Coordination chemistry and reactivity of monomeric alkoxides and amides of magnesium and zinc supported by the diiminato ligand CH(CMeNC(6)H(3)-2,6-(i)Pr(2))(2). A comparative study

The preparation and characterization of a series of closely related magnesium and zinc compounds are reported: LMg(N(i)Pr(2))(THF), 1; LZn(N(i)Pr(2)), 2; LMg(O(t)Bu)(THF), 3; LZn(O(t)Bu), 4; and LZn(OSiPh(3))(THF), 6; where L = CH(CMeNC(6)H(3)-2,6-(i)Pr(2))(2). Their dynamic solution behavior has been examined by variable-temperature NMR studies and reveals that THF reversibly dissociates in toluene-d(8) or CD(2)Cl(2) and that exchange with free THF occurs by a dissociative process. Compounds 1-4 and 6 all initiate and subsequently sustain ring-opening polymerization (ROP) of lactides. For a related series of compounds LMX(THF)(n)(), where n = 1 or 0, the rate of initial ring-opening follows the order M = Mg > Zn and X = O(t)Bu > N(i)Pr(2) > NSi(2)Me(6) > OSiPh(3). In THF at 25 degrees C, compounds 3 and 4 polymerize 100 equiv of rac-lactide to >95% conversion in 5 and 80 min for M = Mg and Zn, respectively, and yield ca. 90% heterotactic PLA, (isi + sis tetrads). The reactions proceed faster in methylene chloride, but for M = Mg, a Bernoulian distribution of tetrads is formed from rac-lactide (3iii:2isi:sii:sis:iis) prior to trans-esterification. Polymerization of L-LA in toluene-d(8) and THF-d(8) by 3 and 4 have been studied by VT (1)H NMR spectroscopy: the resting state for zinc is proposed to be a monomeric species akin to LZn(eta(2)-OCHMeC(O)OMe), whereas the magnesium complex appears to be dimeric LMg(mu-OP)(2)MgL. None of the compounds is capable of initiating homopolymerization of propylene oxide (PO) or cyclohexene oxide (CHO), although the magnesium amide 1 effects ring-opening by allylic proton abstraction and the dimeric compound [LMg(mu-OC(6)H(9))](2), 7, is formed. Reactions with carbon dioxide are also described, along with the characterization of LZnO(2)CN(i)Pr(2), 8, which is shown to be inert with respect to CHO and PO at room temperature. All the compounds are hydrolytically sensitive, and LZn(mu-OH)(2)ZnL, 5, has been isolated from hydrolysis of compound 4. The crystal and molecular structures are reported for compounds 1-5, 7, and 8. These results are compared with those recently reported by Coates et al.     

Preparation of stable and metastable coordination compounds: insight into the structural, thermodynamic, and kinetic aspects of the formation of coordination polymers

The reaction of ZnI2 and pyrimidine in acetonitrile results in the formation of the 1:2 compound ZnI2(pyrimidine)2 (1), which consists of discrete tetrahedral building blocks. Slow heating of 1 at 1 degrees C/min leads to its transformation into the ligand-deficient intermediate 1:1 compound ZnI2(pyrimidine) (3), which upon further heating decomposes into the most ligand-deficient 2:1 compound (ZnI2)2(pyrimidine) (4). In contrast, the 2:3 compound (ZnI2)2(pyrimidine)3 (2) is formed as an intermediate by decomposing 1 using a faster heating rate of 8 degrees C/min. Compound 2 consists of oligomeric units in which each ZnI2 unit is coordinated by two iodine atoms and one bridging and one terminal pyrimidine ligand. The crystal structure of compound 3 is built up of ZnI2 units, which are connected by the ligands into chains. For the thermal transformation of 1 into 3 via 2 as the intermediate, a smooth reaction pathway is found in the crystal structure, for which only small translational and rotational changes are needed. The metastable solvated compound (ZnI2)(pyrimidine)(acetonitrile)0.25 (5) consisting of (ZnI2)4(pyrimidine)4 rings is obtained by quenching the reaction of ZnI2 and pyrimidine in acetonitrile using an antisolvent. On heating, 5 decomposes into a new polymorphic 1:1 compound 6, which consists of (ZnI2)(pyrimidine) chains. On further heating, 6 transforms into a third polymorphic 1:1 compound 7, which consists of (ZnI2)3(pyrimidine)3 rings, and finally into the 1:1 compound 3. Solvent-mediated conversion experiments reveal that compounds 1-4 are thermodynamically stable, whereas compounds 5-7 are metastable. Time-dependent crystallization experiments unambiguously show that compound 7 is formed by kinetic control and transforms within minutes into compound 6, which finally transforms into 3. Compound 3 represents the thermodynamically most stable 1:1 modification, whereas compounds 6 and 7 are metastable. The different compounds obtained by thermal decomposition and by crystallization from solution represent a snapshot of the species in solution and thus provide insight into the formation of coordination compounds.     

