Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 3. A new highly electron-deficient octacationic macrocycle: tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazine, [(2-Mepy)8TPyzPzH(2)]8+

A new octacationic macrocycle, tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazine, was obtained in its hydrated form as the water-soluble iodide salt. This compound, abbreviated as [(2-Mepy)(8)TPyzPzH(2)](I(8)).8H(2)O (2-Mepy = 2(N-methyl)pyridiniumyl moiety), was obtained by demetalation of the corresponding Mg(II) complex, [(2-Mepy)(8)TPyzPzMg(H(2)O)](I(8)).5H(2)O, which in turn was prepared from its corresponding neutral hydrated species tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato(monoaquo)magnesium(II), [Py(8)TPyzPzMg(H(2)O)].4H(2)O, by reaction with CH(3)I in N,N-dimethylformamide. The quaternization reactions by using CH(3)I or methyl p-toluenesulfonate were also conducted on the monomeric precursor 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN)(2)Py(2)Pyz], with formation of the monoquaternized ion [(CN)(2)Py(2-Mepy)Pyz](+) neutralized by iodide and p-toluenesulfonate anions. Single-crystal X-ray work allowed elucidation of the structure of the two salt-like species. The diquaternized ion [(CN)(2)(2-Mepy)(2)Pyz](2+) could also be obtained as a p-toluenesulfonate salt, but attempts at direct macrocyclization of this dicationic species were unsuccessful. The iodide salt [(2-Mepy)(8)TPyzPzH(2)](I(8)).8H(2)O is water-soluble, with different solubilities depending on the range of pH explored. It was established that the macrocycle [(2-Mepy)(8)TPyzPzH(2)](8+) undergoes facile deprotonation and behaves as a strong acid. Aggregation phenomena are observed for both the octacation [(2-Mepy)(8)TPyzPzH(2)](8+) and its corresponding centrally deprotonated species [(2-Mepy)(8)TPyzPz](6+). Nevertheless, both cationic moieties exist in their monomeric form under specific experimental conditions. UV-visible monitored titrations with NaOH provide information about the type of protonation/deprotonation equilibria which are complicated by the occurrence of aggregation phenomena.     

Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 2. Metal complexes of tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine: linear and nonlinear optical properties and electrochemical behavior

A series of metal complexes of tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine, [Py(8)TPyzPzH(2)], having the general formula [Py(8)TPyzPzM].xH(2)O (M = Mg(II)(H(2)O), Mn(II), Co(II), Cu(II), Zn(II); x = 3-8) were synthesized by reaction of the free-base macrocycle with the appropriate metal acetate in pyridine or dimethyl sulfoxide under mild conditions. Clathrated water and retained pyridine molecules for the Mn(II) and Co(II) species are easily eliminated by heating under vacuum, the water molecules being recovered by exposure of the unsolvated macrocycles to air. Magnetic susceptibility measurements and EPR spectra of the materials in the solid state provide basic information on the spin state of the Cu(II), Co(II), and Mn(II) species. Colloidal solutions caused by molecular aggregation are formed in nondonor solvents (CH(2)Cl(2), CHCl(3)), a moderately basic solvent (pyridine), and an acidic solvent (CH(3)COOH), with the extent of aggregation depending on the specific solvent and the central metal ion. UV-vis spectral monitoring of the solutions after preparation indicates that disaggregation systematically occurs as a function of time leading ultimately to the formation of clear solutions containing the monomeric form of the porphyrazine. Cyclic voltammetry and thin-layer spectroelectrochemistry show that each compound with an electroinactive metal ion undergoes four reversible one-electron reductions, leading to formation of the negatively charged species [Py(8)TPyzPzM](n-) (n = 1 - 4). The stepwise uptake of four electrons is consistent with a ring-centered reduction, but in the case of the cobalt complex a metal-centered (Co(II) --> Co(I)) reduction occurs in the first process and only three additional reductions are observed. No oxidations are observed in pyridine or CH(2)Cl(2) containing 0.1 M tetrabuthylammonium perchlorate (TBAP). The nonlinear optical properties (NLO) of the species [Py(8)TPyzPzM] (M = 2H(I), Cu(II), Zn(II), Mg(II)(H(2)O)) have also been examined with nanosecond pulses at 532 nm in dimethyl sulfoxide solution. Reverse saturable absorption is shown by all of the [Py(8)TPyzPzM] species, which exhibit distinct behavior depending on the nature of M and extent of aggregation.     

Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 4. UV-visible spectral and electrochemical evidence of the remarkable electron-deficient properties of the new tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazinatometal octacations, [(2-Mepy)8TPyzPzM]8+ (M = MgII(H2O), CoII, CuII, ZnII)

Metal derivatives of the octacationic tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazine macrocycle [(2-Mepy)(8)TPyzPzH(2)](8+) (2-Mepy = 2-(N-methyl)pyridiniumyl ring) isolated as water-soluble hydrated iodide salts of the general formula [(2-Mepy)(8)TPyzPzM](I(8)).xH(2)O, (M = Mg(II)(H(2)O), Co(II), Cu(II), Zn(II); x = 2-5) were prepared from the corresponding neutral complexes [Py(8)TPyzPzM].xH(2)O previously reported. Reaction of these complexes with CH(3)I in N,N-dimethylformamide under mild conditions led to full quaternization of all eight pyridine N atoms and formation of the octacations [(2-Mepy)(8)TPyzPzM](8+). Clathrated water molecules could be eliminated from the species [(2-Mepy)(8)TPyzPzM](I(8)).xH(2)O by mild heating ( Co(I) process, but the site of electron transfer is reversed and the final product upon a further one-electron reduction is formulated as a Co(II) dianion as opposed to a Co(I) pi-anion radical. This sequence is similar to what was earlier reported for reduction of the same compound in pyridine. Reversible one-electron oxidations are also observed for the unmethylated species [Py(8)TPyzPzM].xH(2)O where M = Co(II) and Mn(II) in DMSO. Remarkably, the octacationic macrocycles [(2-Mepy)(8)TPyzPzM](I(8)).xH(2)O, (M = Mg(II)(H(2)O), Co(II), Cu(II), and Zn(II); x = 2-5) are more easily reduced at any step of the reduction than the corresponding unquaternized species with the same metal ion. This indicates a higher tendency to stepwise electron uptake after the quaternization process, which enhances the charge redistribution capability within the species formed by the electroreduction.     

Monomeric and dimeric copper(II) complexes of a novel tripodal peptide ligand: structures stabilized via hydrogen bonding or ligand sharing

The novel tripodal ligand N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide (Py3AH) affords monomeric and dimeric copper(II) complexes with coordinated carboxamido nitrogens. Although many chloro-bridged dimeric copper(II) complexes are known, [Cu(Py3A)(Cl)] (1) remains monomeric and planar with a pendant pyridine and does not form either a chloro-bridged dimer or the ligand-shared dimeric complex [Cu(Py3A)(Cl)]2 (4) in solvents such as CH3CN. When 1 is dissolved in alcohols, square pyramidal alcohol adducts [Cu(Py3A)(Cl)(CH3OH)] (2) and [Cu(Py3A)(Cl)(C2H5OH)] (3) are readily formed. In 2 and 3, the ROH molecules are bound at axial site of copper(II) and the weak axial binding of the ROH molecule is strengthened by intramolecular hydrogen bonding between ROH and the pendant pyridine nitrogen. Two ligand-shared dimeric species [Cu(Py3A)(Cl)]2 (4) and [Cu(Py3A)]2(ClO4)2 (5) have also been synthesized in which the pendant pyridine of one [Cu(Py3A)] unit completes the coordination sphere of the other [Cu(Py3A)] neighbor. These ligand-shared dimers are obtained in aqueous solutions or in complete absence of chloride in the reaction mixtures.     

Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 5. Synthesis, physicochemical and theoretical studies of a novel pentanuclear palladium(II) complex and related mononuclear species

