Steric Effects on the Structures,Reactivity, and Coordination Chemistry of Tris(2‐pyridyl)aluminates

Introducing substituents in the 6‐position of the 2‐pyridyl rings of tris(pyridyl)aluminate anions, of the type [EtAl(2‐py′)₃]^? (py′=a substituted 2‐pyridyl group), has a large impact on their metal coordination characteristics. This is seen most remarkably in the desolvation of the THF solvate [EtAl(6‐Me‐2‐py)₃Li?THF] to give the monomer [EtAl(6‐Me‐2‐py)₃Li] ( 1 ), containing a pyramidal, three‐coordinate Li⁺ cation. Similar monomeric complexes are observed for [EtAl(6‐CF₃‐2‐py)₃Li] ( 2 ) and [EtAl(6‐Br‐2‐py)₃Li] ( 3 ), which contain CF₃ and Br substituents (R). This steric influence can be exploited in the synthesis of a new class of terminal Al?OH complexes, as is seen in the controlled hydrolysis of 2 and 3 to give [EtAl(OH)(6‐R‐2‐py)₂]^? anions, as in the dimer [EtAl(OH)(6‐Br‐2‐py)₂Li]₂ ( 5 ). Attempts to deprotonate the Al?OH group of 5 using Et₂Zn led only to the formation of the zincate complex [LiZn(6‐Br‐py)₃]₂ ( 6 ), while reactions of the 6‐Br substituted 3 and the unsubstituted complex [EtAl(2‐py)₃Li] with MeOH give [EtAl(OMe)(6‐Br‐2‐py)₂Li]₂ ( 7 ) and [EtAl(OMe)(2‐py)₂Li]₂ ( 8 ), respectively, having similar dimeric arrangements to 5 . The combined studies presented provide key synthetic methods for the functionalization and elaboration of tris(pyridyl)aluminate ligands.     

Syntheses,structures and properties of isonicotinamidium,thionicotinamidium, 2- and 3-(hydroxymethyl)pyridinium nitrates

New salts containing cations of selected pyridine derivatives of the composition [pyH]NO₃, where py is 2-pyridylmethanol (2-(hydroxymethyl)pyridine, 2pm), 3-pyridylmethanol (3-(hydroxymethyl) pyridine, 3pm), isonicotinamide (4-(aminocarbonyl)-pyridine, inia) and thionicotinamide (4-(aminothiocarbonyl)pyridine, tnia) were synthesised using two methods. By the first method, the above salts were obtained from reaction mixtures prepared from Fe(NO₃)₃ · 9H₂O and the appropriate pyridine derivative py in ethanol without the addition of acids. The protons required for protonation of the given pyridine derivatives are formed by the protolytic reaction of [Fe(H₂O)₆]³⁺, which acts as a cationic Brønstedt acid. These cations are present in the solid state of Fe(NO₃)₃ · 9H₂O as well as in its solutions. Under the second procedure, the salts were prepared by a direct reaction of the selected pyridine derivative py with a diluted solution of HNO₃. The first method affords crystals with lower yields but the second method produces microcrystals with higher yields. All the compounds were characterised by elemental analysis, infrared and NMR spectroscopic analyses and [3pmH]NO₃ and [2pmH]NO₃ by X-ray structure analysis also. [3pmH]NO₃ crystallises in the monoclinic and [2pmH]NO₃ in the triclinic system.     

Synthesen und Strukturen der Lithiumtitanate(III) und ‐(IV), (py)2Li[(py)2Ti(OPh)4] und (py)2Li[(py)Ti(OPh)5]

Syntheses and Structures of the Lithiumtitanates(III)/(IV) (py)₂Li[(py)₂Ti(OPh)₄] and (py)₂Li[(py)Ti(OPh)₅] The new lithiumtitanates (py)₂Li[(py)₂Ti(OPh)₄] ( 1 ) and (py)₂Li[(py)Ti(OPh)₅] ( 2 ) have been obtained from the reaction of titaniumtrichloride (respectively titaniumtetrachloride 2 ) with LiOPh in the presence of the base pyridine (py). The crystal structures of both compounds show that the titanium atoms are in the centres of distorted octahedral coordination figures. In compound 1 , four oxygen and two nitrogen atoms (in cis orientation) are bonded to titanium, whereas in 2 , five oxygen and one nitrogen atom form the coordination polyeder around titanium. In both compounds, the lithium atoms are attached through phenolate bridges to the octahedra. The titanate (py)₂Li[(py)₂Ti(OPh)₄] ( 1 ) has a single absorption band in the visible region of the UV‐spectrum showing a shoulder shifted to the bathochromic region, due to the Jahn‐Teller‐effect for d¹‐systems.     