Phosphonate- and ester-substituted 2-cyanoethylene-1,1-dithiolate clusters of zinc: aerial CO2 fixation and unusual binding patterns

Treatment of [Zn(tmeda)Cl2] (tmeda = N, N, N', N'-tetramethylethylenediamine) with a phosphonate-substituted 2-cyanoethylene-1,1-dithiolato ligand in air yields a tetranuclear zinc-carbonate complex 1 having the formula of [Zn4(tmeda)3(mu3-CO3){S2CC(CN)P(O)(OEt)2}3] in which four zinc atoms form a trigonal pyramid with the apical zinc atom in a hitherto unknown S3O3 coordination sphere. It is the first example of aerial CO2 fixation to afford a metal-carbonato compound incorporating 1,1-ethenedithiolate ligands. In sharp contrast, reaction with an isobutyl ester-substituted 2-cyanoethylene-1,1-dithiolate forms a trimeric zinc complex [Zn(tmeda){S2CC(CN)(CO2(i)Bu)}]3, 2, which does not contain the metal-bound carbonate. Compound 2 is the first example of a trinuclear zinc complex composed of four-, five-, and six-coordinated Zn atoms. The unsymmetrical ligand orientation around three zinc centers in 2 suggests that the other structural isomer, which would have an idealized C3 axis, may exist. The reaction of the ethyl ester derivative of 2-cyanoethylene-1,1-dithiolate with [Zn(tmeda)Cl2] affords [{Zn(tmeda)Cl}2{S2CC(CN)(CO2Et)}], 3. The ester-functionalized 1,1-dithiolate ligands in compounds 2 and 3 display a bimetallic, triconnective coordination mode, which is rare for these types of ligands. Some probable intermediates generated from the formation of compound 1 have also been proposed.     

Layered single-metal hydroxide/ethylene glycol as a new class of hybrid material

Neutral ethylene glycol (EG) molecules have been intercalated into zinc hydroxide layers to produce a new hybrid material in which only one kind of metal ion is included. Initially, layered basic zinc acetate (LBZA, Zn(5)(OH)(8)(CH(3)COO)(2).2H(2)O) was prepared from a methanolic zinc acetate dihydrate solution. The immersion of LBZA in EG resulted in its intercalation, which was accompanied by an interlayer expansion of 7.12 A, as revealed by X-ray diffractometry. A Fourier transform infrared spectroscopic study indicated that the new compound contained both the acetate groups and the EG molecules. Together with thermogravimetry-differential thermal analysis, a composition of the new compound was estimated to be Zn(5)(OH)(8)(CH(3)COO)(2)(HOC(2)H(4)OH)(2).2H(2)O. The EG intercalation was found to increase the dehydration temperature of the zinc hydroxide layers from 130 to 180 degrees C. So the thermally stable material is then promising as a new class of precursors in creating organic-inorganic nanocomposites.     

