Experimental and theoretical electron density distribution and magnetic properties of the butterfly-like complex [Fe(4)O(2)(O(2)CCMe(3))(8)(NC(5)H(4)Me)(2)].2CH(3)CN

The structure and electron density distribution (EDD) of the carboxylate-bridge iron complex [Fe(III)(4)(micro(3)-O)(2)(O(2)CCMe(3))(8)(NC(5)H(4)Me)(2)].2CH(3)CN, 1, has been determined from synchrotron X-ray diffraction data (R(int) = 0.025) collected with the crystal cooled to 16(5) K. At this temperature complex 1 crystallized in the triclinic space group P with cell parameters a = 12.6926(7) A, b = 12.9134(8) A, c = 13.4732(8) A, alpha = 115.372(2) degrees, beta = 107.702(3) degrees, and gamma = 102.731(2) degrees. The theoretical EDD determined from a density functional theory (DFT) single point calculation of an entire molecule of 1 at the experimental geometry has been analyzed and compared to the experimental EDD. The latter is expressed in the framework of a multipolar model with parameters determined by least-squares refinement (R(w)(F(2)) = 0.024) based on the X-ray diffraction data. The central micro(3)-oxygen atom in 1 is significantly out of the plane spanned by the three Fe atoms coordinated to this oxygen. Comparison of measures for the bonding geometry around the iron atoms in 1 with the corresponding values for the iron atoms in relevant trinuclear complexes suggests that there are significant differences in the Fe-(micro(3)-O) bonds in the two cases. Analyses of both the experimental and theoretical EDDs reveal very significant differences between the two Fe-(micro(3)-O) bonds in 1, with one bond being much more directed and stronger than the other bond. A topological analysis of the EDDs using the atoms in molecules approach also reveals very distinct differences between the properties of the two Fe(III) atoms. A clear exponential relationship is found between the Laplacian of the experimental density at the bond critical points in the Fe-ligand bonds and their bond lengths. M?ssbauer spectroscopy of 1 shows two easily separable doublets corresponding to the two different iron sites. Magnetic susceptibility measurements between 4.2 and 300 K indicate antiferromagnetically coupled Fe(III) atoms constituting an S = 0 ground state.     

Iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin

The iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin (OTPP)H have been investigated. Insertion of iron(II) followed by one-electron oxidation yielded a high-spin, six-coordinate (OTPP)Fe(III)Cl(2) complex. The reduction of (OTPP)Fe(III)Cl(2) has been accomplished by means of moderate reducing reagents producing high-spin five-coordinate (OTPP)Fe(II)Cl. The molecular structure of (OTPP)Fe(III)Cl(2) has been determined by X-ray diffraction. The iron(III) 21-oxaporphyrin skeleton is essentially planar. The furan ring coordinates in the eta(1) fashion through the oxygen atom, which acquires trigonal geometry. The iron(III) apically coordinates two chloride ligands. Addition of potassium cyanide to a solution of (OTPP)Fe(III)Cl(2) in methanol-d(4) results in its conversion to a six-coordinate, low-spin complex [OTPP)Fe(III)(CN)(2)] which is spontaneously reduced to [OTPP)Fe(II)(CN)(2)](-) by excess cyanide. The spectroscopic features of [OTPP)Fe(III)(CN)(2)] correspond to the common low-spin iron(III) porphyrin (d(xy))(2)(d(xz)d(yz))(3) electronic configuration. Titration of (OTPP)Fe(III)Cl(2) or (OTPP)Fe(II)Cl with n-BuLi (toluene-d(8), 205 K) resulted in the formation of (OTPP)Fe(II)(CH(2)CH(2)CH(2)CH(3)). (OTPP)Fe(II)(n-Bu) decomposes via homolytic cleavage of the iron-carbon bond to produce (OTPP)Fe(I). The EPR spectrum (toluene-d(8), 77 K) is consistent with a (d(xy))(2)(d(xz))(2)(d(yz))(2)(d(z)(2)(1)(d[(x)(2)-(y)(2)])(0) ground electronic state of iron(I) oxaporphyrin (g(1) = 2.234, g(2) = 2.032, g(3) = 1.990). The (1)H NMR spectra of (OTPP)Fe(III)Cl(2), (OTPP)Fe(III)(CN)(2), ([(OTPP)Fe(III))](2)O)(2+), and (OTPP)Fe(II)Cl have been analyzed. There are considerable similarities in (1)H NMR properties within each iron(n) oxaporphyrin-iron(n) regular porphyrin or N-methylporphyrin pair (n = 2, 3). Contrary to this observation, the pattern of downfield positions of pyrrole resonances at 156.2, 126.5, 76.3 ppm and furan resonance at 161.4 ppm (273 K) detected for the two-electron reduction product of (OTPP)Fe(III)Cl(2) is unprecedented in the group of iron(I) porphyrins.     