Synthesis,Structure and Reactivity of Organoindium 1,2-Benzenedithiolates and 2-Amidobenzenethiolates

Organoindium compounds of redox active 1,2-benzenedithiolate and 2-amidobenzenethiolate ligands were synthesized and tested for reactivity against mild oxidants. The reaction of Me₃In and (NCN)InMe₂ [NCN=2,6-bis(dimethylaminomethy)phenyl] with 3,4-toluenedithiol (H₂tdt) at room temperature afforded [MeIn(tdt)(py)]₂ ( 1 ) and (NCN)In(tdt) ( 2 ), respectively. A similar reaction of Me₃In with 2-aminobenzenethiol (H₂abt) in toluene under reflux afforded [MeIn(abt)(py)]₂ ( 3 ). The reaction of (NCN)InCl₂ with one equivalent of Li₂(abt) or two equivalents of Li(Habt) afforded the compounds [(NCN)In(abt)]⋅LiCl(thf)₂ ( 4 ⋅LiCl(thf)₂) and (NCN)In(Habt)₂ ( 5 ), respectively. The X-ray crystal structures of 1 and 3 are similar and show dimeric structures via μ-S-(tdt) and μ-N-(abt) ligands, respectively. Compounds 2 and 4 possess similar monomeric structures and tridentate NCN pincer ligands. DFT computational studies have been used to rationalize the observed solid-state structures and discern the potential reactivity of compounds 1 – 4 against oxidants. The reaction of 1 and 2 with excess iodine resulted in loss of the 3,4-toluenedithiolate ligand and the formation of the oligomeric disulfide [tdt]_n, while 3 and 4 showed no reactivity under similar conditions. This contrasts the reactivity of previously reported organoindium o-amidophenolate complexes which undergo oxidative addition of iodine to afford ligand-centered radical species.     

A Uranium‐Based UO2+–Mn2+ Single‐Chain Magnet Assembled trough Cation–Cation Interactions

Single‐chain magnets (SCMs) are materials composed of magnetically isolated one‐dimensional (1D) units exhibiting slow relaxation of magnetization. The occurrence of SCM behavior requires the fulfillment of stringent conditions for exchange and anisotropy interactions. Herein, we report the synthesis, the structure, and the magnetic characterization of the first actinide‐containing SCM. The 5f–3d heterometallic 1D chains [{[UO₂(salen)(py)][M(py)₄](NO₃)}]_n, (M=Cd ( 1 ) and M=Mn ( 2 ); py=pyridine) are assembled trough cation–cation interaction from the reaction of the uranyl(V) complex [UO₂(salen)py][Cp*₂Co] (Cp*=pentamethylcyclopentadienyl) with Cd(NO₃)₂ or Mn(NO₃)₂ in pyridine. The infinite UMn chain displays a high relaxation barrier of 134±0.8 K (93±0.5 cm^?1), probably as a result of strong intra‐chain magnetic interactions combined with the high Ising anisotropy of the uranyl(V) dioxo group. It also exhibits an open magnetic hysteresis loop at T<6 K, with an impressive coercive field of 3.4 T at 2 K.     

