Synthesis and Magnetic Characterization of [Fe(.eta.5-C9Me7)2].bul.+[A].bul.- (A = TCNE, TCNQ, DDQ). X-ray Structure of [Fe(.eta.5-C9Me7)2].bul.+[TCNQ].bul.-

Homoleptic permethylpentalene complexes: "double metallocenes" of the first-row transition metals

The synthesis of the bimetallic permethylpentalene complexes Pn*2M2 (M = V, Cr, Mn, Co, Ni; Pn* = C8Me6) has been accomplished, and all of the complexes have been structurally characterized in the solid state by single-crystal X-ray diffraction. Pn*2V2 (1) and Pn*2Mn2 (3) show very short intermetallic distances that are consistent with metal-metal bonding, while the cobalt centers in Pn*2Co2 (4) exhibit differential bonding to each side of the Pn* ligand that is consistent with an eta(5):eta(3) formulation. The Pn* ligands in Pn*2Ni2 (5) are best described as eta(3):eta(3)-bonded to the metal centers. (1)H NMR studies indicate that all of the Pn*2M2 species exhibit D(2h) molecular symmetry in the solution phase; the temperature variation of the chemical shifts for the resonances of Pn*2Cr2 (2) indicates that the molecule has an S = 0 ground state and a thermally populated S = 1 excited state and can be successfully modeled using a Boltzmann distribution (DeltaH(o) = 14.9 kJ mol(-1) and DeltaS(o) = 26.5 J K(-1) mol(-1)). The solid-state molar magnetic susceptibility of 3 obeys the Curie-Weiss law with mu(eff) = 2.78 muB and theta = -1.0 K; the complex is best described as having an S = 1 electronic ground state over the temperature range 4-300 K. Paradoxically, attempts to isolate the "double ferrocene" equivalent, Pn*2Fe2, led only to the isolation of the permethylpentalene dimer Pn*2 (6). Solution electrochemical studies were performed on all of the organometallic compounds; 2-5 exhibit multiple quasi-reversible redox processes. Density functional theory calculations were performed on this series of complexes in order to rationalize the observed structural and spectroscopic data and provide estimates of the M-M bond orders.

High-temperature metal–organic magnets

For over two decades there have been intense efforts aimed at the development of alternatives to conventional magnets, particularly materials comprised in part or wholly of molecular components. Such alternatives offer the prospect of realizing magnets fabricated through controlled, low-temperature, solution-based chemistry, as opposed to high-temperature metallurgical routes, and also the possibility of tuning magnetic properties through synthesis. However, examples of magnetically ordered molecular materials at or near room temperature are extremely rare, and the properties of these materials are often capricious and difficult to reproduce. Here we present a versatile solution-based route to a new class of metal-organic materials exhibiting magnetic order well above room temperature. Reactions of the metal (M) precursor complex bis(1,5-cyclooctadiene)nickel with three different organics A-TCNE (tetracyanoethylene), TCNQ (7,7,8,8-tetracyanoquinodimethane) or DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone)--proceed via electron transfer from nickel to A and lead to materials containing Ni(II) ions and reduced forms of A in a 2:1 Ni:A ratio--that is, opposite to that of conventional (low Curie temperature) MA(2)-type magnets. These materials also contain oxygen-based species within their architectures. Magnetic characterization of the three compounds reveals spontaneous field-dependent magnetization and hysteresis at room temperature, with ordering temperatures well above ambient. The unusual stoichiometry and striking magnetic properties highlight these three compounds as members of a class of stable magnets that are at the interface between conventional inorganic magnets and genuine molecule-based magnets.

Bis(1,2,3-trimethylindenyl)iron(III) 2,3-Dicyanonaphtho-1,4-quinonide, a Non-Metallocene, Charge-Transfer Salt Metamagnet with Complementary Donor−Acceptor Geometries

Bis(1,2,3-trimethylindenyl)iron(III) can be paired with 2,3-dicyanonaphtho-1,4-quinone to give an air-stable pi-stacked metamagnet with T(c) = 4.1 K, the first example of a non-metallocene CT salt magnet in this class. A single crystal X-ray structure of the Fe(1,2,3-Me(3)C(9)H(4))(2)[DCNQ] salt indicates that it consists of stacks of alternating donors and acceptors, in which the DCNQ ring systems are aligned with indenyl groups above and below, and the long axes of the DCNQ and the indenyl ligand are parallel to each other. This arrangement suggests that the magnetic properties arise from favorable interactions due to geometric similarities between the donor and acceptor, and not from a unique property of the donor itself.

