Cationic Mn Research Articles

Quality of potent Mn porphyrin-based SOD mimics and peroxynitrite scavengers for pre-clinical mechanistic/therapeutic purposes

Cationic Mn porphyrins are among the most potent SOD mimics and peroxynitrite scavengers. They have been widely and successfully used in different models of oxidative stress and are either progressing towards or are in phase I of clinical trials. The most frequently used compounds are Mn(III) meso-tetrakis( N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP 5+ or AEOL10113), its methyl analogue (MnTM-2-PyP 5+ or AEOL10112), and Mn(III) meso-tetrakis(4-benzoic acid)porphyrin (MnTBAP). A great discrepancy between the in vivo data obtained with Calbiochem preparations and those of authentic MnTE-2-PyP 5+ and MnTM-2-PyP 5+ samples were recently observed. Surprisingly, the commercial samples were invariably of poor identity and consisted of mixtures of nearly equal contributions of non-alkylated, mono-, di-, tri- and tetraalkylated porphyrins, lacking thus the major structural entity that determines their antioxidant potency, i.e., the four positively charged ortho N-alkylpyridyl groups that afford thermodynamic tuning of the active site and electrostatic guidance of anionic superoxide and peroxynitrite species toward the metal center. The MnTE-2-PyP 5+ and MnTM-2-PyP 5+ compounds were not even the major species in the commercial samples sold as “MnTE-2-PyP” and “MnTM-2-PyP”, respectively. While we have already reported the insufficient impurity of the MnTBAP samples from Alexis and other suppliers, in one more recent lot the situation is dramatic, as 25% of the sample was not MnTBAP, but metal-free ligand, H 2TBAP. The (unintentional) use of the Mn porphyrins of low quality compromises therapeutic and/or mechanistic conclusions. Simple techniques, which include thin-layer chromatography, electrospray-mass spectrometry, UV–vis spectroscopy, and electrochemistry described here could be used routinely to check the overall quality of Mn porphyrins in order to avoid misleading conclusions and waste of valuable resources (animals, compounds, time, manpower).

Synthesis and Structure of (η5-cyclohexadienyl)Mn(CO)3 and Cationic (η6-arene)Mn(CO)3 Complexes Comprising a Double Bond Conjugated to the π System

Addition of a Grignard reagent to keto-substituted (η5-cyclohexadienyl)Mn(CO)3 complexes leads to the corresponding alcohols in very good yields. After acidic treatment, dehydration occurs, which gives rise to the formation of unprecedented (η5-cyclohexadienyl)Mn(CO)3 complexes substituted by a double bond conjugated to the π system as the major compounds, along with uncoordinated trienones due to the rearrangement of the intermediate carbocation. The structure of one of these η5 complexes has been determined by X-ray crystallography as well as one of the corresponding cationic (η6-arene)Mn(CO)3 complexes formed upon hydride abstraction.

Synthesis, crystal structure and magnetic properties of three polynuclear manganese compounds bearing ferrocenecarboxylato ligands

The reactions of sodium ferrocenecarboxylate (FcCO 2Na) and Mn(ClO 4) 2 · 6H 2O in methanol in the presence of ancillary ligands of 1,10-phenanthroline (phen) or 2,2′-bipyridine (2,2′-bpy) produce three discrete polynuclear complexes bearing ferrocenecarboxylato ligands: [Mn 2(FcCO 2) 3(phen) 2](ClO 4) · 2CH 2Cl 2 ( 1), [Mn 3(FcCO 2) 6(2,2′-bpy) 2] · 2H 2O ( 2) and [Mn 4O 2(FcCO 2) 7(2,2′-bpy) 2]ClO 4 · 2CH 2Cl 2 · 6H 2O ( 3). It is shown that their composition and skeletons are tuned by the ancillary ligands and the ratios of starting materials. In dimanganese complex 1, both Mn(II) ions are pentacoordinated in a distorted trigonal bipyramidal geometry and bridged by three ferrocenecarboxylato ligands in a distorted syn– syn bridging mode, which is rare in triply carboxylato-bridged dimanganese complexes. Compound 2 presents a linear trinuclear [Mn 3(μ 2-η 1:η 1-O 2CFc) 4(μ 2-η 1:η 2-O 2CFc) 2] core, in which six ferrocencarboxylato ligands show two different bridging modes. The cationic Mn 4O 2 core of 3 has a butterfly structure, in which two Mn(III) ions at “body” sites are bridged by an additional ferrocenecarboxylato ligand and they are further connected to the Mn(III) ions at “wing-tip” sites by ferrocenecarboxylato ligands. Magnetic susceptibilities of 1 and 2 were measured. Both of them mediate a weak antiferromagnetic coupling between the Mn(II) ions bridged by ferrocenecarboxylato ligands.

