Synthesis of binuclear complexes of PdCl2 with chiral ethylenediamine dioxime (H2L1), piperazine dioxime (H2L2), and propylenediamine dioxime (H2L3), the derivatives of the natural monoterpenoid (R)-(+)-limonene. The crystal structures of [Pd2(H2L1)Cl4] and [Pd2(H2L2)Cl4]

The diamagnetic complexes [Pd₂(H₂L¹)Cl₄] (I), [Pd₂(H₂L²)Cl₄] (II), and Pd₂(H₂L³)Cl₄(III) with chiral ligands derived from the natural monoterpenoid (R)-(+)-limonene are obtained (H₂ L¹ is ethylenediamine dioxime, H₂L² is piperazine dioxime, and H₂L³ is propylenediamine dioxime). According to X-ray diffraction data, the crystal structures of complexes I and II are composed of binuclear acentric molecules. The coordination polyhedra PdN₂Cl₂ are trapeziums (squares distorted in a tetrahedral manner) made up of two N atoms of the tetradentate bridging cyclic ligands H₂L¹ and H₂L² and two Cl atoms. The fragments PdCl₂ are trans in the complexes. The ¹³C and ¹H NMR spectra of complexes I and II in CDCl₃ also suggest their binuclear structures.     

Synthesis and Stereochemical/Electrochemical Analyses of Cuboctahedral-Based Pd23(CO) x (PR3)10 Clusters (x=20 with R3=Bu n 3, Me2Ph; x=20, 21, 22 with R3=Et3): Geometrically Analogous Pd23(PEt3)10 Fragments with Variable Carbonyl Ligations and Resulting Implications

This research was an outgrowth of previous reactions with [Pd₁₃Ni₁₃(CO)₃₄]^4? which produced a tetragonal crystal form of Pd₂₃(CO)₂₀(PEt₃)₁₀ (1) that has the same cuboctahedral-based Pd₂₃ framework with an identical number of PEt₃ ligands but two fewer CO ligands than the monoclinic crystal form of Pd₂₃(CO)₂₂(PEt₃)₁₀ (3) originally reported from reactions with Pd₁₀(CO)₁₂(PEt₃)₆. A subsequent investigation presented herein to establish whether the carbonyl capacity is influenced by the nature of the phosphine ligands has led to syntheses of Pd₂₃(CO) _x (PR₃)₁₀ [R₃=Et₃ (1), Bu ⁿ ₃ (4), and Me₂Ph (5)] with 20 CO ligands (x=20) from corresponding Pd₁₀(CO)₁₂(PR₃)₆ precursors either by deligation with Pd(OAc)₂, CF₃CO₂H, Ni(1,5-COD)₂, [NMe₄]₂[Ni₆(CO)₁₂], or HCO₂H or by spontaneous enlargement; yields varied from 15 to 79%. Although attempts to obtain the original Pd₂₃(CO)₂₂(PEt₃)₁₀ (3) were unsuccessful, a highly significant outcome was the isolation (one time) of another monoclinic crystal form possessing the triethylphosphine Pd₂₃(CO) _x (PEt₃)₁₀ cluster with 21 COs (2). Both the compositions and atomic arrangements for each of five Pd₂₃ clusters [1a (solvated); 1b (unsolvated); 2, 4, and 5] were unambiguously established from low-temperature single-crystal CCD X-ray crystallographic determinations in accordance with their nearly identical IR carbonyl frequencies. Solution ³¹P{¹H} NMR spectra of 1 and 4 at room temperature displayed three distinct signals with expected integral ratios of 2/4/4 that are consistent with the solid-state structures of Pd₂₃(CO)₂₀(PR₃)₁₀ [R₃=Et₃ (1), Bu ⁿ ₃ (4)] remaining intact in solution. The metal-core geometries of all of these Pd₂₃(CO) _x (PR₃)₁₀ clusters, including the thermodynamically stable ones with 20 CO ligands and the kinetic products with additional CO ligands (x=21, 22), are essentially the same. The common Pd₂₃ core may be best described as possessing a centered hexacapped cuboctahedral Pd₁₉ kernel (alternatively denoted as a centered ν₂ Pd₁₉ octahedron) with four edge-connected exopolyhedral wingtip Pd(exo) atoms that reduce the pseudo metal-core symmetry from O_h to D_2h. The 10 PR₃ ligands are linked to the six tetracapped Pd(cap) and four edge-capped wingtip Pd(exo) atoms; the latter four Pd(exo) atoms are each composed of four trigonal-planar Pd(μ₂-CO)₂(PR₃) units. These crystallographic results provide compelling geometrical evidence for a heretofore unknown stereochemical example involving variable carbonyl ligation (x=20, 21, 22) of a close-packed nanosized Pd _n (CO) _x (PR₃) _y cluster (in this case with identical PEt₃ ligands) without significant changes being induced in either the overall metal-core architecture or steric dispositions of the same number of PR₃ ligands. These experimental findings have particular relevance to the long-standing Muetterties cluster/surface science analogy in showing that the different number (as well as different modes) of carbonyl ligations observed in these large metal carbonyl clusters are directly related to pressure-induced dissociative/nondissociative migratory coverages in CO chemisorptions on metal surfaces. The observed expanded capacity of CO coordination on the same Pd₂₃ polyhedron without notable changes in geometry is no doubt a consequence of its virtually nanosized metal-core architecture; distances between outermost centrosymmetrically related pairs of Pd(cap) and Pd(exo) atoms in the Pd₂₃ framework are 0.8 and 0.9 nm, respectively. An electrochemical (CV) study revealed that 1 undergoes one quasi-reversible two-electron reduction to 1 ^2? (E_1/2=?0.91 V) and two consecutive quasi-reversible one-electron oxidations to 1/1 ⁺ at E_1/2=0.08 V and 1 ⁺/1 ²⁺ at E_1/2=0.32 V (THF; Ag/AgCl as reference electrode). A stereochemical/electronic analysis with the isostructural Au₂Pd₂₁(CO)₂₀(PEt₃)₁₀ analogue (9) and resulting implications are given.     

