Kirsten Folting

Manganese carboxylate clusters: From structural aesthetics to single-molecule magnets

Abstract An overview is provided of some recent developments in manganese carboxylatecluster chemistry. A variety of synthetic methodologies are described together with the structuresof the resultant products, which span metal nuclearities of 4 to 18 and oxidation states of II to IV,including mixed-valency. The spins of the ground states of these products are often large andsometimes abnormally large, and in certain cases when this is coupled to a sufficiently largemagnetoanisotropy, the clusters function as single-molecule magnets i.e., they can be magnetizedby an external magnetic field below a critical temperature. These complexes display hysteresis inmagnetization vs . magnetic field studies, and clear evidence for quantum tunnelling ofmagnetization. Such results establish single-molecule magnetism as a new magnetic phenomenon,and one that holds great promise for next-century technological applications.

Characterization of aluminium isopropoxide and aluminosiloxanes

Abstract Aluminium isopropoxide, in the form of a crystalline solid of melting point 127°C, has been shown by X-ray diffraction to be a tetrameric molecular species of formula Al[(μ-OiPr)2Al(OiPr)2]3, consistent with earlier proposals and spectroscopic data. A central aluminium achieves coordination number six via two bridging alkoxide groups from each of three Al(OiPr)4− groups. The resulting planar Al(μ2-O)2Al rings have widened (∼ 132°) angles at oxygen to increase the non-bonded AlAl distance. While the terminal OiPr groups show the shortest (1.70 A) AlO distances in the molecule, they are nevertheless strongly bent (∼ 140°) at oxygen. The 1H NMR spectrum of Al4(OiPr)12 is analysed based on the structure reported here. Characterization of aluminosiloxane derivatives Al(OiPr)3-x(OSiMe3)x (x = 1−3) by 1H and 27Al NMR, mass spectrometry and IR spectroscopy is also reported. For x = 1 and 2, these show co-existence of several oligomers. The effect of incorporation of OSiMe3 groups is to favour smaller oligomers.

Single-Molecule Magnets: Different Rates of Resonant Magnetization Tunneling in Mn12 Complexes**

Two new molecular magnets, the dodecanuclear manganese complexes of the type [Mn12 O12 (O2 CR)16 (H2 O)4 ] (known for R = CH3 , new for R = o-ClC6 H4 , o-BrC6 H4 ) have contributed to a better quantum mechanical understanding of single-molecule magnets. For instance, appreciable differences in the steps seen in the magnetization hysteresis loops of these high-spin clusters are attributed to changes in the rates of magnetization tunneling from one complex to another.

The reactions of Cu2(O2CMe)4(H2O)2 with 2,2′-bipyridine (bpy): Influence of the Cu: bpy ratio, and the structure of a linear polymer comprising two alternating types of Cu2 units