New palladium(II) complexes of the free-base tetrakis[2,3-(5,6-di-2-pyridylpyrazino)porphyrazine], [Py 8TPyzPzH 2], have been prepared and their physicochemical properties examined. The investigated compounds are the pentanuclear species [(PdCl 2) 4Py 8TPyzPzPd], the monopalladated complex [Py 8TPyzPzPd], and its corresponding octaiodide salt [(2-Mepy) 8TPyzPzPd](I) 8. All three Pd (II) complexes have a common central pyrazinoporphyrazine core and differ only at the periphery of the macrocycle, where the simple dipyridinopyrazine fragments present in [Py 8TPyzPzPd] bear four PdCl 2 units coordinated at the pyridine N atoms in the pentanuclear complex, [(PdCl 2) 4Py 8TPyzPzPd], or carry pyridine-N(CH 3) (+) moieties in the iodide of the octacation [(2-Mepy) 8TPyzPzPd] (8+). The structural features of the pentanuclear complex [(PdCl 2) 4Py 8TPyzPzPd], partly supported by X-ray data and solution (1)H NMR spectra of the [(CN) 2Py 2PyzPdCl 2] precursor, were elucidated through one- and two-dimensional (1)H NMR spectra in solution and density functional theory (DFT) calculations. Structural information on the monopalladated complex [Py 8TPyzPzPd] was also obtained from DFT calculations. It was found that in the complex [(PdCl 2) 4Py 8TPyzPzPd] the peripheral PdCl 2 units adopt a py-py coordination mode and the generated N 2PdCl 2 moieties are directed nearly perpendicular to the plane of the pyrazinoporphyrazine ring, strictly recalling the arrangement found for the palladated precursor [(CN) 2Py 2PyzPdCl 2]. NMR and DFT results consistently indicate that of the four structural isomers predictable for [(PdCl 2) 4Py 8TPyzPzPd], one having all four N 2PdCl 2 moieties pointing on the same side of the macrocyclic framework (i.e., isomer 4:0, plus the 3:1 and the 2:2-cis and 2:2-trans isomers), the 4:0 isomer ( C 4 v symmetry) is the predominant form present. According to cyclic voltammetry and spectroelectrochemical results in pyridine, dimethyl sulfoxide (DMSO), and dimethylformamide (DMF), the monopalladated complex [Py 8TPyzPzPd] undergoes four reversible or quasi-reversible one-electron ligand-centered reductions, similar to the behavior also observed for the pentanuclear complex [(PdCl 2) 4Py 8TPyzPzPd], which shows an additional reduction peak attributable to the presence of PdCl 2. Owing to the electron-withdrawing properties of the PdCl 2 units, the pentanuclear complex is easier to reduce than the mononuclear complex [Py 8TPyzPzPd], some related [Py 8TPyzPzM] complexes, and their porphyrin or porphyrazine analogues, so much so that the corresponding monoanion radical is generated at potentials close to 0.0 V vs SCE in DMSO or DMF. In turn, the monoanion of [(2-Mepy) 8TPyzPzPd](I) 8 is also extremely easy to generate electrochemically. Indeed, because of the eight positively charged N-CH 3 (+) groups in this complex the first reduction occurs at potentials close to +0.10 V in DMSO or DMF. The redox behavior of the mono- and pentapalladated complexes has been rationalized on the basis of a detailed DFT analysis of their ground-state electronic structure.     

High and low spin mononuclear and dinuclear iron(II) complexes of 4-amino and 4-pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazoles

The first dinuclear iron(II) complexes of any 4-substituted 3,5-di(2-pyridyl)-4H-1,2,4-triazole ligands, [Fe(II)2(adpt)2(H2O)1.5(CH3CN)2.5](BF4)4 and [Fe(II)2(pldpt)2(H2O)2(CH3CN)2](BF4)4, are presented [where adpt is 4-amino-3,5-di(2-pyridyl)-4H-1,2,4-triazole and pldpt is 4-pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole]. Both dinuclear complexes feature doubly triazole bridged iron(II) centers that are found to be [high spin-high spin] at all temperatures, 4-300 K, and to exhibit weak antiferromagnetic coupling. In the analogous monometallic complexes, [Fe(II)(Rdpt)2(X)2](n+), the spin state of the iron(II) center was controlled by appropriate selection of the axial ligands X. Specifically, both of the chloride complexes, [Fe(II)(adpt)2(Cl)2] x 2 MeOH and [Fe(II)(pldpt)2(Cl)2] x 2 MeOH x H2O, were found to be high spin whereas the pyridine adduct [Fe(II)(adpt)2(py)2](BF4)2 was low spin. Attempts to prepare [Fe(II)(pldpt)2(py)2](BF4)2 and the dinuclear analogues [Fe(II)2(Rdpt)2(py)4](BF4)4 failed, illustrating the significant challenges faced in attempts to develop control over the nature of the product obtained from reactions of iron(II) and these bis-bidentate ligands.     

Rhodium complexes with the chelating and binucleating ligands P(CH2CH2Py)nPh3-n (Py = 2-pyridyl; n = 1,2): structures and fluxional behavior

Several rhodium(I) complexes of the type [RhX(CO)(PePy2)], [Rh(diene)(PePy)]+, and [Rh(diene)(PePy2)]+ (PePyn = P(CH2CH2Py)nPh3-n; Py = 2-pyridyl; n = 1, 2) have been prepared. The two former are square planar; the latter are pentacoordinated for diene = tetrafluorobenzobarrelene or norbornadiene (confirmed by X-ray diffraction), but an equilibrium of 4- and 5-coordinate isomers exists in solution for diene = 1,5-cyclooctadiene. The fluxional behavior of all these complexes is studied by NMR spectroscopy. The complex [Rh(NBD)(PePy2)]PF6.Cl2CH2 crystallizes in the monoclinic space group P21/n with a = 8.455(1) A, b = 18.068(3) A, c = 19.729(3) A, beta = 99.658(3)degrees, and Z = 4. The complexes [Rh(diene)(PePy2)]+ react with CO to give the dimeric complex [Rh2(CO)2[P(CH2CH2Py)2Ph]2](BF4)2 with the pyridylphosphine acting as P,N-chelating and P,N-bridging.     