Benzoannelation stabilizes the d(xy)1 state of low-spin iron(III) porphyrinates

A series of low-spin, six-coordinate complexes [Fe(TBzTArP)L(2)]X (1) and [Fe(TBuTArP)L(2)]X (2) (X = Cl(-), BF(4)(-), or Bu(4)N(+)), where the axial ligands (L) are HIm, 1-MeIm, DMAP, 4-MeOPy, 4-MePy, Py, and CN(-), were prepared. The electronic structures of these complexes were examined by (1)H NMR and electron paramagnetic resonance (EPR) spectroscopy as well as density functional theory (DFT) calculations. In spite of the fact that almost all of the bis(HIm), bis(1-MeIm), and bis(DMAP) complexes reported previously (including 2) adopt the (d(xy))(2)(d(xz), d(yz))(3) ground state, the corresponding complexes of 1 show the (d(xz), d(yz))(4)(d(xy))(1) ground state at ambient temperature. At lower temperature, the electronic ground state of the HIm, 1-MeIm, and DMAP complexes of 1 changes to the common (d(xy))(2)(d(xz), d(yz))(3) ground state. All of the other complexes of 1 and 2 carrying 4-MeOPy, 4-MePy, Py, and CN(-) maintain the (d(xz), d(yz))(4)(d(xy))(1) ground state in the NMR temperature range, i.e., 298-173 K. The EPR spectra taken at 4.2 K are fully consistent with the NMR results because the HIm and 1-MeIm complexes of 1 and 2 adopt the (d(xy))(2)(d(xz), d(yz))(3) ground state, as revealed by the rhombic-type spectra. The DMAP complex of 1 exists as a mixture of two electron-configurational isomers. All of the other complexes adopt the (d(xz), d(yz))(4)(d(xy))(1) ground state, as revealed by the axial-type spectra. Among the complexes adopting the (d(xz), d(yz))(4)(d(xy))(1) ground state, the energy gap between the d(xy) and d(π) orbitals in 1 is always larger than that of the corresponding complex of 2. Thus, it is clear that the benzoannelation of the porphyrin ring stabilizes the (d(xz), d(yz))(4)(d(xy))(1) ground state. The DFT calculation of the bis(Py) complex of analogous iron(III) porphyrinate, [Fe(TPTBzP)(Py)(2)](+), suggests that the (d(xz), d(yz))(4)(d(xy))(1) state is more stable than the (d(xy))(2)(d(xz), d(yz))(3) state in both ruffled and saddled conformations. The lowest-energy states in the two conformers are so close in energy that their ordering is reversed depending on the calculation methods applied. On the basis of the spectroscopic and theoretical results, we concluded that 1, having 4-MeOPy, 4-MePy, and Py as axial ligands, exists as an equilibrium mixture of saddled and ruffled isomers both of which adopt the (d(xz), d(yz))(4)(d(xy))(1) ground state. The stability of the (d(xz), d(yz))(4)(d(xy))(1) ground state is ascribed to the strong bonding interaction between the iron d(xy) and porphyrin a(1u) orbitals in the saddled conformer caused by the high energy of the a(1u) highest occupied molecular orbital in TBzTArP. Similarly, a bonding interaction occurs between the d(xy) and a(2u) orbitals in the ruffled conformer. In addition, the bonding interaction of the d(π) orbitals with the low-lying lowest unoccupied molecular orbital, which is an inherent characteristic of TBzTArP, can also contribute to stabilization of the (d(xz), d(yz))(4)(d(xy))(1) ground state.     

