9 %) by ion-exchange methods in water. The resin column (l ϭ 775 mm, л i ϭ 14.2 mm) was filled with acidic cation-exchange resin (Merck), and ion-exchange was performed with a 5 ml·min Ϫ1 flow rate of HN 3 . The white product was collected after evaporation of the solvent. Alkali metal azidoaurates, A[Au(N 3 ) 4 ] (A ϭ K, Rb, Cs; in the further text referred to as: A ϭ A[Au(N 3 ) 4 ], K ϭ K[Au(N 3 ) 4 ], Rb ϭ Rb[Au(N 3 ) 4 ], Cs ϭ Cs[Au(N 3 ) 4 ]), were synthesized by reaction of the binary azides with HAuCl 4 (Alfa). The starting materials were dissolved in water or ethanol, the solutions were mixed with a slight excess of the alkali azide according to (1) and kept for 12 Ϫ 24 hours in a slightly tilted petri dish. Temperature treatment experiments were performed using either a heat plate or an ice bath in the range of 273 K Ϫ 323 K. Orange-red, brittle and often twinned crystals which are highly explosive when exposed to pressure, heat, or intense radiation were obtained during evaporation of the sol-

Synthesis, Crystal Structures, and Vibrational Spectra of Novel Azidopalladates of the Alkali Metals Cs2[Pd(N3)4] and Rb2[Pd(N3)4]·2/3H2O

“…The range 500–700 cm –1 is dominated by the in‐plane and out‐of‐plane deformation vibrations of the azido groups whereas the respective (N–N–N) stretching vibrations are registered as two separated sets of frequencies between 1200–1300 cm –1 and 1900–2100 cm –1 . The differences in the (N–N) wave numbers harmonize well with the measured bond lengths for the azidopalladate anions and the ELI calculations for [Au(N 3 ) 4 ] – 6, which indicates that the (N‐N) bonds for the outermost atoms in the azido groups ( – N –N c – N o ) are significantly shorter than those of the inner atoms ( –N i – N c –N). The respective stretching force constants follow the same order as for the bonds, with f (N–N) = 15.44 N · cm –1 and 10.18 N · cm –1 for the outermost and the inner (N–N) bonds, respectively.…”

“…Using the force field and initial force constants values previously employed on [Au(N 3 ) 4 ] – 6, the following (N–N) and (Pd–N) stretching ( f ), bond interaction ( f ′), deformation ( f D ) and torsion (τ) force constants were calculated giving the best fit with the experimental frequencies obtained for 1 : f (N o –N c ) = 14.61 N · cm –1 , f (N i –N c ) = 10.92 N · cm –1 , f (Pd–N) = 2.41 N · cm –1 , f′ (N o –N i ) = 1.53 N · cm –1 , f D (N–N–N) = 0.60 N · cm, f D (N–Pd–N) = 0.82 N · cm, f D (N–N–Pd) = 0.63 N · cm, τ = 0.02 N · cm.…”

“…Here the [Pd II (N 3 ) 4 ] 2– moieties show square‐planar symmetry ( C 4 h ). Our interest in the effect of the substitution of this large cation by smaller alkali metal cations on both the crystal structure and local anionic environments was raised by the structural changes observed in the corresponding azidoaurate series A [Au(N 3 ) 4 ] – ( A = K, Rb, Cs) 6. The preparations led to two new dark orange compounds, Cs 2 [Pd(N 3 ) 4 ] and Rb 2 [Pd(N 3 ) 4 ]· 2 / 3 H 2 O, which were both isolated by slow crystallization from aqueous solutions and characterized by means of their crystal structures and vibrational spectra.…”

Chemical bonding analysis and properties of La7Os4C9—A new structure type containing C- and C2-units as Os-coordinating ligands

“…The raw ELI-D (and ELF) disynaptic bond basin populations are not directly related to the formal bond order derived from the difference between the number of occupied bonding and antibonding MOs. It was shown, that usage of a suitable reference system may yield effective bond orders, which are consistent with interatomic force constants from lattice dynamical models fitted to experimental vibrational spectra [40]. We choose CaC 2 (tetragonal crystal structure from [41]) as the prototype compound for a C 2 2À unit.…”

“…Moreover, there are found 0.8e À more in the lone pair type basins and 0.6e À less in the bonding basin. Calculating a type of effective bond order from the ratio between the bond basin populations of the reference and the actual C 2 unit [40] yields 3 Â 2.56/3.25 ¼ 2.4, which is roughly the same as obtained from COHP analysis. Thus, although topologically there is only one lone pair type of attractor for each C atom of the C 2 species as in CaC 2 , the present C 2 species displays an effective bond order between that of the C 2 2À and the C 2 4À unit.…”