Leonhard Walz

Direct theoretical ab initio calculations in exchange coupled copper(II) dimers: Influence of the choice of the atomic basis set on the singlet–triplet splitting in modeled and real copper dimers

The singlet–triplet splitting (2J=EST) is calculated in bis‐[bromo‐(N,N‐diethylaminoethanolato)copper(II)], belonging to the group of alkoxo‐bridged copper(II) dimers, by a recently proposed ab initio method. The singlet–triplet splitting energy is obtained by a perturbation expansion closely related to Anderson’s formalism. The role of all valence electrons is taken into account and it is shown to be very important in order to obtain a satisfying agreement with the experimental result. Two important facts, from a computational point of view, are tested: influence of the atomic basis set size, and influence of modifying of the ligands. Changes in the basis set of the bridging atoms can induce variations in the results from 10% to 20%. As a final result, the theoretical value of the real complex is calculated to 2J(calc)=−1095 cm−1 and agrees with the experimental one 2J(exp)=−817 cm−1.

Crystal and molecular structures and magnetic properties of tetrameric copper(II) complexes with 3-hydroxy-5-hydroxymethyl-4-(4′-hydroxy-4′-phenyl-2′-azabut-1′-en-1′-yl)-2-methylpyridine (H2L3), [Cu4L34]·9CH3OH and 3-hydroxy-5-hydroxymethyl-4-(4′-hydroxy-3′-methyl-4′-phenyl-2′azabut-1′-en-1′-yl)-2-methylpyridine (H2L1), [Cu4-L14]· 8CH3CH2OH : two complexes with ferromagnetic ground states

The crystal and molecular structures of the title compounds [Cu4L34]·9CH3OH (3) and [Cu4L14]·8CH3CH2OH (4) have been determined from single-crystal X-ray diffraction data and refined to final R values of 0.062 (R′= 0.052) using 2 191 independent reflections for (3) and 0.062 (R′= 0.055) using 2 458 independent reflections for (4). Both tetrameric complexes crystallize in the tetragonal space group P42/n with two molecules in an unit cell with dimensions a= 18.193(4) and c= 12.615(4)A for (3) and a= 17.991(4) and c= 14.296(4)A for (4). Both molecules exhibit the highest possible point symmetry . While compound (3) is comparable with its 4′-(3″,4″-dichlorophenyl) derivative [Cu4L24]·9CH3OH (2) which crystallizes in a monoclinic lattice having an infinite network of hydrogen bonds, (4) is isomorphous to [Cu4L14]·8CH3OH (1). Moreover these two forms of structures are distinguishable by the considerably larger Cu–O distance between two pseudo-monomeric units within the pseudo-dimeric unit in (1) and (4) compared with (2) and (3). The magnetism of the two complexes can be explained on the basis of the isotropic Heisenberg–Dirac–van Vleck model. Compound (4) is very similar in its magnetic behaviour [g= 2.16(2), J12= 0 (fixed), J13= 17.4(2.0) cm–1, and θ=–1.8(1.0) K] to (1). In contrast to (2), compound (3) definitely has a ferromagnetic ground state [g= 2.085(20), J12=–7.1(2.0), and J13= 28.5(2.0) cm–1]. The principal difficulties of fitting theoretical magnetic susceptibility equations to experimental ones in ferromagnetically coupled systems is discussed. The discrepancy of the magnetic exchange constants between (3) and (2) which has really C1 symmetry is discussed in order to test by which model of higher symmetry the magnetism of this compound can be optimally described. It can be shown that a C2v model leads to more plausible exchange constants for (2) with regard to the geometrical sizes of the highly distorted molecule.