2-D interwoven and 3-D 5-fold interpenetrating silver(I) complexes of 1-(isocyanidomethyl)-1H-benzotriazole and 1,3-bis(dicyanomethylidene)indan

This paper presents novel and distinctive organosilver polymers with intriguing structure motifs, constructed from iodoacetonitrile (L1), 1-(isocyanidomethyl)-1H-benzotriazole (L2), 1,3-bis(dicyanomethylidene)indan (L3), and silver(I) salts, respectively. Treatment of L1 with AgClO4 generated [Ag(L1)(ClO4)]n (1), whose X-ray determination revealed a 2-D wavy sheet structure with square grids. Reaction of L2 with AgPF6 gave rise to a novel 2-D wavy interwoven network, ([Ag(L2)(PO2F2)0.5])n (2). The complex [Ag2(L3)2]n (3) obtained by reaction of AgClO4 with L3 can be regarded as unprecedented 3-D 5-fold interpenetrating nets with columnar aromatic stacks and indicates semiconductive behavior. The IR, ESR spectroscopic results, conductivities, and structural features of the complexes are discussed, respectively. The present findings may provide insight into the coordination versatility of silver(I) and polynitrile ligands and an inspiration for the self-assembly of novel supramolecular networks with multifunctional ligands. Crystal data: 1, C2H2AgINClO4, orthorhombic, Pca2(1) (No. 29), a = 14.503(1) A, b = 5.104(2) A, c = 10.2019(9) A, Z = 4; 2, C8H6AgN4PF4O, orthorhombic, Pnna (No. 52), a = 12.2705(3) A, b = 21.150(1) A, c = 10.040(1) A, Z = 8; 3, C30H10Ag2N8, triclinic, P1 (No. 2), a = 14.920(2) A, b = 11.896(2) A, c = 7.400(4) A, alpha = 86.55(2) degrees, beta = 80.87(2) degrees, gamma = 74.47(1) degrees, Z = 2.

New Adducts of Dirhodium(II) Formamidinate Complexes with Polycyano Acceptor Molecules. X-ray Crystal Structure of the Tricyanomethanide Complex Rh(2)(form)(4)[C(CN)(3)] (form = N,N'-Di-p-tolylformamidinate)

The dirhodium(II) formamidinate complexes Rh(2)(form)(2)(O(2)CCF(3))(2)(H(2)O)(2) (I) and Rh(2)(form)(4) (II, form = N,N'-di-p-tolylformamidinate) react with the polycyano acceptor molecules tetracyanoethylene (TCNE), tetracyano-p-quinodimethane (TCNQ), 2,5-dimethyl-N,N'-dicyano-p-quinonediimine (2,5-DMDCNQI), and N,N'-naphthocyano-p-quinonediimine (NCNQI) giving species whose nature is critically dependent on the redox potentials of the two parent complexes. Complex I reacts via axial coordination with negligible charge transfer (CT) from the dimetal unit to the ligand. With TCNE, it gives the labile monoaxial adduct Rh(2)(form)(2)(O(2)CCF(3))(2)(TCNE) (1), which easily loses the cyano ligand restoring the parent complex. TCNQ, 2,5-DMDCNQI, and NCNQI react with I giving polymeric materials of composition {[Rh(2)(form)(2)(O(2)CCF(3))(2)](2)TCNQ)}(n)() (2) and [Rh(2)(form)(2)(O(2)CCF(3))(2)X](n)() (X = 2,5-DMDCNQI (3), NCNQI (4)). The reaction of II with TCNE, TCNQ, and 2,5-DMDCNQI proceeds via a single electron transfer from the dimetal unit to the cyano ligand to form the CT species [Rh(2)(form)(4)X] (X = TCNE (5), TCNQ (6), 2,5-DMDCNQI (7)). Electrochemical and EPR measurements suggest a different extent of coordination between the polycyano fragment and the dirhodium unit, depending upon the polarity of the solvents. Attempts to crystallize complex 5 from acetonitrile unexpectedly led to the formation of the tricyanomethanide complex Rh(2)(form)(4)[C(CN)(3)] (5A), arising from the unprecedented transformation of the tetracyanoethylenide ion into the tricyanomethanide anion. The complex crystallizes in the tetragonal P4/ncc space group with a = 14.169(6) Å, c = 29.20(2) Å, V = 5863(5) Å(3), and Z = 4. The molecule consists of a dirhodium unit symmetrically bridged by four formamidinate ligands and one tricyanomethanide anion N-coordinated at the axial position of Rh(2).