Mark M. Turnbull

The hydrolysis products of cis-diamminedichloroplatinum(II) 9. Chloride and bromide anation kinetics for some [PtII(N)2(OH2)2]2+ complexes and the structures of [PtIVBr4(N)2] ((N)2 = en, tn)1

Abstract The rate of the first step in the chloride ion anation of [Pt(N)2(OH2)2]2+ (k−2, M−1s−1) has been measured spectrophotometrically (I = 1.0 M) for (N)2 = cis-(NH3)2, cis-(py)2, en, chxn, tn, Me2tn and trans-(NH3)2. Kinetic parameters at 25°C are: cis-(NH3)2, 102k−2 = 9.27 M−1s−1, ΔH≠ = 66.3 kJ mol−1, ΔS≠ = −42 J K−1mol−1; cis-(py)2, 20.0, 72.0, −17; en, 24.5, 58.8, −59; chxn, 21.4, 66.0, −36; tn, 34.4, 67.2, −28; Me2tn, 33.2, 57.4, −61; trans-(NH3)2, 151, 50.6, −72. Similar data for the bromide ion anation of cis-[Pt(py)2(OH2)2]2+ are: 97, 58.8, −48. Bromide ion anation rates for [PtBr(N)2(OH2)]+ (k−1, M−1s−1) have also been measured giving kinetic parameters (25°C, I = 1.0 M): cis-(NH3)2, 102 k−1 = 1.99 M−1s−1, ΔH≠ = 57.8 kJ mol−1, ΔS≠ = −84 J K−1mol−1; cis-(py)2, 2.10, 57.2, −85; en, 6.40, 63.5, −55; chxn, 9.72, 56.6, −17; tn, 9.25, 52.9, −87; Me2tn, 8.70, 54.8, −62; trans-(NH3)2; 12.6, 69.0, −31. These data also allow an estimation of the rate of bromide release from [PtBr2(N)2] (k1, s−1) with kinetic parameters (25°C, I = 1.0 M): cis-(NH3)2, 104 k1 = 4.25 s−1, ΔH≠ = 87.0 kJ mol−1, ΔS≠ = −17 J K−1mol−1; cis-(py)2, 15.8, 38.5, −93; en, 5.12, 70.0, −73; chxn, 17.4, 53.3, −42; tn, 6.05, 112, +70; Me2tn, 9.88, 109, +141; trans-(NH3)2, 15.2, 45.7, −69. Dilute solutions of [Pt(N)2(OH2)2]2+, in the presence of excess bromide ion and on long (weeks) exposure to air, slowly deposit orange crystals of [Pt(IV)Br4(N)2] on spontaneous evaporation. The structures of ( N ) 2 = en ( monoclinic , C2/c, a = 10.414(3), b = 8.356(2), c = 11.651(9) A , β = 112.77(3)°, V = 934.8(8) A 3 , Z = 4) and ( N ) 2 = tn ( orthorhombic , Pnma, a = 12.666(4), b = 9.789(5), c = 8.352(3) A , V = 1035.5(7) A 3 , Z = 4) have been determined by single crystal X-ray diffraction. The average Pt(IV)-Br and Pt(IV)-N distances are 2.455(5) and 2.04(2) A, respectively.

Characterization of a quasi-one-dimensional spin-1/2 magnet which is gapless and paramagnetic for g μ B H ≲ J and k B T ≪ J

High field mangetization, field-dependent specific heat measurements, and zero field inelastic magnetic neutron scattering have been used to explore the magnetic properties of copper pyrazine dinitrate (Cu(C4H4N2)(NO3)2). The material is an ideal one-dimensional spin-1/2 Heisenberg antiferromagnet with nearest neighbor exchange constant J=0.90(1) meV and chains extending along the orthorhombic a-direction. As opposed to previosly studied molecular-based spin-1/2 magnetic systems, coppyer pyrazine dinitrate remains gapless and paramagnetic for g mu_B H/J at least up to 1.4 and for k_B T/J at least down to 0.03 this makes the material an excellent model system for exploring the T=0 critical line which is expected in the H - T phase diagram on the one-dimensional spin-1/2 Heisenberg antiferromagnet. As a first example of such a study we present accurate measurements of the Sommerfeld constant of the spinon gas versus g mu_B H/J < 1.4 which reveal a decrease of the averages spinon velocity by 32% in that field range. The results are in excellent agreement with numerical calculations based on the Bethe ansatz with no adjustable parameters.