Electronic structure of six-coordinate iron(III) monoazaporphyrins

The electronic structures of six-coordinate iron(III) octaethylmonoazaporphyrins, [Fe(MAzP)L 2] (+/-) ( 1), have been examined by means of (1)H NMR and EPR spectroscopy to reveal the effect of meso-nitrogen in the porphyrin ring. The complexes carrying axial ligands with strong field strengths such as 1-MeIm, DMAP, CN (-), and (t)BuNC adopt the low-spin state with the (d xy ) (2)(d xz , d yz ) (3) ground state in a wide temperature range where the (1)H NMR and EPR spectra are taken. In contrast, the complexes with much weaker axial ligands, such as 4-CNPy and 3,5-Cl 2Py, exhibit the spin transition from the mainly S = 3/2 at 298 K to the S = 1/2 with the (d xy ) (2)(d xz , d yz ) (3) ground state at 4 K. Only the THF complex has maintained the S = 3/2 throughout the temperature range examined. Thus, the electronic structures of 1 resemble those of the corresponding iron(III) octaethylporphyrins, [Fe(OEP)L 2] (+/-) ( 2). A couple of differences have been observed, however, in the electronic structures of 1 and 2. One of the differences is the electronic ground state in low-spin bis( (t)BuNC) complexes. While [Fe(OEP)( (t)BuNC) 2] (+) adopts the (d xz , d yz ) (4)(d xy ) (1) ground state, like most of the bis( (t)BuNC) complexes reported previously, [Fe(MAzP)( (t)BuNC) 2] (+) has shown the (d xy ) (2)(d xz , d yz ) (3) ground state. Another difference is the spin state of the bis(3,5-Cl 2Py) complexes. While [Fe(OEP)(3,5-Cl 2Py) 2] (+) has maintained the mixed S = 3/2 and 5/2 spin state from 298 to 4 K, [Fe(MAzP)(3,5-Cl 2Py) 2] (+) has shown the spin transition mentioned above. These differences have been ascribed to the narrower N4 cavity and the presence of lower-lying pi* orbital in MAzP as compared with OEP.     

镧系四元混合配体配合物[Ce(CH2ClCOO)2(NO3)(phen)(H2O)]2的晶体结构、芳环堆积效应和2D氢键网络

The quaternary complex, ［Ce(CH2ClCOO)2(NO3)(phen)(H2O)］2, was synthesized. Interestedly, the title compound is a dimer comparing with the 1D polymer ［La(CH2ClCOO)2(NO3)(phen)*(H2O)］n and powder compound ［Nd(CH2ClCOO)2(NO3)(phen)］. In the title compound there is a monodentate NO-3, which is a first example in the all synthesized quaternary mixed anion complexes, and the NO-3 extended the complex into a 2D network with water from other molecules by inter-molecular hydrogen bonds. The intermolecular hydrogen bonds lead to the weaker Ce—O(COO), Ce—O(NO3) and Ce—N bonds comparing with other quaternary mixed anion complexes of cerium. Also the stacking effect, which makes the compound more stable in the situation of weaker Ce—O and Ce—N bonds, was first found in the series compounds.     

Electronic structure of highly ruffled low-spin iron(III) porphyrinates with electron withdrawing heptafluoropropyl groups at the meso positions

Bis(pyridine)[meso-tetrakis(heptafluoropropyl)porphyrinato]iron(III), [Fe(THFPrP)Py(2)](+), was reported to be the low-spin complex that adopts the purest (d(xz), d(yz))(4)(d(xy))(1) ground state where the energy gap between the iron d(xy) and d(π)(d(xz), d(yz)) orbitals is larger than the corresponding energy gaps of any other complexes reported previously (Moore, K. T.; Fletcher, J. T.; Therien, M. J. J. Am. Chem. Soc. 1999, 121, 5196-5209). Although the highly ruffled porphyrin core expected for this complex contributes to the stabilization of the (d(xz), d(yz))(4)(d(xy))(1) ground state, the strongly electron withdrawing C(3)F(7) groups at the meso positions should stabilize the (d(xy))(2)(d(xz), d(yz))(3) ground state. Thus, we have reexamined the electronic structure of [Fe(THFPrP)Py(2)](+) by means of (1)H NMR, (19)F NMR, and electron paramagnetic resonance (EPR) spectroscopy. The CD(2)Cl(2) solution of [Fe(THFPrP)Py(2)](+) shows the pyrrole-H signal at -10.25 ppm (298 K) in (1)H NMR, the CF(2)(α) signal at -74.6 ppm (298 K) in (19)F NMR, and the large g(max) type signal at g = 3.16 (4.2 K) in the EPR. Thus, contrary to the previous report, the complex is unambiguously shown to adopt the (d(xy))(2)(d(xz), d(yz))(3) ground state. Comparison of the spectroscopic data of a series of [Fe(THFPrP)L(2)](+) with those of the corresponding meso-tetrapropylporphyrin complexes [Fe(TPrP)L(2)](+) with various axial ligands (L) has shown that the meso-C(3)F(7) groups stabilize the (d(xy))(2)(d(xz), d(yz))(3) ground state. Therefore, it is clear that the less common (d(xz), d(yz))(4)(d(xy))(1) ground state can be stabilized by the three major factors: (i) axial ligand with low-lying π* orbitals, (ii) ruffled porphyrin ring, and (iii) electron donating substituent at the meso position.     

