INTERCONVERSION OF BACTERIOCHLOROPHYLL c AGGREGATES IN SOLID FILMS UPON ORGANIC VAPOR TREATMENT

Bacteriochlorophyll c (BChl c) solid films were prepared from a carbon tetrachloride solution on CaF₂ plates as artificial aggregates. Effects of organic vapor such as acetone and tetrahydrofuran (THF) on the BChl c films were studied by absorption and Fourier-transform infrared spectroscopy. Two major homologs (R[E,E]BChl c_F and R[P,E]BChl c_F) and one minor homolog (S[I,E]BChl c) isolated from the green photosynthetic bacterium Chlorobium limicola strain 6230 were examined for the experiments. The BChl c polymeric aggregates absorbing at739–753 nm similar to those in the chlorosome were induced for all homologs upon the treatment of BChl c solid film with acetone vapor. The 13¹-keto C=O stretching band in the R[E,E]BChl c_F solid film showed a downward shift from 1651 cm^?1to 1643 cm^?1 with a concomitant shift of the 3¹-OH stretching bands from 3337 and 3238 cm^?1 to 3163 cm^?1. It was suggested that the lower aggregates brought about by Mg…O=C(13¹) and (3¹)O…O=C(13¹) bonds were transformed into the higher aggregates strongly hydrogen-bonded in a Mg…(3¹)O-H…O=C(13^l) interaction. They were transformed to a monomer-like form absorbing at 667 nm upon exposure to THF vapor and were reversibly converted to the higher aggregates upon removal of THF molecules in vacuo.     

The effects of epimerization at the 3(1)-position of bacteriochlorophylls c on their aggregation in chlorosomes of green sulfur bacteria. Control of the ratio of 3(1) epimers by light intensity

R- and S-epimerization at the 3(1) position of bacteriochlorophyll (BChl) c and the formation of rod-like aggregates in chlorosomes of green sulfur bacteria were markedly affected in Chlorobium (Cb.) tepidum and Cb. limicola by cultivation under various light intensities (photon fluence rate). The stronger the light, the higher the ratio of the S-epimer to the R-epimer for each homolog of BChl c in the bacteria. S[P,E] BChl cF and S[I,E] BChl cF were found to be the major S-epimers in Cb. tepidum and Cb. limicola, respectively. R[P,E] BChl cF decreased markedly compared to R[E,E] BChl cF in Cb. tepidum, whereas no observable change in the ratio of R[P,E]/R[E,E] was detected for Cb. limicola. With increase in light intensity the Qy absorption maximum of the bacteria shifted to shorter wavelengths. In vitro spectroscopic studies of the aggregates showed a marked difference in the formation of aggregates from R- and S-epimers of BChl c; the S-epimers formed aggregates much more slowly than did the R-epimers. These results suggest that the ratio of the epimers of BChl c might significantly affect the aggregation of BChl in the chlorosome. We propose different roles for the R- and S-epimers in chlorosomes of Cb. limicola and Cb. tepidum.     

The Crystal Structure of Ba3Cu2Al2F16: a Relative of Ba4Cu2Al3F21

Ba₃Cu₂Al₂F₁₆ is monoclinic: a = 7.334(1)Å, b = 5.320(2)Å, c = 16.022(1)Å, β = 96.34(1)°, Z = 2. Its crystal structure was solved in the space group P2₁ (No. 4) from synchrotron X‐ray single crystal data using 2685 unique reflections (2639 with F_o/σ(F_o) > 4). The final R factor is 0.044. The structure consists of a succession along the c‐axis of the cell of three layers of two different kinds of sheets developing in the (a, b) plane. The first one, formulated [(AlF₅)₂]_∞^4— and hereafter named A, is built up from infinite cis‐chains of aluminium‐fluorine octahedra [AlF₆], linked by two vertices and distanced by a. The second one, formulated [Cu₂AlF₁₁]_∞^4— and named B, is bidimensional. It is constituted of distorted copper‐fluorine octahedra [CuF₆], linked by edges, which form infinite chains interconnected by three vertices of isolated [AlF₆] octahedra. The stacking sequence of the sheets is (A, B, B)_∞. The barium ions, 12‐coordinated, are inserted between the sheets. The crystal structure of Ba₃Cu₂Al₂F₁₆ is closely related to that of Ba₄Cu₂Al₃F₂₁. Only the proportion and the stacking sequence of the two kinds of sheets in the c‐direction differ, according to two different compositions and two different symmetries.     

