Stability and acidity contributions of heteropolymetalates: a theoretical study of the Keggin and Dawson ions

The Dawson-type anion [X⁽ⁿ⁾₂M₁₈O₆₂]^{2(8 − n)}−, is derived from the Keggin anion [X⁽ⁿ⁾M₁₂O₄₀]^{(8 −n)−} (X=Si, Ge, P, S) by fusing two trivalant shells, producing an oval shaped closed framework. The central oxoanions, contributing an overall charge to the clathratic cluster, retain tetrahedral coordination. Generally, the Dawson heteropolyoxometalates are more thermally stable and catalytically more active than the corresponding Keggin ions. In this work, the comparisons among the Keggin and Dawson ions are addressed in terms of relative stability, hardness and acidity. These predictions are based on the theoretical results obtained from the extended Hückel, EH calculations. This analysis of the Dawson structure presently represents the most significant modelling work on large oxyanions. Absolute comparisons between the EH and density functional are not available for Dawson structures. The correlations between these methods have been shown valid for the Keggin ions and are expected to be similar for the Dawson ions. The substitution chemistry of the central oxoanions is similar to that of the Keggin clusters in both the stability and acidity.     

A Keggin Polyoxometalate Shows Water Oxidation Activity at Neutral pH: POM@ZIF‐8, an Efficient and Robust Electrocatalyst

Keggin‐type polyoxometalate anions [XM₁₂O₄₀]^n? are versatile, as their applications in interdisciplinary areas show. The Keggin anion [CoW₁₂O₄₀]^6? turns into an efficient and robust electrocatalyst upon its confinement in the well‐defined void space of ZIF‐8, a metal–organic framework (MOF). [H₆CoW₁₂O₄₀]@ZIF‐8 is so stable to water oxidation that it retains its initial activity even after 1000 catalytic cycles. The catalyst has a turnover frequency (TOF) of 10.8 mol O₂(mol Co)^?1 s^?1, one of the highest TOFs for electrocatalytic oxygen evolution at neutral pH. Controlled experiments rule out the chances of formation and participation of CoO_x in this electrocatalyic water oxidation.     

Aluminum‐ and Gallium‐Containing Open‐Dawson Polyoxometalates

Al‐ and Ga‐containing open‐Dawson polyoxometalates (POMs), K₁₀[{Al₄(μ‐OH)₆}{α,α‐Si₂W₁₈O₆₆}] · 28.5H₂O ( Al₄ ‐ open ) and K₁₀[{Ga₄(μ‐OH)₆}(α,α‐Si₂W₁₈O₆₆)] · 25H₂O ( Ga₄ ‐ open ) were synthesized by the reaction of trilacunary Keggin POM, [A‐α‐SiW₉O₃₄]^10–, with Al(NO₃)₃ · 9H₂O or Ga(NO₃)₃ · nH₂O, and unequivocally characterized by single‐crystal X‐ray analysis, ²⁹Si and ¹⁸³W NMR, and FT‐IR spectroscopy as well as elemental analysis and TG/DTA. Single‐crystal X‐ray analysis revealed that the {M₄(μ‐OH)₆}⁶⁺ (M = Al, Ga) clusters were included in an open pocket of the open‐Dawson polyanion, [α,α‐Si₂W₁₈O₆₆]^16–, which was constituted by the fusion of two trilacunary Keggin POMs via two W–O–W bonds. These two open‐Dawson structural POMs showed clear difference of the bite angles depending on the size of ionic radii. In cases of both compounds, the solution ²⁹Si and ¹⁸³W NMR spectra in D₂O showed only one signal and five signals, respectively. These spectra were consistent with the molecular structures of Al₄ ‐ and Ga₄ ‐ open , suggesting that these polyoxoanions were obtained as single species and maintained their molecular structures in solution.     

