Jörn Bruns

Octahedral Pd2+ coordination and ferromagnetic ordering in Pd(S2O7).

It is well known that square-planar coordination is typical for divalent palladium exhibiting an electronic d configuration. Only with ligands that cause a weak ligand field splitting might an octahedral coordination be stabilized. This situation has been shown especially for palladium fluorides, and in addition to both modifications of PdF2 [1–4] the polynary fluorides APdF3 (A = K, Rb), [2] PdZrF6, [5] CsPd2F5, [6] PdAu2F8, [7] LiPdGaF6, and RbPdAlF6 [8] show essentially undistorted [PdF6] octahedra. In contrast, with oxygen ligands, the typical square-planar palladium coordination is nearly always observed. The simplest example is the structure of PdO itself, that consists of vertex-connected [PdO4] polyhedra, at least in the bulk material. When the donor oxygen atoms of ligand molecules are considered, then the coordination chemistry of Pd is clearly dominated by a square-planar metal coordination environment. Nevertheless, it has been shown that octahedral oxygen coordination of Pd can be achieved if very rigid and stable frameworks are established, housing the Pd ions in octahedral voids. Two solid-state examples for this type of frameworks are known, namely Ca2PdWO6 [11] and PdAs2O6, [12] which are closely related to the structures of perovskite and aluminum trichloride, respectively. Two other highly interesting examples originate from polyoxometalate chemistry: In the anions [Pd13(AsPh)8O32] 6 and [Pd13Se8O32] 6 one of the thirteen Pd ions is in the center of a large cage providing octahedral or even cubic oxygen coordination. Finally, an oxalate framework has been described that clearly contains Pd in a distorted octahedral coordination environment, as demonstrated by powder diffraction and X-ray absorption (EXAFS) measurements. With respect to the efforts required to date to stabilize this uncommon coordination geometry, it is remarkable and unexpected that we now found an octahedral oxygen coordination environment for Pd in Pd(S2O7), a compound been obtained as highly moisture sensitive blue crystals from the reaction of elemental palladium with SO3 (Figure 1). It is the first time that this type of Pd coordination has been

Bis(tetrasulfato)palladate, [Pd(S4O13)2]2−

SOS: The first coordination compound containing polysulfate ligands was obtained under harsh conditions from the reaction of K(2)[PdCl(4)] and SO(3). The compound contains a Pd(2+) ion coordinated by two chelating tetrasulfate anions (see structure, Pd red, S yellow, O blue), which leads to a significant stabilization of the polysulfate anions compared to their uncoordinated analogues.

Ba2[Pd(HS2O7)2(S3O10)2]: A Heteroleptic Polysulfatopalladate

The oxidation of elemental palladium with oleum (65 % SO3) in the presence of barium carbonate in torch-sealed glass ampoules at 180 °C leads to yellow single crystals of the heteroleptic palladate Ba2[Pd(HS2O7)2(S3O10)2] (triclinic, P1; Z=1; a=884.18(3), b=927.68(3), c=938.77(4) pm; α=60.473(1), β=80.266(2), γ=87.746(2)°). The crystal structure shows the Pd(2+) ions in a square-planar coordination of oxygen atoms of two hydrogendisulfate as well as of two trisulfate anions. The compound is the first example of the rarely seen S3O10(2-) and HS2O7(-) anions acting as ligands in a complex anion and, moreover, the first heteroleptic polysulfatometallate known so far. The complex formation leads to a stabilization of the trisulfate anion relative to its uncoordinated congener. Ba2[Pd(HS2O7)2(S3O10)2] has been further characterized by vibrational spectroscopy and quantum chemical calculations. Thermal analyses by means of thermogravimetric/differential thermal analysis (TG/DTA) measurements show that the compound decomposes to yield elemental palladium and BaSO4.