A New Cu, Al Fluoride Disilicate CuAl2F2(Si2O7) and its Relations to Topaz

CuAl₂F₂(Si₂O₇) has been prepared by hydrothermal synthesis and its crystal structure was determined by single crystal X‐ray diffraction: space group Pnma, a = 8.8697(9), b = 14.084(2), c = 4.7553(5) Å, wR₂ = 0.056, R = 0.022. Cu²⁺ shows elongated square pyramidal coordination. Edge‐ and corner‐sharing [AlO₄F₂] octahedra with fluorine atoms in cis position form layers parallel to the ac plane. Along b these layers are linked by Si₂O₇ groups to form a three‐dimensional framework [Al₂F₂(Si₂O₇]^2–. In addition, the [CuO₅] pyramides connect two Al octahedra of neighbouring layers. The crystal structure is discussed as a derivative from topaz structure. The modular (or polysomatic) approach is used for this purpose, and for modelling hypothetical related compounds.     

Further Evidence for ‘Extended’ Cumulene Complexes: Derivatives from Reactions with Halide Anions and Water

Reactions of [Ru{C=C(H)-1,4-C₆H₄C≡CH}(PPh₃)₂Cp]BF₄ ([ 1 a ]BF₄) with hydrohalic acids, HX, results in the formation of [Ru{C≡C-1,4-C₆H₄-C(X)=CH₂}(PPh₃)₂Cp] [X=Cl ( 2 a-Cl ), Br ( 2 a-Br )], arising from facile Markovnikov addition of halide anions to the putative quinoidal cumulene cation [Ru(=C=C=C₆H₄=C=CH₂)(PPh₃)₂Cp]⁺. Similarly, [M{C=C(H)-1,4-C₆H₄-C≡CH}(LL)Cp ]BF₄ [M(LL)Cp’=Ru(PPh₃)₂Cp ([ 1 a ]BF₄); Ru(dppe)Cp* ([ 1 b ]BF₄); Fe(dppe)Cp ([ 1 c ]BF₄); Fe(dppe)Cp* ([ 1 d ]BF₄)] react with H⁺/H₂O to give the acyl-functionalised phenylacetylide complexes [M{C≡C-1,4-C₆H₄-C(=O)CH₃}(LL)Cp’] ( 3 a – d ) after workup. The Markovnikov addition of the nucleophile to the remote alkyne in the cations [ 1 a–d ]⁺ is difficult to rationalise from the vinylidene form of the precursor and is much more satisfactorily explained from initial isomerisation to the quinoidal cumulene complexes [M(=C=C=C₆H₄=C=CH₂)(LL)Cp’]⁺ prior to attack at the more exposed, remote quaternary carbon. Thus, whilst representative acetylide complexes [Ru(C≡C-1,4-C₆H₄-C≡CH)(PPh₃)₂Cp] ( 4 a ) and [Ru(C≡C-1,4-C₆H₄-C≡CH)(dppe)Cp*] ( 4 b ) reacted with the relatively small electrophiles [CN]⁺ and [C₇H₇]⁺ at the β-carbon to give the expected vinylidene complexes, the bulky trityl ([CPh₃]⁺) electrophile reacted with [M(C≡C-1,4-C₆H₄-C≡CH)(LL)Cp’] [M(LL)Cp’=Ru(PPh₃)₂Cp ( 4 a ); Ru(dppe)Cp* ( 4 b ); Fe(dppe)Cp ( 4 c ); Fe(dppe)Cp* ( 4 d )] at the more exposed remote end of the carbon-rich ligand to give the putative quinoidal cumulene complexes [M{C=C=C₆H₄=C=C(H)CPh₃}(LL)Cp’]⁺, which were isolated as the water adducts [M{C≡C-1,4-C₆H₄-C(=O)CH₂CPh₃}(LL)Cp’] ( 6 a–d ). Evincing the scope of the formation of such extended cumulenes from ethynyl-substituted arylvinylene precursors, the rather reactive half-sandwich (5-ethynyl-2-thienyl)vinylidene complexes [M{C=C(H)-2,5-^cC₄H₂S-C≡CH}(LL)Cp’]BF₄ ([ 7 a – d ]BF₄ add water readily to give [M{C≡C-2,5-^cC₄H₂S-C(=O)CH₃}(LL)Cp’] ( 8 a – d )].     

