Biomedical subjects
Publications and source records attributed to John A Schlueter.
[Cu(HF2)(pyz)2]BF4 consists of rare mu(1,3) bridging HF2- anions and micro-pyrazine ligands leading to a 3D pseudo-cubic framework that antiferromagnetically orders below 1.54(1) K.
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.
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.
The reaction product of cobalt carbonyl decomposition depends on the concentration of the oleic acid ligand. With a low concentration of ligand, nanocrystals nucleate and grow to large ferromagnetic particles through the process of Ostwald ripening and coalescence coarsening. With a high concentration of ligand, stable cluster complexes are formed. Addition or removal of ligand from the reaction products can interchange the formation of cluster complexes and nanocrystals.
A novel electron spin-reorientation transition is discovered by 13C NMR in the quasi-two-dimensional organic antiferromagnet kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl. The spin reorientation occurs as an external field is swept through the orientation of the characteristic vector of the Dzialoshinskii-Moriya (DM) interaction, thus providing a precise determination of the orientation of the DM vector. Such a spin reorientation could help to characterize the DM interaction in other antiferromagnetic systems.
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.
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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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.
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.
Using aqueous conditions, three new coordination polymers containing Cu(2+) cations, dicyanamide (dca) anions, and pyrimidine (pym) were isolated and structurally and magnetically characterized. Comprising the bulk of the product yield, Cu(dca)(2)(pym)(2), 1, crystallizes in the monoclinic space group P2(1)/c with a = 7.3569(5) A, b = 13.4482(9) A, c = 7.4559(5) A, beta = 98.984(3) degrees, and V = 728.6(1) A and forms linear 1D chains. The second compound, Cu(dca)(NO(3))(pym)(H(2)O), 2, is also monoclinic, P2(1)/n, with a = 7.6475(3) A, b = 12.2422(5) A, c = 11.0286(4) A, beta = 106.585(2) degrees, and V = 989.6(1) A(3). A 2D network structure consisting of both bridging mu-dca and pym ligands is formed while the NO(3)(-) and H(2)O are axially bonded to the Cu center. Cu(3)(dca)(6)(pym)(2).0.75H(2)O, 3, is triclinic, Ponemacr;, with a = 7.7439(4) A, b = 9.3388(5) A, c = 10.1779(5) A, alpha = 86.014(2) degrees, beta = 88.505(2) degrees, gamma = 73.623(2) degrees, and V = 704.46(9) A(3). The structure of 3 is quite unique in that [Cu(3)(pym)(2)](6+) trimers are interconnected via mu-dca ligands affording a complex 3D self-penetrating framework. Magnetically, 1 exhibits extremely weak exchange interactions along the Cu-(dca)(2)-Cu ribbons while 2 and 3 display very strong magnetic couplings mediated by the mu-bonded pym ligands. Moreover, 2 shows a broad maximum in chi(T) at 40 K and behaves as a uniform 1D antiferromagnetic chain with g = 2.09(1), J/k(B) = -42.6(1) K, and TIP = -66 x 10(-)(6) emu/mol. An S = (1)/(2) trimer model that includes intertrimer interactions successfully described the magnetic behavior of 3, yielding g = 2.10(1), J/k(B) = -69.4(5) K, theta = -0.28(3) K, and TIP = -180 x 10(-)(6) emu/mol. It is found that mu-bonded dca and pym ligands mediate very weak and very strong exchange interactions, respectively, between Cu(2+) centers.
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.
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.
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.