Catalytic performance of ZnFe2O4 nanoparticles prepared from the [ZnFe2O(CH3COO)6(H2O)3]·2H2O complex under microwave irradiation

Research on Chemical Intermediates - Using the heterometallic oxo-centered trinuclear [ZnFe2O(CH3COO)6(H2O)3]·2H2O complex as a novel precursor, pure and single-phase ZnFe2O4 nanostructure was...     

mer-[Fe(pcq)(CN)3]-: a novel cyanide-containing building block and its application to assembling cyanide-bridged trinuclear FeIII2MnII complexes [pcq- = 8-(pyridine-2-carboxamido)quinoline anion

A new cyanide-containing building block K[Fe(pcq)(CN)(3)] [1; pcq(-) = 8-(pyridine-2-carboxamido)quinoline anion] containing a low-spin Fe(III) center with three cyanide groups in a meridional arrangement has been successfully designed and synthesized. Three cyanide-bridged trinuclear Fe(III)(2)Mn(II) complexes, [Fe(pcq)(CN)(3)](2)[Mn(CH(3)OH)(2)(H(2)O)(2)].2H(2)O (2), [Fe(pcq)(CN)(3)](2)[Mn(bipy)(2)].CH(3)OH.2H(2)O (3), and [Fe(pcq)(CN)(3)](2)[Mn(phen)(2)].CH(3)OH.2H(2)O (4), have been synthesized and structurally characterized. The magnetic susceptibilities of the three heterometallic complexes have been investigated.     

Metal-porphyrin orbital interactions in highly saddled low-spin iron(III) porphyrin complexes

Substituent effects of the meso-aryl (Ar) groups on the 1H and 13C NMR chemical shifts in a series of low-spin highly saddled iron(III) octaethyltetraarylporphyrinates, [Fe(OETArP)L2]+, where axial ligands (L) are imidazole (HIm) and tert-butylisocyanide ((t)BuNC), have been examined to reveal the nature of the interactions between metal and porphyrin orbitals. As for the bis(HIm) complexes, the crystal and molecular structures have been determined by X-ray crystallography. These complexes have shown a nearly pure saddled structure in the crystal, which is further confirmed by the normal-coordinate structural decomposition method. The substituent effects on the CH2 proton as well as meso and CH2 carbon shifts are fairly small in the bis(HIm) complexes. Since these complexes adopt the (d(xy))2(d(xz), d(yz))3 ground state as revealed by the electron paramagnetic resonance (EPR) spectra, the unpaired electron in one of the metal dpi orbitals is delocalized to the porphyrin ring by the interactions with the porphyrin 3e(g)-like orbitals. A fairly small substituent effect is understandable because the 3e(g)-like orbitals have zero coefficients at the meso-carbon atoms. In contrast, a sizable substituent effect is observed when the axial HIm is replaced by (t)BuNC. The Hammett plots exhibit a large negative slope, -220 ppm, for the meso-carbon signals as compared with the corresponding value, +5.4 ppm, in the bis(HIm) complexes. Since the bis((t)BuNC) complexes adopt the (d(xz), d(yz))4(d(xy))1 ground state as revealed by the EPR spectra, the result strongly indicates that the half-filled dxy orbital interacts with the specific porphyrin orbitals that have large coefficients on the meso-carbon atoms. Thus, we have concluded that the major metal-porphyrin orbital interaction in low-spin saddle-shaped complexes with the (d(xz), d(yz))4(d(xy))1 ground state should take place between the d(xy) and a(2u)-like orbital rather than between the dxy and a(1u)-like orbital, though the latter interaction is symmetry-allowed in saddled D(2d) complexes. Fairly weak spin delocalization to the meso-carbon atoms in the complexes with electron-withdrawing groups is then ascribed to the decrease in spin population in the d(xy) orbital due to a smaller energy gap between the d(xy) and dpi orbitals. In fact, the energy levels of the d(xy) and dpi orbitals are completely reversed in the complex carrying a strongly electron-withdrawing substituent, the 3,5-bis(trifluoromethyl)phenyl group, which results in the formation of the low-spin complex with an unprecedented (d(xy))2(d(xz), d(yz))3 ground state despite the coordination of (t)BuNC.     