Structural flexibility and role of vicinal 2-thienyl rings in 2,3-dicyano-5,6-di(2-thienyl)-1,4-pyrazine, [(CN)2Th2Pyz], its palladium(II) complex [(CN)2Th2Pyz(PdCl2)2], and the related pentametallic pyrazinoporphyrazines [(PdCl2)4Th8TPyzPzM] (M = Mg(II)(H2O), Zn(II))

The solid state and solution structure of 2,3-dicyano-5,6-di(2-thienyl)-1,4-pyrazine, [(CN)(2)Th(2)Pyz], and its Pd(II) derivative, [(CN)(2)Th(2)Pyz(PdCl(2))(2)]·H(2)O, formed by reaction of [(CN)(2)Th(2)Pyz] with [(C(6)H(5)CN)(2)PdCl(2)] were characterized by X-ray, UV-visible, (1)H and (13)C NMR, and extended X-ray absorption fine structure (EXAFS) spectral measurements. The X-ray crystal structure of [(CN)(2)Th(2)Pyz] shows the presence of one thienyl ring positioned orthogonal to the rest of the molecule, with the two vicinal thienyl rings lying orthogonal to each other in a rare arrangement. NMR studies of [(CN)(2)Th(2)Pyz] in the solid state and in solutions of dimethylformamide or dimethyl sulfoxide confirm a nonequivalence of the thienyl rings in the solid state and also in solution. EXAFS results indicate that two distinct Pd(II) coordination sites are formed at the di(2-thienyl)pyrazino moiety of [(CN)(2)Th(2)Pyz(PdCl(2))(2)]·H(2)O, with identical Pd-N(pyz) (2.03(3) ?) and Pd-Cl (2.36(3) ?) bond lengths but with different Pd-S1 (2.25(4) ?) and Pd-S2 (3.21(5) ?) bond distances in an overall asymmetric molecular framework. Density functional theory (DFT) and time-dependent DFT (TDDFT) theoretical studies also provide information about the structure and spectral behavior of the precursor and its metalated Pd(II) derivative. (1)H/(13)C NMR and UV-visible spectral measurements were also carried out on two heteropentametallic porphyrazine macrocycles which were prepared by a reaction of PdCl(2) with [Th(8)TPyzPzM] where Th(8)TPyzPz = tetrakis-2,3-[5,6-di-(2-thienyl)-pyrazino]porphyrazinato dianion and M = Mg(II)(H(2)O) or Zn(II). Spectroscopic data on the newly synthesized [(PdCl(2))(4)Th(8)TPyzPzM] compounds suggest that the binding of PdCl(2) involves coordination sites of the type S(2(th))PdCl(2) with the two thienyl rings of each di(2-thienyl)pyrazino fragment bound to Pd(II) in an equivalent manner ("th-th" coordination). This is similar to what was found for the corresponding octapyridinated analogues ("py-py" coordination).     

Equilibrium of low- and high-spin states of Ni(II) complexes controlled by the donor ability of the bidentate ligands

Low-spin nickel(II) complexes containing bidentate ligands with modulated nitrogen donor ability, Py(Bz)2 or MePy(Bz)2 (Py(Bz)2 = N,N-bis(benzyl)-N-[(2-pyridyl)methyl]amine, MePy(Bz)2 = N,N-bis(benzyl)-N-[(6-methyl-2-pyridyl)methyl]amine), and a beta-diketonate derivative, tBuacacH (tBuacacH = 2,2,6,6-tetramethyl-3,5-heptanedione), represented as [Ni(Py(Bz)2)(tBuacac)](PF6) (1) and [Ni(MePy(Bz)2)(tBuacac)](PF6) (2) have been synthesized. In addition, the corresponding high-spin nickel(II) complexes having a nitrate ion, [Ni(Py(Bz)2)(tBuacac)(NO3)] (3) and [Ni(MePy(Bz)2)(tBuacac)(NO3)] (4), have also been synthesized for comparison. Complexes 1 and 2 have tetracoordinate low-spin square-planar structures, whereas the coordination environment of the nickel ion in 4 is a hexacoordinate high-spin octahedral geometry. The absorption spectra of low-spin complexes 1 and 2 in a noncoordinating solvent, dichloromethane (CH2Cl2), display the characteristic absorption bands at 500 and 540 nm, respectively. On the other hand, the spectra of a CH2Cl2 solution of high-spin complexes 3 and 4 exhibit the absorption bands centered at 610 and 620 nm, respectively. The absorption spectra of 1 and 2 in N,N-dimethylformamide (DMF), being a coordinating solvent, are quite different from those in CH2Cl2, which are nearly the same as those of 3 and 4 in CH2Cl2. This result indicates that the structures of 1 and 2 are converted from a low-spin square-planar to a high-spin octahedral configuration by the coordination of two DMF molecules to the nickel ion. Moreover, complex 1 shows thermochromic behavior resulting from the equilibrium between low-spin square-planar and high-spin octahedral structures in acetone, while complex 2 exists only as a high-spin octahedral configuration in acetone at any temperature. Such drastic differences in the binding constants and thermochromic properties can be ascribed to the enhancement of the acidity of the nickel ion of 2 by the steric effect of the o-methyl group in the MePy(Bz)2 ligand in 2, which weakens the Ni-N(pyridine) bond length compared with that of the nonsubstituted Py(Bz)2 ligand in 1.     