Cyclic Voltammetry Study of the Mn‐Substituted Polyoxoanions [MnII4(H2O)2(H4AsW15O56)2]18− and [((MnIIOH2)MnII2PW9O34)2(PW6O26)]17−: Electrodeposition of Manganese Oxides Electrocatalysts for Dioxygen Reduction

The electrochemical behavior of two manganese (Mn)‐substituted polyoxoanions, the dissymmetrical Dawson sandwich‐type [Mn^II₄(H₂O)₂(H₄AsW₁₅O₅₆)₂]^18? and the Keggin sandwich banana‐shaped [((Mn^IIOH₂)Mn^II₂PW₉O₃₄)₂(PW₆O₂₆)]^17? is investigated. At pH 5, the oxidation of the Mn^II‐centers results in one oxidation wave for [Mn^II₄(H₂O)₂(H₄AsW₁₅O₅₆)₂]^18? and two oxidation waves for [((Mn^IIOH₂)Mn^II₂PW₉O₃₄)₂(PW₆O₂₆)]^17?. To the best of our knowledge, presence of the second Mn‐based wave is rarely observed in the electrochemistry of Mn‐containing polyoxometalates. Deposition of Mn‐oxides electrocatalysts for dioxygen reduction is noticed by cyclic voltammetry, which can be distinguished by the significant positive shift in potentials of the dioxygen reduction reaction.     

Metal‐catalyzed reversible conversion between chemical and electrical energy designed towards a sustainable society

Proton dissociation of an aqua‐Ru‐quinone complex, [Ru(trpy)(q)(OH₂)]²⁺ (trpy = 2,2′ : 6′,2″‐terpyridine, q = 3,5‐di‐t‐butylquinone) proceeded in two steps (pK_a = 5.5 and ca. 10.5). The first step simply produced [Ru(trpy)(q)(OH)]⁺, while the second one gave an unusual oxyl radical complex, [Ru(trpy)(sq)(O^?.)]⁰ (sq = 3,5‐di‐t‐butylsemiquinone), owing to an intramolecular electron transfer from the resultant O^2? to q. A dinuclear Ru complex bridged by an anthracene framework, [Ru₂(btpyan)(q)₂(OH)₂]²⁺ (btpyan = 1,8‐bis(2,2′‐terpyridyl)anthracene), was prepared to place two Ru(trpy)(q)(OH) groups at a close distance. Deprotonation of the two hydroxy protons of [Ru₂(btpyan)(q)₂(OH)₂]²⁺ generated two oxyl radical Ru‐O^?. groups, which worked as a precursor for O₂ evolution in the oxidation of water. The [Ru₂(btpyan)(q)₂(OH)₂](SbF₆)₂ modified ITO electrode effectively catalyzed four‐electron oxidation of water to evolve O₂ (TON = 33500) under electrolysis at +1.70 V in H₂O (pH 4.0). Various physical measurements and DFT calculations indicated that a radical coupling between two Ru(sq)(O^?.) groups forms a (cat)Ru‐O‐O‐Ru(sq) (cat = 3,5‐di‐t‐butylcathechol) framework with a μ‐superoxo bond. Successive removal of four electrons from the cat, sq, and superoxo groups of [Ru₂(btpyan)(cat)(sq)(μ‐O₂^?)]⁰ assisted with an attack of two water (or OH^?) to Ru centers, which causes smooth O₂ evolution with regeneration of [Ru₂(btpyan)(q)₂(OH)₂]²⁺. Deprotonation of an Ru‐quinone‐ammonia complex also gave the corresponding Ru‐semiquinone‐aminyl radical. The oxidized form of the latter showed a high catalytic activity towards the oxidation of methanol in the presence of base. Three complexes, [Ru(bpy)₂(CO)₂]²⁺, [Ru(bpy)₂(CO)(C(O)OH)]⁺, and [Ru(bpy)₂(CO)(CO₂)]⁰ exist as an equilibrium mixture in water. Treatment of [Ru(bpy)₂(CO)₂]²⁺ with BH₄^? gave [Ru(bpy)₂(CO)(C(O)H)]⁺, [Ru(bpy)₂(CO)(CH₂OH)]⁺, and [Ru(bpy)₂(CO)(OH₂)]²⁺ with generation of CH₃OH in aqueous conditions. Based on these results, a reasonable catalytic pathway from CO₂ to CH₃OH in electro‐ and photochemical CO₂ reduction is proposed. A new pbn (pbn = 2‐pyridylbenzo[b]‐1,5‐naphthyridine) ligand was designed as a renewable hydride donor for the six‐electron reduction of CO₂. A series of [Ru(bpy)_3‐n(pbn)_n]²⁺ (n = 1, 2, 3) complexes undergoes photochemical two‐ (n = 1), four‐ (n = 2), and six‐electron reductions (n = 3) under irradiation of visible light in the presence of N(CH₂CH₂OH)₃. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 169–186; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200800039     