New semiconducting coordination polymers from zinc sulfide clusters and chains

Two new semiconducting zinc coordination polymers, Zn(8)S(SPh)(14)(bpy) (1) and Zn(2)(SPh)(4)(bpy) (2), have been synthesized by a dual-ligand approach. Single-crystal structural analyses indicate that compound 1 has a helical-chain structure with P1 clusters bridging with bipyridyl (bpy) ligands and compound 2 possesses a layered structure with zinc sulfide chains cross-linked with bpy ligands. The diffuse-reflectance spectra reveal that the band gaps of the two compounds are 2.41 eV for 1 and 2.56 eV for 2.     

Structural and functional models of the active site of zinc phosphotriesterase

In an attempt to prepare structural and functional models for the active site of the hydrolytic enzyme zinc phosphotriesterase, five new zinc complexes of the ligands 2,6-bis[N-(N-(carboxylmethyl)-N-((1-methylimidazol)methyl)amine)methyl]-4-methylphenolate (BCIMP) and the corresponding asymmetric ligand 2-(N-isopropyl-N-((1-methylimidazolyl)methyl)aminomethyl)-6-(N-carboxylmethyl-N-((1-methylimidazolyl)methyl)aminomethyl)-4-methylphenol (ICIMP) have been synthesized, viz. Na[Zn(2)(BCIMP)Ac(2)] (1), [Zn(2)(BCIMP)(Ph(2)Ac)] (2), [Zn(2)(ICIMP)Ac(2)] (3), [Zn(4)(ICIMP)(2)(Me(3)Ac)(2)][ClO(4)](2) (4), and [Zn(4)(ICIMP)(2)(Ph(2)Ac)(2)][ClO(4)](2) (5). The X-ray structure of complex 5 has been determined and reveals that the complex is a dimer of dimers in the solid state, which in solution dissociates to potent structural models. Studies using NMR show that only one carboxylate coligand bridges the dizinc units in the case of diphenyl acetate and pivalate, while the steric bulk of acetate is sufficiently small to permit the coordination of two acetates/dizinc unit. Functional studies involving the hydrolysis/transesterification of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) show that the complex with ICIMP (compound 5) has a significantly higher rate of catalysis than the BCIMP complex (compound 2). This is attributed to the vacant/labile coordination site that is available in the ICIMP complex but not the BCIMP complex.     

Neutral zinc, lower-order zincate and higher-order zincate derivatives of pyrrole: synthesis and structural characterisation of zinc complexes with one, two, three or four pyrrolyl ligands

Towards a systematic development of the zinc chemistry of the important five-membered nitrogen heterocycle pyrrole, this work reports the synthesis and characterisation of five crystalline zinc-pyrrolyl complexes. Pyrrolyl in this context means where conversion of the N-H bond to an N-zinc bond has occurred. Two neutral complexes, [(t)BuZn(NC(4)H(4))(TMEDA)·HNC(4)H(4)] 1 and [Zn(NC(4)H(4))(2)(TMEDA)] 2, containing one and two pyrrolyl ligands, respectively, were synthesised by reacting di-t-butylzinc with different amounts of pyrrole in the presence of TMEDA (TMEDA is N,N,N',N'-tetramethylethylenediamine). X-ray crystallographic studies established that both adopt mononuclear structures with the salient feature of the former the presence of an additional parent protonated pyrrole molecule which engages its anionic counterpart in N-H…πC-C interactions. Employing a similar synthetic approach but adding n-butylsodium to the reaction mixture in attempts to form ate derivatives delivered three distinct sodium zincate (anionic zinc) compounds in [{(THF)(2)·NaZn(THF)(NC(4)H(4))(3)}(∞)] 3, [{(TMEDA)·Na}(2)Zn(NC(4)H(4))(4)] 4, and [{(PMDETA)·Na}(2)Zn(NC(4)H(4))(4)] 5 (PMDETA is N,N,N',N',N'-pentamethyldiethylenetriamine). From their crystal structures, the 1?:?1, Na:Zn complex 3 can be classified as a lower-order zincate having three pyrrolyl ligands bound to zinc in a polymeric chain arrangement, while the 2?:?1, Na:Zn complexes 4 and 5 are molecular higher-order zincates having Zn centres fully saturated by four pyrrolyl ligands. Discussion of the structures of 1-5 focuses on the interplay of σ-bonding and π-bonding between the pyrrolyl ligands and the metal centres. Revealingly, the zinc-free sodiopyrrole complex [{(PMDETA)·Na(NC(4)H(4))}(2)] 6, made and characterised for comparison, shows that on its own sodium prefers the former type of bonding, but is forced to switch to the latter type when combined with the stronger Lewis acid zinc in the zincate compositions. Complexes 1-6 have also been characterised in solution by NMR spectroscopy.     