Ferromagnetic Ordering in the Layer‐Structured Pd(HS2O7)2

The reaction of (NO2 )(CF3 SO3 ) and elemental palladium in oleum (65 % SO3 ) leads to violet single crystals of Pd(HS2 O7 )2 (monoclinic, P21 /c, Z=2, a=927.80(9), b=682.58(7), c=920.84(9) pm, β=117.756(2)°, wR2 =0.0439). In the crystal structure, the Pd(2+) ions show an uncommon octahedral coordination of six oxygen atoms belonging to six HS2 O7 (-) ions. The linkage of [PdO6 ] octahedra and the hydrogendisulfate anions leads to a layer structure, and the layers are held together by hydrogen bonds. The unusual coordination of the Pd(2+) ions results in an electronic d(8) high-spin configuration, which leads to the paramagnetic behavior of the compound. Moreover, at low temperature, a ferromagnetic ordering was observed with a Curie temperature of 8 K.

Oxoanionic Noble Metal Compounds from Fuming Nitric Acid: The Palladium Examples Pd(NO3)2 and Pd(CH3SO3)2

The oxidation of elemental palladium at 100 °C in a mixture of fuming nitric acid and a pyridine-SO3 complex leads to the anhydrous nitrate Pd(NO3)2 (monoclinic, P2(1)/n, Z=2, a=469.12(3) pm, b=593.89(3) pm, c=805.72(4) pm, β=105.989(3)°, V=215.79(2) Å(3)). The Pd(2+) ions are in square-planar coordination with four monodentate nitrate groups which are connected to further palladium atoms, leading to a layer structure. The reaction of elemental palladium with a mixture of fuming nitric acid and methanesulfonic acid at 120 °C leads to single crystals of Pd(CH3SO3)2 (monoclinic, P2(1)/n, Z=2, a=480.44(1) pm, b=1085.53(3) pm, c=739.78(2) pm, β=102.785(1)°, V=376.254(17) Å(3)). Also in this structure the Pd(2+) ions are in square-planar coordination with four monodentate anions; however, the connection to adjacent palladium atoms leads to a chain-type structure. The thermal decomposition of the compounds has been investigated by means of DSC/TG measurements. Furthermore, IR and Raman spectra have been recorded, and an assignment of the observed vibrational frequencies has been carried out based on theoretical investigations.

Oxidizing Elemental Platinum with Oleum under Harsh Conditions: The Unique Tris(disulfato)platinate(IV) [Pt(S2O7)3]2− Anion

For the first time, direct oxidation of elemental platinum by a mineral acid to its tetravalent state was observed in course of the reaction of platinum with oleum (65 % SO3) in the presence of barium carbonate. The reaction has been carried out in torch-sealed glass ampoules at 160 °C and gave yellow single crystals of Ba[Pt(S2O7)3](H2SO4)0.5(H2S O7)0.5 (triclinic, P1, Z=2, a=992.05(2), b=1069.07(3), c=1114.22(3) pm, α=69.49(7), β=72.96(2), γ=72.93(1)°, V=1033.95(5) Å(3)). The structure of Ba[Pt(S2O7)3](H2SO4)0.5(H2S2O7)0.5 exhibits the unique tris-(disulfato)-platinate anion [Pt(S2O7)3](2-) with three chelating disulfate groups coordinated to the platinum atom. Charge balance is achieved by the Ba(2+) ions, which are coordinated by (S2O7)(2-) groups from the platinate complex and by disordered sulfuric acids and disulfuric acid molecules. Thermal decomposition of the bulk material revealed elemental platinum and barium sulfate as decomposition residual.

Chelating and Linking S4O132– Anions: Synthesis and Characterization of the Bis-(tetrasulfato) Palladates M2[Pd(S4O13)2] (M = NH4, Rb, NO) and the Sodium Palladium Tetrasulfate Na2Pd(S4O13)2