Tetra-2,3-pyrazinoporphyrazines with externally appended thienyl rings: synthesis, UV-visible spectra, electrochemical behavior, and photoactivity for the generation of singlet oxygen

A series of pyrazinoporphyrazine macrocycles carrying externally appended 2-thienyl rings, represented as [Th(8)TPyzPzM], where Th(8)TPyzPz = tetrakis-2,3-[5,6-di(2-thienyl)pyrazino]porphyrazinato anion and M = Mg(II)(H(2)O), Zn(II), Co(II), Cu(II), or 2H(1), were prepared and isolated as solid air-stable hydrated species. All of the compounds, completely insoluble in water, were characterized by their UV-visible spectra and electrochemical behavior in solutions of dimethylformamide (DMF), dimethyl sulfoxide, and pyridine. Molecular aggregation occurs at concentrations of ca. 10(-4) M, but monomers are formed in more dilute solutions of 10(-5) M or less. The examined octathienyl compounds [Th(8)TPyzPzM] behave as electron-deficient macrocycles, and UV-visible spectral measurements provide useful information about how the peripheral thienyl rings influence the electronic distribution over the entire macrocyclic framework. Cyclic voltammetric and spectroelectrochemical data confirm the easier reducibility of the compounds as compared to the related phthalocyanine analogues, and the overall redox behavior and thermodynamic potentials for the four stepwise one-electron reductions of the compounds are similar to those of the earlier examined octapyridinated analogues [Py(8)TPyzPzM]. Quantum yields (Φ(Δ)) for the generation of singlet oxygen, (1)O(2), the cytotoxic agent active in photodynamic therapy (PDT), and fluorescence quantum yields (Φ(F)) were measured for the Zn(II) and Mg(II) complexes, [Th(8)TPyzPzZn] and [Th(8)TPyzPzMg(H(2)O)], and the data were compared to those of corresponding octapyridino macrocycles [Py(8)TPyzPzZn] and [Py(8)TPyzPzMg(H(2)O)] and their related octacations [(2-Mepy)(8)TPyzPzZn](8+) and [(2-Mepy)(8)TPyzPzMg(H(2)O)](8+). These measurements were carried out in DMF and in DMF preacidified with HCl (ca. 10(-4) M). All of the examined Zn(II) compounds behave as excellent photosensitizers (Φ(Δ) = 0.4-0.6) both in DMF and DMF/HCl solutions, whereas noticeable fluorescence activity (Φ(F) = 0.36-0.43) in DMF/HCl solutions is shown by the Mg(II) derivatives; these data might provide perspectives for applications in PDT (Zn(II)) and imaging response and diagnosis (Mg(II)).     

electrochemical generation of a nonheme oxoiron(IV) complex

The complex [Fe(IV)O(N4Py)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) has been prepared by bulk electrolysis in aqueous CH3CN and CH2Cl2, and its redox properties characterized. Bulk chronocoulometry and spectropotentiometry experiments in CH3CN show that [Fe(II)(N4Py)(NCCH3)]2+ can be oxidized quantitatively to its iron(III) derivative at an applied potential of +0.71 V vs ferrocene and then to the oxoiron(IV) complex (in the presence of added water) at potentials above +1.3 V. The E1/2 value for the Fe(IV/III) couple has been estimated to be +0.90 V from spectropotentiometric titrations in CH3CN and cyclic voltammetric measurements in CH2Cl2.     

