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Urs Geiser

Publications and source records attributed to Urs Geiser.

10 recordsLinked to original sources
PubMed2005

Bis(4,4'-bipyridinium) hexacyanoplatinate(IV) bis(4,4'-bipyridine).

In the title compound, (C10H9N2)2[Pt(CN)6].2C10H8N2 or [(Hbpy)+]2[Pt(CN)6](2-).2bpy, where bpy is 4,4'-bipyridine, the Hbpy+ cations and bpy molecules form a hydrogen-bonded two-dimensional cationic approximately square grid parallel to the (110) plane. The [Pt(CN)6]2- dianions reside in the cavities within this grid, with the nitrile N atoms forming weak hydrogen bonds with the CH groups in the cationic lattice.

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PubMed2005

Structural and magnetic diversity in tetraalkylammonium salts of anionic M[N(CN)2]3(-) (M = Mn and Ni) three-dimensional coordination polymers.

Tetraalkylammonium cations, (NR4)+ (R = C3H7, C4H9, and C5H11), have been used as templates to form a new family of [M(dca)3]- [M = Mn and Ni; dca = dicyanamide or N(CN)2(-)] salts. The tetrapropylammonium (TPrA) salts possess a perovskite-type anion structure. (TPrA)[Mn(dca)3] (1) crystallizes in the tetragonal space group P42(1)c, with a = 16.2945(8) A, c = 17.4321(8) A, and V = 4628.4(6) A(3) at T = 298 K. At room temperature, (TPrA)[Ni(dca)3] (2) crystallizes in the orthorhombic space group Pnna, with a = 17.171(2) A, b = 22.992(2) A, c = 22.750(2) A, and V = 8981(2) A3, but undergoes a first-order phase transition within the temperature range 150-220 K to the tetragonal space group P42(1)c, with a = 16.0985(7) A, c = 17.0287(8) A, and V = 4413.2(5) A3 at T = 160 K. At 110 K, 2 returns to the Pnna space group with a = 17.116(2) A, b = 22.800(3) A, c = 22.641(3) A, and V = 8835(3) A3. The tetrabutylammonium (TBA) salts possess a triple rutile structure. (TBA)[Mn(dca)3] (3) crystallizes in the orthorhombic space group P2(1)2(1)2, with a = 16.0107(6) A, b = 16.0114(6), c = 21.5577(8) A, and V = 5526.4(5) A3. (TBA)[Ni(dca)3] (4) also crystallizes in the orthorhombic space group P2(1)2(1)2, with a = 15.6842(5) A, b = 15.6841(6) A, c = 21.1551(8) A, and V = 5204.0(5) A3. The tetrapentylammonium (TPnA) salts crystallize with a LiSbO3 structure type, space group Pnna. Lattice parameters for (TPnA)[Mn(dca)3] (5) are a = 13.2236(6) A, b = 11.6300(6) A, c = 20.3176(9) A, and V = 3124.6(4) A3, and for (TPnA)[Ni(dca)3] (6), a = 12.9380(4) A, b = 11.6233(4) A, c = 19.8038(7) A, and V = 2978.1(2) A3. Long-range antiferromagnetic ordering has been observed in the manganese salts below 2.1 K, as indicated by alternating current susceptibility measurements. Magnetic susceptibility data for the nickel salts do not show evidence for long-range magnetic ordering but can be described using an S = 1 zero-field splitting model with the exchange Hamiltonian H = -J sigma(S(i)S(i+1)) + D sigma((S(i)z)2) + g mu(beta)B sigma(S(i)), giving absolute value(D)/kB values that range between 1.98(1) K and 3.20(2) K.

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PubMed2004

Spin canting in the 3D anionic dicyanamide structure (SPh(3))Mn(dca)(3) (Ph = phenyl, dca = dicyanamide).

Through use of the SPh(3)(+) (Ph = phenyl, C(6)H(5)) cation as a molecular template, a new three-dimensional Mn(dca)(3)(-) [dca = dicyanamide, N(CN)(2)(-)] anionic structure has been crystallized. At room temperature, (SPh(3))Mn(dca)(3) (1) crystallizes in the monoclinic space group P2(1)/c, with a = 11.7079(5) A, b = 12.8554(5) A, c = 16.8605(6) A, beta = 100.666(2) degrees, and V = 2493.8(3) A(3). Magnetic susceptibility measurements indicate that this salt exhibits a spin canted long range antiferromagnetically ordered ground state below 2.5 K.

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PubMed2004

Synthesis, crystal structure, and physical properties of (BEDT-TTF)[Ni(tdas)2] (BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene; tdas = 1,2,5-thiadiazole-3,4-dithiolate): first monomeric [Ni(tdas)2]- monoanion.