Variation of Heterometallic Structural Motifs Based on [W(CN)8]3− Anions and MnII Ions as a Function of Synthetic Conditions

Reactions of [W(CN)(8)](3-/4-) anions with complexes of Mn(2+) ion with tridentate organic ligand 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) lead to a series of heterobimetallic complexes. The crystal structures of these compounds are derived from the same basic structural fragment, namely a W(2)Mn(2) square constructed of alternating cyanide-bridged W and Mn ions. In [Mn(II)(tptz)(OAc)(H(2)O)(2)](2){[Mn(II)(tptz)(MeOH)(1.58)(H(2)O)(0.42)](2)[W(V)(CN)(8)](2)}.5 MeOH.9.85 H(2)O (3), isolated molecular squares are co-crystallized with mononuclear cationic Mn(II) complexes. The structure of {[Mn(II)(tptz)(MeOH)](2)[W(IV)(CN)(8)].2 MeOH}(infinity) (4) is based on an infinite chain of vertex-sharing squares, while {[Mn(II) (2)(tptz)(2)(MeOH)(3)(OAc)][W(V)(CN)(8)].3.5 MeOH0.25 H(2)O}(infinity) (5) and {[Mn(II) (2)(tptz)(2)(MeOH)(3)W(V)(CN)(8)][Mn(II)(tptz)(MeOH)W(V)(CN)(8)].2 H(2).OMeOH}(8) (7) are derived from such an infinite chain by removing one of the W-C[triple bond]N-Mn linkages in each of the squares. The decanuclear cluster [Mn(II) (6)(tptz)(6)(MeOH)(4)(DMF)(2)W(V) (4)(CN)(32)].8.2 H(2)O.2.3 MeOH (6) is a truncated version of structure 4 and consists of three vertex-sharing W(2)Mn(2) squares. The structure of [Mn(II)(tptz)(MeOH)(NO(3))](2)[Mn(II)(tptz)(MeOH) (DMF)](2)[W(V)(CN)(8)](2).6 MeOH (8) consists of a hexanuclear cluster, in which the central W(2)Mn(2) square is extended by two Mn side-arms attached via CN(-) ligands to the W corners of the square. The magnetic behavior of these heterobimetallic complexes (except for 4) is dominated by antiferromagnetic coupling between Mn(II) and W(V) ions mediated by cyanide bridges. Compounds 3, 6, and 8 exhibit high spin ground states of S=4, 13, and 9, respectively, while 5 and 7 exhibit behavior typical of a ferrimagnetic chain with alternating spin centers. Complex 4 contains diamagnetic W(IV) centers but holds promise as a potential photomagnetic solid.

Selective alkene epoxidation and alkane hydroxylation with sodium periodate catalyzed by cationic Mn(III)-salen supported on Dowex MSC1

Dicationic Mn(III)-salen, containing phosphonium groups at 5,5′-positions of salen ligand, is supported on an ion-exchange resin, Dowex MSC1, via electrostatic interaction. The catalyst, Mn(salen)-Dowex, has been characterized by FTIR, UV–vis spectroscopic techniques, scanning electron micrograph (SEM), thermal and elemental analysis. This heterogenized homogeneous manganese(III)-salen complex can be used as catalyst in the alkene epoxidation with sodium periodate. This catalytic system shows a good activity in the epoxidation of cyclic, aromatic and especially linear alkenes and exhibits a high selectivity in epoxidation of α-pinene and R-(+)-limonene. Alkyl aromatic and cycloalkanes were oxidized efficiently to their corresponding alcohols and ketones in the presence of this catalyst. The stability and reusability of this new heterogenized metallosalen complex was also investigated.