Ring-opening Copolymerization of Cyclohexene Oxide and Maleic Anhydride Catalyzed by Mononuclear [Zn（L）（H2O）] or Binuclear [Zn2（L）（OAc）2（H2O）] Complex Based on the Salen-type Schiff-base Ligand

From the self-assembly of the typical Salen-type Schiff-base ligand H2L and Zn(OAc)2·2H2O in the molar ratio of 1:1 or 1:2, the mononuclear [Zn(L)(H2O)](1) or binuclear [Zn2(L)(OAc)2(H2O)](2) are obtained, respectively. For both complexes 1 and 2, the unsaturated five-coordinate coordination environment to the catalytic active centers(Zn2+ ions) permits the monomer insertion for the effective solution copolymerization of cyclohexene oxide and maleic anhydride. All the solution copolymerizations afford poly(ester-co-ether)s, while lower catalyst and co-catalyst concentrations are helpful for the formation of alternating polyester. Of the three co-catalysts, 4-(dimethylamino)pyridine is found to be the most efficient, while an excess thereof is detrimental for chain growth of the copolymers.     

Neutral and monocationic dinuclear (carbonyl)(cyclopentadienyl)(phenylchalcogenate) iron complexes of the general formulas [(RC5H4)Fe(CO)EPh]2 and [(RC5H4)Fe(CO)EPh]2PF6 (E = S or Te; R = H or Me): Synthesis, molecular structures, and EPR spectra

Heating of the compounds (RC₅H₄)Fe(CO)₂TePh (R = H (I) and Me (II)) in heptane afforded the dinuclear complexes [(RC₅H₄)Fe(CO)TePh]₂ (III and IV, respectively). By oxidation with Fc⁺PF ₆ ^? , these complexes were transformed into the paramagnetic cationic complexes [(RC₅H₄)Fe(CO)TePh]₂PF₆ (V and VI, respectively). Structures III–V and [(C₅H₅)Fe(CO)SPh]₂PF₆ (VII) were characterized by X-ray diffraction.     