Crystal Structures and Proton Conductivities of a MOF and Two POM–MOF Composites Based on CuII Ions and 2,2′‐Bipyridyl‐3,3′‐dicarboxylic Acid

We have succeeded in constructing a metal–organic framework (MOF), [Cu(bpdc)(H₂O)₂]_n (H₂bpdc=2,2′‐bipyridyl‐3,3′‐dicarboxylic acid, 1 ), and two poly‐POM–MOFs (POM=polyoxometalate), {H[Cu(Hbpdc)(H₂O)₂]₂[PM₁₂O₄₀] ? n H₂O}_n (M=Mo for 2 , W for 3 ), by the controllable self‐assembly of H₂bpdc, Keggin‐anions, and Cu²⁺ ions based on electrostatic and coordination interactions. Notably, these three compounds all crystallized in the monoclinic space group P2₁/n, and the Hbpdc^? and bpdc^2? ions have the same coordination mode. Interestingly, in compounds 2 and 3 , Hbpdc^? and the Keggin‐anion are covalently linked to the transition metal copper at the same time as polydentate organic ligand and as polydentate inorganic ligand, respectively. Complexes 2 and 3 represent new and rare examples of introducing the metal N‐heterocyclic multi‐carboxylic acid frameworks into POMs, thereby, opening a pathway for the design and the synthesis of multifunctional hybrid materials based on two building units. The Keggin‐anions being immobilized as part of the metal N‐heterocyclic multi‐carboxylic acid frameworks not only enhance the thermal stability of compounds 2 and 3 , but also introduce functionality inside their structures, thereby, realizing four approaches in the 1D hydrophilic channel used to engender proton conductivity in MOFs for the first time. Complexes 2 and 3 exhibit good proton conductivity (10^?4 to ca. 10^?3 S cm^?1) at 100 °C in the relative humidity range 35 to about 98 %.     

Cobalt(II) and cadmium(II) square grids supported with 4,4′‐bipyrazole and accommodating 3‐carboxyadamantane‐1‐carboxylate

In poly[[bis(μ‐4,4′‐bi‐1H‐pyrazole‐κ²N²:N^2′)bis(3‐carboxyadamantane‐1‐carboxylato‐κO¹)cobalt(II)] dihydrate], {[Co(C₁₂H₁₅O₄)₂(C₆H₆N₄)₂]·2H₂O}_n, (I), the Co²⁺ cation lies on an inversion centre and the 4,4′‐bipyrazole (4,4′‐bpz) ligands are also situated across centres of inversion. In its non‐isomorphous cadmium analogue, {[Cd(C₁₂H₁₅O₄)₂(C₆H₆N₄)₂]·2H₂O}_n, (II), the Cd²⁺ cation lies on a twofold axis. In both compounds, the metal cations adopt an octahedral coordination, with four pyrazole N atoms in the equatorial plane [Co—N = 2.156 (2) and 2.162 (2) Å; Cd—N = 2.298 (2) and 2.321 (2) Å] and two axial carboxylate O atoms [Co—O = 2.1547 (18) Å and Cd—O = 2.347 (2) Å]. In both structures, interligand hydrogen bonding [N...O = 2.682 (3)–2.819 (3) Å] is essential for stabilization of the MN₄O₂ environment with its unusually high (for bulky adamantanecarboxylates) number of coordinated N‐donor co‐ligands. The compounds adopt two‐dimensional coordination connectivities and exist as square‐grid [M(4,4′‐bpz)₂]_n networks accommodating monodentate carboxylate ligands. The interlayer linkage is provided by hydrogen bonds from the carboxylic acid groups via the solvent water molecules [O...O = 2.565 (3) and 2.616 (3) Å] to the carboxylate groups in the next layer [O...O = 2.717 (3)–2.841 (3) Å], thereby extending the structures in the third dimension.     