Die Pyridinaddukte der Goldhalogenide. 1. Darstellung und Struktur von [Hpy][AuCl4], AuCl3 · py, [AuCl2(py)2]Cl · H2O und [AuCl2(py)2][AuCl2]

Pyridine Adducts of the Gold Halides. 1. Synthesis and Structure of [Hpy][AuCl₄], AuC1₃ · py, [AuCl₂(py)₂]Cl · H₂O, and [AuCl₂(py)₂] [AuCl₂] HAuCl₄ reacts with pyridine in aqueous solution to form sparingly soluble [Hpy] [AuCl₄]. This goes into solution as [AuCl₂(py)₂]⁺ on adding an excess of pyridine. [Hpy][AuCl₄] decomposes above 195°C to HCl and AuCl₃ · py, which can also be obtained from NaAuCl₄ and pyridine. AuCl₂ · py is formed by the reaction of AuCl₂ · S(CH₂C₆H₄)₂ with pyridine in CHCl₃. According to the vibrational spectrum the complex is built up of trans[AuCl₂(py)₂]⁺ cations and [AuCl₂]^? anions. The IR spectra of [Hpy][AuCl₄], AuCl₃ · py, and [AuCl₂(py)₂]Cl · H₂O are discussed and assigned with respect to the crystal structures. [Hpy][AuCl₄] crystallizes monoclinic in the space group C2/m. In its structure alternating layers of [Hpy]⁺ cations and [AuCl₄]^? anions are observed. The monoclinic AuCl₃ · py (space group C2/c) consists of molecular complexes, wherein the gold atom is surrounded by three Cl atoms and one pyridine molecule in a square planar arrangement. The coordination is completed to an elongated octahedron by two more distant Cl atoms of neighbouring complexes. [AuCl₂(py)₂]Cl · H₂O crystallizes in the monoclinic space group P2₁/n. It forms planar trans[AuCl₂(py)₂]⁺ cations, weakly coordinated with an additional Cl^? ion and one H₂O molecule. The Au? Cl bond lengths in the complexes under investigation are in the range of 227 to 229 pm, the Au? N distances are between 197 and 199 pm.     

Synthesis of mono- and binuclear dioxomolybdenum(VI) complexes derived from N(4)-substituted thiosemicarbazones: X-ray crystal structures of [(MoO2L)2], [MoO2Lpy] and [MoO2Lpy]

Four molybdenum(VI) thiosemicarbazonato complexes have been synthesized and characterized. The dinuclear complexes [(MoO₂L¹)₂] (1) and [(MoO₂L²)₂] (3) have been prepared by the reaction of [MoO₂(acac)₂] with 2-hydroxyacetophenone N(4)-cyclohexyl (H₂L¹) and N(4)-phenyl (H₂L²) thiosemicarbazones in alcoholic medium. Mononuclear dioxomolybdenum(VI) complexes of the type [MoO₂L¹py] (2) and [MoO₂L²py] (4) have been prepared by the reaction of 1 or 3 with pyridine (py) in alcoholic medium. In all the complexes, molybdenum is coordinated by two terminal oxo-oxygen atoms, (O_t), oxygen, nitrogen and sulfur atoms from the principal ligand and by an oxygen atom from the second unit in 1, and by a nitrogen atom from pyridine in complexes 2 and 4. All complexes have been spectroscopically characterized. The molecular structures of complexes 1, 2 and 4 have been determined by the single crystal X-ray diffraction method.     

Study of the Bonding Modes of Di‐2‐pyridyl ketoxime Ligand towards Ruthenium,Rhodium and Iridium Half Sandwich Complexes

The bonding modes of the ligand di‐2‐pyridyl ketoxime towards half‐sandwich arene ruthenium, Cp*Rh and Cp*Ir complexes were investigated. Di‐2‐pyridyl ketoxime {pyC(py)NOH} react with metal precursor [Cp*IrCl₂]₂ to give cationic oxime complexes of the general formula [Cp*Ir{pyC(py)NOH}Cl]PF₆ ( 1a ) and [Cp*Ir{pyC(py)NOH}Cl]PF₆ ( 1b ), for which two coordination isomers were observed by NMR spectroscopy. The molecular structures of the complexes revealed that in the major isomer the oxime nitrogen and one of the pyridine nitrogen atoms are coordinated to the central iridium atom forming a five membered metallocycle, whereas in the minor isomer both the pyridine nitrogen atoms are coordinated to the iridium atom forming a six membered metallacyclic ring. Di‐2‐pyridyl ketoxime react with [(arene)MCl₂]₂ to form complexes bearing formula [(p‐cymene)Ru{pyC(py)NOH}Cl]PF₆ ( 2 ); [(benzene)Ru{pyC(py)NOH}Cl]PF₆ ( 3 ), and [Cp*Rh{pyC(py)NOH}Cl]PF₆ ( 4 ). In case of complex 3 the ligand coordinates to the metal by using oxime nitrogen and one of the pyridine nitrogen atoms, whereas in complex 4 both the pyridine nitrogen atoms are coordinated to the metal ion. The complexes were fully characterized by spectroscopic techniques.     