Synthesis and crystal structure of the double cluster [Cp3Fe4(CO)4(C5H4)]2(p-C6H4)

[Cp₄Fe₄(CO)₄] (1) reacts with p-BrC₆H₄Li and MeOH in sequence to afford the functionalized cluster [Cp₃Fe₄(CO)₄(C₅H₄-p-C₆H₄Br)] (2), while the reaction of 2 with n-BuLi and MeOH produces [Cp₂Fe₄(CO)₄(C₅H₄Bu)(C₅H₄-p-C₆H₄Br)] (3). The double cluster [Cp₃Fe₄(CO)₄(C₅H₄)]₂(p-C₆H₄) (4) has been prepared by treatment of [Cp₄Fe₄(CO)₄] with p-C₆H₄Li₂ and MeOH in sequence. The electrochemistry of 2 and 4, as well as the crystal structure of 4 have been investigated.     

Phase diagrams for the [Th(NO3)4(TBP)2]-decane-[UO2(NO3)2(TBP)2] liquid ternary system

We report a phase diagram (on the mole fraction scale) for the [Th(NO₃)₄(TBP)₂]-decane-[UO₂(NO₃)₂(TBP)₂](1-2-3) ternary liquid system, where TBP stands for tributyl phosphate, at T = 298.15 K. This system is characterized by a homogeneous solution field and a two-liquid field (immiscibility field); one phase (phase I) is enriched in [Th(NO₃)₄(TBP)₂] and [UO₂(NO₃)₂(TBP)₂], and the other (phase II) is enriched in decane. Molecular interaction parameters and excess Gibbs energies G ^ex were calculated for the binary systems and the ternary liquid system along the binodal curve proceeding from miscibility in the [Th(NO₃)₄(TBP)₂]-decane system and the ternary system and using equations of the NTRL model. For the ternary system, G ^ex > 0. G ^ex decreases in the following order of pairs of liquids: (1, 2) > (2, 3) > (1, 3).     

Synthetic and Structural Studies on Some New Butterfly Fe/S Cluster Complexes Containing 2,6-(CH2)2C5H3N or (CH2)2 Groups

Four new butterfly Fe/S cluster complexes bearing 2,6-(CH₂)₂C₅H₃N or (CH₂)₂ groups, as the active site models of [FeFe]-hydrogenase, have been prepared by condensation reaction and structurally characterized. Treatments of the parent complex Fe₂(CO)₆[(μ-SCH₂)₂CHCO₂H] (A) with 2,6-(HOCH₂)₂C₅H₃N or HOCH₂CH₂OH in the presence of 4-dimethylaminopyridine and dicyclohexylcarbodiimide afforded the single-butterfly Fe/S complexes Fe₂(CO)₆[(μ-SCH₂)₂CHC(O)OCH₂(2,6-C₅H₃N)CH₂OH] (1) and Fe₂(CO)₆[(μ-SCH₂)₂CHC(O)OCH₂CH₂OH] (3) and the double-butterfly Fe/S complexes [Fe₂(CO)₆(μ-SCH₂)₂CHC(O)OCH₂]₂(2,6-C₅H₃N) (2) and [Fe₂(CO)₆(μ-SCH₂)₂CHC(O)OCH₂]₂ (4). The new complexes 1–4 were fully characterized by elemental analysis, ESI-MS, IR, and ¹H (¹³C) NMR spectroscopy.     

Synthesis and crystal structures of zirconium(IV) nitrate complexes (NO2)[Zr(NO3)3(H2O)3]2(NO3) 3, Cs[Zr(NO3)5], and (NH4)[Zr(NO3)5](HNO3)

The zirconium nitrate complexes (NO₂)[Zr(NO₃)₃(H₂O)₃]₂(NO₃)₃ (1), Cs[Zr(NO₃)₅] ((2), (NH₄)[Zr(NO₃)₅](HNO₃) (3), and (NO₂)_0.23(NO)_0.77[Zr(NO₃)₅] ((4) were prepared by crystallization from nitric acid solutions in the presence of H₂SO₄ or P₂O₅. The complexes were characterized by X-ray diffraction. The crystal structure of 1 consists of nitrate anions, nitronium cations, and [Zr(NO₃)₃(H₂O)₃]⁺ complex cations in which the Zr^IV atom is coordinated by three water molecules and three bidentate nitrate groups. The coordination polyhedron of the Zr^IV atom is a tricapped trigonal prism formed by nine oxygen atoms. The island structures of 2 and 3 contain [Zr(NO₃)₅]^? anions and Cs⁺ or NH₄ ⁺ cations, respectively. In addition, complex 3 contains HNO₃ molecules. Complex 4 differs from (NO₂)[Zr(NO₃)₅] in that three-fourth of the nitronium cations in 4 are replaced by nitrosonium cations NO⁺, resulting in a decrease in the unit cell parameters. In the [Zr(NO₃)₅]^? anion involved in complexes 2–4, the Zr^IV atom is coordinated by five bidentate nitrate groups and has an unusually high coordination number of 10. The coordination polyhedron is a bicapped square antiprism.     