Following the Reaction of Heteroanions inside a {W18O56} Polyoxometalate Nanocage by NMR Spectroscopy and Mass Spectrometry

By incorporating phosphorus(III)‐based anions into a polyoxometalate cage, a new type of tungsten‐based unconventional Dawson‐like cluster, [W₁₈O₅₆(HP^IIIO₃)₂(H₂O)₂]^8?, was isolated, in which the reaction of the two phosphite anions [HPO₃]^2? within the {W₁₈O₅₆} cage could be followed spectroscopically. As well as full X‐ray crystallographic analysis, we studied the reactivity of the cluster using both solution‐state NMR spectroscopy and mass spectrometry. These techniques show that the cluster undergoes a structural rearrangement in solution whereby the {HPO₃} moieties dimerize to form a weakly interacting (O₃PH???HPO₃) moiety. In the crystalline state the cluster exhibits a thermally triggered oxidation of the two P^III template moieties to form P^V centers (phosphite to phosphate), commensurate with the transformation of the cage into a Wells–Dawson {W₁₈O₅₄} cluster.     

Co‐Adsorption of O2 and CO on Au2−: Infrared Photodissociation Spectroscopy and Theoretical Study of [Au2O2(CO)n]− (n=2–6)

The co‐adsorption of O₂ and CO on anionic sites of gold species is considered as a crucial step in the catalytic CO oxidation on gold catalysts. In this regard, the [Au₂O₂(CO)_n]^? (n=2–6) complexes were prepared by using a laser vaporization supersonic ion source and were studied by using infrared photodissociation spectroscopy in the gas phase. All the [Au₂O₂(CO)_n]^? (n=2–6) complexes were characterized to have a core structure involving one CO and one O₂ molecule co‐adsorbed on Au₂^? with the other CO molecules physically tagged around. The CO stretching frequency of the [Au₂O₂(CO)]^? core ion is observed around =2032–2042 cm^?1, which is about 200 cm^?1 higher than that in [Au₂(CO)₂]^?. This frequency difference and the analyses based on density functional calculations provide direct evidence for the synergy effect of the chemically adsorbed O₂ and CO. The low lying structures with carbonate group were not observed experimentally because of high formation barriers. The structures and the stability (i.e., the inertness in a sense) of the co‐adsorbed O₂ and CO on Au₂^? may have relevance to the elementary reaction steps on real gold catalysts.     

Two Keggin Templated Supramolecular Compounds by Exerting the Chelate and Linking Dual Roles of the Ligand 2, 2′‐Biimidazole

Two new Keggin templated supramolecular compounds, [Zn₂(H₂biim)₅(SiM₁₂O₄₀)] · 4H₂O [M = W ( 1 ), Mo ( 2 )] (H₂biim = 2, 2′‐biimidazole), were synthesized under hydrothermal conditions by using the ligand 2, 2′‐biimidazole. They were characterized by single‐crystal X‐ray diffraction, elemental analyses, IR and photoluminescence spectroscopy as well as cyclic voltammetry. The two isostructural compounds are constructed by two discrete supramolecular moieties: the inorganic chains consist of Keggin anions and metal‐organic chains constructed by [Zn₂(H₂biim)₅]⁴⁺ subunits. In the dinuclear [Zn₂(H₂biim)₅]⁴⁺ subunit, the H₂biim ligands exhibit a dual role, chelating and linking. The metal‐organic chains further construct a 3D supramolecular framework with channels, in which the Keggin‐based inorganic chains are accommodated. The electrochemical behaviors of compounds 1 and 2 bulk‐modified carbon paste electrodes ( 1 ‐CPE, 2 ‐CPE) were studied.     