Two-dimensional S = 1 2 Heisenberg antiferromagnets: Synthesis, structure, and magnetic properties

The magnetic susceptibility and magnetization of two layered S=½ Heisenberg antiferromagnets with moderate exchange are reported. The two isostructural compounds, (2-amino-5-chloropyridinium) 2 CuBr 4 [(5CAP) 2 CuBr 4 ] and (2-amino-5-methylpyridinium) 2 CuBr 4 [(5MAP) 2 CuBr 4 ], contain S=½, Cu(II) ions related by C centering, yielding four equivalent nearest neighbors The crystal structure of the synthesized compound, (5CAP) 2 CuBr 4 , shows the existence of layers of distorted copper(II)-bromide tetrahedra parallel to the ab plane, separated by the organic cations along the c axis. Magnetic pathways are available through the bromide-bromide contacts within the layers and provide for moderate antiferromagnetic exchange. Susceptibility measurements indicate interaction strengths to he 8.5(2) K and 6.5(2) K and ordering temperatures of 5.1(2) K and 3.8(2) K for (5CAP) 2 CuBr 4 and (5MAP) 2 CuBr 4 , respectively. High-field magnetization experiments on both compounds show upward curvature of M(H,T). Magnetization measurements made at T = 1.3 K show saturation occurs in (5MAP) 2 CuBr 4 at 18.8 T and in (5CAP) 2 CuBr 4 at 24.1 T. The magnetization curves are consistent with recent theoretical predictions. Single-crystal magnetization measured at 2.0 K indicates a spin-flop transition at 0.38 T and 0.63 T for (5CAP) 2 CuBr 4 and (5MAP) 2 CuBr 4 , respectively.

Synthesis, X-ray structures and magnetic properties of linear chain 4-cyanopyridine compounds: [Cu(4-CNpy)4(H2O)](ClO4)2 and M(4-CNpy)2Cl2 (M Mn, Fe, Co, Ni, Cu)