Synthesis and derivatization, structures and transition metal (Mo(0), Fe(II), Pd(II) and Pt(II)) complexes of phenylaminobis(diphosphonite), PhN{P(OC6H4OMe-o)2}2

The synthesis, derivatization and coordination behavior of a new aminobis(diphosphonite), PhN{P(OC₆H₄OMe-o)₂}₂ (1) is described. The ligand 1 reacts with H₂O₂, elemental sulfur or selenium to give the corresponding dichalcogenides PhN{P(E)(OC₆H₄OMe-o)₂}₂ (E = O, 2; S, 3; Se, 4) in good yield. Reactions of 1 with Mo(CO)₆, Pd(NCCH₃)₂Cl₂ and Pt(COD)Cl₂ resulted in the formation of the chelate complexes, Mo(CO)₄[PhN{P(OC₆H₄OMe-o)₂}₂] (5) and MCl₂[PhN{P(OC₆H₄OMe-o)₂}₂] (M = Pd,7; M = Pt, 8) whereas in the reaction of 1 with [CpFe(CO)₂]₂, one of the P-N bonds cleaves due to the metal assisted hydrolysis to give a mononuclear complex, [CpFe(CO){P(O)(OC₆H₄OMe-o)₂}{PhN(H)(P(OC₆H₄OMe-o)₂)}] (6). The molecular structures of 1, 4, 5 and 6 are determined by X-ray studies.     

Formation and structural characterization of novel polynuclear palladium selenolato complexes [Pd3Se(SePh)3(PPh3)3]Cl and [Pd6Cl2Se4(SePh)2(PPh3)6]

In addition to well-known dinuclear phenylselenolato palladium complexes, the reaction of [PdCl₂(PPh₃)₂] and NaSePh affords small amounts of novel trinuclear and hexanuclear complexes [Pd₃Se(SePh)₃(PPh₃)₃]Cl (1) and [Pd₆Cl₂Se₄(SePh)₂(PPh₃)₆] (2). Complex 1 is triclinic, P1?, a=13.6310(2), b=16.2596(2), c=16.9899(3) Å, α=83.1738(5), β=78.9882(5), γ=78.7635(5)°. Complex 2 is monoclinic, C2/c, a=25.7165(9), b=17.6426(8), c=27.9151(14) Å, β=110.513(2)°. There are no structural forerunners for 1, but the hexanuclear complex 2 is isostructural with [Pd₆Cl₂Te₄(TeR)₂(PPh₃)₆] (R=Ph, C₄H₃S) that have been observed as one of the products in the oxidative addition of R₂Te₂ to [Pd(PPh₃)₄]. Mononuclear palladium complexes may play a significant role as building blocks in the formation of the polynuclear complexes.     

Chemie des 5,7-Dihydroxy-2H-thiopyrano[2,3-b]pyridin-4(3H)-ons

Hydrolysis of the 4-alkyliminothiopyrano[2,3-b]pyridinedioles (5) and 4-alkylaminothiopyrano[2,3-b]pyridones (6) resp. with 10% NaOH gives 5,7-dihydroxy-2H-thiopyrano[2,3-b]pyridine-4(3H)-one (7).7 can be obtained in better yield by reaction of 4-dimethylamino-2(1H)-pyridinethione (8) with bistrichlorphenylethylamlonate (2). Aminolysis of7 affords the two isomeric products5 and6. On treatment with hydrazines,7 reacts only to 4-hydrazonoderivatives5. By heating in bromobenzene5d is cyclisized to 1H-5,1,2,6-thiatriaza-acenaphthylen-7-ol (11). On methylation with methyljodide5,6 and7 furnish the 7-methoxyproducts13,14 and12. By heating in 20% NaOH7 is transformed into the 2-thioxo-3-pyridylmethylketone16 A and its tautomer, 2-mercapto-3-pyridylmethylketone16 B. The structures of5,6 and7 are discussed.     

