Tertiary arsine-stabilised arsenium salts: syntheses and comparisons with phosphine analogues

The first tertiary arsine-stabilised arsenium salts, [(L)AsMePh]OTf (L = Ph3As, Me2PhAs, [2-(MeOCH2)C6H4]Ph2As, [2-(MeOCH2)C6H4]Me2As), have been prepared by chloride abstraction from chloromethylphenylarsine with trimethylsilyl triflate in the presence of the arsine. The complexes have been characterised by crystallography and 1H NMR spectroscopy. The chiral cations in the complexes have structures based on the trigonal pyramid in which the arsine is coordinated orthogonally to the prochiral, six-electron MePhAs+ ion that forms the base of the pyramid. The NMR data for the complexes in dichloromethane-d2 are consistent with rapid exchange of the arsine on the arsenium ion, even at 183 K. The corresponding phosphine-stabilised complexes are considerably more stable than their arsine counterparts in dichloromethane-d2 with the free energy of activation DeltaG = ca. 60 kJ mol(-1) being calculated for phosphine exchange in [(Me2PhP)AsMePh]OTf at 281 K; for [(Me2[2-(MeOCH2)C6H4]P)AsMePh]OTf in the same solvent, DeltaG = ca. 70 kJ mol(-1) at 323 K.     

Metallo-macrocycles with labile coordination sites through self assembly: binuclear phenyl bridged bisbipyridine manganese complexes

Self assembly of phenyl bridged bisbipyridines with manganese perchlorate gave structurally different metallo-macrocycles having cis-labile coordination sites which can catalyse olefin epoxidation with peracetic acid in good yield.     

Metal(II) complexes and metal(II) salts ofN-carbamoylpyrazole: N,O and N,N coordination

Summary Several new coordination compounds are reported withN-carbamoylpyrazole (Hcpz) as the ligand;viz. M(cpz)₂ where M = Cu^II and Ni^II; M(Hcpz)Cl₂ where M = Mn^II, Co^II, Cu^II, Zn^II and Cd^II; M(Hcpz)₂Cl₂ Where M = Fe^II, Co^II and Ni^II: M(Hcpz)₃(BF₄)₂ where M = Fe^II, Co^II, Ni^II, Zn^II and Cd^II; and Cu(Hcpz)₂(BF₄)₂. In the salts, Hcpz is coordinated through the nitrogen atoms of the pyrazole ring and the nitrogen atom of the carbamoyl group. In the Hcpz complexes, coordination takes place through the nitrogen atom of the pyrazole ring and the oxygen atom of the carbamoyl group.     

The interplay of metal and supporting ligand in labile coordination to pincer complexes of Ag(I)

The bis(imino)pyridine scaffold provides support for the synthesis and characterization of unique Ag(I) pincer complexes [{ArN=CPh}(2)(NPh)]Ag(+)(OTf)(-) (Ar = 2,5-(t)Bu(2)C(6)H(3)3; 2,6-(i)Pr(2)C(6)H(3) 4). The bonding interactions between the cation-anion and between the bis(imino)pyridine ligand and the Ag centre are presented. Coordination of pyridine, toluene, 2-butyne and cyclooctene to the Ag centre led to the isolation and crystallographic characterization of labile transient adduct species. Bonding analysis of the adducts revealed conventional ligand-Ag coordination and important unconventional electron donation from the ligand to a π*-orbital of the bis(imino)pyridine group.     

Heteroleptic copper dipyrromethene complexes: synthesis, structure, and coordination polymers

The synthesis of neutral [Cu(dpm)2] and [Cu(dpm)(acac)] (dpm = dipyrromethene, acac = acetylacetonato) complexes is presented. The formation of the asymmetric metal complexes was monitored by electronic absorption and infrared spectroscopy. Two of the complexes investigated, containing pyrdpm ligands (pyrdpm = pyridyldipyrromethene), form 1-dimensional coordination polymers. The coordination polymers formed by these complexes have been characterized by single-crystal X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. The complexes possess square pyramidal coordination geometries with the apical position occupied by the meso-pyridyl donor of a neighboring complex in the crystal lattice. The features of these coordination complexes that facilitate formation of extended solids have been probed. Symmetric [Cu(pyrdpm)2] complexes are unable to form coordination solids due to steric hindrance at the metal center. Use of cyano donors in complexes such as [Cu(cydpm)(acac)] (cydpm = cyanodipyrromethene) in lieu of pyridyl donors also fail to form network solids. Through these systematic studies, both the basic coordination chemistry of these complexes and the fundamental design requirements for synthesizing this novel class of coordination polymers have been defined.     