310 PUBLICATION The use of a panel of monoclonal antibodies to enrich circulating breast cancer cells facilitates their detection

Ascorbate (Asc) as a single agent suppressed growth of several tumor cell lines in a mouse model. It has been tested in a Phase I Clinical Trial on pancreatic cancer patients where it exhibited no toxicity to normal tissue yet was of only marginal efficacy. The mechanism of its anticancer effect was attributed to the production of tumoricidal hydrogen peroxide (H2O2) during ascorbate oxidation catalyzed by endogenous metalloproteins. The amount of H2O2 could be maximized with exogenous catalyst that has optimized properties for such function and is localized within tumor. Herein we studied 14 Mn porphyrins (MnPs) which differ vastly with regards to their redox properties, charge, size/bulkiness and lipophilicity. Such properties affect the in vitro and in vivo ability of MnPs (i) to catalyze ascorbate oxidation resulting in the production of H2O2; (ii) to subsequently employ H2O2 in the catalysis of signaling proteins oxidations affecting cellular survival pathways; and (iii) to accumulate at site(s) of interest. The metal-centered reduction potential of MnPs studied, E1/2 of MnIIIP/MnIIP redox couple, ranged from −200 to +350 mV vs NHE. Anionic and cationic, hydrophilic and lipophilic as well as short- and long-chained and bulky compounds were explored. Their ability to catalyze ascorbate oxidation, and in turn cytotoxic H2O2 production, was explored via spectrophotometric and electrochemical means. Bell-shape structure-activity relationship (SAR) was found between the initial rate for the catalysis of ascorbate oxidation, vo(Asc)ox and E1/2, identifying cationic Mn(III) N-substituted pyridylporphyrins with E1/2>0 mV vs NHE as efficient catalysts for ascorbate oxidation. The anticancer potential of MnPs/Asc system was subsequently tested in cellular (human MCF-7, MDA-MB-231 and mouse 4T1) and animal models of breast cancer. At the concentrations where ascorbate (1 mM) and MnPs (1 or 5 µM) alone did not trigger any alteration in cell viability, combined treatment suppressed cell viability up to 95%. No toxicity was observed with normal human breast epithelial HBL-100 cells. Bell-shape relationship, essentially identical to vo(Asc)ox vs E1/2, was also demonstrated between MnP/Asc-controlled cytotoxicity and E1/2-controlled vo(Asc)ox. Magnetic resonance imaging studies were conducted to explore the impact of ascorbate on T1-relaxivity. The impact of MnP/Asc on intracellular thiols and on GSH/GSSG and Cys/CySS ratios in 4T1 cells was assessed and cellular reduction potentials were calculated. The data indicate a significant increase in cellular oxidative stress induced by MnP/Asc. Based on vo(Asc)ox vs E1/2 relationships and cellular toxicity, MnTE-2-PyP5+ was identified as the best catalyst among MnPs studied. Asc and MnTE-2-PyP5+ were thus tested in a 4T1 mammary mouse flank tumor model. The combination of ascorbate (4 g/kg) and MnTE-2-PyP5+ (0.2 mg/kg) showed significant suppression of tumor growth relative to either MnTE-2-PyP5+ or ascorbate alone. About 7-fold higher accumulation of MnTE-2-PyP5+ in tumor vs normal tissue was found to contribute largely to the anticancer effect.

Tuning the redox properties of a 1-D supramolecular array via selective deprotonation of coordinated imidazoles around a Mn(II) center

A neutral 1-D supramolecular array containing [Mn(H 2) 2] building blocks was synthesized by the selective deprotonation of two coordinated imidazole moieties from the cationic Mn(II) complex, [Mn(H 2 2) 2] 2+. Upon deprotonation the redox potential of [Mn(H 2) 2] shifts significantly more negative, when compared to the cationic Mn(II) complex. However, X-ray crystallographic studies done on both complexes show a very similarly distorted octahedral geometry around the Mn(II) ion. Interestingly, while [Mn(H 2) 2] lacks both charge and counterion to assist in crystal packing, both the neutral and cationic complexes self-organize, using primarily π–π and edge-to-π aryl interactions, into very similar 1-D zigzag ribbons in the solid-state.