Zur Kenntnis der Substitutionsprodukte der (2H)-Imidazol-4(3H)-thione und 2H-Imidazol-4(3H)-one

2H-Imidazole-4(3H)-thiones (a), available from methyl alkyl and methyl aryl ketones with sulfur and ammonia, react via their corresponding N-sodium compounds or in presence of tert. amines with alkyl and aryl carboxylic acid chlorides to give the corresponding intensely coloured (orange to violett) cryst. 3-acyl-2H-imidazole-4(3H)-thiones4 a-q and6–26. With dicarboxylic acid dichlorides the colourless cryst. N,N′-diacyl-bis-3-imidazoline-5-thiones5 a-d and27–32 are obtained. With carbamic acid chlorides and chloroformic acid esters the corresponding urea (33–35) and urethane derivatives36, 37 are formed. In an analogous way 2H-imidazol-4(3H)-ones react with acid chlorides to 3-acyl-2-imidazol-4(3H)-ones (44–50), which can also be obtained by treating the corresponding 3-acyl-2H-imidazole-4(3H)-thione with KMnO₄.     

Supramolecular approach to crystallization of polynuclear chromium(III) aqua hydroxo complexes: synthesis and crystal structures of complexes [Cr2(OH)2(H2O)8]4+ and [Cr4(OH)6(H2O)12]6+ with cucurbit[n]uril (n = 7, 8)

Supramolecular compounds of the compositions {[Cr₂(OH)₂(H₂O)₈](C₄₂H₄₂N₂₈O₁₄)₂}-(NO₃)₄·18.75H₂O (1) and {[Cr₄(OH)₆(H₂O)₁₂](C₄₈H₄₈N₃₂O₁₆)₃(NO₃)₆·55H₂O (2) were synthesized from aqueous solutions of chromium(III) nitrate and the macrocyclic cavitand cucurbit[n]uril (C_6n H_6n N_4n O_2n , where n = 7 or 8, respectively). According to the X-ray diffraction study, the polynuclear chromium aqua complexes are disposed in cavities formed by the cucurbit[n]uril molecules and are linked to these molecules through hydrogen bonds between the hydroxo and aqua ligands of the polycations and the portal oxygen atoms of the macrocycles. Compound 1 is the first example of supramolecular compounds of cucurbit[7]uril with metal aqua complexes. The isolation of the supramolecular adduct with cucurbit[8]uril 2 in the single-crystalline state allows the determination of the structure of the tetranuclear chromium aqua complex having an adamantane-like structure, [Cr₄(μ₂-OH)₆(H₂O)₁₂]⁶⁺, which has been previously unknown in the solid state.     

Hexapalladium cluster: Unique cluster construction reaction of cyclic Pd3(CNC6H3Me2-2,6)6 and linear [Pd3(CNC6H3Me2-2,6)8]

Reaction of a triangle Pd(0) complex, Pd₃(CNXyl)₆ (1; Xyl = 2,6-C₆H₃Me₂), with a dicationic linear trinuclear complex [Pd₃(CNXyl)₈][PF₆]₂ (3) afforded a dicationic hexapalladium complex [Pd₆(CNXyl)₁₂][PF₆]₂ (4), while the reaction of 1 with a dicationic dinuclear complex [Pd₂(CNXyl)₆][PF₆]₂ (2) resulted in the formation of 3. The molecular structure of the complex 4 was determined by X-ray crystallography and spectroscopic analysis.     