Homoleptic pnictogen-chalcogen coordination complexes

The synthesis and structural characterization of dicationic selenium and tellurium analogues of the carbodiphosphorane and triphosphenium families of compounds are reported. These complexes, [Ch(dppe)][OTf](2) [Ch = Se, Te; dppe = 1,2-bis(diphenylphosphino)ethane; OTf = trifluoromethanesulfonate], are formed using [Ch](2+) reagents via a ligand-exchange protocol and represent extremely rare examples of homoleptic pnictogen → chalcogen coordination complexes. The corresponding arsenic compounds were also prepared, [Ch(dpAse)][OTf](2) [Ch = Se, Te; dpAse = 1,2-bis(diphenylarsino)ethane], exhibiting the first instance of an arsenic → chalcogen dative bond. The electronic structures of these unique compounds were determined and compared to previously reported chalcogen dications.     

From coordination complexes to coordination polymers through self-assembly

Metal ion coordination in metallo-supramolecular assemblies offers the opportunity to fabricate and study devices and materials that are equally important for fundamental research and new technologies. Metal ions embedded in a specific ligand field offer diverse thermodynamic, kinetic, chemical, physical and structural properties that make these systems promising candidates for active components in functional materials. In particular, dynamic coordination polymers offer exciting opportunities to provide materials with responsive properties. In addition, this approach allows to incorporate the well known properties of metal complexes in polymeric architectures. This review highlights the improvements and the possible applications based on metallo-supramolecular systems with an emphasis on materials science. Examples for new materials such as molecular magnets, coordination polymers as carrier package as well as molecular electronics are featured in this article.     

Tetrathiafulvalene-based lanthanide coordination complexes: Synthesis,crystal structure,optical and electrochemical characterization

The explorative lanthanide coordination chemistry of 4′,5′-bis-(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2′,3′-c]phenazine (TTF-dppz) is described. Thereby, four new Ln(III) complexes, [Ln(NO₃)₃(TTF-dppz)₂] with Ln(III) = Nd (1), Eu (2), Gd (3), Tb (4), have been prepared and characterized. An X-ray crystallographic study of [Gd(NO₃)₃(TTF-dppz)₂] (3) shows that the Gd(III) ion is coordinated to six oxygen atoms from three bidentate nitrate ligands and four nitrogen atoms from two bidentate TTF-dppz molecules forming a distorted bicapped square antiprism coordination geometry. The UV-vis spectra of the four Ln(III) complexes show very strong absorption bands in the UV region consistent with ligand centred electronic π-π* transitions and an intense broad absorption band in the visible region corresponding to a spin-allowed electronic π-π* ¹ILCT transition from the TTF-dppz ligand. Upon coordination, the ¹ILCT band of the free TTF-dppz ligand is bathochromically shifted. The electrochemical studies reveal that all complexes undergo two reversible oxidation and one (quasi)reversible reduction processes, ascribed to the successive oxidations of the TTF moiety and the reduction of the dppz unit, respectively. Moreover, the magnetic properties of complexes 3 and 4 are discussed.     

Metal complexes of porphycene,corrphycene, and hemiporphycene: stability and coordination chemistry

Porphyrin (P), porphycene (Pc), corrphycene (Cn), and hemiporphycene (Hpc) represent a series of well defined "4-N in" constitutional porphyrin isomers. These isomers, in the form of their octaethyl derivatives, represent a congruent set of porphyrinoids whose properties can be compared. In this study we report how variations in electronic structure and nitrogen-core size in the free-base forms of these four systems are reflected in the properties of their corresponding metal complexes. Specifically, the effects that these differences have on the axial ligation properties of the Zn(II), Mg(II), Ni(II), and Co(II) complexes of P, Pc, Cn, and Hpc in toluene using pyridine as the axial ligand are detailed. Also reported are the relative stabilities of these complexes under acidic conditions. It is shown that for the zinc, magnesium, and cobalt complexes, there are distinct differences in the ability to maintain four-, five-, or six-coordinate geometries in the presence of similar concentrations of pyridine. By contrast, no apparent differences in axial ligand binding affinity are seen for the four nickel complexes. Little difference in stability was likewise seen when these same complexes were subject to acid-mediated demetallation, with all four falling into stability class II, according to the accepted porphyrin stability ranking system. High stabilities were also seen in the case of the cobalt complexes, with the Pc and Cn complexes being of stability class III and the P and Hpc derivatives falling into stability class II. The Zn(II) and Mg(II) complexes were all far less stable than the corresponding Ni(II) and Co(II) complexes. In this case, semiquantitative analyses of the rate of acid-induced decomposition revealed the following stability sequence P>Cn>Hpc>Pc for both the Zn(II) and Mg(II) complexes. Single-crystal X-ray diffraction structures were solved for the Zn(II), Mg(II), and Ni(II) complexes of the octaethyl derivatives of Hpc, Cn, and Pc as well as a Co(II) octamethylcorrphycene and are reported as part of this study. These solid-state structures confirm four-coordinate species for the Ni(II) complexes, four- and five-coordinate species for the Mg(II) and Zn(II) complexes, and a six-coordinate species for the lone Co(II) complex.     