Synthesis, Characterization and Crystal Structure of a One-dimensional Diamagnetic Metal-radical Complex: [Zn(NIT4py)2(DTB)2(H2O)2]

A novel one-dimensional complex [Zn(NIT4py)₂(DTB)₂(H₂O)₂] (1), with mixed ligands [where NIT4py is 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and DTB is 3,5-dinitrobenzoate] has been synthesized and characterized by elemental analyses, i.r., u.v.–vis spectra, thermogravimetric analysis, X-ray single crystal diffraction and magnetic measurements. The complex crystallizes in the triclinic crystal system and space group Pî. The Zn ^II ion is in a distorted octahedral environment: two nitrogen atoms from two NIT4py entities, two oxygen atoms from two DTB units in the basal plane; and two oxygen atoms from the two water molecules in the axial position. The [Zn(NIT4py)₂(DTB)₂(H₂O)₂] units are connected as a one dimension chain by the intermolecular hydrogen bonds. The complex exhibits intramolecular antiferromagnetic interactions between the two radicals.     

Synthesen und Strukturen der Titan(III)‐siloxane [Ti(OSiPh3)3(thf)2] und [Ti(OSiPh3)3(py)2]

Syntheses and Structures of the Titanium(III) Siloxanes [Ti(OSiPh₃)₃(thf)₂] and [Ti(OSiPh₃)₃(py)₂] The new titaniumtrioxysilanes [Ti(OSiPh₃)₃(thf)₂] ( 1 ) and [Ti(OSiPh₃)₃(py)₂] ( 2 ) have been obtained from the reaction of titaniumtrichloride with LiOSiPh₃ in the presence of the corresponding bases tetrahydrofurane (thf) and pyridine (py). From the crystal structures of both compounds it is evident that the titanium atoms are in the centres of trigonal‐bipyramidal coordination figures, with the donor atoms in axial positions. The compounds 1 and 2 have slightly different structures (mean values: 1 : Ti‐O(Si) 1.897(9), Ti‐O(C) 2.136(8) Å; 2 : Ti‐O 1.902(9), Ti‐N2.252(8) Å) and have a single absorption band in the visible region of the UV‐spectrum. The exchange of the thf‐ligands in 1 by pyridine (in high molar excess) seems to be hindered as deduced from UV‐spectroscopy.     

Studies on the interaction of peroxy radicals with transition metals complexes: I. Effect of 2-cyano-2-propyl and 2-cyano-2-propyl peroxy radicals on cobaloximes

Reactions of CH₃Co(DH)₂py (1) and [Co(DH)₂py]₂ (2) with (CH₃)₂(CN)C (r) and (CH₃)₂(CN)COO (rO₂) radicals were investigated. At 60°C, reaction or r with (1) results in non-homogeneous ligand decomposition, whereas for 2, complex (CH₃)₂CNCCo(DH)₂py (6) and a precipitate are formed. Ligand decomposition also took place at 60°C when the reaction of rO₂ radicals with 1 and 2 was investigated. However, the same reaction with rO₂ radicals at −10°C, yielded two complexes, CH₃OOCo(DH)₂py (3) and Co(DH)₂py (4) with 1, and complex 6 for the reaction of rO₂ with 2.     