Synthesis,structure, and magnetic properties of the single-molecule magnet [Ni(21)(cit)(12)(OH)(10)(H(2)O)(10)](16-)

The preparation of two new compounds containing the cluster [Ni(21)(cit)(12)(OH)(10)(H(2)O)(10)](16-) is presented, together with a detailed magnetic investigation of one of the compounds. We found that this cluster shows an unexpected stability and that it exists as different stereoisomers. Compound 1 contains the achiral cluster with a Delta-Lambda configuration, and compound 2 contains a pair of enantiomeric clusters with the configurations Delta-Delta and Lambda-Lambda, respectively. Magnetic measurements of 1 in the millikelvin range were necessary to determine the spin ground state of S = 3, and they also revealed a magnetic anisotropy within the ground state. A frequency-dependent out-of-phase signal was found in alternating current susceptibility measurements at very low temperatures, which indicates a slow relaxation of the magnetization. Thus, individual molecules are acting as single magnetic units, which is a rare phenomenon for nickel clusters. The energy barrier exhibited by compound 1 has been calculated to be 2.9 K.     

Mononuclear and dinuclear manganese compounds stabilized by supramolecular interactions

New manganese compounds [Mn(HphpzMe)(2)(H(2)phpzMe)(HCO(2))] (1), [Mn(2)(phpzMe)(2)(HphpzMe)(2)(OCH(3))]·2CH(3)OH (2), Na{[Mn(HphpzPh)(phpzPh)(MeOH)(2)](2)}(HCO(2)) (3), [Mn(HphpzPh)(2)(EtOH)(2)]ClO(4)·2EtOH (4) and [Mn(HphpzPh)(2)N(3)] (5) were synthesized and characterized with various techniques. 1, 4 and 5 are mononuclear manganese(iii) compounds, 2 is a mixed-valence dinuclear manganese(iii/iv) compound, and 3 is a trinuclear compound containing two manganese(iii) ions and a sodium(i) ion. A remarkable feature is the spontaneous formation of the formate ion as a result of the methanol or methoxide oxidation in compounds 1 and 3. Using ethanol precludes the formation of the formate and compound 4 is obtained. The molecular structure of all compounds is stabilized by supramolecular interactions, including strong hydrogen bonding and π-π interactions.     

Solubilizing sodium fluoride in acetonitrile: synthesis, molecular structure, and complexation behavior of bis(organostannyl)methyl-substituted crown ethers

The synthesis of the crown-ether-substituted bis(organostannyl)methanes Ph(3)SnCH(2)Sn(Ph(2))-CH(2)-[16]crown-5 (1) and Ph(2)ISnCH(2)Sn(I)(Ph)-CH(2)-[16]crown-5 (2) is reported. Both compounds have been characterized by elemental analyses, (1)H, (13)C, (19)F, and (119)Sn NMR spectroscopy, and in the case of compound 2 also by electrospray ionization mass spectrometry. Single-crystal X-ray diffraction analysis revealed for the aqua complex 2.H(2)O trigonal-bipyramidal-configured tin atoms with intramolecular Sn(1)-O(1) and Sn(2)-O(1W) distances of 2.555(2) and 2.440(3) A, respectively. The water molecule is trapped in a sandwich-like fashion between the crown ether oxygen atoms O(2) and O(4) and the Sn(2) atom. NMR spectroscopy unambiguously proved the ability of compound 2 in acetonitrile to overcome the high lattice energy of sodium fluoride and to complex the latter under charge separation.     