A Mono‐Cobalt Substituted Wells–Dawson Phosphotungstate with an Antenna Ligand

A mono‐cobalt substituted Wells–Dawson polyoxometalate with an antenna ligand linked to the Co^II atom, was prepared by reaction of the mono‐vacant Wells–Dawson precursor [P₂W₁₇O₆₁]^10– with a imidazole‐cobalt complex by using the bench method. It was isolated as the imidazole salt: (HIm)₇H[P₂W₁₇O₆₁Co(Im)] · 4H₂O ( 1 ) (Im = imidazole). Compound 1 was characterized by elemental analysis, IR and UV/Vis spectroscopy, TG analysis, cyclic voltammetry and single‐crystal/powder X‐ray diffraction. This is the first example of the 3d transition metal mono‐substituted Wells–Dawson polyoxometalate with an antenna ligand.     

Werner Complexes with ω‐Dimethylaminoalkyl Substituted Ethylenediamine Ligands: Bifunctional Hydrogen‐Bond‐Donor Catalysts for Highly Enantioselective Michael Additions

The racemic carbonate complex [Co(en)₂O₂CO]⁺ Cl^? (en=1,2‐ethylenediamine) and (S)‐[H₃NCH((CH₂)_nNHMe₂)CH₂NH₃]³⁺ 3 Cl^? (n=1–4) react (water, charcoal, 100 °C) to give [Co(en)₂((S)‐H₂NCH((CH₂)_nNHMe₂)CH₂NH₂)]⁴⁺ 4 Cl^? ( 3 a – d H⁴⁺ 4 Cl^?) as a mixture of Λ/Δ diastereomers that separate on chiral‐phase Sephadex columns. These are treated with NaOH/Na⁺ BAr_f^? (BAr_f=B(3,5‐C₆H₃(CF₃)₂)₄) to give lipophilic Λ‐ and Δ‐ 3 a–d ³⁺ 3 BAr_f^?, which are screened as catalysts (10 mol %) for additions of dialkyl malonates to nitroalkenes. Optimal results are obtained with Λ‐ 3 c ³⁺ 3 BAr_f^? (CH₂Cl₂, ?35 °C; 98–82 % yields and 99–93 % ee for six β‐arylnitroethenes). The monofunctional catalysts Λ‐ and Δ‐[Co(en)₃]³⁺ 3 BAr_f^? give enantioselectivities of <10 % ee with equal loadings of Et₃N. The crystal structure of Δ‐ 3 a H⁴⁺ 4 Cl^? provides a starting point for speculation regarding transition‐state assemblies.     

Cation Effect on Formation of Preyssler‐type 30‐Tungsto‐5‐phosphate: Enhanced Yield of Na‐encapsulated Derivative and Direct Synthesis of Ca‐ and Bi‐Encapsulated Derivatives

The effect of cations in a reaction mixture for the preparation of the Preyssler‐Jeannin‐Pope type 30‐tungsto‐5‐phosphate [P₅W₃₀O₁₁₀Na]^14– is investigated. Reaction of phosphate and tungstate with a P/W ratio of ca. 3.9 in an acidic aqueous solution without cations selectively leads to the Dawson‐type 18‐tungsto‐2‐phosphate, [P₂W₁₈O₆₂]^6–. Amongst all the alkali cations, only Na⁺ allows formation of the Preyssler‐type polyanion [P₅W₃₀O₁₁₀Na]^14–, with an encapsulated Na⁺ ion, and the product yield can be improved by increasing Na⁺ amount. The presence of Li⁺ ions instead results in the Dawson‐type polyanion [P₂W₁₈O₆₂]^6–, whereas K⁺, Rb⁺, and Cs⁺ selectively result in the Keggin‐type polyanion [PW₁₂O₄₀]^3–. An improved synthetic procedure for the Na⁺‐encapsulated Preyssler‐ion leading to a higher isolated yield is presented. Furthermore, addition of Ca²⁺ and Bi³⁺ compounds allows formation of the Ca²⁺‐ and Bi³⁺‐encapsulated Preyssler‐type polyanions, [P₅W₃₀O₁₁₀Ca]^13– and [P₅W₃₀O₁₁₀Bi]^12–, respectively. Furthermore, single‐crystal XRD structure of the Bi³⁺‐encapsulated Preyssler‐type polyanions, [P₅W₃₀O₁₁₀Bi]^12–, is presented for the first time.     