Influence of basic residues on dissociation kinetics and dynamics of singly protonated peptides: time‐resolved photodissociation study

Product ion yields in postsource decay and time‐resolved photodissociation at 193 and 266 nm were measured for some peptide ions with lysine ([KF₆ + H]⁺, [F₆K + H]⁺, and [F₃KF₃ + H]⁺) formed by matrix‐assisted laser desorption ionization. The critical energy (E₀) and entropy (ΔS^?) were determined by RRKM fitting of the data. The results were similar to those found previously for peptide ions with histidine. To summarize, the presence of a basic residue, histidine or lysine, inside a peptide ion retarded its dissociation by lowering ΔS^?. On the basis of highly negative ΔS^?, presence of intramolecular interaction involving a basic group in the transition structure was proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthese und Molekülstruktur von [Al(SiMe3)3(DBU)] (DBU = 1,8-Diazabicyclo[5.4.0]undec-7-en)

Synthesis and Molecular Structure of [Al(SiMe₃)₃(DBU)] (DBU = 1,8-Diazabicyclo[5.4.0]undec-7-ene) [Al(SiMe₃)₃(OEt₂)] reacts with DBU (DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene) at 0 °C yielding [Al(SiMe₃)₃ · (DBU)] ( 1 ). 1 was characterised spectroscopically (¹H, ¹³C, ²⁹Si, ²⁷Al NMR, IR, MS) and by X-ray structure determination [monoclinic, C2/c, a = 33.053(2), b = 9.307(1), c = 20.810(1) Å, β = 124.07(2)°, V = 5302.4(5) ų, Z = 8, 218(2) K]. 1 does not react with [Cp₂ZrCl₂] even in boiling toluene.     

Substrates to study the mechanism of vitamin D hydroxylation: synthesis of 25-R-[26-2H3]-cholecalciferol

25-R[26-²H₃]-Cholecalciferol has been synthesised from a C-22 aldehyde derived from egosterol and R-3-[²H₃]-methylbutyl bromide. This vitamin is designed to study the mechanism of enzymic hydroxylation at C-25 in the production of 25S, 26-dihydroxycholecalciferol.     

Low-Valent Group 14 NHC-Stabilized Phosphinidenide ate Complexes and NHC-Stabilized K/P-Clusters

The N-heterocyclic carbene (NHC)-stabilized phosphinidenide, SIMesPK [SIMes=1,3-bis(2,4,6-trimethylphenyl)imidazolidine-2-ylidene], was used as an (NHC)P-transfer reagent for the synthesis of the low-valent Group 14 ate complexes K[(SIMesP)₃E] (E=Ge: 2 , Sn: 3 , Pb: 4 ), which were characterized by ¹H NMR, ³¹P NMR, IR spectroscopy as well as elemental and X-ray analysis. Furthermore, SIMesPK was used in reactions with potassium amides and alkoxides to form the molecular phosphorus–potassium clusters [K₄(SIMesP)₂(hmds)₂] [ 5 , hmds=N(SiMe₃)₂] and [K₆(SIMesP)₂(OtBu)₄] ( 6 ). Finally, the reaction of SIMesPK with Li[Al(OC₄F₉)₄] led to the potassium-rich ionic compound [(SIMesP)₄K₅][Al(OC₄F₉)₄] ( 7 ).     

The crystal structure of (NH4)2[Mo2(S2)6].8/3H2

The black crystal of (NH₄)[Mo₂(S₂)₆]* 8/3 H₂O belongs to the orthorhombic system, space group D³₂-P22₁2₁, with a = 12.064(6), b = 12.534(4), c = 19.558(9)Å, V =2957(3)ų, Z = 4 and D_c = 2.23g.cm^?3. The intensity data were collected on a Syntex R3 four-circle diffractometer. The structure was solved by Patterson method and direct method, the light atoms (except H atoms) were obtained from ΔF syntheses. The structure was refined by least-squares with anisotropic thermal parameters. The values of R and R_w were 0.092 and 0.072 respectively. The crystal structure contains discrete dimeric cluster [Mo₂(S₂)₆]^2? ions, NH₄⁺ cations and H₂O molecules. There are two crystallographically independent [Mo₂S₂)₆]^2? ions in the crystal, one locates on general position [Figure 1(a)], the other locates on two-fold axis [Figure 1(b)]. It contains one and a half [Mo₂S₂)₆]^2? ions in an asymmetric unit. In [Mo₂S₂)₆]^2? each Mo is coordinated side on by four S₂^2? groups in a distorted dodecahedral arrangement, two of which are bridging and the other two are terminal. The Mo? S bond length is 2.441 Å (mean), and S? S is 2.049 Å (mean). The Mo? Mo distance is 2.784 Å (mean), which is to be regarded as a single bond length. The formal oxidation state of Mo is five, it is probably a mixed valence Mo^IV? Mo^VI, and so shows a remarkable deep colour.     