Self-assembly of a cyclic metalladecapyridine from the reaction of 2,6-bis(bis(2-pyridyl)methoxymethane)pyridine with silver(I)

Reaction of Ag( p-MeC 6H 4SO 3) with 2,6-bis(bis(2-pyridyl)methoxymethane)pyridine (PY5) in CH 2Cl 2 gave [Ag (I) 2(PY5) 2](p-MeC 6H 4SO 3) 2 (1). Treatment of 2,6-bis(bis(2-pyridyl)hydroxymethane)pyridine (PY5-OH) with AgNO 3 in MeOH gave [Ag (I) 2(PY5-OH) 2](NO3) 2 (2); in the presence of PPh 3, this reaction afforded [Ag (I)(PY5-OH)(PPh 3)]NO 3 (3). The structures of 1- 3 have been determined by X-ray crystal analysis, revealing four-coordinate Ag (I) ions in these complexes. Both 1 and 2 feature a quadruply branched 28-membered C 16N 10M 2 metallamacrocycle fused to 10 pyridyl groups. On the basis of (1)H NMR measurements, the dinuclear 1 and 2 dissociate into a mononuclear complex upon dissolving in MeCN but in MeOH an equilibrium between the mono- and dinuclear species can be detected.     

Synthesis and properties of rhodium(III) porphyrin cyclic tetramer and cofacial dimer

Rhodium(III) porphyrin complexes, [Rh(4-PyT(3)P)Cl](4) (1) and [Rh(2-PytB(3)P)Cl](2) (2) (4-PyT(3)P = 5-(4-pyridyl)-10,15,20-tritolylporphyrinato dianion, 2-PytB(3)P = 5-(2-pyridyl)-10,15,20-tri(4-tert-butyl)phenylporphyrinato dianion), were self-assembled and characterized by (1)H nuclear magnetic resonance spectroscopy, infrared spectroscopy, and electron spray ionization-mass spectroscopy methods. The spectroscopic results certified that the rhodium porphyrin complexes 1 and 2 have a cyclic tetrameric structure and a cofacial dimeric structure, respectively. The X-ray structure analysis of 1 confirmed the cyclic structure of the complex. The Soret bands of both oligomers were significantly broadened by excitonic interactions between the porphyrin units, compared to those observed for a corresponding analogue of Rh(TTP)(Py)Cl (TTP = 5,10,15,20-tetratolylporphyrinato dianion, Py = pyridine). Stepwise oxidation of the porphyrin rings in the oligomers was observed by cyclic voltammetry. The oligomers 1 and 2 are very stable in solution, and they slowly undergo reactions with pyridine to give corresponding monomer complexes only at high temperatures (approximately 80 degrees C).     

Stoichiometric reactions of methylparathion with a palladium aryl oxime metallacycle

The reaction of [Pd(3)(OAc)(6)] with (E)-acetophenone oxime and pyridine in CHCl(3) under reflux affords the metallacycle [Pd(OAc)[C,N-(C(6)H(4)C(CH(3))=NOH)-2](py)] (1) as a yellow air-stable complex. The same reaction carried out at room temperature in the absence of pyridine affords the trinuclear oximato complex [Pd(mu-(E)-ON=C(CH(3))Ph)(mu-OAc)](3) (2), which can be converted into 1 upon heating in the presence of pyridine. As indicated by (1)H and (31)P NMR spectroscopy, complex 1 reacts with methylparathion in acetone-d(6)-D(2)O solutions to afford [Pd(SP(=O)(OCH(3))(2))[C,N-(C(6)H(4)C(CH(3))=NOH)-2](py)] (3) and [Pd(mu-SP(=O)(OCH(3))(2))[C,N-(C(6)H(4)C(CH(3))=NOH)-2]](2) (4) as well as free p-nitrophenol. Compounds 1-4 have been characterized by single-crystal X-ray analysis, NMR and EA. Compounds 1 and 3 are mononuclear complexes with the acetate and dimethylthiophosphate ligand, respectively, trans from the phenyl group. Compound 2 is a trinuclear complex whose structure can be derived from that of [Pd(3)(OAc)(6)] by replacing three of the acetate ligands on one side of Pd(3) plane by three N,O-coordinated oximate ligands. Complex 4 is a dinuclear complex in which the two square-planar palladium moieties are linked by the sulfur atoms of the bridging dimethylthiophosphate ligands.     