Electrospray Mass Spectrometry Study on Polynuclear Pd(II) and Ni (II) Complexes of 3, 6, 9, 16, 19, 22‐Hexaazatricyclo [22. 2.2.211,14] triaconta‐11, 13, 24, 26 (1), 27, 29‐Hexaene

Polynuclear Pd(II) and Ni(II) complexes of macrocyclic polyamine 3,6,9,16,19,22‐hexaazatricyclo[22.2.2.2^11,14]‐triaconta 11,13,24,26(l),27,29‐hexaene (L) in solution were investigated by electrospray ionization mass spectrometry (ESIMS). For methanol solution of complexes M₂LX₄ (M = Pd(II) and Ni(II), X= Cl and I), two main clusters of peaks were observed which can be assigned to [M₂LX₃]⁺ and [M₂LX₂]²⁺. When Pd₂LCl₄ was treated with 2 or 4 mol of AgNO₃, it gave rise formation of Pd₂LCl₂ (NO₃)₂ · H₂O and [Pd₂L(H₂O)_m(NO₃)_n]^(4‐n)+, respectively. ESMS spectra show that the dissociation of the former in the ionization process gave peaks of [Pd₂LCl₂]²⁺ and [(Pd₂LCl₂)NO₃]⁺, while dissociation of the later gave the peaks of [Pd₂L(CH₃CO₂)₂]²⁺ and [Pd₂L(CH₃CO₂)₂](NO₃) ⁺ in the presence of acetic acid. Similar species were observed for Pd₂LI₄ when treated with 4 mol of AgNO₃. When [Pd₂L · (H₂O)_m(NO₃)_n]^(4‐n)+ reacted with 2 mol of oxalate anions at 40°C, [Pd₄L₂(C₂O₄)₂(NO₃)₂]²⁺ and [Pd₄L₂(C₂O₄)₂ (NO₃)]³⁺ were detected. This implies the formation of square‐planar molecular box Pd₄L₂(C₂O₄)₂(NO₃)₄ in which C₂O₄^? may act as bridging ligands as confirmed by crystal structure analysis. The dissociation form and the stability of complex cations in gaseous state are also discussed. This work provides an excellent example of the usefulness of ESIMS in the identification of metal complexes in solution.     

A 3D Polyoxometalate‐Based Framework Constructed from Ag/trz Metal‐Organic Ribbons and P2W18 Polyoxoanions: Synthesis,Structure and Electrochemical Properties

A Wells‐Dawson Polyoxometalate‐based hybrid, Ag₉(trz)₃(Htrz)₄ (H₂O)(P₂W₁₈O₆₂)·3H₂O ( 1 ) (Htrz = 1,2,4‐1H‐triazole) was hydrothermally synthesized through using trz ligand and silver nitrate in the presence of [P₂W₁₈O₆₂]^6– polyoxoanion. In the 3D framework structure of compound 1 , two kinds of wave‐like Ag/trz chains originated from trz ligands and silver cations are aggregated in a “2+1” mode by {Ag₂/trz} linkages to result in a 1D Ag/trz metal‐organic ribbon, which is further extended into a 3D framework structure by [P₂W₁₈O₆₂]^6– polyoxoanions through Ag‐O covalent bonds. Additionally, the electrochemical properties of compound 1 have also been investigated.     

