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A brief comparison of seven straightforward methods for molecular crystal-volume estimation revealed that their precisions are comparable. A chiral diamine, N2, N3-bis[2,6-bis(propan-2-yl)phenyl]butane-2,3-diamine, C28H44N2, has been used to illustrate the application of the methods. Three stereoisomers of the diamine cocrystallize in the centrosymmetric space group P21/ c with Z′ = 1.5. The molecules occupying general positions are RR and SS, whereas that residing on an inversion center is meso. This is one of only ten examples of three stereoisomers with two asymmetric atoms cocrystallizing together reported to the Cambridge Structural Database (CSD). The conformations of the SS/ RR and meso molecules differ considerably and lead to statistically significantly different C(asymmetric)-C(asymmetric) bond lengths in the diastereomers. An advanced Python script-based CSD searching technique for chiral compounds is presented. [ABSTRACT FROM AUTHOR]

The synthesis of two new radical-bridged compounds [Co3(bptz)3(dbm)3]-2toluene (l) and [Co4(bptz)4(dbm)4] -4MeCN (2) (bptz = 3,6-bis- (pyridyl)-1,2,4,5-tetrazine; dbm = 1,3-diphenyl-1,3-pro- panedionate) is reported. The presence of the ligand- centered radical has been confirmed by X-ray crystallography and SQUID magnetometry. These complexes are the first metallacycles bearing nitrogen heterocyclic radicals as bridges. Magnetic studies reveal strong antiferromagnetic metal---radical coupling with coupling constants of J = -67.5 and -66.8 cm[sup -1] for 1 and 2, respectively. DFT calculations further support the strong antiferromagnetic coupling between CoII ions and bptz radicals and confirm S = 3 and S = 4 spin ground states for 1 and 2, respectively. [ABSTRACT FROM AUTHOR]

Two new strongly AEE active (I/I0≈ 94) tetraphenylsilole-containing cyclosiloxanes with cyan emissions (λem = 500 nm) and ∼100% solid state fluorescence quantum yields are reported. The intra- and intermolecular C–H…π interactions in the crystal play a major role in the observed high solid state fluorescence quantum yields. [ABSTRACT FROM AUTHOR]

Four ring-shaped silafluorene-containing compounds (1-4) were synthesized and characterized as potentially promising monomers for fluorescent polymers. Their optical properties in solution and solid state (thin film and powder) were studied. These compounds have low quantum yields in solution (Φfl=0.13-0.15) with fluorescence maxima at about 355 nm, but high quantum yields in the solid state (powder, Φfl=0.35-0.54) with fluorescence maxima at about 377 and 488 nm. Influence of the substituents and the number of silafluorene units in 1-4 on their optical properties was investigated. Extensive study of the X-ray crystal structures of 1-4 was undertaken to analyze and qualitatively estimate the role, extent, and influence of silafluorene moieties' interactions on solid-state fluorescent properties. Excited state UV/Vis and theoretical molecular orbital (MO) calculations were performed to explore possible fluorescence mechanisms and differences in quantum yields among these compounds. [ABSTRACT FROM AUTHOR]

In (η6- p-cymene)(difluorophosphinato-κ O){2-[(1 H-pyrazol-1-yl)methyl-κ N2]pyridine-κ N}ruthenium(II) 0.85-hexafluorophosphate 0.15-tetrafluoroborate, [Ru(PO2F2)(C10H14)(C9H9N3)](PF6)0.85(BF4)0.15, (I), the [PO2F2]− ligand exhibits positional disorder due to one F atom and one O atom sharing the same two positions related by a mirror reflection across the O-P-F plane. The correct composition of this coordinated anion was successfully determined to be [PO2F2]− by refining the complex with various tetrahedral anions in which terminal atoms have similar atomic form factors. The noncoordinated counter-ion is compositionally disordered between [PF6]− and [BF4]−. The difficulty in determining the correct composition of this anion illustrates the importance of a crystallographer remaining impartial and open to encountering unexpected moieties in the process of elucidating a structure. [ABSTRACT FROM AUTHOR]

We report here the syntheses, X-ray crystal structures, electro-chemistry, and density functional theory (DFT) single-point calculations of three new complexes: tetrakis(monothiosuccinimidato)dimolybdenum(II) [Mo2(SNO5)4, la], tetrakis(6-thioxo-2-piperidinonato)dimolybdenum(II) [Mo2 ( SNO6 )4, lb], and chlorotetrakis(monothiosuccinimidato)- pyridinelithiumdimolybdenum(II) [pyLiMo2(SNOS)4Cl, 2-py]. X-ray crystallography shows unusually short axial Mo2--Cl bond lengths in 2-py, 2.6533(6) Å, and dimeric 2-dim, 2.644(1) Å, which we propose result from an increased Lewis acidity of the Mo2 unit in the presence of the proximal Li+ ion. When 2-py is dissolved in MeCN, the lithium reversibly dissociates, forming an equilibrium mixture of (MeCNLiMo2(SN05)4Cl) (2-MeCN) and [Li(MeCN)4]+[Mo2(SN05)4Cl]- (3). Cyclic voltammetry was used to determine the equilibrium lithium binding constant (room temperature, Keq = 95 ± 1). From analysis of the temperature dependence of the equilibrium constant, thermodynamic parameters for the formation of 2-MeCN from 3 (ΔH° = --6.96 ± 0.93 kj mol-1 and ΔS° = 13.9 ± 3.5 J mol-1 K-1) were extracted. DFT calculations indicate that Li+ affects the Mo--CI bond length through polarization of metal--metal bonding/antibonding molecular orbitals when lithium and chloride are added to the dimolybdenum core. [ABSTRACT FROM AUTHOR]