Inhibitory effects of water-soluble cationic manganese porphyrins on peroxynitrite-induced SOS response in Salmonella typhimurium TA4107/pSK1002

We have investigated the protective effects of water-soluble cationic Mn(III) porphyrins against peroxynitrite (ONOO −)-induced DNA damage in the cells of Salmonella typhimurium TA4107/pSK1002 and lipid peroxidation of red blood cell membranes. Mn(III) tetrakis ( N-methylpyridinium-4-yl) porphine (TMPyP) and the brominated form, Mn(III) octabromo-tetrakis ( N-methylpyridinium-4-yl) porphine (OBTMPyP) effectively reduced the damage and peroxidation induced by N-morpholino sydnonimine (SIN-1), which gradually generates ONOO − from O 2 − and NO produced through hydrolysis. Mn(III)OBTMPyP became 10-fold more active than the non-brominated form. In the presence of authentic ONOO −, the Mn(III) porphyrins were ineffective against damage and strongly enhanced lipid peroxidation, while the coexistence of ascorbic acid inhibited peroxidation. Using a diode array spectrophotometry, the reactions of Mn(III)TMPyP with authentic ONOO − and SIN-1 were measured. Mn(III)TMPyP is known to be catalytic for ONOO − decomposition in the presence of antioxidants. OxoMn(IV)TMPyP with SIN-1 was rapidly reduced back to Mn(III) without adding any oxidants. Further, in the SIN-1 system, the concentration of NO 2 − and NO 3 − were colorimetrically determined by Griess reaction based on the two-step diazotization. NO 2 − increased by addition of Mn(III) porphyrin and the ratio of NO 2 − to NO 3 − was 4–7 times higher than that (1.05) of SIN-1 alone. This result suggests that O 2 − from SIN-1 acts as a reductant and NO cogenerated is oxidized to NO 2 −, a primarily decomposition product of NO. Under the pathological conditions where biological antioxidants are depleted and ONOO − and O 2 − are extensively generated, the Mn(III) porphyrins will effectively cycle ONOO − decomposition using O 2 −.

Complementation of SOD-deficient Escherichia coli by manganese porphyrin mimics of superoxide dismutase activity

Cationic Mn(III) porphyrins substituted on the methine bridge carbons (meso positions) with N-alkylpyridinium or N,N′-diethylimidazolium groups have been prepared and characterized, both chemically and as SOD mimics. The ortho tetrakis N-methylpyridinium compound was substantially more active than the corresponding para isomer. This ortho compound also exhibited a more positive redox potential and greater ability to facilitate the aerobic growth of a SOD-deficient Escherichia coli. Analogs with longer alkyl side chains and with methoxyethyl side chains, as well as with N,N′-diethylimidazolium and N,N′-dimethoxyethylimidazolium groups on the meso positions, have been prepared in anticipation of greater penetration of the cells due to greater lipophilicity. We now report that the more lipophilic compounds were effective at complementing the SOD-deficient E. coli at lower concentrations than were needed with the less lipophilic compounds. The greater efficacy of the more lipophilic compounds was achieved at the cost of greater toxicity that became apparent when these compounds were applied at higher concentrations.

Total Internal Reflection Resonance Raman Microspectroscopy for the Liquid/Liquid Interface. Ion-Association Adsorption of Cationic Mn(III) Porphine

The interfacial adsorption of meso-tetrakis(N-methylpyridyl)porphyrinatomanganese(III) (Mn(TMPyP)5+) with dihexadecyl phosphate (DHP) at the toluene/water interface was studied by means of a total internal reflection resonance Raman microspectroscopy. The intensity of interfacial Raman spectra of Mn(TMPyP)5+ was significantly enhanced by the addition of DHP. Since the Raman spectra were not shifted by the presence of DHP, the enhancement was ascribed to the electrostatic Stern layer adsorption of Mn(TMPyP)5+ to the negatively charged interface by the adsorption of DHP. The interfacial adsorption of Mn(TMPyP)5+ was confirmed by the measurement of interfacial tension lowering under the absence and the presence of DHP. Polarized Raman spectra suggested that the average tilt angle of the porphyrin plane of the Mn(TMPyP)5+ molecule to the interface normal was 65° at the interface adsorbed by DHP. The interfacial ion association adsorption of Mn(TMPyP)5+ was analyzed by the Langmuir isotherm, and the adsorption parameters were obtained.