Syntheses,crystal structures,and magnetic properties of the banana-shaped tungstophosphates: [M6(H2O)2(PW9O34)2(PW6O26)]17− (MII=NiII,CoII)

Two new banana-shaped tungstophosphates [M₆(H₂O)₂(PW₉O₃₄)₂(PW₆O₂₆)]^{17 ?} (M^II?=?Ni^II, Co^II) incorporating two types of lacunary polyoxometalate units have been synthesized in aqueous solution and characterized by elemental analyses, IR, and UV spectra, and single-crystal X-ray diffraction. Structural analyses show that Na₆H₁₁[Ni₆(H₂O)₂(PW₉O₃₄)₂(PW₆O₂₆)]?·?32H₂O (1) and Na₇H₁₀[Co₆(H₂O)₂(PW₉O₃₄)₂(PW₆O₂₆)]?· 31H₂O (2) are generated from two tri-M^II substituted B-α-[(MOH₂)M₂PW₉O₃₄] Keggin units connected by a hexavacant [PW₆O₂₆]^11? Keggin fragment, leading to the M^II-containing banana-shaped tungstophosphates. Magnetic properties of 2 show decrease of the molar magnetic susceptibility at higher temperatures results from spin-orbit coupling of Co^II and antiferromagnetic interactions whereas the maximum at the lower temperatures is indicative of the ferromagnetic interactions within the trinuclear Co^II spin cluster in the sandwich belt.     

More crystal field theory in action: the metal–4‐picoline (pic)–sulfate [M(pic)x]SO4 complexes (M = Fe,Co, Ni,Cu, Zn,and Cd)

Seven crystal structures of five first‐row (Fe, Co, Ni, Cu, and Zn) and one second‐row (Cd) transition metal–4‐picoline (pic)–sulfate complexes of the form [M(pic)_x]SO₄ are reported. These complexes are catena‐poly[[tetrakis(4‐methylpyridine‐κN)metal(II)]‐μ‐sulfato‐κ²O:O′], [M(SO₄)(C₆H₇N)₄]_n, where the metal/M is iron, cobalt, nickel, and cadmium, di‐μ‐sulfato‐κ⁴O:O‐bis[tris(4‐methylpyridine‐κN)copper(II)], [Cu₂(SO₄)₂(C₆H₇N)₆], catena‐poly[[bis(4‐methylpyridine‐κN)zinc(II)]‐μ‐sulfato‐κ²O:O′], [Zn(SO₄)(C₆H₇N)₂]_n, and catena‐poly[[tris(4‐methylpyridine‐κN)zinc(II)]‐μ‐sulfato‐κ²O:O′], [Zn(SO₄)(C₆H₇N)₃]_n. The Fe, Co, Ni, and Cd compounds are isomorphous, displaying polymeric crystal structures with infinite chains of M^II ions adopting an octahedral N₄O₂ coordination environment that involves four picoline ligands and two bridging sulfate anions. The Cu compound features a dimeric crystal structure, with the Cu^II ions possessing square‐pyramidal N₃O₂ coordination environments that contain three picoline ligands and two bridging sulfate anions. Zinc crystallizes in two forms, one exhibiting a polymeric crystal structure with infinite chains of Zn^II ions adopting a tetrahedral N₂O₂ coordination containing two picoline ligands and two bridging sulfate anions, and the other exhibiting a polymeric crystal structure with infinite chains of Zn^II ions adopting a trigonal bipyramidal N₃O₂ coordination containing three picoline ligands and two bridging sulfate anions. The structures are compared with the analogous pyridine complexes, and the observed coordination environments are examined in relation to crystal field theory.     

Metallkomplexe mit biologisch wichtigen Liganden. CLXVI Metallkomplexe mit Ferrocenylmethyl‐L‐cysteinat und 1,1′‐Ferrocenylbis‐(methyl‐L‐cysteinat) als Liganden