Molybdenum(VI), (V) and (IV) complexes with chiral benzoin thiosemicarbazone

The chiral (ONS) dianionic Schiff base ligand benzoin thiosemicarbazone (H₂L) reacts with MoO₂(acac)₂ to give the polymeric complex [(MoO₂L) _n ] (1) (Type 1). The reaction of MoO₂L with pyridine (py), 3-picoline (3-pic) or 4-picoline (4-pic) gives [Mo^VIO₂LD] (D = py, 3-pic or 4-pic) (Type 1). Further, the reaction of [MoO₂L] or [MoO₂LD] with PPh₃ or reaction of [MoO₂L] with PPh₃ (plus bpy or phen, D) in the presence of donor reagents D gives [Mo^IVOL] or [Mo^IVOLD] (Type 2). On the other hand, the reaction of [MoO₂L] with hydrazides (zdhH₃) such as benzoylhydrazine (bhH₃), isonicotinoylhydrazine (inhH₃), nicotinoylhydrazine (nhH₃), salicyloylhydrazine (slhH₃) and thiosemicarbazide (tscH₃) produced non-oxo–diazenido complexes [MoL(zdh)] (Type 3). The complexes have been characterized by elemental analyses, molar conductance, magnetic moment, electronic, i.r. and e.s.r. spectroscopic measurements.     

Coordinative Behaviour of Tridentate NS2‐Donor Ligands with Cadmium: Synthesis and Crystal Structures of New Complexes

The reaction of cadmium salts with various amounts of the tridentate NS₂‐chelating ligands 1‐(2‐mercapto‐acetophenone)‐4‐triphenylmethylthiosemicarbazone (H₂L¹) and 1‐(5‐mercapto‐3‐methyl‐1‐phenylpyrazole‐4‐carboxaldehyde)‐4‐triphenyl‐methylthiosemicarbazone (H₂L²) in the presence of bases like N‐methylimidazole (N–MeIm), pyridine (py) or triethylamine (Et₃N) provided a series of novel mono‐, di‐, tri‐ and heptanuclear cadmium complexes. They are of the general formulas [CdL¹(N–MeIm)]₂ ( 1 ), [CdL¹(py)]₂ ( 2 ), [CdL²(N–MeIm)]₂ ( 3 ), [CdL²(py)₃] · 0.25 C₆H₁₄ · 0.5 py ( 4 ), [Et₃NH]₂[Cd₃L ] · 7 MeOH ( 5 ), [Et₃NH]₂[Cd₃L ] ( 6 ) and [Et₃NH]₂[Cd₇L ] · 14 MeOH ( 7 ). The compounds were characterized by elemental analysis, IR‐ and ¹H‐NMR‐spectroscopy. Single‐crystal X‐ray structure analyses are reported for the complexes 2 , 4 , 5 and 7 . While 2 has a dimeric structure where each cadmium ion is pentacoordinated in a N₂S₃‐environment, 4 consists of a monomeric cadmium center with distorted octahedral N₄S₂‐coordination. The complexes 5 and 7 exhibit new structural types for tri‐ and heptanuclear cadmium compounds. It is shown that sulfur bridging might proceed via arylthiolates, iminothiolates or even both functions of the ligand. Aggregation is influenced by various factors like solvents, counterions and ligand properties.     

Copper(II) Complexes with Asymmetrical Schiff Base Ligands Derived from 2‐Acetylpyrazine

New copper(II) complexes of asymmetrical tetradentate Schiff bases containing pyrazine have been prepared and thoroughly characterised by elemental analysis, IR and electronic spectroscopy, mass spectrometry and magnetic measurements. Two alternative methods were used in the isolation of the complexes: template synthesis in the preparation of Cu(SalDpyz)ClO₄ (HSalDPyz = derived from the condensation of salicylaldehyde, acetylpyrazine and 1,2‐ethylendiamine, 2‐methyl‐1,2‐propylendiamine, 1,2‐phenylendiamine) and direct interaction between copper perchlorate and the corresponding Schiff base, as in the isolation of Cu(AEPyz)(ClO₄) (HAEPyz = (Z)‐4‐[2‐{[2‐{[(E)‐1‐(pyrazinyl)ethylidene]amino} ethyl)amino]‐3‐penten‐2‐one)]. [Cu(SalEn)(py)(OClO₃)][Cu(SalEn)(py)]ClO₄ ( 1 ) (SalEn = 4‐(2‐hydroxyphenyl)‐3‐aza‐3‐buten‐1‐amino, py = pyridine), metal precursor in the preparation of Cu(SalEnpyz)(ClO₄) (HSalEnpyz = 2‐{E(2‐{[(E)‐1‐(2‐pyrazinyl)ethylidene]amino}ethyl)imino]methyl}phenol), was crystallographically characterised. The crystal structure of [Cu(AEpyz)]ClO₄ ( 2 ) is also reported.     