Crystal and molecular structure and magnetic properties of a tetrameric copper(II) complex with 3-hydroxy-4-[4′-(3″,4″-dichlorophenyl)-4′-hydroxy-2′-azabut-1′-en-1′-yl]-5-hydroxymethyl-2-methylpyridine (H2L2), [(CuL2)4]·9CH3OH

The crystal and the molecular structure of the title compound has been determined using three-dimensional X-ray diffractometer data involving 7 045 independent reflections. The compound crystallizes in the monoclinic space group I2/c with eight formula units [(CuL2)4]·9CH3OH in a unit cell with dimensions a= 27.062(5), b= 25.062(5), c= 26.390(5)A, and β= 92.39(1)°. The structure has been calculated by direct methods and refined by least-squares methods to a final R value of 0.054. In the cubane structure (C1 symmetry) each copper atom is bonded to one deprotonated phenolic oxygen, one imine nitrogen, and three deprotonated alkoxo-oxygen atoms giving a distorted square-pyramidal co-ordination. The six copper–copper distances are in the range 3.021(1)–3.492(2)A(mean 3.254 ± 0.184 A). Within the Cu4O4 core there are eight shorter copper–oxygen distances [1.917(5)–2.057(5)A, mean 1.983 A] and four longer ones [2.327(5)–2.690(6)A, mean 2.496 ± 0.166 A]. There are 72 methanol molecules per unit cell which are easily lost in air, giving an amorphous powder. The magnetic properties of the complex can be explained using the isotropic Heisenberg–Dirac–van Vleck model. The exchange parameters for the complex with approximate S4 symmetry obtained (J12=–9.9 ± 3.0 cm–1, J13= 20.5 ± 3.0 cm–1, and g= 2.08 ± 0.02) are in good agreement with those of similar substances and show the presence of both ferromagnetic and antiferromagnetic interactions. The amorphous modification shows a predominant ferromagnetic interaction.

Crystal and molecular structure and magnetic properties of a tetrameric copper(II) complex with 3-hydroxy-5-hydroxymethyl-4-(4′-hydroxy-3′-methyl-4′-phenyl-2′-azabut-1′-en-1′-yl)-2-methylpyridine (H2L) : [Cu4L4]·8MeOH, a complex with a ferromagnetic ground state

The crystal and molecular structure of the title compound has been determined from single-crystal X-ray diffraction data and refined to a final R value of 0.053 using 2 514 independent reflections. The compound belongs to the space group P42/n of the tetragonal system with two tetrameric molecules in a unit cell of dimensions a= 17.226(4) and c= 14.667(3)A. The tetrameric unit with a Cu4O4 core is of S4 symmetry. Copper–copper distances are 3.481(1)(two), 3.259(1)A(four) and Cu–O distances are 1.945(4)(four), 2.734(4)(four), and 1.977(4)A(four). The co-ordination about the copper atom is distorted square pyramidal with copper bonded to phenolic oxygen O(2), imine nitrogen N(1), and three alkoxo-oxygen atoms O(1). The complex crystallizes with 16 methanol molecules per unit cell. It easily loses in air the methanol molecules of crystallization giving an amorphous powder. The magnetism of the crystallized complex can be explained on the basis of the isotropic Heisenberg–Dirac–van Vleck model. Taking into account intercluster interactions, the fitting procedure yielded the values g= 2.12, J13= 17.1 cm–1, θ=–1.1 K. These parameters indicate a predominance of ferromagnetic interactions with a quintet ground state (S′= 2). The magnetic behaviour of the amorphous powder is quite different and shows weak antiferromagnetic interactions.

The Crystal and Molecular Structures of Four Homologous, Mesogenic trans,trans- 4,4'-dial kyl-( 1 OC, 1 '-bicyclohexyl)-4P- carbon i t ri I (CCN 's)

Abstract The crystal and molecular structures of four homologous (R′(CN)-C6H9-C6H10-R, CCNs) were determined using single crystal x-ray diffraction data. In all four structures the cyano groups occupy axial positions whereas the alkyl groups occupy equatorial ones. The cyclohexane rings are approximately perpendicular to each other in CCN33 (R˭R′˭C 3 H7), in CCN35 (R˭C 3 H7, R′˭C 5 H11) and in CCN38 (R˭C 3 H7, R′˭C 8 H17) leading to a room filling of the free space produced by the cyano groups. More than that, the hydrogen-hydrogen contacts between the cyclohexane rings are minimal in such an arrangement. However, in CCN46 (R˭C 4 H9, R′˭C 6 H13) the molecules contain nearly coplanar bicyclohexyl moieties. These and some other structural features are discussed with regard to the question of the extent to which the crystalline state can be interpreted as a precursor of liquid crystalline states.