Synthesis and Crystal Structure of Pb3O2(SeO3)

Single crystals of Pb₃O₂(SeO₃) have been prepared hydrothermally at 230 °C. The structure (orthorhombic, Cmc2₁, a = 10.529(2), b = 10.722(2), c = 5.7527(12)Å, V = 649.5(2)ų) has been solved by direct methods and refined to R₁ = 0.059 on the basis of 615 unique observed reflections (|F_o| = 4σ_F). The structure is based upon double [O₂Pb₃]²⁺ chains of edge‐sharing [OPb₄]⁶⁺ tetrahedra. These [O₂Pb₃]²⁺ chains run parallel to [001], and their planes are parallel to (010). The pyramidal (SeO₃)^2— anions are located between the chains; their triangular oxygen atom bases lie parallel to (001) and all (SeO₃)^2— groups are pointing in the same direction. A short compilation of [O₂M₃] chains of oxocentred M₄ tetrahedra in minerals and inorganic compounds is provided.     

Reactions of 3-(Polyfluoroalkyl)propane-1,2,3-trione-2-oximes with Diaminoarenes

Novel quinoxaline derivatives have been synthesized via the reaction of 3-trifhioromethyl-1,2,3-propanetrione-2-oximes with 1,2-diaminobenzene or 2,3-diaminonaphthalene: 2-trifluoromethyl-3-aroylquinoxaline and 2-trifluoromethyl-3-aroylbenzo[g]quinoxaline. Under similar conditions, 3-R^F-1,2,3-propanetrione-2-oximes [R^F = C₃F₇, H(CF₂)₄, C₄F₉, and C₆F₁₃] with the same diaminoarenes have given a mixture of the condensation and fragmentation products in different ratios. The structure of (4-methylphenyl)[3-(tri-fluoromethyl)benzo[g]quinoxalin-2-yl]methanone has been elucidated by means of X-ray diffraction analysis.

     

Strukturen von neuen Bis(pentafluorophenyl)halogenomercuraten [{Hg(C6F5)2}3(μ‐X)]— (X = Cl,Br, I)

Structures of New Bis(pentafluorophenyl)halogeno Mercurates [{Hg(C₆F₅)₂}₃(μ‐X)]^— (X = Cl, Br, I) From the reactions of [PNP]Cl or [PPh₄]Y (Y = Br, I) with Hg(C₆F₅)₂ crystals of the composition [Cat][{Hg(C₆F₅)₂}₃X] (Cat = PNP, X = Cl ( 1 ); Cat = PPh₄, X = Br ( 2 ), I ( 3 )) are formed. 1 crystallizes in the triclinic space group P1¯, 2 and 3 crystallize isotypically in the monoclinic space group C2/c. In the crystals the halide anions are surrounded by three Hg(C₆F₅)₂ molecules. The reaction of [PPh₄]Br with Hg(C₆F₅)₂ under slightly changed conditions gives the compound [PPh₄]₂[{Hg(C₆F₅)₂}₃(μ‐Br)][{Hg(C₆F₅)₂}₂(μ‐Br)] ( 4 ).     

1-亚甲基苯并咪唑-1,4,7-三氮环壬烷配体及其铜配合物[Cu(C14H21N5)Br]2•[CuBr4]的合成与晶体结构

采用新的方法合成了1-亚甲基苯并咪唑-1,4,7-三氮环壬烷配体, 利用该配体合成了一个新的铜配合物[Cu(C₁₄H₂₁N₅)Br]₂•[CuBr₄] ([Cu(C₁₄H₂₁N₅)Br]^＋•[CuBr₄]^2－•[Cu(C₁₄H₂₁N₅)Br]^＋), 并测定了它的晶体结构, 结果表明: 该配合物的晶体属于单斜晶系的C2/c空间群, 晶胞参数a＝1.96209(15) nm, b＝0.82319(5) nm, c＝2.39249(15) nm, α＝90.00°, β＝102.996(2)°, γ＝90.00°, V＝3.7653(4) nm³, Z＝4, μ(Mo Kα)＝8.083 mm^－1, D_c＝2.097 Mg/m³, F(000)＝2308, R＝0.0417, wR＝0.0945, GOF＝0.933. 该配合物由两个1-亚甲基苯并咪唑-1,4,7-三氮环壬烷一溴合铜配阳离子和一个四溴合铜配阴离子组成. 在两个配阳离子中, 每个Cu(II)离子与五个配位原子配位(四个氮原子和一个溴阴离子), 位于一个变形四方锥的中心. 在配阴离子中, Cu(II)离子与四个溴阴离子配位, 位于一个稍变形四面体的中心.     