The reaction of SO3 with either the palladium chlorides M2PdCl6 (M = Rb, NH4) or the nitrato-palladate (NO)2[Pd(NO3)4] at elevated temperature led to yellow single crystals of the complex palladates M2[Pd(S4O13)2] (M = NH4: triclinic, P1̅, a = 7.3882(3) Å, b = 8.5223(3) Å, c = 9.2712(4) Å, α = 71.945(2)°, β = 88.910(2)°, γ = 72.603(2)°, V = 527.88(4) Å3; M = NO: triclinic, P1̅, a = 7.2881(3) Å, b = 8.9125(2) Å, c = 8.9220(4) Å, α = 75.546(2)°, β = 89.151(2)°, γ = 69.516(2)°, V = 524.02(4) Å3; M = Rb: triclinic, P1̅, a = 7.4468(4) Å, b = 8.5066(4) Å, c = 9.2477(4) Å, α = 72.321(2)°, β = 88.512(2)°, γ = 72.128(2)°, V = 529.75(4) Å3). In the isotypic compounds, the Pd atom is in square planar oxygen coordination, achieved by two bidentate-chelating tetrasulfate anions. The reaction of Na2PdCl6 with neat SO3 afforded yellow crystals of Na2Pd(S4O13)2 (monoclinic, P21/c, a = 6.9953(4) Å, b = 15.9420(9) Å, c = 9.2299(5) Å, β = 100.235(2)°, V = 1012.45(1) Å3). The structure exhibits no palladate complexes but an anionic two-dimensional network, according to ∞2[Pd(S4O13)(4/2)]2–. The latter shows the tetrasulfate anions acting as bidentate-bridging ligands. The tetrasulfato-palladates were studied in more detail by means of thermal analyses and infrared (IR) spectroscopy. The observed IR bands were assigned according to quantum chemical calculations performed on the anion [Pd(S4O13)2]2–.

CaB2S4O16: A Borosulfate Exhibiting a New Structure Type with Phyllosilicate Analogue Topology

The reaction of Ca(CO3 ) with H3 BO3 in oleum (20 % SO3 ) yielded colorless single-crystals of CaB2 S4 O16 (monoclinic, P21 /c, a=5.5188(2), b=15.1288(6), c=13.2660(6) Å, β=92.88(1)°, V=1106.22(8) Å3 ). X-ray single-crystal structure analysis revealed a phyllosilicate-analogue anionic sub-structure, forming 2D infinite anionic layers, which exhibit an unprecedented arrangement of condensed twelve-membered (zwölfer) and four-membered (vierer) rings of corner-shared (SO4 ) and (BO4 ) tetrahedra. Charge compensation is achieved by Ca2+ cations, residing exclusively above the centers of the twelve-membered rings. DFT investigations on the solid-state structure corroborate the experimental findings and allow for a detailed valuation of charge distribution within the anionic network and an assignment of vibrational frequencies.

Palladium(IV) in an Oxoanionic Environment: The XeF2 Assisted Synthesis of [Pd(S2O7)3]2−

For the first time tetravalent palladium is detected, coordinated exclusively by simple oxoanions. Stabilization was achieved by formation of the [Pd(S2 O7 )3 ](2-) complex in which three chelating disulfate groups surround the metal atom. The salt K2 [Pd(S2 O7 )3 ] could only be obtained if the reaction of K2 [PdCl6 ] and neat SO3 was performed in the presence of XeF2 .

“Naked” S2O72– ions – the serendipitous formation of the disulfates [HPy]2[S2O7] and [bmim][HPy][S2O7] (HPy = pyridinium; bmim = 1-Butyl-3-methylimidazolium)

Abstract [bmim][HPy][S2O7] [monoclinic, P21/n, Z = 4, a = 825.78(2), b = 1545.30(3), c = 1410.80(3) pm, β = 104.726(1)°, V = 1741.16(7) Å3] was obtained as a side product in the reaction of GeCl4, oleum (65% SO3), and the pyridine (Py) complex Py·SO3 in the ionic liquid 1-butyl-3-methylimidazolium hydrogensulfate, [bmim][HSO4], at 50 °C. Charge compensation of the disulfate ion is achieved by the counterions pyridinium, [HPy]+, and 1-butyl-3-methylimidazolium, [bmim]+. The crystal structure shows alternating layers of [bmim]+ cations on one hand and [HPy]+ cations and disulfate anions on the other hand. Pyridinium disulfate, [HPy]2[S2O7] [orthorhombic, P212121, Z = 4, a = 801.35(1), b = 1257.62(2), c = 1357.22(3) pm, V = 1367.80(4) Å3] was formed unexpectedly in the reaction of Eu2O3 and Py·SO3 in pyridine. The crystal structure exhibits a layer-like arrangement of disulfate and pyridinium moieties in the ab plane. In both compounds, the disulfate groups are essentially uncoordinated allowing for a detailed inspection of “naked” S2O72– ions.