We report the synthesis, structure, and physical properties of (BEDT-TTF)[Ni(tdas)2] [BEDT-TTF, or ET, is bis(ethylenedithio)tetrathiafulvalene; tdas is 1,2,5-thiadiazole-3,4-dithiolate], which is the first example of a salt containing monomeric [Ni(tdas)2]- monoanions. This salt, which crystallizes in the monoclinic space group P2(1)/c with a = 17.2324(6) A, b = 13.2740(5) A, c = 10.9467(4) A, beta = 96.974(2) degrees, and V = 2485.5(2) A(3), forms a layered structure. One layer contains dimerized BEDT-TTF electron donor molecules and isolated [Ni(tdas)2]- monoanions, while the second layer contains chains of [Ni(tdas)2]- monoanions. Conductivity measurements show that (BEDT-TTF)[Ni(tdas)2] has a semiconductor-to-semiconductor transition near 200 K, while magnetic measurements indicate that it is an S = 1/2 paramagnet with weak antiferromagnetic coupling. Reflectance spectra reveal bands in the near-infrared region (6.6 x 10(3) and 10.6 x 10(3) cm(-1)) which are typical of (BEDT-TTF)2(2+) dimers. From these data, we can conclude that the unpaired electron lies on the [Ni(tdas)2]- anions. Tight-binding band structure calculations were used to analyze the electronic structure of this salt.

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PubMed2003

Potassium carbamoyldicyanomethanide.

The crystal structure of the title compound, K[(CN)(2)CC(O)NH(2))] or K(+).C(4)H(2)N(3)O(-), conventionally abbreviated as Kcdm, where cdm is carbamoyldicyanomethanide, is described. The bond lengths and angles of the cdm cation are comparable to those reported previously for [M(cdm)(2)(H(2)O)(4)].2H(2)O (M = Ni, Mn and Co). The K atoms are coordinated to four nitrile N atoms and two carbonyl O atoms in a distorted trigonal prismatic fashion, with two further N atoms semicoordinated through the centers of two prism side faces. This coordination leads to the formation of mixed anion-cation sheets parallel to the ab plane, which are joined together via hydrogen-bonding interactions. The cdm anion is potentially useful for the formation of transition metal coordination polymers, in which magnetic superexchange could occur through a bidentate cdm bridge. Kcdm provides a model compound by which the molecular geometry of the cdm anion can be analyzed.

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PubMed2003

Potassium dicyanoargentate(I) 1,4,7,10,13,16-hexaoxacyclooctadecane.

The crystal structure of the title compound, K[Ag(CN)(2)].C(12)H(24)O(6), conventionally denoted K(18-crown-6)Ag(CN)(2), where 18-crown-6 is 1,4,7,10,13,16-hexaoxacyclooctadecane, is characterized by closely packed linear chains formed by the coordination of the nitrile N atoms of the [Ag(CN)(2)](-) anions to the K(+) cations. The K atoms lie on centers of inversion and are additionally bound to the six O atoms of the crown ether.

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PubMed2003

catena-Poly[[diaquamanganese(II)]-di- micro -1,1,3,3-tetracyano-2-ethoxypropenido-kappa4N1:N3].

The crystal structure of the title compound, [Mn(C(9)H(5)N(4)O)(2)(H(2)O)(2)], conventionally denoted Mn(EtO-TCA)(2)(H(2)O)(2), where EtO-TCA is 2-ethoxy-1,1,3,3-tetracyanopropenide, is described. The EtO-TCA anions bridge Mn(II) centers through one of the nitrile N atoms of each of their two dicyanomethanide groups, thus forming dibridged chains along ab. These chains are linked into two-dimensional sheets through hydrogen bonding. The seven-atom bridge, which results in a long Mn.Mn intrachain interaction [9.0044 (4) A], as well as the large interchain separations [8.3288 (4) and 8.5220 (4) A] prohibit long-range magnetic ordering down to temperatures as low as 1.55 K.

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PubMed2003

KMnAg3(CN)6, a new triply interpenetrating network solid.

The single-crystal structure of potassium manganese tris[dicyanoargentate(I)], KMnAg(3)(CN)(6), is described. This is the first Mn-containing example of the triply interpenetrating MAg(3)(CN)(6) type. The K(+) ion is found to be located in an ordered manner on one of two possible interstitial sites, leading to a chiral space group.

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PubMed2002

Tetraaquabis(carbamoyldicyanomethanido-kappaN)manganese(II) dihydrate.

The crystal structure of [Mn(C(4)H(2)N(3)O)(2)(H(2)O)(4)].2H(2)O, conventionally abbreviated [Mn(cdm)(2)(H(2)O)(4)].2H(2)O, where cdm is carbamoyldicyanomethanide, is described. The bond lengths and distances are comparable to those previously reported for the isomorphous Ni and Co analogs. Molecular units are formed by coordination of the nitrile N atoms of two cdm anions and four water molecules to the manganese(II) cation. Although these mononuclear molecular species are connected via hydrogen bonding, no magnetic ordering was observed down to 1.55 K.

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