Reduction from copper(II) to copper(I) upon collisional activation of (pyridine)2CuCl+

Electrospray ionization of dilute aqueous solutions of copper(II) chloride‐containing traces of pyridine (py) as well as ammonia permits the generation of the gaseous ions (py)₂Cu⁺ and (py)₂CuCl⁺, of which the latter is a formal copper(II) compound, whereas the former contains copper(I). Collision‐induced dissociation of the mass‐selected ions in an ion‐trap mass spectrometer (IT‐MS) leads to a loss of pyridine from (py)₂Cu⁺, whereas an expulsion of atomic chlorine largely prevails for (py)₂CuCl⁺. Theoretical studies using density functional theory predict a bond dissociation energy (BDE) of BDE[(py)₂Cu⁺ ‐Cl] = 125 kJ mol^?1, whereas the pyridine ligand is bound significantly stronger, i.e. BDE[(py)CuCl⁺ ‐py] = 194 kJ mol^?1 and BDE[(py)Cu⁺ ‐py] = 242 kJ mol^?1. The results are discussed with regard to the influence of the solvation on the stability of the Cu^I/Cu^II redox couple. Copyright © 2010 John Wiley & Sons, Ltd.     

Trinuclear Schiff base complexes with uranium(V) and copper(II) or zinc(II) ions

Treatment of the uranium(IV) complexes [{ML¹(py)}₂U^IV] (M = Cu, Zn; L¹ = N,N′-bis(3-hydroxysalicylidene)-1,3-propanediamine) with silver nitrate in pyridine led to the formation of the corresponding cationic uranium(V) species which were found to be thermally unstable and were converted back into the parent U^IV complexes; no electron transfer was observed in solution between the U^IV and U^V compounds. In the crystals of [{ML¹(py)}₂U^IV][{ML¹(py)}₂U^V][NO₃], the neutral U^IV and cationic U^V species are clearly identified by the distinct U–O distances. Similar reaction of [{ZnL²(py)}₂U^IV] [L² = N,N′-bis(3-hydroxysalicylidene)-1,4-butanediamine] with AgNO₃ gave crystals of [{ZnL²(py)}U^V{ZnL²(py)₂}][NO₃] but the copper counterpart was not isolated. Crystals of [{ZnL¹(py)}₂U^V][OTf] · THF (OTf = OSO₂CF₃) were obtained fortuitously from the reaction of [Zn(H₂L¹)] and U(OTf)₃.     

Synthesis and characterization of several rhenium(I) complexes of 2-acetylpyridine and ferrocenyl carbaldehyde derivatives of 2-hydroxybenzoic acid hydrazide

The rhenium(I) carbonyl halide (X = Cl and Br) complexes, [ReX(CO)₃{H₂(py)L²}] (1a, 1b) and [ReX(CO)₃{H₂(Fc)L²}] (2a, 2b), of the ligands derived from 2-acetylpyridine and ferrocenyl carbaldehyde derivatives of 2-hydroxybenzoic acid hydrazide [H₂(py)L² and H₂(Fc)L², respectively] have been prepared in good yield. The complexes have been characterized by elemental analysis, MS, IR, UV-Vis and ¹H NMR spectroscopic methods and their structures have been elucidated by X-ray diffraction. The ligand forms a five-membered chelate ring but in H₂(py)L² it is N_pyridine,N′-bidentate while it is O,N-bidentate in H₂(Fc)L² complexes.Reaction of complex 1a with copper(II) nitrate yields the unexpected aqua complex [Re{H(py)L²}(H₂O)(CO)₃] (3) where the ligand is monodeprotonated but maintains the coordination mode observed in 1a, as shown by X-ray diffraction. However, reaction of 1b with glycine yields a conformational polymorph of the original compound, 1b′. The X-ray study shows that the orientation of the O-H phenol group against the carbonyl amide group is the main difference.     