Preparation and catalysis of DMY and MCM-41 encapsulated cationic Mn(III)–porphyrin complex

The synthesis and characterization of the cationic manganese–porphyrin [ meso-tetrakis(1-methyl-4-pyridinio)porphyrinato] manganese(III) penta-acetate complexes encapsulated in zeolite and mesoporous molecular sieve has been accomplished, and their catalytic activity was tested in the epoxidation of styrene and cyclohexene by iodosylbenzene. With mesoporous molecular sieve (MCM-41) and the new NaY zeolite (DMY) as supports, the encapsulated manganese–porphyrin systems show high activity and selectivity for the epoxidation. The effects of solvent and reaction time and the performance of the recovered catalysts have been studied. The mechanism of olefin oxidation has also been discussed.

Preparation of new (η 6-arene)Mn(CO) 3+ complexes involving Pd-catalysed/ exo-hydride abstraction sequence

A novel methodology consisting in a selective palladium cross-coupling reaction starting from (η 5-chlorocyclohexadienyl)Mn(CO) 3 followed by rearomatisation allows the preparation of new cationic (η 6-arene)Mn(CO) 3 complexes, which cannot be obtained directly from the coordination of the corresponding free arenes.

Single and double nucleophilic addition to methylated podocarpic acid coordinated to manganese tricarbonyl

Coordination of the Mn(CO) 3 + moiety to the arene ring in dimethylated podocarpic acid ( 1) occurs with similar probability to both α and β faces ( 2). The nucleophile MeMgCl adds predominantly to the ortho C-13 site when the metal is situated β and to the meta C-14 site when the metal is α, to afford cyclohexadienyl complexes 3(β) and 4(α). The minor isomers 3(α) and 4(β) (Nu=Me) were isolated and characterized by X-ray diffraction, from which it is concluded that the diterpenoid Me-17 group interacts sterically with a carbonyl ligand when the metal is β and the nucleophile is at the meta C-14 position. Complexes 3(β) and 4(α) are readily converted into cationic Mn(CO) 2NO + salts 5(β) and 6(α), which add hydride ion to afford cyclohexadiene complexes.

Utilization of Redox and Acid/Base Chemistry for the Deprotection of a Mn(dmpe)2(C⋮CSiMe3)2 Complex

The reaction of the low-spin d5 complex Mn(dmpe)2(C⋮CSiMe3)2 (1) (dmpe = 1,2-bis(dimethylphosphino)ethane) with [NBu4][Ph3F2M] (M = Si or Sn) yields the SiMe3 metathesis products Mn(dmpe)2(C⋮CMPh3)2 (M = Si 2a, Sn 2b). When the Mn(II) species 1 was dissolved in MeOH in the presence of NaBF4, disproportionation occurred with formation of the Mn(I) products Mn(dmpe)2(C⋮CSiMe3)(CCH2) (3a) and [Mn(dmpe)2(C⋮CSiMe3)(⋮C−CH3)][BF4] (5a) and the cationic Mn(III) complex [Mn(dmpe)2(C⋮CSiMe3)2][BF6] (4a). In a similar way 1 was transformed into [Mn(dmpe)2(C⋮CSiMe3)2][H2F3] (4b) and [Mn(dmpe)2(C⋮CSiMe3)(⋮C−CH3)][H2F3] (5b) by its reaction with excess of HF·pyridine. The reaction of 1 with Li or Na in toluene at 100 °C gave the new d6 cis-bisalkynyl complexes [Mn(dmpe)2(C⋮CSiMe3)2][M] (M = Li 6a, Na 6b). The trans-alkynylvinylidene derivatives Mn(dmpe)2(C⋮CSiMe3)(CC(E)SiMe3) (E = H 3b, SnMe3 3c) were obtained by the reaction of species 6 with stoichiometric MeOH or ClSnMe3. In MeOH/KOH solutions complex 3b or 3c was c...