Synthesis of [Ru(CO)2(PPh3)(SP)] and [Ru(CO)(PPh3)2(SP)] and their catalytic activities for the hydroamination of phenylacetylene

The reaction of [Ru(CO)₂(PPh₃)₃] (1) with o-styryldiphenylphophine (SP) (2) gave [Ru(CO)₂(PPh₃)(SP)] (3) in 83% yield. This styrylphosphine ruthenium complex 3 can also be synthesized by the reaction of [Ru(p-MeOC₆H₄NN)(CO)₂(PPh₃)₂]BF₄ (4) with NaBH₄ and 2 in 50% yield. When “Ru(CO)(PPh₃)₃” generated by the reaction of [RuH₂(CO)(PPh₃)₃] (8) with trimethylvinylsilane reacted with 2, [Ru(CO)(PPh₃)₂(SP)] (10) was produced in moderate yield as an air sensitive solid. The spectral and X-ray data of these complexes revealed that the coordination geometries around the ruthenium center of both complexes corresponded to a distorted trigonal bipyramid with the olefin occupying the equatorial position and the C-C bonding in the olefin moiety in 3 and 10 contained a significant contribution from a ruthenacyclopropane limiting structure. Complexes 3 and 10 showed catalytic activity for the hydroamination of phenylacetylene 11 with aniline 12. Ruthenium complex 3 in the co-presence of NH₄PF₆ or H₃PW₁₂O₄₀ proves to be a superior catalyst system for this hydroamination reaction. In the case of the reaction using H₃PW₁₂O₄₀ as an additive, ketimines (13) was obtained in 99% yield at a ruthenium-catalyst loading of 0.1 mol%. Some aniline derivatives such as 4-methoxy, 4-trifluoromethyl-, and 4-bromoanilines can also be used in this hydroamination reaction.     

Crystal and molecular structure of [RuNO(NO2)4OHCuPy n ] heterometallic complexes

Heterometallic complexes [RuNO(NO₂)₄OHCuPy₂(H₂O)] (I) and [RuNO(NO₂)₄OHCuPy₃] (II) are described structurally for the first time. In complex I, the ruthenium anion is coordinated to the copper atom by the bridging OH group and two bridging nitro groups; in complex II, by the bridging OH group and one bridging nitro group. Dimers are formed in the crystal lattice of complex II due to the interaction of the copper atom and the nitro group of the ruthenium anion in trans position to the bridging NO₂ group.     

Synthesis and structural studies of Rh, Pd, Ni complexes and one-pot synthesis of binuclear Ru complex [(η-p-cymene)Ru(μ2-Cl)3Ru{PhN(P(OC6H4OMe-o)2)2}Cl]

The Rh^I, Ru^II, Pd^I and Ni^II complexes of the aminobis(phosphonite), PhN(P(OC₆H₄OMe-o)₂)₂ (1) are reported. The reactions of 1 with [Rh(COD)Cl]₂ in 1:1 and 2:1 molar ratio afford the mono- and diolefin substituted chloro bridged chelate complexes, [(COD)Rh₂(μ₂-Cl)₂{PhN(P(OC₆H₄OMe-o)₂)₂}] (2) and [Rh(μ₂-Cl){PhN(P(OC₆H₄OMe-o)₂)₂}]₂ (3), respectively. Similarly, the cationic mono- and bis-chelate complexes, [Rh(COD){PhN(P(OC₆H₄OMe-o)₂)₂}]OTf (4) and [Rh{PhN(P(OC₆H₄OMe-o)₂)₂}₂]OTf (5) are obtained by treating 1 with [Rh(COD)Cl]₂ in the presence of AgOTf in appropriate ratios. The dinuclear Rh^I carbonyl complex, [RhCl(CO){μ-PhN(P(OC₆H₄OMe-o)₂)₂}]₂ (6) is prepared by treating 1 with 0.5 equiv. of [Rh(CO)₂Cl]₂. Reaction of 1 with cis-[NiBr₂(DME)] (DME = 1,2-dimethoxyethane) affords [{PhN(P(OC₆H₄OMe-o)₂)₂}NiBr₂] (7) whereas with [Ru-(η⁶-p-cymene)Cl₂]₂ in refluxing THF medium produces an interesting and rare bimetallic Ru^II complex, [(η⁶-p-cymene)Ru(μ₂-Cl)₃Ru{PhN(P(OC₆H₄OMe-o)₂)₂}Cl] (8). Redox condensation of the Pd⁰ and Pd^II derivatives with 1 affords the dinuclear Pd^I complex, [PdBr{μ-PhN(P(OC₆H₄OMe-o)₂)₂}]₂ (9). The formation and structure of complexes 2-9 are assigned through various spectroscopic and micro analysis data. The molecular structures of 5 and 7-9 are confirmed by single crystal X-ray diffraction studies.     