Electronic structure of iron chlorins: characterization of bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(III)triflate and bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(II)

The synthesis and characterization of the two iron chlorin complexes [Fe(III)(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) and Fe(II)(TPC)[(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2))](2) (2) are reported. The crystal structure of complex 1 has been determined. The X-ray structure shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 2.034(4) A, and to the pyrrole trans to it N(2), 2.012(4) A, are longer than the distances to the two remaining nitrogens [N(1), 1.996(4) A, and N(3), 1.984(4) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole. The (1)H NMR isotropic shifts at 20 degrees C of the different pyrrole protons of 1 varied from -0.8 to -48.3 ppm according to bis-ligated complexes of low-spin ferric chlorins. The EPR spectrum of [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) in solution is rhombic and gives the principal g values g(1) = 2.70, g(2) = 2.33, and g(3) = 1.61 (Sigmag(2) = 15.3). These spectroscopic observations are indicative of a metal-based electron in the d(pi) orbital for the [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) complex with a (d(xy))(2)(d(xz)d(yz))(3) ground state at any temperature. The X-ray structure of the ferrous complex 2 also shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 1.991(5) A, and to the pyrrole trans to it N(2), 2.005(6) A, are slightly different from the distances to the two remaining nitrogens [N(1), 1.988(5) A, and N(3), 2.015(5) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole.     

Quantum chemical characterization of the generation of high-valent oxoruthenium species of Keggin type polyoxometalates: electronic structure and bonding features

High-valent transition-metal-substituted Keggin-type polyoxometalates (POMs) are active and robust oxidation catalyst. The important oxidized intermediates of these POM complexes are very difficult to be characterized by using the experimental method, and thus no detail information is available on such species. In the present paper, density functional theory (DFT) calculations have been carried out to characterize the electronic structures of a series of mono-ruthenium-substituted Keggin-type POMs. We find that the aquaruthenium(II/III/IV) species possess d(xy)(2)d(xz)(2)d(yz)(2), d(xy)(2)d(xz)(2)d(yz)(1), and d(xy)(2)d(xz)(1)d(yz)(1) electronic configuration, respectively, and hydroxyl/oxoruthenium(IV/V/VI) species possess d(xy)(2)d(xz)(1)π*(yz)(1), d(xy)(2)π*(xz)(1)π*(yz)(1), d(xy)(1)π*(xz)(1)π*(yz)(1), and d(xy)(1)π*(xz)(1)π*(yz)(0) electronic configuration, respectively. Mulliken spin population shows that spin density is localized on the ruthenium center in aquaruthenium(II/III/IV) POM complexes, and the RuO(a) unit in hydroxyl/oxoruthenium(IV/V/VI) POM complexes. The O(a) atom has substantial radical character in oxoruthenium(IV/V) species, and the radical character of the O(a) atom are significantly weakened in the oxoruthenium(VI) species. The relevant energy of the important Ru-O(a)π*-antibonding unoccupied orbitals with high RuO(a) compositions of oxoruthenium(IV/V/VI) POM complexes decrease in the order: oxoruthenium(IV) > oxoruthenium(V) > oxoruthenium(VI). The pH-independent multiple reduction energies for Ru(III/II), Ru(V/IV), and Ru(VI/V) couples are calculated, which is in agreement with the experimental data.     