Heterodimers and -trimers of meso-tetra-(isophthalicacid)-porphyrin octaanions with meso- and β-tetramethylpyridinium-porphyrin tetracations and their manganese complexes in water. Electrochemistry, spectroelectrochemistry and fluorescence quenching

Non-covalent cofacial heterodimers and -trimers between meso-tetraphenyl-octacarboxylate-porphyrin and β-tetracationic porphyrins have been prepared in bulk water. They are held together by Coulomb interactions between four or eight β-methylpyridinium and meso-phenylcarboxylate ion pairs. The observation of the UV–vis absorption titration indicated quantitative trimerization at concentrations >10 −6 M. The equilibrium constants in water were 2.3×10 6 M −1 for the dimerization and 1.7×10 7 M −1 for the conversion of the dimer to the trimer in water. Fluorescence of free base or zinc porphyrins was strongly diminished on heterodimerization and -trimerization by redox quenching. In the case of Mn(III) heterotrimer, electrochemistry and spectroelectrochemistry showed that all three Mn(III) ions were oxidized simultaneously to Mn(IV) at a potential close to 0.20 V versus Ag ∣ AgCl at pH 12. Electroreduction of the peripheral cationic Mn(III) porphyrins was achieved at −0.20 V versus Ag ∣ AgCl and gave the first multivalent trimers, namely Mn(II)P–Mn(III)P–Mn(II)P. The reduction of the central manganese porphyrin finally occurred at −0.60 V yielding Mn(II)P–Mn(II)P–Mn(II)P trimers. Heterotrimers Mn(III)P–H 2P–Mn(III)P and H 2P–Mn(III)P–H 2P were also studied as reference compounds for electrochemical measurements.

Versatile Routes to Mono- and Bis(alkynyl) Manganese(II) and Manganese(III) Complexes via Manganocenes

With the manganocenes (RC5H4)2Mn (R = H, Me) as starting materials, paramagnetic d5 half-sandwich complexes (RC5H4)Mn(dmpe)(C⋮CR‘) (dmpe = 1,2-bis(dimethylphosphino)ethane; R = Me, R‘ = Ph, 1a; R = Me, R‘ = SiMe3, 2a; R = H, R‘ = Ph, 1b; R = H, R‘ = SiMe3, 2b) have been prepared by the reaction with terminal or SnMe3-substituted acetylenes and dmpe. The derivatives 1a and 2a could be isolated, while 1b and 2b have been identified in mixtures with the bis(dmpe)bis(acetylide)manganese species 3 (R‘ = Ph) and 4 (R‘ = SiMe3). The latter compounds are obtained as the sole products, when the manganocenes are reacted with dmpe and the corresponding acetylenes in a 1:2:2 ratio. 1a and 2a can be reversibly oxidized to the corresponding cationic Mn(III) complexes [(MeC5H4)Mn(dmpe)(C⋮CR‘)][BF4] (R‘ = Ph, [1a]+; R‘ = SiMe3, [2b]+). Compounds 1a and 2a act as scavengers of H• radicals in the 1:1:1 reaction mixtures or in the presence of n-Bu3SnH or (C5Me5)Mo(CO)3H, forming the vinylidene species (MeC5H4)Mn(dmpe)(CC(H)R‘) (R‘ = Ph, 5; R‘ = SiMe3, 6). In the absence of a special H• donor, 1a slowly dimerizes to give the binuclear complex 7. A similar process occurs with [1a]+ to form the bis(carbyne) complex 8. 8 can be reduced to 7 by a reaction with 2 equiv of (MeC5H4)2Co, and in turn 7 can be oxidized to 8 with 2 equiv of a ferrocenium salt. Equal amounts of 7 and 8 comproportionate to afford the mixed-valence complex [7]+. If applicable, the new compounds have been characterized by spectroscopic (NMR, EPR, near-IR) and electrochemical measurements, as well as X-ray diffraction studies (2a, 5, 7, and 8) and DFT calculations.