Reactivity of 2,3-bis(2-pyridyl)pyrazine with [Re2(CO)8(CH3CN)2]: Molecular structures of [Re2(CO)8(C14H10N4)] and [Re2(CO)8(C14H10N4)Re2(CO)8]

The reaction of the labile compound [Re₂(CO)₈(CH₃CN)₂] with 2,3-bis(2-pyridyl)pyrazine in dichloromethane solution at reflux temperature afforded the structural dirhenium isomers [Re₂(CO)₈(C₁₄H₁₀N₄)] (1 and 2), and the complex [Re₂(CO)₈(C₁₄H₁₀N₄)Re₂(CO)₈] (3). In 1, the ligand is σ,σ′-N,N′-coordinated to a Re(CO)₃ fragment through pyridine and pyrazine to form a five-membered chelate ring. A seven-membered ring is obtained for isomer 2 by N-coordination of the 2-pyridyl groups while the pyrazine ring remains uncoordinated. For 2, isomers 2a and 2b are found in a dynamic equilibrium ratio [2a]/[2b]  =  7 in solution, detected by ¹H NMR (−50 °C, CD₃COCD₃), coalescence being observed above room temperature. The ligand in 3 behaves as an 8e-donor bridge bonding two Re(CO)₃ fragments through two (σ,σ′-N,N′) interactions. When the reaction was carried out in refluxing tetrahydrofuran, complex [Re₂(CO)₆(C₁₄H₁₀N₄)₂] (4) was obtained in addition to compounds 1-3. The dinuclear rhenium derivative 4 contains two units of the organic ligand σ,σ′-N,N′-coordinated in a chelate form to each rhenium core. The X-ray crystal structures for 1 and 3 are reported.     

Synthesis and structural characterization of binuclear ytterbium(III) complexes with 2-amino and 3-amino benzoic acid

Two novel homobinuclear ytterbium(III) complexes, [Yb₂(2AMB)₆(H₂O)₄] · 2C₂H₆O (I) and Yb₂(3AMB)₆(H₂O)₄] · 3H₂O (II) (2AMB = 2-aminobenzoic acid, 3AMB = 3-aminobenzoic acid) have been synthesized and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis and X-ray crystallography (CIF files CCDC nos. 950103 (I), 921652 (II)). Complex I crystallizes in triclinic space group \(P\bar 1\) and complex II crystallizes in monoclinic space group P2₁/n. X-ray analysis shows that both complexes (I, II) have the dinuclear structure. The central Yb³⁺ ions in both complexes are eight-coordinated adopting distorted YbO₈ dodecahedral geometry. Each Yb³⁺ ion is coordinated to two O atoms from bridging carboxylate, four O atoms from the chelating carboxylate ligands and two O atoms of water molecules. The crystal structure of I and II are stabilized by N-H…O, O-H…O, O-H…N, and C-H…O hydrogen bonds, C-H…π interactions and weak π-π stacking interactions.     

Hydrothermal synthesis, crystal structure and photoluminescence of [HgCl2(C6NO2H5)]nn[HgCl2]n(C6NO2H5)

The first example of isonicotinic acid compounds with infinite mercury halide chains, [HgCl₂(C₆NO₂H₅)]_n n[HgCl2]n(C₆NO₂H₅) (1), was synthesized through hydrothermal reactions and structurally characterized by X-ray single crystal diffraction. Compound 1 features a one-dimensional (1-D) motif, based on infinite 1-D [HgCl₂(C₆NO₂H₅)]_n chains, neutral HgCl₂ moieties and isolated isonicotinic acid molecules. The [HgCl₂(C₆NO₂H₅)]_n chains, HgCl₂ moieties and isonicotinic acid molecules are interlinked by hydrogen bonds and π-π interactions to give a two-dimensional supramolecular layer. Photoluminescent investigation reveals that the title compound exhibits a strong emission in blue region. The emission band is identified as the π -π* transitions of the isonicotinic acid moieties.