Susan J. Cline

Structural and magnetic properties of di-µ-hydroxo-bis[bis(ethylenediamine)chromium(III)] dithionate

The crystal and molecular structure of the title complex [{Cr(en)2(OH)}2][S2O6]2 has been determined from three dimensional single-crystal X-ray counter data. The complex crystallizes In the orthorhombic space group Pbca with four molecules in a cell of dimensions a= 13.58(1). b= 18.42(2), and c= 10.02(1)A. The observed and calculated densities are 1.85(2) and 1.851 g cm–3, respectively. The structure has been refined by full-matrix least-squares techniques to a value of R(on F) 0.049. The complex consists of dimeric [{Cr(en)2(OH)}2]4+ units which are hydrogen bonded to the dithionate anions. The dimeric cation isolated is the meso form, there being a crystallographic inversion centre in the middle of the dimer. The geometry around each chromium(III) centre is approximately octahedral, the Cr–Cr separation and bridging Cr–O–Cr angle being 3.032(3)A and 100.0(2)°, respectively. The dithionate anion has the staggered conformation [S–S 2.127(3)A, S–O 1.435(6)–1.460(5)A]. The hydrogen bonding is extensive, with all the possible donor and acceptor atoms participating. The magnetic susceptibility of a powdered sample of the complex shows a maximum near 7.3 K, indicative of antiferromagnetic coupling between the metal centres. The best fit of the susceptibility data to the Van Vleck equation (modified by the inclusion of biquadratic exchange) yields values for g. J, j, and ΔE(the singlet–triplet splitting) of 1.947 (7), –1.08(2) cm–1, 0.234(7) cm–1, and –3.68 cm–1, respectively.

The crystal and molecular structure of 9-α-d-arabinofuranosyladenine

Abstract The glycosyl torsional angles in two crystallographically-independent molecules of α-araA are −73 and −64°, both of which are in the “anti” region. The sugar conformations are C(3′)-endo and C(2′)-exo-C(3′)-endo.

Conformation and structure of 9-α-d-arabinofuranosyladenine

The crystal structure of the nucleoside 9-α-d-arabinofuranosyladenine (C10H13N5O4) has been determined by means of three-dimensional X-ray counter data. The adenosine analog crystallizes in space group P212121 of the orthorhombic system with eight formula units in a cell of dimensions a, 6.720(5), b, 40.188(35), c, 8.357(8) A. Hence, there are two crystallographically independent molecules in the unit cell. The structure was solved by direct methods and refined by full-matrix least-squares techniques to a final value of the conventional R-factor of 0.076 using 1173 independent intensity data. In the crystal, both independent molecules (A and B) adopt the anti conformation (for an α-sugar), with glycosyl torsion angles, X, of −73° and −64°; these are comparable to values found in other α-nucleosides. The conformation about the extracyclic C(4′)-C(5′) bond is gauche-gauche in both molecules. The sugar pucker is C(2′)-exo-C(3′)-endo, 2T3, in molecule A and C(3′)-endo, 3E, in molecule B. Conformational analysis of rotation about the N(9)-C(1′) glycosyl bond has been performed by use of CNDO2 molecular orbital calculations. These calculations suggest that the observed conformation may not be the global minimum, but that it lies only 0.4 kcal · mol−1 higher in energy than the global minimum. The highest energy barrier to rotation around the glycosyl bond is calculated to be only 1.1 kcal · mol−1, which is comparable to the value calculated for adenosine.

Structure and spectroscopic properties of bis(N-cyclohexyl-3-methoxy-salicylideneiminato)copper(II)

The structure of the title complex (2) has been determined from three-dimensional X-ray counter data. The material crystallizes in the monoclinic space group P21/c with two monomeric units in a cell of dimensions a= 11.793(5), b= 18.043(14), c= 6.484(3)A, and β= 67.12(2)°. Least-squares refincment of 1 190 independent data has led to final values of R and R′ of 0.047 and 0.046, respectively. The monomeric units are crystallographically constrained to be square planar. The green solid yields reddish solutions in various solvents. Electronic and e.s.r. spectroscopic data support the presence of pseudo-tetrahedrally distorted species in solutions. Spectroscopic data for planar (2) are compared with data for pseudo-tetrahedral bis(N-cyclohexylsalicylidene-iminato)copper(II), (1). Structure-spectra correlations applicable to the solid state cannot necessarily be straightforwardly applied to solution species.

Syntheses of 1,1'-Bicobaltocene Salts of Tetracyano-P-Quinodimethane, Tetrabromoquinone, and Tetrabromodiphenoquinone: and the Structure of 1,1'-Bicobaltocene Co(III)Co(III)(TCNQ)3.

Abstract The reaction of 1,1′-bicobaltocene[Co(III)Co(III)]-(PF6)2, [BFDCO(III, III)] (PF6)2, or the analogous mixed valence compound [Co(III)Co(II)] with excess [(C2H5)3NH][TCNQ]2 and TCNQ yields the complex salt 1,1′-bicobaltocene[Co(III)Co(III)][TCNQ]3. Reaction of [BFDCo(III, III)](PF6)2 with excess tetrabromoquinone (bromanil, BA) and its sodium salt produces [BFD-Co(III, III)][BA]3, while reaction with tetrabromodi-phenoquinone (TBDQ) yields [BFDCo(III, III)] [TBDQ]3. The TCNQ units in the complex salt [BFDCo(III, III)][TCNQ]3 stack to form an alternating chain with two short, adjacent interplanar spacings of 3.15 A, followed by a longer interplanar spacing of 3.45 A. The interplanar spacing of the fulvalene moieties in the cation is 3.270 A, and the cobalt-carbon bond distances range from 2.012(5) to 2.041(5)A. The complex salts are diamagnetic and the electrical conductivities of pressed pellet samples range from 3.0 × 10−2 to 3.0 × 10−4 ohm−1 cm−1.