Formation and Structures of Transition Metal−C60 Clusters

Transition metal (Sc, Ti, V, and Cr)−C60 binary clusters were produced in the gas phase by a two-laser vaporization method. In the mass spectra of cationic Mn(C60)m+, for M = Sc, Ti, and V, clusters having the composition of (n, m) = (1, 1)+, (1, 2)+, (2, 3)+, (3, 4)+, (4, 4)+, and (5, 5)+ were predominantly produced. The peaks having (n, n + 1)+ compositions are explicable in terms of multiple dumbbell structures, in which metal atoms and C60 are alternately stacked. Clusters with composition (4, 4)+ and (5, 5)+ are presumed to be ring structures. For Crn(C60)m+, however, a Cr atom is surrounded by three C60, forming a tricapped structure, and the structure acts as a unit for larger stable clusters of (2, 4)+, (3, 4)+, and (4, 4)+. Ionization energy measurements for neutral Mn(C60)m and a chemical probe method using CO, O2, and C2H4 as reactants gave information concerning the geometrical and electronic structures.

Chemical Bonding in Mn Clusters, MnNand Mn+N(N=2–7)

Electronic states of the neutral and cationic Mn N clusters for N =2–7 are calculated by the spin-polarized density functional method. For neutral clusters, the equilibrium interatomic distances are 20% or more larger than that of the bulk crystal, and the characteristics of the electronic structure remain the same as those of an isolated atom. Atoms consisting of the neutral clusters are bonded non-metallically. For smaller cationic Mn N + clusters ( N =2–4), similar situations exist although the 3 d -4 s mixing increases. For larger cationic Mn N + clusters ( N =5–7), the equilibrium interatomic distances are less than 90% of the value of the bulk crystal. The 3 d levels broaden in energy and constitute band-like structure, and the 4 s metallic bonding occurs. This change from non-metallic to metallic bonding in the cationic clusters seems to correspond to the magic number 5 which is observed in the cationic clusters.

Atomic bonding of neutral and cationic Mn clusters

By using the spin-polarized DV-Xα-LCAO method, electronic states of neutral and cationic Mn N clusters (N=2∼5) are calculated to study atomic bonding of Mn clusters. For the neutral Mn2 cluster, the equilibrium interatomic distance is much larger than that of the bulk crystal. The 3d-derived states are nearly half-filled, and the 4s-derived states are almost fully occupied,i.e. the electronic configuration is close to that of the isolated atom. These indicate that the Mn2 cluster is bound by the van der Waals force. The same situation is true for the larger neutral clusters while the equilibrium interatomic distance becomes smaller and thes-d mixing becomes larger. For the cationic clusters, the behaviors tend to become metallic. The equilibrium interatomic distances are smaller and thes-d mixings are larger than those of the corresponding neutral clusters. However, the Mn 2 + and Mn 4 + clusters still remain the van der Waals characters. Contrary to these clusters, the Mn 5 + cluster, whose interatomic distance is smaller than that of the bulk crystal, shows strong metallic bonding. These results seem to correspond to the magic number observed on the mass spectroscopy of cationic Mn clusters.

The X-ray structure of the hydroxycarbene complex [(DPPP)(CO) 3MnC(OH)CH 3] +[CF 3SO 3] − { facial-[1,3-bis(diphenylphosphino)propane(methyl-hydroxycarbene) tricarbonylmanganese(I)]} triflate

The cationic octahedral manganese(I) hydroxycarbene complex [(DPPP)(CO) 3MnC(OH)CH 3] +] has been synthesized and isolated as its triflate salt, and its structure fully determined by X-ray diffraction. A comparison of our cationic Mn 1 methylhydroxycarbene complex to the neutral isoelectronic Cr 0 and Mo 0 phenylhydroxycarbene structures reported in the literature reveals a number of surprising differences and similarities. In the Cr and Mo complexes the metal fragment and the hydroxy hydrogen are positioned syn( Z-isomer) giving the conformational isomer often seen in alkoxycarbenes. In contrast, in our Mn complex, these substituents are found in the alternate anti conformation ( E-isomer). In addition, dimers are observed in the solid state due to a much more intricate network of hydrogen bonds. Nevertheless, in each of these octahedral isoelectronic hydroxycarbene complexes, the orientation of the memtal framework and the carbene moiety with respect to each other is remarkably similar. A twist of approximately 34° about the MC(carbene) bond and away from the fully eclipsed electronically favored geometry is observed in all three complexes.