Structural Arrangements of the Mesogenic Compounds 4-Ethyl-4′-(4″-pentylcyclohexyl)biphenyl and 4-Ethyl-2 ‘-fluoro-4’ -(4″-pentylcyclo-hexyl)biphenyl (BCH's) in the Crystalline State

Abstract The crystal and molecular structures of 4-ethyl-4′-(4″-pentylcyclohexyl)biphenyl (BCH52) and its fluoro derivative, 4-ethyl-2′-fluoro-4′-(4″-pentylcyclohexyl)biphenyl (BCH52F) are described. The crystal data are: a = 31.564(5), b = 5.511(1), c = 25.243(4) A, 13 = 104.904(4)°, space group C2/c for BCH52 and a 17.156(3), b = 6.792(1), c = 37.334(6) A, space group Pbcn for BCH52F. The structures refined to R values of 0.0711 (BCH52) and 0.0836 (BCH52F) using 2624 reflections for BCH52 and 2781 reflections for BCH52F. The torsion angles between the phenyl rings are radically different, being 3.9° in BCH52 and 41.9° in BCH52F. The torsion angles between the alkyl, phenyl, and cyclohexyl subunits of the molecules are compared and the influence of the fluoro substitution is discussed. The patterns of packing of the crystal structures are discussed, especially in terms of short-range ordering. Comparisons with similar compounds are made.

The Crystal and Molecular Structure of the Mesogenic 4-Cyanophenyl-4′-n-Pentylthiol Benzoate (5SCN)

Abstract The crystal and molecular structure of the mesogenic 4-cyanophenyl-4′-n-pentylthiolbenzoate (SSCN) has been determined by X-ray diffraction method. The crystal data are: monoclinic, space group P21/c, a = 37,204(10) A, b = 5.992(2) A, c = 24.408(8) a, β = 107.45(2)° and Z = 12 with three symmetry independent molecule positions. All the molecules occur in their extended form and the two phenyl rings are twisted against each other. Shorter intermolecular distances were observed.

Synthesis, X-ray structure, and magnetic properties of di-µ-chloro-bis[N-(2-hydroxy-2-phenylethyl)salicylideneiminatocopper(II)]

The crystal and molecular structure of [Cu2Cl2L2]·dmf·H2O [L =N-(2-hydroxy-2-phenylethyl)salicylideneiminate; dmf = dimethylformamide] has been determined and refined to a final R value of 0.0329 (R′= 0.0257) using 3 979 independent reflections. The dinuclear units crystallize in the monoclinic space group P21/c with dimensions a= 8.771(1), b= 13.440(2), c= 29.060(4)A, and a= 97.113(4)°. Each copper atom is co-ordinated in a distorted square-planar manner by one tridentate Schiff-base anion and one chlorine atom, with normal copper-chlorine distances (mean 2.261 ± 0.002 A). The chlorine atoms also form long bonds (mean 2.824 ± 0.019 A) with the second copper atom. The magnetic susceptibilities measured from 5.1 K show a weak antiferromagnetic spin coupling. Fitting of the experimental data by the Bleaney–Bowers equation yielded the parameters g= 2.09(2), 2J12=–7.1(4) cm–1, and Nα= 131(10)× 10–6 c.g.s. units. The contribution of intramolecular hydrogen bonds to the overall antiferromagnetic exchange interaction is discussed. The temperature-dependent e.s.r. spectra are reported.