Metal Complexes of Biologically Important Ligands. CLXVI Metal Complexes with Ferrocenylmethylcysteinate and 1,1′‐Ferrocenylbis‐(methylcysteinate) as Ligands A series of complexes of transition metal ions ( Cr³⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ ) and of lanthanide ions ( La³⁺, Nd³⁺, Gd³⁺, Dy³⁺, Lu³⁺ ) with the anions of ferrocenylmethyl‐L‐cysteine [(C₅H₅)Fe(C₅H₄CH(R)SCH₂CH(NH₃⁺)CO₂^?] (L¹) and with the dianions of 1,1′‐ferrocenylbis(methyl‐L‐cysteine) [Fe(C₅H₄CH(R)SCH₂CH(NH₃⁺) CO₂^?)₂] (R = H, Me, Ph) (L²) as N,O,S‐donors were prepared. With the monocysteine ferrocene derivative L¹ as ligands complexes [M^IIL¹₂] or [Cr^IIIL¹₂]Cl type complexes are formed whereas the bis(cysteine) ligand L² yields insoluble complexes of type [ML²]_n, presumably as coordination polymers. The magnetic moments of [Mn^IIL²]_n, [Pr^IIIL²]_n(OH)_n and [Dy^IIIL²]_n(OH)_n exhibit “normal” paramagnetism.     

Cd2Cu(PO4)2

During an investigation of the insufficiently known system M1O–M2O–X₂O₅–H₂O (M1 = Cd²⁺, Sr²⁺ and Ba²⁺; M2 = Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺ and Mg²⁺; X = P⁵⁺, As⁵⁺ and V⁵⁺), single crystals of the novel compound dicadmium copper(II) bis[phosphate(V)], Cd₂Cu(PO₄)₂, were obtained. This compound belongs to a small group of compounds adopting a Cu₃(PO₄)₂‐type structure and having the general formula M1₂M2(XO₄)₂ (M1/M2 = Cd²⁺, Cu²⁺, Mg²⁺ and Zn²⁺; X = As⁵⁺, P⁵⁺ and V⁵⁺). The crystal structure is characterized by the interconnection of infinite [Cu(PO₄)₂]_n chains and [Cd₂O₁₀]_n double chains, both extending along the a axis. Exceptional characteristics of this structure are its novel chemical composition and the occurrence of double chains of CdO₆ polyhedra that were not found in related structures. In contrast to the isomorphous compounds, where the M1 cations are coordinated by five O atoms, the Cd atom is coordinated by six. The dissimilarity in the geometry of M1 coordination between Cd₂Cu(PO₄)₂ and the isomorphous compounds is mostly due to the larger ionic radius of the Cd cation in comparison with the Cu, Mg and Zn cations. Sharing a common edge, two CdO₆ polyhedra form Cd₂O₁₀ dimers. Each such dimer is bonded to another dimer sharing common vertices, forming [Cd₂O₁₀]_n double chains in the [100] direction. The Cu atoms, located on an inversion centre (site symmetry ), form isolated CuO₄ squares interconnected by PO₄ tetrahedra, forming [Cu(PO₄)₂]_n chains similar to those found in related structures. Conversely, the [Cd₂O₁₀]_n double chains, which were not found in related structures, are an exclusive feature of this structure.     

Bis(pyridine‐2,6‐dimethanol‐N,O,O′)cobalt(II) and ‐copper(II) disacchar­inate dihydrate: three‐dimensional structures with extensive hydrogen bonds and aromatic π–π‐stacking interactions

Bis­(pyridine‐2,6‐di­methanol‐N,O,O′)­cobalt(II) disaccharinate dihydrate, [Co(C₇H₉NO₂)₂](C₇H₄NO₃S)₂·2H₂O, (I), and bis­(pyridine‐2,6‐di­methanol‐N,O,O′)copper(II) disaccharinate dihydrate, [Cu(C₇H₉NO₂)₂](C₇H₄NO₃S)₂·2H₂O, (II), collectively [M(dmpy)₂](sac)₂·2H₂O (where M is Co^II or Cu^II, sac is the saccharinate anion and dmpy is pyridine‐2,6‐di­methanol), are isostructural. The [M(dmpy)₂]²⁺ cations exhibit distorted octahedral geometry in which the two neutral dmpy species act as tripodal N,O,O′‐tridentate ligands. The crystal packing is determined by hydrogen bonding, as well as by weak pyridine–saccharinate π–π‐stacking interactions.