Pd2L2 metallacycles as molecular containers for small molecules

M(2)L(2) type metallacyclic complexes, [Pd(2)(L1)(2)Cl(4)]·1.5CH(2)Cl(2) (1), [Pd(2)(L1)(2)Cl(4)]·2CHCl(3) (2), [Pd(2)(L2)(2)Cl(4)]·2CH(2)Cl(2)·2CH(3)CN (3), [Pd(2)(L2)(2)Cl(4)]·2CHCl(3)·2CH(3)CN (4) and [Pd(2)(L3)(2)Cl(4)]·CH(2)Cl(2)·2CH(3)CN (5), have been prepared from three semi-rigid benzimidazol or benzotriazol ligands, 1,4-bis(benzimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene (L1), 1,4-bis(5,6-dimethylbenzimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene (L2) and 1,4-bis(benzotriazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene (L3). All the complexes were structurally characterized by single-crystal X-ray diffraction and the phase purity was confirmed by powder X-ray diffraction (PXRD) measurements. The solution structure of representative complex 1 was studied by (1)H NMR titration and ESI mass spectroscopy. The thermal stability and guest-exchange properties of 1, 3 and 4 were investigated, revealing that the Pd(2)L(2) metallacycles can act as a selective receptor for CH(2)Cl(2) or CHCl(3) guest molecules. The catalytic activity of 1 in Suzuki-Miyaura coupling reaction was also studied and 1 could be recycled at least 5 times under heterogeneous conditions, indicative of a potential self-supported catalyst.     

Reversible and irreversible vapor-induced guest molecule exchange in spin-crossover compounds

Spin-crossover (SCO) complex [Fe(tpa)(NCS)(2)] (tpa = tri(2-pyridylmethyl)amine) crystallized in two solvate forms, yellow [Fe(tpa)(NCS)(2)]·X [Fe:X = 1:1; X = n-PrOH (complex is named as n-PrOH), i-PrOH (i-PrOH), CH(2)Cl(2) (CH(2)Cl(2)), CHCl(3) (CHCl(3)), MeCN (MeCN)] and red [Fe(tpa)(NCS)(2)](2)·Y [Fe:Y = 2:1; Y = MeOH (MeOH), EtOH (EtOH)], respectively. Between the two forms, interesting solvent-vapor induced in situ reversible and irreversible guest molecule exchanges, [Fe(tpa)(NCS)(2)]·X ? [Fe(tpa)(NCS)(2)](2)·Y, occurred in the solid state followed by dramatic color changes as well as distinct structural and SCO behavior transformations. Comprehensive studies on structures and SCO behaviors associating guest exchanges have been conducted by X-ray single-crystal diffraction, PXRD, IR, elemental analysis, and magnetic measurements, respectively. This discrete molecular system shows unique solvent-dependent SCO behavior related to the nature of solvent molecules; the distinct color changes during guest exchange originate from the alternations of electronic states of the guest-sensitive Fe(II) centers, providing an effective route to fine-tune and optimize materials' properties by systematic structural perturbation, or serving for detection of toxic gases, such as CH(2)Cl(2) and CHCl(3).     

Complexation of molybdenum(V) with glycolic acid: an unusual orientation of glycolato ligand in {Mo2O4}2+ complexes

(PyH)5[Mo(V)OCl4(H2O)]3Cl2 and (PyH)n[Mo(V)OBr4]n reacted with glycolic acid (H2glyc) or its half-neutralized ion (Hglyc(-)) to afford a series of novel glycolato complexes based on the {Mo(V)2O4}2+ structural core: (PyH)3[Mo2O4Cl4(Hglyc)]. (1)/ 2CH 3CN (1), (PyH) 3[Mo 2O 4Br 4(Hglyc)].Pr(i)OH(2), (PyH)2[Mo2O4(glyc) 2Py 2] (3), (PyH) 4[Mo 4O 8Cl 4(glyc) 2].2EtOH (4), and [Mo 4O 8(glyc) 2Py 4] (5) (Py = pyridine, C 5H 5N; PyH(+) = pyridinium cation, C 5H 5NH (+) and glyc (2-) = a doubly ionized glycolate, (-)OCH 2COO (-)). The compounds were fully characterized by X-ray crystallography and infrared spectroscopy. The Hglyc (-) ion binds to the {Mo 2O 4} (2+) core through a carboxylate end in a bidentate bridging manner, whereas the glyc (2-) ion adopts a chelating bidentate coordination through a deprotonated hydroxyl group and a monodentate carboxylate. The orientations of glyc (2-) ions in 3- 5 are such that the alkoxyl oxygen atoms occupy the sites opposite the multiply bonded oxides. {(C6H5) 4P}[Mo(VI)O 2(glyc)(Hglyc)] ( 6), an oxidized complex, features a reversed orientation of the glyc(2-) ion. The theoretical DFT calculations on the [Mo(V)2O4(glyc) 2Py 2](2-) and [Mo(VI)O2(glyc)2](2-) ions confirm that binding of glycolate with the alkoxyl oxygen to the site opposite the MoO bond is energetically more favorable in {Mo(V)2O4}(2+) species, whereas a reversed orientation of the ligand is preferred in Mo(VI) complexes. An explanation based on the orbital analysis is put forward.     

