Wayne E. Marsh

Structure of bis-(4-methylpyridine)dichlorocopper(II): a dislocated linear chain

Abstract The crystal and molecular structure of bis(4-methylpyridine)dichlorocopper(II), Cu(C6H7N)2Cl2, has been determined from three-dimensional photographic X-ray data obtained from a twinned and highly mosaic crystal. The complex crytallizes in space group P21/c of the monoclinic system with two formula units in a cell of dimensions a = 9.745(7), b = 3.932(4), c = 19.035(9) A, β = 111.8(2)°. The observed diffraction pattern, however, is nearly consistent with orthorhombic symmetry and the space group Cmma. The chain axis is parallel to the monoclinic crystallographic b-axis, and the twinning occurs perpendicular to this axis; the twinning causes dislocations in the chain by limiting the chain lengths to the sizes of the ordered crystal domains along the chain axis. The geometry at each copper atom is (4 + 2) tetragonally-elongated octahedral, the in-plane ligands being two trans-nitrogen atoms [CuN =2.07(3) A] and two trans-chlorine atoms [CuCl =2.35(1) A]. The axial ligands are symmetry-related chlorine atoms, which are in-plane ligands of the adjacent copper atoms in the chain, the axial CuCl and CuCu′ distances being 3.19(1) and 3.932(4) A, respectively. Each chain is very similar to that found in the analogous pyridine complex, but the arrangement of the chains in the crystal is more like that in the thiazole complex Cu(thz)2Cl2.

The Synthesis and Static Magnetic Properties of First-Row Transition-Metal Compounds with Chain Structures

The most authoritative reviews of exchange coupling in one-dimensional linear chain systems of transition-metal ions are now several years old.1–4 Recent advances are largely a result of systematic studies of magnetic properties in conjunction with structural determinations. Since a large number of systems have been investigated, we will discuss only one example of each type of behavior that has been found for each of the first-row transition-metal ions, and tabulate data for other systems which have figured prominently in the development of the field. For the most part, only those chain compounds for which rather complete structural and magnetic data are available will be considered here.

Structure and magnetism in the chloro-bridged copper(II) complex Di-μ-chloro-bis[chlorobis(4-methyloxazole)copper(II)

Abstract The dimeric complex bis[dichlorobis(4-methyloxazole)copper(II)], [Cu(4-Meox) 2 Cl 2 ] 2 or [CuC 4 H 5 NO) 2 Cl 2 ] 2 has been synthesized and its structure has been determined from three-dimensional counter X-ray data. The complex crystallizes in the monoclinic space group P2 1 /n with two dimeric formula units in a cell of dimensions a= 8.177(2), b = 12.866(5), c = 11.063(6) A,β = 98.31(3)°. The structure has been refined by least-squares techniques to a value of the conventional R-factor (on F) of 0.033 based on 2071 independent data. The geometry at each copper center is severely distorted tetragonal pyramidal, the basal ligands being two trans nitrogen atoms from the 4-Meox ligands and two trans chloride ligands while the apical site is occupied by an inversion-related chloride ion. Thus, the dimeric entity is of the axial-equatorial type in which the inversion-related bridging chloride ligands are each axial to one copper and equatorial to the other. The CuCu separation in the dimer is 3.507(1) A and the bridging CuClCu′ angle (φ) is 89.46(2)°. The magnetic susceptibility of the complex exhibits a maximum near 2 K, and the data have been fitted to the magnetization expression yielding g = 2.118 and a singlet-triplet separation of 2.6 cm −1 with the singlet as the ground state.

Synthesis and structural and magnetic characterization of the dimeric complex bis[dibromobis(4-methyloxazole)copper(II)]

Abstract The crystal and molecular structure of the copper(II) complex bis[dibromobis(4-methyloxazole)copper(II)], [CuBr 2 (C 4 H 5 NO) 2 ] 2 , has been determined from three-dimensional X-ray counter data. The complex crystallizes in the monoclinic space group P2 1 /n with two dimeric formula units in a cell of dimensions a = 8.546(4), b = 13.062(5), c = 11.049(6) A, and β = 96.88(4)°. The observed and calculated densities are 2.07 and 2.113 g cm −3 , respectively. The structure has been refined by least-squares methods to a final value of the weighted R -factor (on F ) of 0.037 based on 1579 independent data with I ⩾3σ(I). The complex is dimeric, with severely distorted tetragonal pyramidal geometry at each copper center. The four ligands in the base plane are two trans nitrogen atoms from the 4-methyloxazole ligands and two bromide ligands, one of which is apical to the other copper atom, while the apical ligand is a bridging ion. The out-of-plane CuBr distance is 2.710(1) A an the CuCu distance is 3.626(1) A, leading to a bridging CuBrCu angle of 87.00(3)°. The geometric distortion in the complex is evidenced by the in-plane Br(1)CuBr(2) angle of only 157.15(4)°. The magnetic susceptibility of the complex has been measured as a function of temperature, and the data have been fitted to both the Van Vleck expression and (equally well) to a magnetization expression yielding g = 2.087 and a singlet-triplet separation of approximately 15.15 cm −1 with the singlet as the ground state. This relatively large singlet-triplet splitting is discussed in the light of the observed structure.

Intradimer and interdimer exchange coupling in the mixed ligand complex bis-μ-chloro-bis[chloro(4-methylthiazole)dimethylformamidecopper(II)]: a spin ladder system

Abstract The structure of the mixed ligand complex bis-μ-chloro-bis[chloro(4-methylthiazole)dimethylformamidecopper(II)] has been determined from three-dimensional X-ray counter data. The complex [Cu-(C4H5NS)(DMF)Cl2]2 crystallizes in the monoclinic space group P 2 1 n with two formula units in a cell of dimensions a = 7.349(7), b = 20.306(7), c = 8.909(3) A and β = 112.53(6)°. The final weighted R factor is 0.032 based on 1646 data. In this first example of a mixed ligand bis-μ-chloro-copper(II) complex, copper is five-coordinate, with the coordination geometry being distorted from an idealized tetragonal pyramidal. The Cu2Cl2 bridging unit is constrained to be planar by the presence of a center of symmetry, and the CuCl distances are 2.296(2) and 2.724(1) A with a CuCl⋯Cu′ angle of 95.29(7)°. Magnetic susceptibility measurements reveal antiferromagnetic exchange coupling, and the best fit of equation for an exchange coupled pair of S = 1 2 ions yields J = −1.7 cm−1 and g = 2.105. The exchange coupling constant lies in the range of values for a φ R o value of 35 deg A−1. The quality of the fit is markedly improved if intermider exchange interactions are taken into account. The dimers pack in the solid state to form a ladder-like structure with copper(II)sulfur contacts of 3.906(3) A. Best fit exchange coupling constants for the spin ladder of −1.17 and −1.0 cm−1 were obtained from a calculation on a closed ring of 10 spins with nearest neighbor and next-nearest neighbor interactions.