Abstract Further investigation of the Cu 2 (O 2 CMe) 4 (H 2 O) 2 /bpy reaction system is described, including the determination of the influence of the Cu II : bpy ratio ( x ) on the identity of the reaction products. Values of x in the 1-2 range have been employed. Reaction of Cu 2 (O 2 CMe) 4 (H 2 O) 2 with two equivalents of bpy ( x = 1) in MeCN yields [Cu 2 (O 2 CMe) 4 (bpy) 2 ]·2H 2 O ( 1 ) in 79% yield. Treatment of Cu 2 (O 2 CMe) 4 (H 2 O) 2 with 1.33 equivalent of bpy ( x = 1.5) in MeCN leads to precipitation of the polymeric compound [—Cu 2 (O 2 CMe) 2 (bpy) 2 —O 2 CMe—Cu 2 (O 2 CMe) 4 —O 2 CMe—] n ( 2 ); from the filtrate 1 slowly crystallizes in 15% yield. A high yield (89%) of pure 2 can be obtained by increasing x from 1.5 to 2. Treatment of 1 with Cu 2 (O 2 CMe) 4 (H 2 O) 2 in MeCN provides an additional route to 2 . Compound 2 reacts with equimolar bpy in EtOH to yield complex 1 . Complex 1 undergoes facile carboxylate substitution in MeCN with an excess of PhCOOH, leading to reasonable yields (40-65%) of [Cu 2 (O 2 CPh) 4 (bpy) 2 ]· MeCN ( 3a ) or [Cu 2 (O 2 CPh) 4 (bpy) 2 ]· 2H 2 O ( 3b ), depending on the rate of crystallization. Complex 2 is converted to the known compound Cu 2 (O 2 CPh) 4 (EtOH) 2 ( 4 ) or 3b by treatment with excess PhCOOH in EtOH or MeCN, respectively. Complexes 1 and 2 undergo a variety of additional reactions that lead to the dinuclear complexes [Cu 2 (O 2 CMe) 3 (bpy) 2 ](ClO 4 ) ( 5 ), [Cu 2 (OH)(H 2 O)(O 2 CMe)(bpy) 2 ](ClO 4 ) 2 ( 6 ), Cu 2 (OH) 2 (bpy) 2 (ClO 4 ) 2 ( 7 ), [Cu 2 (O 2 CMe) 2 (H 2 O) 2 (bpy) 2 ](ClO 4 ) 2 · H 2 O ( 8 ) and Cu 2 (O 2 CMe) 2 (ClO 4 ) 2 (bpy) 2 ( 9 ). Complex 1 crystallizes in the triclinic space group P 1 with (at — 143°C) a = 8.842(2), b = 12.266(2), c = 7.708(1) A, α = 98.72(1), β = 106.35, γ = 109.68(1)°, Z = 1 and V = 726.68 A 3 . A total of 2318 unique reflections with F > 3.00σ( F ) were refined to values of R and R w of 2.67 and 2.87%, respectively. Compound 2 crystallizes in the triclinic space group P 1 with (at — 155°C) a = 9.272(2), b = 14.718(3), c = 8.023(1) A α = 102.66(1), β = 103.89(1), γ = 94.00(1)°, Z = 1 and V = 1028.21 A 3 . A total of 2319 unique reflections with F > 3.00σ( F ) were refined to values of R and R w of 3.68 and 3.96%, respectively. The structure of 1 consists of a [Cu 2 (O 2 CMe) 4 (bpy) 2 ] molecule located at a centre of symmetry with two syn,anti acetate bridges. The molecules of 1 form infinite ladder-like chains as a result of hydrogen-bonding interactions with the water molecules. The structure of 2 is composed of one-dimensional, well-separated polymeric chains and contains two different types of copper(II) dinuclear units, each at a crystallographic centre of symmetry. The chains are formed by alternating Cu 2 (O 2 CMe) 4 and [Cu 2 (O 2 CMe) 2 (bpy) 2 ] 2+ units which are linked by syn,anti bridging acetates. The Cu 2 (O 2 CMe) 4 unit has a tetra-bridged structure with four syn,syn bridging acetates and two oxygens from the two syn,anti acetates occupying the axial positions. The other dinuclear unit has a structure with two acetate groups forming mono-atomic bridges. From the IR and UV-vis solution spectra, it is concluded that the polymeric structure of 2 is not retained in MeCN. A cyclic voltammetric study of 1 in MeCN reveals a quasi-reversible reduction at −0.82 V vs ferrocene, and an irreversible reduction at −1.82 V yielding copper metal which deposits on the electrode. Complex 3b displays almost identical processes. Compound 2 displays two reduction processes at −0.84 and −1.82 V.

Mononuclear, three-coordinate metal thiolates: Preparation and crystal structures of [NBun4][Hg(SPh)3] and [NPrn4] [Pb(SPh)3]

Abstract Dissolution of HgO or PbO in methanolic solutions of NaSPh yields homogeneous solutions from which highly crystalline [NBun4][Hg(SPh)3] (1) or [NPrn4][PB(SPh)3] (2) can be isolated on addition of appropriate quaternary ammonium salts. 1 crystallizes in monoclinic space group P21/a with a = 20.663(7), b = 16.812(6), c = 9.757(3) A, β = 95.52(2)° and Z = 4. The anion consists of a rare example of trigonal planar coordinated Hg; there are no weaker, intermolecular Hg ... S axial interactions. 2 crystallizes in triclinic space group Pl with a = 12.689(7), b = 11.255(6), c = 12.046(7) A, α = 107.93(3), β = 109.64(3), γ = 86.01(3)°, and Z = 2. The anion consists of a trigonal pyramidal coordinated PbS3 unit. The structures were solved using data collected at approx. − 160°C and refined to conventional R values of 5.7 and 4.6%, respectively for 1 and 2.