Palladium(II) complexes of bowls, pinwheels, cages, and N,C,N-pincers of starburst ligands 1,3,5-Tris(di-2-pyridylamino)benzene and 2,4,6-Tris(di-2-pyridylamino)-1,3,5-triazene

The reactions of Pd(II) ions with starburst ligands 1,3,5-tris(di-2-pyridylamino)benzene (tdab) and 2,4,6-tris(di-2-pyridylamino)-1,3,5-triazene (tdat) have been investigated. Complexes with the Pd:tdab (or tdat) ratio being 1:1 and 3:1 have been isolated and characterized. The structures of five new Pd(II) complexes containing the starburst ligands have been determined by X-ray diffraction analyses, which include chelate compounds [PdCl(2)(tdab)], 1, [(PdCl(2))(3)(tdab)], 2, [(Pd(OAc)(2))(3)(tdab)], 4, and [(Pd(OAc)(2))(3)(tdat)], 5, and a cyclometalated compound [Pd(OAc)(NCN-tdab)], 3. The Pd(II) ion in the 1:1 compound 1 is chelated by two pyridyl groups. Similarly, each Pd(II) center in the 3:1 compounds 2, 4, and 5 is chelated by two pyridyl groups. However, these three compounds display distinct structural features: 2 adopts a "bowl-shaped" structure, 4 has a "pinwheel"-like structure, and 5 has a "up-and-down" structure. Compounds 4 and 5 were examined in solution by variable-temperature (1)H NMR, which revealed that both compounds retain the "pinwheel" and the "up-and-down" structure, respectively. The observed structural preference by 4 and 5 is attributed to both electronic and steric factors.     

Copper(I) coordination polymers of 2,2'-dipyridylamine derivatives: syntheses, structures, and luminescence

Reactions of CuX (X = Br(-), I(-) or CN(-)) with various types of 2,2'-dipyridylamine (dpa) derivatives have been performed via a hydrothermal-solvothermal method and the products have been structurally characterized by X-ray crystallography. Four ligands with different coordination motifs were employed in the reactions, including angular N,N,N',N'-tetra(2-pyridyl)-2,6-pyridinediamine (tppda); linear N,N,N',N'-tetra(2-pyridyl)-1,4-phenylenediamine (tppa) and N,N,N',N'-tetra(2-pyridyl)biphenyl-4,4'-diamine (tpbpa); and star-shaped tris-[4-(2,2'-dipyridylamino)-phenyl]amine (tdpa), which yielded eight copper(I) complexes exhibiting different stoichiometries of Cu-dpa and variable coordination modes of dpa. The compound [Cu(2)(tppda)(μ-I)(2)](n) (1) forms a one dimensional (1D) coordination polymer exclusively through double μ(2)-I bridges, which arranges to two dimensional (2D) metal-organic frameworks (MOFs) via the face-to-face π···π stacking interactions from pyridyl rings. The compound [Cu(6)(tppa)(μ(3)-Br)(6)](n) (2) forms a 2D network linked through multiple μ(3)-Br bridges. The compound [Cu(2)(tppa)(μ-CN)(2)](n) (3) is also a 2D MOF containing 1D (CuCN)(n) chains. The compounds [Cu(tpbpa)Br](n) (4) and [Cu(4)(tpbpa)(2)(μ-I)(4)](n) (5) display two different 1D assemblies: a zig-zag chain for 4 and a linear structure for 5. The compound [Cu(4)(tpbpa)(μ-CN)(4)](n) (6) shows a pseudo-4,8(2) topological net, while the compound [Cu(8)(tpbpa)(μ-CN)(8)](n)·2nH(2)O (7) exhibits a three-dimensional (3D) framework containing a ···PM··· double helical structure, although both of them contain (CuCN)(n) chains. The compound [Cu(2)(tdpa)(μ-I)(2)](n) (8) is a zig-zag chain based on the star-shaped molecule tpda, in which one of three dpa-arms is free of coordination to metal ions. All complexes exhibit luminescence in the solid state.     