Ionic crystals [M3O(OOCC6H5)6(H2O)3]4[α-SiW12O40] (M = Cr, Fe) as heterogeneous catalysts for pinacol rearrangement

Complexation of trinuclear oxo-centered carboxylates with a silicododecatungstate resulted in the formation of ionic crystals of [M(3)O(OOCC(6)H(5))(6)(H(2)O)(3)](4)[α-SiW(12)O(40)]·nH(2)O·mCH(3)COCH(3) [M = Cr (Ia), Fe (IIa)]. Treatments of Ia and IIa at 373 K in vacuo formed guest-free phases Ib and IIb, respectively. Compounds Ib and IIb heterogeneously catalyzed the pinacol rearrangement to pinacolone with high conversion at 373 K, and the catalysis is suggested to proceed size selectively in the solid bulk.     

Structural and magnetic properties of iron(II) complexes with 1,4,5,8,9,12-hexaazatriphenylene (HAT)

Reactions of Fe(II) salts with the ligand 1,4,5,8,9,12-hexaazatriphenylene (HAT) led to the isolation and characterization of four new compounds: [Fe3(HAT)(H2O)12](SO4)3.3.3H2O (1), [Fe2(HAT)(SO4)(H2O)5](SO4).2H2O.CH3OH (2), [Fe2(HAT)(SO4)(H2O)5](SO4).3H2O (3), and [Fe3Cl5(HAT)(CH3OH)4(H2O)]Cl (4). Compound 1 crystallizes as a trinuclear cluster in which HAT acts as a tris-chelating ligand. Compounds 2 and 3 are two polymorphs of an infinite one-dimensional structure in which the Fe atoms are coordinated to HAT and then connected into the chain through bridging sulfate anions. Compound 4 exhibits a similar chain structure, but with bridging chloride ligands. The magnetic behavior of the new compounds is indicative of weak antiferromagnetic coupling between the Fe(II) centers through the HAT ligand.     

A STUDY ON MULTIPLE CENTER d-p π BOND IN OXO-CENTERED TRINUCLEAR TRANSITION METAL CARBOXYLATE COMPLEXES

<正> The self-empirical SCC-EHMO calculation has been carried out for a series of oxo-centered trinuclear metal carboxylate complexes. The results indicated that the four-center d-p ?π bonds, formed by combination of centered oxygen atom 2p2 orbital with metal atom dxz,dyz orbitals in core M3O or M2M1O (simplified as M3O in the following) ,are of importance for this class complexes. In the opinion of isolobal contrast, these bonds would be similar to four-center p-p π bonds in C(CH2)3 and can be used for explaining some characteristics of these complexes, such as stability, planar configuration of M3O core, chemical reactivity and so on .     

Unusual electronic structure of bis-isocyanide complexes of iron(III) porphyrinoids

A series of isocyanide complexes, [Fe(Porphyrinoid)((t)BuNC)(2)](+), were synthesized and examined for their physicochemical properties. The molecular structure of the bis((t)BuNC) adduct of the iron(III) porphycene (1) and corrphycene (2) adopting the (d(xy))(2)(d(xz), d(yz))(3) ground state were determined for the first time. Furthermore, 1 and 2 showed unusual crossover phenomena between different electron configurations, (d(xy))(2)(d(xz), d(yz))(3) ground state and (d(xz), d(yz))(4)(d(xy))(1) ground state, by the addition of the external stimuli.     

Electronic structures of six-coordinate ferric porphyrin complexes with weak axial ligands: usefulness of 13C NMR chemical shifts