The chemistry of sterically crowded aryloxide ligands—VII. Synthesis, structure and spectroscopic properties of some group 4 and group 5 metal derivatives of 2,6-diphenylphenoxide

Abstract A series of early transition metal organometallic derivatives containing the ancillary ligand 2,6-diphenylphenoxide (OAr-2,6Ph 2 ) have been synthesized. Compounds of stoichiometry Ti(OAr-2,6Ph 2 ) 2 (R) 2 (R = CH 3 , CH 2 SiMe 3 , CH 2 Ph and Ph) and Ti(OAr-2,6Ph) 3 (R) (R = CH 3 , CH 2 SiMe 3 ) are obtained by treating the corresponding homoleptic alkyl, TiR 4 , with the required amount of phenol, HOAr-2,6Ph 2 . For the Group 5 metals Nb and Ta, the methyl derivatives M(OAr-2,6Ph 2 ) 2 (CH 3 ) 3 and M(OAr-2,6Ph 2 ) 3 (CH 3 ) 2 are obtained via methylation of the corresponding chloro-aryloxides. Besides routine spectroscopic characterization the diphenyl Ti(OAr-2,6Ph 2 ) 2 (Ph) 2 and mono-alkyl Ti(OAr-2,6Ph 2 ) 3 (CH 2 SiMe 3 ) have been structurally characterized by X-ray diffraction techniques. Both molecules contain a pseudo-tetrahedral environment about the titanium atom with short 1.794(3)–1.806(2) A, TiO distances and large, 153–179°, TiOAr angles. The TiC distances appear normal for these types of compounds.

Site-specific ligand variation in manganese–oxide cubane complexes, and unusual magnetic relaxation effects in [Mn4O4X(OAc)3(dbm)3](X = N3–, OCN– Hdbm = dibenzoylmethane)

Treatment of [Mr4O2(OAc)6(py)2(dbm)2]1(py = pyridine, Hdbm = dibenzoylmethane) in hot MeCN with Me3SiX (X = N3–, OCN –) yields [Mn4O3X(OAc)3(dbm)3] containing extremely rare η1, µ3-N3– or -OCN– groups; alternating-current magnetic susceptibility studies reveal unusual magnetic relaxation effects and indicate these species to be the newest and smallest examples yet of truly molecular magnets.

Reactions involving alkynes and tungsten-tungsten triple bonds supported by alkoxide ligands

Abstract W2(OR)6Ln compounds [R = But n = 0; R = Pri or Np (Np = neopentyl), L = py (py = pyridine) or HNMe2, n = 2] react with alkynes (R′C-CR′) under mild conditions (hexane solutions, room temperature or below) to yield a variety of products depending upon the nature of the alkoxide, the alkyne and the mole ratio of the reactants. The products include alkylidyne complexes Ln(RO)3W CR′ (n = 1 or 0) (Schrock et al., Organometallics 1985, 4, 74), alkyne adducts, W2(OR)6(py)n(μ-C2R′2), alkylidyne-capped tritungsten complexes, W3(μ3-CR′)(OR)9, and W2(OR)6(L)(μ-C4R′4) or W2(OR)6(μ-C4R′4) (μ2-C2R′2) compounds. Evidence for equilibria involving alkyne adducts and alkylidyne species is found for certain combinations of R and R′. (1) The alkylidyne complexes (ButO)3 WCMe and (py)2(PriO)3 W CNMe2 react with CO (1 atm 22°C, in hexane) to yield alkyne adducts W2(OBut)6(μ-C2Me2)(CO) and W2[(OPri)6(CO)2(η2-C2(NMe2)2], respectively. (2) The alkylidyne complexes [PriO)2(HNMe2)(R′C)W(μ-OPri)]2 react with alkynes R′CCR′ (> 2 equiv, hexane, 22°C) to give W2(OPri)6(μ-C4R′4)(η2-C2R′2) compound (R′ = Me or Et). (3) The alkyne adducts W2(ONp)6(py)n(μ-C2R′2) (R′ = Et or Ph, n = 1; R′ = Me, n = 2) react with W2(ONp)6(py)2 in a 1:2 mole ratio at 22°C in hexane to yield W3(μ3-CR′)(ONp)(9 compounds. In related reactions involving 1,2-bishydrocarbyl-tetraalkoxides, W2(CH2R″)2(OR)4, and alkynes (R′CCR′) (2 equiv), alkyne adducts of formula W2(CH2R″)2(η2-C2R′2)2(OPri)4 and W2(CH3)2(μ-C2R′2)(OBut)4(py), alkylidyne-bridged complexes HW2(μ-CR″)(μ-C4R′4)(OPri)4 and products of WW and CC metathesis have been isolated for various combinations of R, R′ and R″.

