(6), PPh 3 (7), P(OEt) 3 (8)] were prepared as Fe-only hydrogenase-active-site models by controllable CO displacement of [(μ-pdt)Fe 2 (CO) 6 ] by tertiary phosphanes. The coordination configurations of 3-6 were characterized by X-ray crystallography. Disubstituted diiron complex 6 features an

The displacement of CO in a few simple Fe(I)-Fe(I) hydrogenase model complexes by bisphosphine ligands Ph2P-(CH2)n-PPh2 [with n = 1 (dppm) or n = 2 (dppe)] is described. The reaction of [{mu-(SCH2)2CH2}Fe2(CO)6] (1) and [{mu-(SCH2)2N(CH2CH2CH3)}Fe2(CO)6] (2) with dppe gave double butterfly complexes [{mu-(SCH2)2CH2}Fe2(CO)5(Ph2PCH2)]2 (3) and [{mu-(SCH2)2N(CH2CH2CH3)}Fe2(CO)5(Ph2PCH2)]2 (4), where two Fe2S2 units are linked by the bisphosphine. In addition, an unexpected byproduct, [{mu-(SCH2)2N(CH2CH2CH3)}Fe2(CO)5{Ph2PCH2CH2(Ph2PS)}] (5), was isolated when 2 was used as a substrate, where only one phosphorus atom of dppe is coordinated, while the other has been converted to P=S, presumably by nucleophilic attack on bridging sulfur. By contrast, the reaction of 1 and 2 with dppm under mild conditions gave only complexes [{mu-(SCH2)2CH2}Fe2(CO)5(Ph2PCH2PPh2)] (6) and [{mu-(SCH2)2N(CH2CH2CH3)}Fe2(CO)5(Ph2PCH2PPh2)] (8), where one ligand coordinated in a monodentate fashion to one Fe2S2 unit. Furthermore, under forcing conditions, the complexes [{mu-(SCH2)2CH2}Fe2(CO)4{mu-(Ph2P)2CH2}] (7) and [{mu-(SCH2)2N(CH2CH2CH3)}Fe2(CO)4{mu-(Ph2P)2CH2}] (9) were formed, where the phosphine acts as a bidentate ligand, binding to both the iron atoms in the same molecular unit. Electrochemical studies show that the complexes 3, 4, and 9 catalyze the reduction of protons to molecular hydrogen, with 4 electrolyzed already at -1.40 V versus Ag/AgNO3 (-1.0 V vs NHE).

Seven new manganese(II, III, IV) pyridinecarboxylate compounds (Et4N)[MnCl2(pic)2] (1, Hpic = picolinic acid) [MnCl(pic)2(H2O)]·H2O (2), [MnCl(pic)(H2O)2]n (3), [Mn(pic)2]n (4), [MnCl(pic)]n (5), [MnCl2(4‐C5H4NHCOO)]n (6) and [Mn2O2(pic)4] (7) were synthesized and structurally characterized. The picolinate ligand coordinates to the Mn ion forming a chelating five‐membered ring which constructs diverse architectures by various bridging modes, such as μ‐Cl, μ1,1‐ and μ1,3‐carboxylate bridges (syn‐syn and syn‐anti modes). The interaction between the pyridyl rings is discussed, displaying a face‐to‐face π‐π stacking for complex 6 and a T‐shaped C−H···π attraction for complex 4. Complex 3 has an infinite zigzag chain structure in which two neighboring Mn ions are linked by a carboxylate bridge in a syn‐anti mode. In complex 4, the Mn(pic)2 fragments are joined to each other by double μ1,1‐carboxylate bridges, forming a 2D layer structure. Complex 5 contains Mn4O4 square subunits which are connected by double μ‐Cl bridges to form a grid‐like 2D structure. The isonicotinate complex 6 has a zigzag chain structure containing mixed double μ‐Cl and μ1,3‐carboxylate bridges in a syn‐syn mode. Protonation at the pyridyl‐N position was found and identified by the IR and magnetic properties of 6. The participation of an oxidizing agent like MnO4− leads to complexes containing higher valent manganese (1, 2 and 7). The IR spectra of these complexes are discussed and found to be consistent with the structural features. The magnetic properties of complexes 4, 5 and 6 have been investigated. Antiferromagnetic coupling interactions were observed and satisfactory fitting results were obtained with J values ranging from −0.63 cm−1 to −2.35 cm−1. The magnetic parameters of these complexes, together with the parameters of other Mn complexes with comparable structures, are compared and discussed based on the bridging modes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

No abstract

(7; pyz = pyrazine), have been synthesized by treatment of the appropriate Mn 2+ salt and H 2 phth with different diimine ligands. They were characterized by X-ray diffraction and show a variety of nuclearities, ranging from di-

The use of phosphonic acids in the synthesis of mixed-metal CeMn complexes has led to the formation of two phosphonate complexes with unusual topologies: [Ce(2)Mn(6)O(6)(OH)(5)(t-BuPO(3))(6)(O(2)CMe)(3)] x 53 H(2)O (1 x 53 H(2)O) and [Ce(22)Mn(12)O(34)(MePO(3))(12)(O(2)CMe)(33)(OMe)(6)(NO(3))(H(2)O)(12)](n) (2). The two mixed-metal CeMn complexes were both prepared from a reaction system containing Mn(O(2)CMe)(2) and (NH(4))(2)[Ce(NO(3))(6)] with similar procedures except for using different phosphonic acids (tert-butylphosphonic acid and methylphosphonic acid, respectively) as coligands. Both complexes possess rare topology of triangular type, with compound 1 being a 0D discrete cluster, whereas, compound 2 is a 1D polymer. The octanuclear core of complex 1 is composed of three symmetry equivalent distorted cubanes {Ce(IV)(2)Mn(IV)(2)O(2)(OH)(2)} sharing a trigonal-bipyramidal unit {Ce(IV)(2)(OH)(3)} in the centre. Compound 2 is a one-dimensional chain polymer of identical Ce(22)Mn(12)O(34) units linked together by NO(3)(-) and MeCO(2)(-) groups, while the Ce(22)Mn(12)O(34) unit is constituted by two centrosymmetric Ce(9)(IV)Ce(2)(III)Mn(IV)(6)O(17) subunits, which features three identical distorted cubanes {Ce(IV)(2)Mn(IV)(2)O(4)} connecting to a central trigonal-bipyramidal unit {Ce(IV)(3)O(2)}, and two additional Ce(III) ions capping the top and bottom of the central trigonal bipyramid by six MePO(3)(2-) ligands. Complexes 1 and 2 are the first high-nuclearity Mn/Ln aggregates reported to date using phosphonates as ligands. Magnetic susceptibility measurements reveal that compound 1 displays dominant ferromagnetic interactions between the adjacent metal ions with the best fit parameters for the exchanges are J(1) = 6.186 cm(-1), J(2) = 4.172 cm(-1), and with a result of S = 9 ground state confirmed by the M versus HT(-1) data, which indicates the spins of all the six Mn(IV) ions in the cluster are parallel to each other. In contrast, the data for 2 reveals overall antiferromagnetic couplings within the cluster and a resulting S = 6 ground state. Both the in-phase signal chi'(M)T and out-of-phase signal chi''(M) of the two complexes exhibit frequency-dependent below approximate 3 K.

No abstract

No abstract