Deprotonative metalation using ate compounds: synergy, synthesis, and structure building

Historically, single-metal organometallic species such as organolithium compounds have been the reagents of choice in synthetic organic chemistry for performing deprotonation reactions. Over the past few years, a complementary new class of metalating agents has started to emerge. Owing to a variable central metal (magnesium, zinc, or aluminum), variable ligands (both in their nature and number), and a variable second metallic center (an alkali metal such as lithium or sodium), "ate" complexes are highly versatile bases that exhibit a synergic chemistry which cannot be replicated by the homometallic magnesium, zinc, or aluminum compounds on their own. Deprotonation accomplished by using these organometallic ate complexes has opened up new perspectives in organic chemistry with unprecedented reactivities and sometimes unusual and unpredictable regioselectivities.     

Syntheses,Structures, and Properties of Five Coordination Polymers Involving Phthalic Acid

Five new coordination polymers Cu(phen)(H2O)(phth)·CH3OH(1), [Cu(2,2'-bipy)(H2O)](phth)·3.5H2O(2), Zn(phen)(phth)(H2O)·1.125H2O(3) and [M(4,4'-bipy)(H2O)2](phth)·2H2O[M=Zn(4), Mn(5)](H2phth=phthalic acid, bipy=bipyridine, phen=1,10-phenanthroline) have been synthesized from the amino acid derivatives(phthalyl-l- valine, H2L) and structurally characterized. H2L was hydrolyzed into phth2– group during the reaction, but the strucure feature was different from that of the complex directly synthesized from H2phth in the reported literature, revealing that H2L played an important role in composing the novel compounds. Compounds 1, 2 and 3 are all 1D chains, but the differences are that compound 1 is further hydrogen-bonded into 2D networks, and compound 2 is further extended into 3D supramolecular network through π-π stacking and hydrogen-bonding interactions. However, compound 3 is a 1D helix chain structure and further links into 2D networks through π-π stacking. Compounds 4 and 5 are isostructural and exhibit the same 2D layers, which are further connected by hydrogen-bonding interactions to form 3D supramolecular network. Antiferromagnetic superexchange was observed for compounds 1, 2 and 5.     

Cobalt N-heterocyclic carbene alkyl and acyl compounds: synthesis, molecular structure and reactivity

The N-heterocyclic-carbene containing cobalt carbonyl compound [Co(IMes)(CO)3(Me)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene), 1, has been synthesised by tertiary phosphine displacement from [Co(PPh3)(CO)3(Me)]. Subsequent carbonylation afforded the acyl derivative [Co(IMes)(CO)3(COMe)], 2. Similarly, the compound [Co(IMes)(CO)3(COEt)], 3, has been synthesised. The compounds 2 and 3 have been shown to react with dihydrogen to form the cobalt hydride compound [Co(IMes)(CO)3(H)], 4. The molecular structures of compounds 1 and 2 have been determined.     

Modulation of the intercalation properties of copper-zinc mixed-metal phosphonate materials

New layered mixed divalent metal vinylphosphonates Cu(II) (1-x)Zn(II) (x)(O(3)PC(2)H(3)).H(2)O have been prepared from a range of pre-formed copper-zinc oxides Cu(II) (1-x)Zn(II) (x)O obtained by isomorphous substitution of zinc into the tenorite-type structure of Cu(II)O. The corresponding mixed divalent copper-zinc vinylphosphonates have been characterised by powder X-ray diffraction, elemental analysis, infrared spectroscopy and thermogravimetric analysis. All compounds have been shown to consist of a single-phase solid solution that crystallises in an monoclinic unit cell, space group P2(1)/c with a=9.86-9.90, b=7.61-7.64, c=7.32-7.35 A and beta=95.9-96 degrees, with the exception of the pure zinc vinylphosphonate (x=1), the structure of which is comparable to other Zn(II)(O(3)PR).H(2)O materials. Studies of the intercalation of n-butylamine into the range of copper-zinc vinylphosphonates have demonstrated that significant modulation of the adsorption properties occurs; whereas one mole of amine is intercalated into the pure zinc vinylphosphonate to give Zn(II)(O(3)PC(2)H(3)).(C(4)H(9)NH(2)), for all other members of the series two moles of amine are coordinated to give intercalated compounds of composition Cu(II) (1-x)Zn(II) (x)(O(3)PC(2)H(3)).[(C(4)H(9)NH(2))(1-x)(C(4)H(9)NH(2))(x)](2) from which the amine can be sequentially removed from the different metal sites; this opens up possibilities for further applications of these materials.     