On the Critical Effect of the Metal (Mo vs. W) on the [3+2] Cycloaddition Reaction of M3S4 Clusters with Alkynes: Insights from Experiment and Theory

Whereas the cluster [Mo₃S₄(acac)₃(py)₃]⁺ ([ 1 ]⁺, acac=acetylacetonate, py=pyridine) reacts with a variety of alkynes, the cluster [W₃S₄(acac)₃(py)₃]⁺ ([ 2 ]⁺) remains unaffected under the same conditions. The reactions of cluster [ 1 ]⁺ show polyphasic kinetics, and in all cases clusters bearing a bridging dithiolene moiety are formed in the first step through the concerted [3+2] cycloaddition between the C?C atoms of the alkyne and a Mo(μ‐S)₂ moiety of the cluster. A computational study has been conducted to analyze the effect of the metal on these concerted [3+2] cycloaddition reactions. The calculations suggest that the reactions of cluster [ 2 ]⁺ with alkynes feature ΔG^≠ values only slightly larger than its molybdenum analogue, however, the differences in the reaction free energies between both metal clusters and the same alkyne reach up to approximately 10 kcal mol^?1, therefore indicating that the differences in the reactivity are essentially thermodynamic. The activation strain model (ASM) has been used to get more insights into the critical effect of the metal center in these cycloadditions, and the results reveal that the change in reactivity is entirely explained on the basis of the differences in the interaction energies E_int between the cluster and the alkyne. Further decomposition of the E_int values through the localized molecular orbital‐energy decomposition analysis (LMO‐EDA) indicates that substitution of the Mo atoms in cluster [ 1 ]⁺ by W induces changes in the electronic structure of the cluster that result in weaker intra‐ and inter‐fragment orbital interactions.     

Ligand Exchange Processes on Solvated Beryllium Cations. IV [Be(H2O)2(imidazole‐based Chelate)]1)

The water exchange reaction of [Be(H₂O)₂(1H‐imidazole‐4,5‐dicarboxylate)] and [Be(H₂O)₂(1H‐imidazol‐3‐ium‐4,5‐dicarboxylate)]⁺ in water was studied by DFT calculations (RB3LYP/6‐311+G**) and identified as an associative interchange mechanism. The activation barriers for [Be(H₂O)₂(1H‐imidazole‐4,5‐dicarboxylate)] (16.6 kcal/mol) and [Be(H₂O)₂(1H‐imidazol‐3‐ium‐4,5‐dicarboxylate)]⁺ (13.8 kcal/mol) are similar to the barrier for [Be(H₂O)₄)]²⁺ and independent of the overall charge. NICS calculations show no indication that the aromaticity of the imidazole ring is affected during the water exchange process.     

Synthesis and structural characterization of three copper coordination polymers with pyridine derivatives from hydro(solvo)thermal in situ decarboxylation reactions of 2,5-dicarboxylpyridine

The hydro(solvo)thermal self-assembles of CuI, KI and 2,5-dicarboxylpyridine [2,5-(COOH)₂py] in different molar ratios in H₂O/alcohol solutions produced three Cu coordination polymers as 2-D [N-C₂H₅py][Cu₃I₄] 1, 1-D [N-CH₃py][Cu₂I₃] 2 as well as 1-D [Cu(2-COOpy)₂]H₂O 3 (N-C₂H₅py=N-ethylpyridine, N-CH₃py=N-methylpyridine, 2-COOpy=2-carboxylpyridine). N-C₂H₅py in 1 and N-CH₃py in 2 derived from the solvothermal in situ simultaneous decarboxylation and N-alkylation reactions of 2,5-(COOH)₂py. The semi-decarboxylation reaction of 2,5-(COOH)₂py into 2-COOpy occurred in the preparation of 3. X-ray single-crystal analysis revealed that CuI is transformed into a 2-D [Cu₃I₄]⁻ layer in compound 1 and a 1-D chain in compound 2, templated by [N-C₂H₅py]⁺ and [N-CH₃py]⁺, respectively. Compound 3 is a divalent Cu compound. The Cu(II) centers with a 4+2 geometry are coordinated by μ₃-mode 2-COOpy ligands. All of the title compounds were characterized by CHN analysis, IR spectrum analysis and TG analysis. Compounds 1 and 2 exhibit fluorescence properties with the maximum emissions at 581 nm for 1 and 537 nm for 2.