1H NMR, (13)C NMR, and EPR spectra of six-coordinate ferric porphyrin complexes [Fe(Por)L2]ClO4 with different porphyrin structures are presented, where porphyrins (Por) are planar 5,10,15,20-tetraphenylporphyrin (TPP), ruffled 5,10,15,20-tetraisopropylporphyrin (TiPrP), and saddled 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin (OETPP), and axial ligands (L) are weak oxygen ligands such as pyridine-N-oxide, substituted pyridine-N-oxide, DMSO, DMF, MeOH, THF, 2-MeTHF, and dioxane. These complexes exhibit the spin states ranging from an essentially pure high-spin (S = 5/2) to an essentially pure intermediate-spin (S = 3/2) state depending on the field strength of the axial ligands and the structure of the porphyrin rings. Reed and Guiset reported that the pyrrole-H chemical shift is a good probe to determine the spin state in the spin admixed S = 5/2,3/2 complexes (Reed, C. A.; Guiset, F. J. Am. Chem. Soc. 1996, 118, 3281-3282). In this paper, we report that the chemical shifts of the alpha- and beta-pyrrole carbons can also be good probes to determine the spin state because they have shown good correlation with those of the pyrrole-H or pyrrole-C(alpha). By putting the observed or assumed pyrrole-H or pyrrole-C(alpha) chemical shifts of the pure high-spin and pure intermediate-spin complexes into the correlation equations, we have estimated the carbon chemical shits of the corresponding complexes. The orbital interactions between iron(III) and porphyrin have been examined on the basis of these chemical shifts, from which we have found that both the d(xy)-a(2u) interaction in the ruffled Fe(T(i)PrP)L2+ and d(xy)-a(1u) interaction in the saddled Fe(OETPP)L2+ are quite weak in the high-spin and probably in the intermediate-spin complexes as well. Close inspection of the correlation lines has suggested that the electron configuration of an essentially pure intermediate-spin Fe(T(i)PrP)L2+ changes from (d(xy), d(yz))3(d(xy))1(d(z)2)1 to (d(xy))2(d(xz), d(yz))2(d(z)2)1 as the axial ligand (L) changes from DMF to MeOH, THF, 2-MeTHF, and then to dioxane. Although the DFT calculation has indicated that the highly saddled intermediate-spin Fe(OETPP)(THF)2+ should adopt (d(xy), d(yz))3(d(xy))1(d(z)2)1 rather than (d(xy))2(d(xz), d(yz))2(d(z)2)1 because of the strong d(xy)-a(1u) interaction (Cheng, R.-J.; Wang, Y.-K.; Chen, P.-Y.; Han, Y.-P.; Chang, C.-C. Chem. Commun. 2005, 1312-1314), our 13C NMR study again suggests that Fe(OETPP)(THF)2+ should be represented as (d(xy))2(d(xz), d(yz))2(d(z)2)1 because of the weak d(xy)-a(1u) interaction. The contribution of the S = 3/2 state in all types of the spin admixed S = 5/2,3/2 six-coordinate complexes has been determined on the basis of the (13)C NMR chemical shifts.     

Polyoxoanions Derived from [gamma-SiO(4)W(10)O(32)](8-)-Containing Oxo-Centered Dinuclear Chromium(III) Carboxylato Complexes: Synthesis and Single-Crystal Structural Determination of [gamma-SiO(4)W(10)O(32)(OH)Cr(2)(OOCCH(3))(2)(OH(2))(2)](5-)

The previously unknown heteropolyoxometalates [gamma-SiO(4)W(10)O(32)(OH)Cr(2)(OOCR)(2)(OH(2))(2)](5-) (R = H, CH(3)) have been prepared by the reaction of [gamma-SiO(4)W(10)O(32)](8-) with [Cr(OH(2))(6)](3+) in formate or acetate buffer solution. Isolation of these new Cr(III)-substituted polyoxometalates was accomplished both as Cs(+) salts and as the Bu(4)N(+) salt for the acetate-containing anion. The compounds were characterized by elemental analysis, UV/vis, IR, and ESR spectroscopy, and cyclic voltammetry. The single-crystal X-ray structural analysis of (Bu(4)N)(3)H(2)[gamma-SiO(4)W(10)O(32)(OH)Cr(2)(OOCCH(3))(2)(OH(2))(2)].3H(2)O [P2(1)2(1)2(1); a = 17.608(12), b = 20.992(13), c = 24.464(11) ?; Z = 4; R = 0.057 for 6549 observed independent reflections] reveals that the two corner-linked CrO(6) octahedra are additionally bridged by two acetate groups, demonstrating the relationship to the well-studied oxo-centered trinuclear carboxylato complexes of Cr(III).     