Crystal and molecular structures and magnetic properties of bromo(3-dimethylaminopropan-1-olato)copper(II), chloro(3-dimethylaminopropan-1-olato) copper(II), and (3-diethylaminopropan-1-olato)isocyanatocopper(II)

The crystal and molecular structures of the title compounds have been determined using three-dimensional X-ray diffractometer data and refined to a final R value of 0.0263 for bromo(3-dimethylaminopropan-1-olato)copper(II)(1), 0.0349 for chloro(3-dimethylaminopropan-1-olato)copper(II)(2), and 0.0268 for (3-diethylaminopropan-1-olato)isocyanatocopper(II)(3). The compounds crystallize in the monoclinic space group P21/c. The unit-cell dimensions are a= 6.273(3), b= 10.282(5), c= 12.403(5)A, β= 99.62(2)°, Z= 4 for (1); a= 7.484(3), b= 6.145(3), c= 17.152(6)A, β= 101.55(2)°, Z= 4 for (2); and a= 7.363(3), b= 12.422(5), c= 11.117(5)A, β= 96.37(2)°, Z= 4 for (3). The structures of (1) and (2) consist of infinite chains of alkoxo-bridged copper(II) dimers connected by halogen bridges with long halogen–copper bonds [3.127(1)A for (1) and 2.905(1)A for (2)]. Neglecting these additional fifth co-ordination sites the co-ordination of the copper ions is distorted square planar. The structure of (3) consists of discrete dimeric molecules. The copper–copper distances are 3.063(1) for (1), 3.060(1) for (2), and 3.044(1)A for (3). The magnetic susceptibilities measured from 11.1 K show very strong antiferromagnetic spin coupling for all three compounds. The magnetic behaviour can be explained using the Bleaney–Bowers equation. By fitting the experimental data to the Bleaney–Bowers equation good agreement can be obtained with the parameters g= 2.18(2), 2J12=–1 065(20) cm–1, x= 0.004(1), Nα= 63(5)× 10–6 c.g.s.u. for (1), g= 2.21 (2), 2J12=–1 020(20) cm–1, x= 0.003(1), Nα= 54(5)× 10–6 c.g.s.u. for (2) and g= 2.26(2), 2J12=–1 056(20) cm–1, x= 0.013(3), Nα= 108(5)× 10–6 c.g.s.u. for (3). The evident differences between these results and those expected from magnetostructural correlations for related compounds are discussed. A magnetostructural correlation is presented which shows the influence of the co-ordination geometry at the copper atom on the exchange interaction in spin-coupled alkoxo-bridged copper(II) complexes.

Crystal and molecular structures and magnetic properties of four new exchange-coupled copper(II) complexes derived from different 3-N,N-dialkylamino-1-propanols and pseudohalogens

The crystal and molecular structures of (3-N,N-dimethylamino-1-propanolato) isocyanatocopper(II)(1), (3-N,N-dimethylamino-1-propanolato) isothiocyanatocopper(II)(2), (3-N,N-diethylamino-1-propanolato) isothiocyanatocopper(II)(3), and (3-N,N-di-n-butylamino-1-propanolato)isothiocyanatocopper(II)(4) have been determined using three-dimensional X-ray diffractometer data. Final R values were 0.0237 for (1), 0.0250 for (2), 0.0297 for (3), and 0.0464 for (4). Compounds (1) and (2) crystallize in monoclinic lattices (space group P21/c), (3) and (4) in triclinic ones (space group P). The structure of (1) consists of an infinite two-dimensional network of alkoxo-bridged dimers connected by cyanato-groups in the plane (100); the three remaining structures consist of infinite chains of alkoxo-bridged dimers connected by the thiocyanato-groups. Within the dimeric units the copper atoms have distorted square-planar co-ordination. The connection between the dimers leads to a fifth co-ordination with longer copper–ligand bonds. The magnetic susceptibilities measured from 11.1 K show for all four compounds very strong antiferromagnetic spin coupling (|2J| > 850 cm–1). A correlation between the exchange constants and the Cu–O–Cu′ bridging angles within the dimers for all known (3-N,N-dialkylamino-1-propanolato)-halogenocopper(II) and -pseudohalogenocopper(II) complexes is given and shows that these complexes are systematically more strongly coupled than the related complexes derived from analogous aminoethanols.