The synthesis, structure and spectroscopic properties of the di- and tri-nuclear Ni(II) thiolate complexes

Abstract The anions [Ni2(edt)3]2− (edt = ethane-1,2-dithiolate) and [Ni3(edt)4]2− have been prepared by the reaction of Na2(edt) with NiCl2 · 6H2O and, with subsequent work-up, isolated as their [PPh4]+ salts. For the first time, the structure of di- and tri-nuclear NI(II) thiolates with identical ligands can be compared. The complex [PPh4]2[Ni2(edt)3] (1) crystallizes in the triclinic space group P 1 - with unit cell parameters (at −152°C) a = 12.861(7), b = 21.057(14), c = 10.324(5)A, α = 96.03(3)°, β = 109.88(3)°, γ = 76.82(3)°, and Z = 2, while [PPh4]2[Ni3(edt)4] (2) crystallizes in the monoclinic space group P21/c with (at −60°C) a = 13.713(3), b = 13.255(3), c = 15.754(5)A, β = 96.53(2)° and Z = 2. The structures were solved by direct methods and Fourier techniques from 4576 and 2671 diffractometer data, respectively, and refined to respective R values of 0.0552 and 0.0649. In the anion of1, one of the ligands provides two terminal thiolate-groups, and the other two each provide one terminal and one μ-thiolate-group such that each Ni(II) has an approximately square planar coordination geometry. The central NiS2Ni unit is not planar, being folded along the vector joining the two bridging sulphur atoms. The anion of2 is best considered as chelation of two identical [Ni(edt)2]2− units to a third, central Ni(II) atom. The anion has a crystallographically observed centre of symmetry, with the central nickel atom thus lying in a perfect plane formed by its four coordinated sulphur atoms. The outer two nickel atoms are approximately square planar and the Ni(NiS4)2 core exists in a chair conformation. Both of the anions described have short Ni ⋯ Ni distances [2.9414(22) in (1) and 2.8301(13)Ain (2)]. The structures and the spectroscopic properties achieved for these complexes are described and discussed herein.

Dynamics and structure of some tricarbonylferrole-iron tricarbonyl derivatives

Abstract A series of compounds of the formula Fe2(CO)6-x(PR3)x(R′C2R″)2 (x = 0, R′ and R″ = Ph, R′ and R″ = H, R′ = Ph and R″ = H; x = 1, K = Ph or n-Bu, and R′ and R″ = Ph) were studied by 13C NMR to observe their solution properties. The tricarbonylferrole unit was found to be static from −125 to +95° C, while the π-Fe(CO)3 group appeared to be fluxional over the same temperature range. Definite assignments of the carbonyl carbon and ferrole ring carbon resonances have been made. A low temperature single crystal X-ray study of Fe2(CO)5PPh3(PhC2Ph)2 demonstrated that the phosphine ligand was attached to the ferrole iron contrary to previous belief based on chemical evidence.