Single-molecule magnets: a new family of Mn(12) clusters of formula [Mn(12)O(8)X(4)(O(2)CPh)(8)L(6)

The reaction of (NBu(n)(4))[Mn(8)O(6)Cl(6)(O(2)CPh)(7)(H(2)O)(2)] (1) with 2-(hydroxymethyl)pyridine (hmpH) or 2-(hydroxyethyl)pyridine (hepH) gives the Mn(II)(2)Mn(III)(10) title compounds [Mn(12)O(8)Cl(4)(O(2)CPh)(8)(hmp)(6)] (2) and [Mn(12)O(8)Cl(4)(O(2)CPh)(8)(hep)(6)] (3), respectively, with X = Cl. Subsequent reaction of 3 with HBr affords the Br(-) analogue [Mn(12)O(8)Br(4)(O(2)CPh)(8)(hep)(6)] (4). Complexes 2.2Et(2)O.4CH(2)Cl(2), 3.7CH(2)Cl(2), and 4.2Et(2)O.1.4CH(2)Cl(2) crystallize in the triclinic space group P1, monoclinic space group C2/c, and tetragonal space group I4(1)/a, respectively. Complexes 2 and 3 represent a new structural type, possessing isomeric [Mn(III)(10)Mn(II)(2)O(16)Cl(2)] cores but with differing peripheral ligation. Complex 4 is essentially isostructural with 3. A magnetochemical investigation of complex 2 reveals an S = 6 or 7 ground state and frequency-dependent out-of-phase signals in ac susceptibility studies that establish it as a new class of single-molecule magnet. These signals occur at temperatures higher than those observed for all previously reported single-molecule magnets that are not derived from [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(x)]. A detailed investigation of forms of complex 2 with different solvation levels reveals that the magnetic properties of 2 are extremely sensitive to the latter, emphasizing the importance to the single-molecule magnet properties of interstitial solvent molecules in the samples. In contrast, complexes 3 and 4 are low-spin molecules with an S = 0 ground state.     

Interaction of carbene and olefin donors with [Cl2PN]3: exploration of a reductive pathway toward (PN)3

The iminophosphine-phosphazene [P(III)-P(V)] heterocyclic adduct [IPr·PN(PCl(2)N)(2)] was prepared via reduction of the cyclic phosphazene [Cl(2)PN](3) in the presence of the carbene donor IPr {IPr = [(HCNDipp)(2)C:], where Dipp = 2,6-(i)Pr(2)C(6)H(3)}. By contrast, the treatment of [Cl(2)PN](3) with the N-heterocyclic olefin IPr═CH(2) yielded the olefin-grafted phosphazene ring [(IPr═CH)P(Cl)N(PCl(2)N)(2)].     

Structural and magnetic resolution of a two-step full spin-crossover transition in a dinuclear iron(II) pyridyl-bridged compound

A dinuclear iron(II) complex containing the new pyridyl bridging ligand, 2,5-di(2',2'-dipyridylamino)pyridine (ddpp) has been synthesised and characterised by single-crystal X-ray diffraction, magnetic susceptibility and M?ssbauer spectral methods. This compound, [Fe(2)(ddpp)(2)(NCS)(4)]4 CH(2)Cl(2), undergoes a two-step full spin crossover. Structural analysis at each of the three plateau temperatures has revealed a dinuclear molecule with spin states HS-HS, HS-LS and LS-LS (HS: high spin, LS: low spin) for the two iron(II) centres. This is the first time that resolution of the metal centres in a HS-LS ordered state has been achieved in a two-step dinuclear iron(II) spin-crossover compound. Thermogravimetric data show that the dichloromethane solvate molecules can be removed in two distinct steps at 120 degrees C and 200 degrees C. The partially de-solvated clathrate, [Fe(2)(ddpp)(2)(NCS)(4)]CH(2)Cl(2), undergoes a one-step transition with an increased transition temperature with respect to the as synthesised material. Structural characterisation of this material reveals subtle changes to the coordination geometries at each of the iron(II) centres and striking changes to the local environment of the dinuclear complex. The fully de-solvated material remains high spin over all temperatures. Interestingly, the solvent can be re-introduced into the monosolvated solid to achieve complete conversion back to the original two-step crossover material, [Fe(2)(ddpp)(2)(NCS)(4)]4 CH(2)Cl(2).