Abstract The synthesis, structures and magnetic properties of linear chain complexes of metal ions with 4-cyanopyridine are reported (4-CNpy=4-cyanopyridine): [Cu(4-CNpy) 4 (H 2 O)](ClO 4 ) 2 and M(4-CNpy) 2 Cl 2 (MMn, Fe, Co, Ni, Cu). All compounds crystallize in monoclinic systems. Crystallographic data for [Cu(4-CNpy) 4 (H 2 O)](ClO 4 ) 2 ] n ( 1 ): space group P 2 1 / c with a = 13.225(3), b = 10.567(2), c = 20.522(3) A , β = 99.71(2)°, V = 2826.7(9) A 3 , Z = 4, D calc = 1.640 Mg m −3 , μ = 3.430 mm −1 . The compound contains primer CuL 4 units with the ligands bounded to copper ions through the ring nitrogens. These units are weakly linked into chains through semi-coordinated bonds between the nitrile nitrogen and an adjacent copper ion via the axial sites. The magnetic data show only a weak antiferromagnetic interaction ( θ CW = −0.52(1) K). Crystallographic data for [Cu(4-CNpy) 2 Cl 2 ] n ( 2 ): space group P 2 1 / n with a = 3.779(2), b = 25.711(12), c = 7.104(4) A , β = 95.98(4)°, V = 686.48(4) A 3 , Z = 2, D calc = 1.658 Mg m −3 , μ = 5.575 mm −1 . Crystallographic data for [Mn(4-CNpy) 2 Cl 2 ] n ( 6 ): space group P 2 1 / c with a = 3.700(2), b = 7.198(2), c = 26.520(5) A , β = 92.13(3)°, V = 705.8(4) A 3 , Z = 2, D calc = 1.572 Mg m −3 , μ = 1.303 mm −1 . Both dichloride compounds similar structures, consisting of chains of metal ions bibridged by chlorides with the 4-CNpy ligands coordinated to the metal ions in the axial sites through the pyridine nitrogens. The difference in space groups is caused by the different modes of packing the chains into 3D lattices. Infrared spectra and powder X-ray diffraction patterns indicate that the remaining compounds form an isostructural series. The powder magnetic susceptibilities have been measured between 2 and 300 K for all compounds. Antiferromagnetic exchange (Cu, Mn) or ferromagnetic exchange (Ni, Co, Fe) exists within the chains. The Ni, Co and Fe compounds order antiferromagnetically at 7.2(2), 2.1(2) and 4.6(2) K, respectively. Magnetic field induced transitions have been observed in these three compounds below their ordering temperatures. The copper and manganese data have been fit to models for Heisenberg antiferromagnetic linear chain with S = 1 2 and S = 5 2 with exchange constants J Co / k = −13.7(2) K and J Mn / k = −0.5 7(1) K, respectively. The nickel and cobalt data have been fit to models for ferromagnetic linear chains, with the nickel compound corresponding to a S = 1 Heisenberg model with exchange constant J / lk = +4.8(2) K, and the cobalt compound to a S = 1 2 ferromagnetic Ising linear chain with exchange constant J / k = + 6.6(2) K. The iron data has not been successfully to fit to any model. It is concluded that the total magnetic interaction between the chains has been increased by approximately 50% by the substitution of 4-CNpy for pyridine.

Transition metal halide salts of 2-amino-3-methylpyridine: synthesis, crystal structures and magnetic properties of (3-MAP)2CuX4 [3-MAP=2-amino-3-methylpyridinium; X=Cl, Br]

Abstract The reaction of CuX2·nH2O with HX [X=Cl, Br] and 2-amino-3-methylpyridine in aqueous solution gave compounds of the formula (3-MAP)2(CuX4) [3-MAP=2-amino-3-methylpyridinium]. The compounds have been characterized by single-crystal X-ray diffraction. The complexes crystallize as salts with the 3-MAP cations separating layers of tetrahalometallate anions. Both compounds have two independent molecules in their asymmetric units. Weak antiferromagnetic interactions are observed, which suggest a primarily low-dimensional magnetic exchange network.