Cavity-directed synthesis of labile silanol oligomers within self-assembled coordination cages.

This paper introduces a concept that is referred to as cavity-directed synthesis by showing the selective oligomerization of trialkoxysilanes, RSi(OMe)3 (7), in self-assembled hollow compounds. Pd(II)-linked coordination hosts (cage, bowl, or tube) are found to strictly control the oligomerization of 7 (R = 2-naphthyl) in such a way that their optimal guests are produced in their cavities. Thus, within coordination tube 1, one molecule of 7 is accommodated and subsequently hydrolyzed to give silanetriol RSi(OH)3 (4). Under ordinary aqueous conditions, this reactive compound undergoes rapid polycondensation (so-called sol-gel condensation) leading to Si-O networks. Within the cavity of 1, however, 4 remains very stable and the polycondensation is completely suppressed. On the other hand, coordination bowl 2 and cage 3 give its dimers RSi(OH)2OSi(OH)2R (5) and cyclic trimers [RSi(OH)O]3 (6), respectively. X-ray crystallographic studies clearly show that the cavity size and the shape of 1, 2, and 3 nicely fit with those of 4, 5, and 6, respectively, demonstrating that the cavities strictly direct the oligomerizaion reaction of 7.     

Nitrosophenol complexes of transition metal salts

Complexes derived from 4-substituted-2-nitrosophenols, 3-Me-2-nitrosophenol, nitrosophyrogallol, nitrososalicylic acid and nitrosogallic acid with cobalt(II), nickel(II) and copper(II) have been prepared and characterized by elemental analysis, electronic and vibrational spectra, together with magnetic susceptibility measurements. The e.s.r. spectra of the copper(II) complexes were investigated, and detailed thermal properties of selected complexes are discussed.     

Selective CO2 adsorption in a robust and water-stable porous coordination polymer with new network topology

A robust and water-stable porous coordination polymer [Cd(NDC)(0.5)(PCA)]·G(x) (1) (H(2)NDC = 2,6-napthalenedicarboxylic acid, HPCA = 4-pyridinecarboxylic acid, G = guest molecules) with new network topology has been synthesized solvothermally. The framework is 3D porous material and forms a 1D channel along the c-axis, with the channel dimensions ~9.48 × 7.83 ?(2). The compound has high selectivity in uptake of CO(2) over other gases (H(2), O(2), Ar, N(2), and CH(4)). The framework is highly stable in presence of water vapor even at 60 °C. The high CO(2) selectivity over other gases and water stability makes the compound promising candidate for industrial postcombustion gas separation application.     

Bimetallic coordination polymers via combination of substitution-inert building blocks and labile connectors

A rational approach to the synthesis of silver-chromium mixed-metal coordination polymers is presented: 3-cyanoacetylacetone (HacacCN) features two potential binding sites. After deprotonation, it has been used as a chelating dionato ligand in the pseudo octahedral complex Cr(acacCN) 3; two polymorphs of this compound have been identified. In its protonated form, HacacCN was employed as a N donor toward Ag(I). Both functionalities may be exploited within the same solid: The chromium complex and silver salts of weakly coordinating anions have been successfully combined to mixed-metal coordination polymers. Cr(acacCN) 3 plays the role of a substitution-inert tecton with predictable bonding geometry which interacts with the conformationally soft silver cations via two or all three of its peripheric nitrile groups. From an equimolar amount of both constituents, six solids featuring a 1:1 ratio between Cr- and Ag-derived building blocks were obtained in good yield; their structures depend on the counteranions and the cocrystallized solvent and correspond either to 2D networks with (6,3) or augmented (4,4) topology or, in one case, adopt a 3D connectivity. In addition, three products with a Cr/Ag = 2:1 stoichiometry have been isolated: they adopt two-dimensional network structures.