Diversity of lanthanide(III)-organic extended frameworks with a 4,8-disulfonyl-2,6-naphthalenedicarboxylic acid ligand: syntheses, structures, and magnetic and luminescent properties

A sulfonate-carboxylate ligand, 4,8-disulfonyl-2,6-naphthalenedicarboxylic acid (H(4)-DSNDA), and eight new lanthanide coordination polymers {[Pr(4)(OH)(4)(DSNDA)(2)(H(2)O)(12)](H(2)O)(10)}(n) (1), [Ln(H(2)-DSNDA)(0.5)(DSNDA)(0.5)(H(2)O)(5)](n) (Ln = La(2), Nd(3), Sm(4), Eu(5), Gd(6), and Dy(7)), and {[Er(H-DSNDA)(H(2)O)(4)](H(2)O)}(n) (8) have been synthesized. Detailed crystal structures of these compounds have been investigated. Compound 1 has a 3D framework featuring the unique cubane-shaped [Pr(4)(μ(3)-OH)(4)] clusters and is a binodal 4,8-connected network with (4(16)·6(12))(4(4)·6(2))(2) topology. Compounds 2-7 are isostructural and have 2D layered structures. Compound 8 is also a 2D layer but belongs to different structural types. The luminescence behavior of compound Eu(5) shows that the π-rich aromatic organic ligands efficiently transfer the absorbed light energy to the Eu(III) ions, thus enhancing the overall luminescent properties of compound Eu(5). The magnetic properties of all compounds except for the diamagnetic La(2) compound have been investigated. In addition, elemental analysis, IR spectra, and thermogravimetric analysis of these compounds are also described.     

Polynuclear lanthanide hydroxo complexes: new chemical precursors for coordination polymers

The synthesis of hexanuclear lanthanide hydroxo complexes by controlled hydrolysis led to polymorphic compounds. The hexanuclear entities crystallize in four different ways that depend on the extent of their hydration. The four structures can be described as hexanuclear lanthanide entities with formula [Ln(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](2+). Two additional NO(3)(-) ions intercalate between the hexanuclear entities in order to ensure the electroneutrality of the crystal structure. Some crystallization water molecules fill the intermolecular space. The three first families of compounds (1-3) exhibit crystal structures that have previously been reported. The fourth family of compounds (4) is described here for the first time. Its chemical formula is [Ln(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](NO(3))(2).2H(2)O (Ln = Gd, Er, and Y). In this paper, the chemical and thermal stabilities of the hexanuclear lanthanide compounds are reported together with the magnetic properties of the Gd(III)-containing species. To use these entities as precursors for new materials, the substitution of the nitrato groups by chloride ions has been studied. Two byproduct compounds have so been obtained: The first (compound 5) is a nitrato/chloride hexanuclear compound of chemical formula [Er(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](NO(3))Cl.2H(2)O. The second one (compound 6) is a polymeric compound in which the hexanuclear entities are linked by an unexpected and original N(2)O(4) bridge. Its chemical formula is [Er(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(4)(H(2)O)(11)(OH)(ONONO(2))]Cl(3).2H(2)O. Its crystal structure can be described as the juxtaposition of chainlike molecular motifs. To the best of our knowledge, this is the first example of a coordination polymer synthesized from an isolated polylanthanide hydroxo complex.     