Crystal chemistry of the copper bromide/2-aminopyrimidine system

Abstract The preparation and crystal structures are reported for seven compounds obtained from the interaction of copper(II) bromide with 2-aminopyrimidine. This includes four copper(II) bromide compounds and three copper(I) bromide complexes. The L = 2-aminopyrimidine moiety can exist as neutral L species, as well as either a monoprotonated LH + cation or a diprotonated LH 2 2+ dictation in which one or two of the ring nitrogen atoms, respectively, are protonated. The neutral ligand is found to coordinate to one or two Cu ions through the ring nitrogen atoms, while the monocation may or may not coordinate through the unprotonated ring nitrogen atom. The crystals are stabilized by hydrogen bonding between the halide ions and the −NH 2 and/or > N  H + fragments. The Cu(II) species show a range of coordination geometries L 2 CuBr 2 contains isolated four-coordinate species with a planar coordination geometry ( CuN = 1.996(5) and CuBr = 2.401(1) A ) (LH) 2 CuBr 4 contains isolated six-coordinate species with a square planar CuBr 4 2− arrangement ( CuBr = 2.427(1) and 2.487(1) A ) augmented by two LH ligands ( CuN = 2.787(6) A ). The (LH) 2 Cu 2 Br 6 salt contains planar bibridged Cu 2 Br 6 2− dimers (CuBr(av.) = 2.424 A) which aggregate into stacks through the formation of semicoordinate CuBr bonds ( distances = 3.067(1) and 3.335(1) A ). Finally, (LH) 2 CuBr 4 contains isolated distorted tetrahedral CuBr 4 2− anions, with CuBr = 2.388 A (av.) and the larger trans BrCuBr angles of 135.4° (av.). The Cu(I) compounds all contain a common structural element: a (CuBr) n chain as illustrated in I with CuBr ≌ 2.52−2.56 A and CuBrCu = 99–107°. In each chain, the Cu(I) ion completes a tetrahedral coordination by forming bonds to Br − ions or ring N atoms in the ligands. In LCuBr, the pyrimidine ligands bridge Cu atoms on adjacent chains, forming a rectangular two dimensional network. This gives the Cu(I) ion a N 2 Br 2 coordination environment. For the LCu 2 Br 2 compound, the (CuBr) n chains dimerize through the formation of CuBr linkages between chains. The pyrimidine ligands now bridge between Cu atoms on adjacent dimerized chains. Thus the Cu(I) ion has a Br 3 N coordination environment. Finally, in (LH)CuBr 2 , each copper ion in the chain completes its coordination sphere by coordinating to one pyridinium cation and to one bromide ion, to also attain a Br 3 N coordination sphere.

Review: A gentle introduction to magnetism: units, fields, theory, and experiment

We present an introduction to the workings, units of measure, and general properties of magnetic materials. This is intended as a “primer to interpretation of magnetic data” for those who are entering the field, or those who are encountering magnetic measurements in the literature. We expect this work will serve as an initial guide to the reader to familiarize them with the basics in the hope that those working in the field of magnetochemistry will wish to explore additional, more detailed literature as their specific investigations demand. Topics covered include: magnetic fields and units (SI and cgs), paramagnetism (magnetization and magnetic susceptibility), Curie and Curie–Weiss behavior, magnetic exchange interactions, magnetic anisotropy, dimeric systems and exchange-coupled networks (including chains, ladders, and layers), and long-range order. Graphical Abstract

Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain.

Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/J< or =0.025 for H=0 and H=8.7 T, where the system is approximately 30% magnetized. At H=0, the results are in agreement with exact calculations of the dynamic spin correlation function for a two-spinon continuum. At H=8.7 T, there are multiple overlapping continua with incommensurate soft modes. The boundaries of these continua confirm long-standing predictions, and the intensities are consistent with exact diagonalization and Bethe ansatz calculations.

Field-induced Tomonaga-Luttinger liquid phase of a two-leg spin-1/2 ladder with strong leg interactions

We study the magnetic-field-induced quantum phase transition from a gapped quantum phase that has no magnetic long-range order into a gapless phase in the spin-1/2 ladder compound bis(2,3-dimethylpyridinium) tetrabromocuprate (DIMPY). At temperatures below about 1 K, the specific heat in the gapless phase attains an asymptotic linear temperature dependence, characteristic of a Tomonaga-Luttinger liquid. Inelastic neutron scattering and the specific heat measurements in both phases are in good agreement with theoretical calculations, demonstrating that DIMPY is the first model material for an S=1/2 two-leg spin ladder in the strong-leg regime.

Synthesis, structure, and magnetic properties of bis(3-amino-2-chloropyridinium) tetrahalocuprate(II) [halide = Cl or Br]

The reaction of CuX2 (X = Cl or Br) with 3-amino-2-chloropyridine in aqueous acids (HX; X = Cl or Br) yields bis(3-amino-2-chloropyridinium)tetrachlorocuprate(II) and bis(3-amino-2-chloropyridinium)tetrabromocuprate(II). Both compounds have been characterized by IR, powder X-ray diffraction, single-crystal X-ray diffraction and temperature dependent magnetic susceptibility. The compounds are isomorphous and exhibit weak antiferromagnetic interactions.