Reaction of ferricytochrome c with the iron nitrosyl complex {Fe2[S(CH2)2NH3]2(NO)4}SO4 • 2.5H2O

By an example of cysteamine iron nitrosyl complex {Fe₂[S(CH₂)₂NH₃]₂(NO)₄}SO₄ ? 2.5H₂O (CAC) it was shown for the first time that the NO donor hydrolysis in the presence of ferricytochrome c (cyt c³⁺) affords the iron nitrosyl complex NO—cyt c³⁺. It was found that cyt c³⁺ can serve as a depot for NO evolved during the hydrolysis of CAC. In the presence of CAC, the rate of NO—cyt c³⁺ complex decomposition to NO and cyt c³⁺ depends on the molar ratio [cyt c³⁺]: [CAC] and at [cyt c³⁺]: [CAC] = 0.3 it was found to be lower than that in decomposition of CAC in the absence of cyt c³⁺. As a result, the total NO evolving process becomes 5.6 times more prolonged. The number of NO groups evolved from CAC can be determined by the reaction of CAC with cyt c³⁺ in the presence of ferricyanide: at most one NO group is evolved to a solution in the spontaneous hydrolysis of CAC (pH 7.0), and no less than three of them are evolved from oxidized CAC.     

Syntheses and Structures of Two Selenite Chloride Hydrates: Co(HSeO3)Cl · 3 H2O and Cu(HSeO3)Cl · 2 H2O

The first selenite chloride hydrates, Co(HSeO₃)Cl · 3 H₂O and Cu(HSeO₃)Cl · 2 H₂O, have been prepared from solution and characterised by single‐crystal X‐ray diffraction. The cobalt phase adopts an unusual “one‐dimensional” structure built up from vertex‐sharing pyramidal [HSeO₃]^2–, and octahedral [CoO₂(H₂O)₄]^2– and [CoO₂(H₂O)₂Cl₂]^4– units. Inter‐chain bonding is by way of hydrogen bonds or van der Waals' interactions. The atomic arrangement of the copper phase involves [HSeO₃]^2– pyramids and Jahn‐Teller distorted [CuCl₂(H₂O)₄] and [CuO₄Cl₂]^8– octahedra, sharing vertices by way of Cu–O–Se and Cu–Cl–Cu bonds. Crystal data: Co(HSeO₃)Cl · 3 H₂O, M_r = 276.40, triclinic, space group P 1 (No. 2), a = 7.1657(5) Å, b = 7.3714(5) Å, c = 7.7064(5) Å, α = 64.934(1)°, β = 68.894(1)°, γ = 71.795(1)°, V = 337.78(7) ų, Z = 2, R(F) = 0.036, wR(F) = 0.049. Cu(HSeO₃)Cl · 2 H₂O, M_r = 263.00, orthorhombic, space group Pnma (No. 62), a = 9.1488(3) Å, b = 17.8351(7) Å, c = 7.2293(3) Å, V = 1179.6(2) ų, Z = 8, R(F) = 0.021, wR(F) = 0.024.     

[Au(C6F5)3(PPh2H)]: A Precursor for the Synthesis of Gold(III) Phosphide Complexes

The covalent radius of Au ^I is about 0.07 Å smaller than that of Ag^I. This was determined from the crystal structures of the isostructural complexes [N(PPh₃)][{Au(C₆F₅)₃(μ-PPh₂)}₂M] (M=Au (structure shown in the picture), Ag). These mixed Au^III–M phosphides were synthesized from [Au(C₆F₅)₃(PPh₂H)], the first gold complex to contain a secondary phosphane.     