Ligand-bridged dinuclear cyclometalated Ir(III) complexes: from metallamacrocycles to discrete dimers

Metallamacrocycles 1, 2, and 3 of the general formula [{Ir(ppy)(2)}(2)(μ-BL)(2)](OTf)(2) (ppyH = 2-phenyl pyridine; BL = 1,2-bis(4-pyridyl)ethane (bpa) (1), 1,3-bis(4-pyridyl)propane (bpp) (2), and trans-1,2-bis(4-pyridyl)ethylene (bpe) (3)) have been synthesized by the reaction of [{(ppy)(2)Ir}(2)(μ-Cl)(2)], first with AgOTf to effect dechlorination and later with various bridging ligands. Open-frame dimers [{Ir(ppy)(2)}(2)(μ-BL)](OTf)(2) were obtained in a similar manner by utilizing N,N'-bis(2-pyridyl)methylene-hydrazine (abp) and N,N'-(bis(2-pyridyl)formylidene)ethane-1,2-diamine (bpfd) (for compounds 4 and 5, respectively) as bridging ligands. Molecular structures of 1, 3, 4, and 5 were established by X-ray crystallography. Cyclic voltammetry experiments reveal weakly interacting "Ir(ppy)(2)" units bridged by ethylene-linked bpe ligand in 3; on the contrary the metal centers are electronically isolated in 1 and 2 where the bridging ligands are based on ethane and propane linkers. The dimer 4 exhibits two accessible reversible reduction couples separated by 570 mV indicating the stability of the one-electron reduced species located on the diimine-based bridge abp. The "Ir(ppy)(2)" units in compound 5 are noninteracting as the electronic conduit is truncated by the ethane spacer in the bpfd bridge. The dinuclear compounds 1-5 show ligand centered (LC) transitions involving ppy ligands and mixed metal to ligand/ligand to ligand charge transfer (MLCT/LLCT) transitions involving both the cyclometalating ppy and bridging ligands (BL) in the UV-vis spectra. For the conjugated bridge bpe in compound 3 and abp in compound 4, the lowest-energy charge-transfer absorptions are red-shifted with enhanced intensity. In accordance with their similar electronic structures, compounds 1 and 2 exhibit identical emissions. The presence of vibronic structures in these compounds indicates a predominantly (3)LC excited states. On the contrary, broad and unstructured phosphorescence bands in compounds 3-5 strongly suggest emissive states of mixed (3)MLCT/(3)LLCT character. Density functional theory (DFT) calculations have been carried out to gain insight on the frontier orbitals, and to rationalize the electrochemical and photophysical properties of the compounds based on their electronic structures.     

Molecular, 1D,and 2D systems built from phenylcyanamido ligands. Syntheses,crystal structures,and characterization of their magnetic properties

Several MnII compounds with phenylcyanamido ligands have been synthesized and characterized by means of single-crystal X-ray structural determination. The reported compounds show a wide variety of nuclearity from mononuclear and dinuclear systems to 1D chains and 2D networks in which X-phenylcyanamide (X-pcyd) anions act as the bridging ligand. Mononuclear compound [Mn(H2O)2(4-bzpy)2(3-Cl- pcyd)2] (2) crystallizes in the monoclinic system, P21/a space group, dinuclear compounds (mu 1,3-3-Cl-pcyd)2[Mn(2,2'-bpy)(3-Cl-pcyd)(MeOH)]2 (2) and (mu 1,3-3-Cl-pcyd)2[Mn(2,2'-bpy)(3-Cl-pcyd)(EtOH)]2 (3) crystallize in the triclinic system, P1 space group, 1D chain [(mu 1,3-4-Cl-pcyd)2[Mn(2,2'-bpy)]]n (4) crystallizes in the monoclinic system, /2/a space group, and 2D network [Mn(mu-4,4'-bpy)(mu 1,3-3-F-pcyd)2]n (5) crystallizes in the monoclinic system, C2 space group. Susceptibility measurements on compounds 2-4 reveal moderate antiferromagnetic coupling in all cases. MO calculations have been made to elucidate the main factors that control the superexchange pathway for this kind of ligand. Comparison of their magnetic behavior with that of related ligands such as azido and dicyanamido is reported.