Synthesis and spectroscopic studies on iron(III) complexes of 1-benzotriazol-1-yl-1-[(p-X-phenyl)hydrazono]propan-2-one

A new series of iron(III) complexes are synthesized from the reaction of the polyfunctional ligands 1-benzotriazol-1-yl-1-[p-X-phenyl]hydrazono]propan-2-one (X=H, Cl, NO(2), CH(3) or OCH(3) corresponding to HL(1),HL(2), HL(3), HL(4) or HL(5), respectively, with iron(III) chloride in the presence of LiOH by the conventional and microwave induced energy methods. The conventional method led to the formation of [FeL(3)].nH(2)O but the microwave induced energy gave [FeLCl(2)], n=1-3 and L is the anion of HL(1)-HL(5). The complexes are characterized by the elemental analysis, molar conductivity, magnetic and spectral (FT-IR, UV-vis and ESR) studies. The magnetic and spectral studies showed that [FeLCl(2)] are polymeric octahedral, [Fe(L(1))(3)].H(2)O is a low spin octahedral and (d(xz),d(yz))(4) (d(xy))(1) ground state, [FeL(3)].nH(2)O, L=anion of HL(4) or HL(5) and are octahedral with intermediate spin (S=32) with ground state (d(xy))(2)(d(xz),d(yz))(3) electronic configuration while for the anions of HL(2) and HL(3), they have (t(2g))(3)(e(g))(5) admixed with (d(xy))(2)(d(xz),d(yz))(3) configurations. From the ESR data, the contribution of the high spin (S=52) and low spin (S=32) to the quantum mechanical spin intermediate (QMS), and the crystal field parameters Delta and V are calculated and related to the electronic and steric effects of the ligands. The electronic spectral data confirm that obtained from the ESR, and the different ligand field parameters as well as the pi-->t(2g), t(2g)-->e(g), e(g)-->pi*, pi-->pi* transitions are estimated and compared with that experimentally obtained.     

Theoretical insights into the ferromagnetic coupling in oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear complexes with aromatic diimine ligands

Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)(2)Co(Me(2)phen)(H(2)O)(2)][Cr(bpy)(ox)(2)]·4H(2)O (1) and [Cr(phen)(ox)(2)Mn(phen)(H(2)O)(2)][Cr(phen)(ox)(2)]·H(2)O (2) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and Me(2)phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the "complex-as-ligand/complex-as-metal" strategy by using Ph(4)P[CrL(ox)(2)]·H(2)O (L = bpy and phen) and [ML'(H(2)O)(4)](NO(3))(2) (M = Co and Mn; L' = phen and Me(2)phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononuclear anions, [Cr(III)L(ox)(2)](-), and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear cations, [Cr(III)L(ox)(μ-ox)M(II)L'(H(2)O)(2)](+)[M = Co, L = bpy, and L' = Me(2)phen (1); M = Mn and L = L' = phen (2)]. These oxalato-bridged Cr(III)M(II) dinuclear cationic entities of 1 and 2 result from the coordination of a [Cr(III)L(ox)(2)](-) unit through one of its two oxalato groups toward a [M(II)L'(H(2)O)(2)](2+) moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct Cr(III) ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin M(II) ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the Cr(III) (S(Cr) = 3/2) ion and the high-spin Co(II) (S(Co) = 3/2) or Mn(II) (S(Mn) = 5/2) ions across the oxalato bridge within the Cr(III)M(II) dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cm(-1) (2); H = -JS(Cr)·S(M)]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 Cr(III)Co(II) and S = 4 Cr(III)Mn(II) ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the σ- and/or π-type pathways of the oxalato bridge, mainly involving the d(yz)(Cr)/d(xy)(M), d(xz)(Cr)/d(xy)(M), d(x(2)-y(2))(Cr)/d(xy)(M), d(yz)(Cr)/d(xz)(M), and d(xz)(Cr)/d(yz)(M) pairs of orthogonal magnetic orbitals and the d(x(2)-y(2))(Cr)/d(x(2)-y(2))(M), d(xz)(Cr)/d(xz)(M), and d(yz)(Cr)/d(yz)(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in 1 and 2.     

Syntheses,crystal structures,spectroscopic and magnetic properties of two trinuclear iron complexes with carboxylate and oximate mixed-bridge ligands

Transition Metal Chemistry - Two trinuclear oxo-centered iron(III) complexes [Fe3(μ3-O)Salox(L1)5(MeOH)2] (1) and [Fe3(μ3-O)Salox(L1)5(EtOH)2]·2EtOH·2H2O (2)...