CHARACTERIZATION OF GALLIUM-NITROGEN ADDUCTS BY X-RAY STRUCTURAL AND NMR SPECTRAL STUDIES. CRYSTAL STRUCTURE OF [(PhMe2CCH2)2GaCI]2 AND OF ITS MONOMERIC t-BUTYLAMINE ADDUCT, (PhMe2CCH2)2GaCI[NH2(t-Bu)]

Abstract

The nature of [(PhMe₂CCH₂)₂GaCl]₂ and its adducts with NH₂(t-Bu) and NH₂(n-Pr) have been investigated. [(PhMe₂CCH₂)₂GaCl]₂ crystallizes in the monoclinic space group P2₁/c with a=11.2495(16)Å, b = 21.4977(32)A, c = 7.8337(15)Å, β = 93.489(14)°, V= 1891.0(5)ų and D(calcd.)= 1.305 Mg/m³ for Z = 2. The structure was refined to R(F) = 4.2% for 1672 reflections above 6[sgrave](F). The molecule has perfect C_i symmetry, a planar Ga(μ-Cl)₂Ga core and an expanded C(α)-Ga-C(α) angle of 137.9(3)° between the neophyl ligands. (PhMe₂CCH₂)₂-GaCl[NH₂(t-Bu)] crystallizes in the monoclinic space group P2₁/n with a = 6.4023(10) A, b= 17.4274(25) A, c = 22.2389(38) Å, β = 94.939(13)°, V= 2472.2(7)ų and D(calcd.) = 1.225 Mg/m³ for Z = 4. This structure was refined to R(F) = 3.9% for 1700 reflections above 6[sgrave](F). The crystal structure is stabilized by intermolecular Cl … H-N hydrogen bonds and the central Ga(III) atom has a distorted tetrahedral geometry. A benzene solution of (PhMe₂-CCH₂)₂GaCl[NH₂(t-Bu)] is in equilibrium with [(PhMe₂CCH₂)₂GaCl]₂[NH₂(t-Bu)] and free amine according to ¹HNMR studies. In contrast to this, a solution of (PhMe₂CCH₂)-GaCl₂[NH₂(t-Bu)] is in equilibrium with [(PhMe₂CCH₂)GaCl₂]₂[NH₂(t-Bu)], free [(PhMe₂-CCH₂)-GaCl₂]₂ and free amine. Solutions of (PhMe₂CCH₂)₂GaCI[NH₂(n-Pr)] and (PhMe₂CCH₂)GaCl₂[NH₂(n-Pr)] show no evidence for similar equilibria.     

Lithium barium silicate,Li2BaSiO4, from synchrotron powder data

The structure of lithium barium silicate, Li₂BaSiO₄, has been determined from synchrotron radiation powder data. The title compound was synthesized by high‐temperature solid‐state reaction and crystallizes in the hexagonal space group P6₃cm. It contains two Li atoms, one Ba atom (both site symmetry ..m on special position 6c), two Si atoms [on special positions 4b (site symmetry 3..) and 2a (site symmetry 3.m)] and four O atoms (one on general position 12d, and three on special positions 6c, 4b and 2a). The basic units of the structure are (Li₆SiO₁₃)⁵⁻ units, each comprising seven tetrahedra sharing edges and vertices. These basic units are connected by sharing corners parallel to [001] and through sharing (SiO₄)⁴⁻ tetrahedra in (001). The relationship between the structures and luminescence properties of Li₂SrSiO₄, Li₂CaSiO₄ and the title compound is discussed.     

Coordination Chemistry of Higher Oxidation States. Part 36. Periodato Complexes of Palladium(IV) and Platinum(IV). Crystal Structure of K4Na2[Pt(OH)2(HIO6)2]·10H2O

Abstract

Periodate complexes of Pd(IV) and Pt(IV) have been prepared from [MC1₆]^2- (M = Pd or Pt) and IO₄ ^? in aqueous alkaline solution. They are formulated as M'₆[M(OH)₂(HIO₆)₂].nH₂O (M' = Na or K) on the basis of analysis, vibrational spectroscopy, and an X-ray structure determination of the platinum complex. The title compound crystallizes in the triclinic space group PI with unit cell parameters a = 7.588(2), b = 8.110(2), c = 9.864(2) Å, a = 82.00(2), β = 83.79(2), γ = 81.76(2)° with Z = 1. Based on 2283 observed reflections (F > 3σ(F)), the structure refined to R = 0.034. Two bidentate [HIO₆]^4- anions coordinate to a central Pt atom which is also coordinated by two trans OH groups. The charge balance is maintained by sodium and potassium cations which are extensively hydrated. ¹⁹⁵Pt and ¹²⁷I NMR data are reported, and the variation in the former with pH interpreted in terms of differing degrees of protonation of the anions. EXAFS data are reported for the platinum complex in solution at pH = 2.