Trapping virtual pores by crystal retro-engineering

Stable guest-free porous molecular crystals are uncommon. By contrast, organic molecular crystals with guest-occupied cavities are frequently observed, but these cavities tend to be unstable and collapse on removal of the guests—this feature has been referred to as ‘virtual porosity’. Here, we show how we have trapped the virtual porosity in an unstable low-density organic molecular crystal by introducing a second molecule that matches the size and shape of the unstable voids. We call this strategy ‘retro-engineering’ because it parallels organic retrosynthetic analysis, and it allows the metastable two-dimensional hexagonal pore structure in an organic solvate to be trapped in a binary cocrystal. Unlike the crystal with virtual porosity, the cocrystal material remains single crystalline and porous after removal of guests by heating

Some errors from the crystallographic literature, some amplifications and a questionable result

The space groups of {[Mo-2(O2CCH3)(4)('linker')](n)}are corrected from P (1) over bar to C2/m for 'linker' = pyrazine and 1,4-diazabicyclo[2.2.2]octane (dabco) and from P (1) over bar 1 to C2/c for 'linker' = 4,4'-bipyridine. Also, {[tris-(2-pyridylmethyl)amine]-BrV(mu-O)VBr[tris-(2-pyridylmethyl)amine]}Br.H2O is corrected from P (1) over bar to C2/c. These Laue class changes allow more reliable crystallochemical comparisons to be made among families of related structures. Space groups are corrected for 4-methyl-2,6-bis(4-methylbenzylidene)cyclohexanone, 2,6-bis(4-dimethylaminobenzylidene)cyclohexanone, K[Cr(tetramethylenediamine-N,N,N', N'-tetraacetate)].H2O and {bis(11,11-dimethyl-3,4:8,9-dibenzobicyclo[4.4.1]undeca-3,8-diene)- (tetracyanoethylene)}. The conflicting reports for Cu(H2O)(phenanthroline)(2) (X)(2), where X = ClO4, NO3 and BF4, are resolved. Three related examples of open framework host-guest structures with space groups 'Cc or C2/c' are discussed. Adding centers to 2,2'-bi-1H-imidazolium dipicrate and {tris(2,20 -bi-1H-imidazole)bis[2-(2-1H-imidazolyl)-1H-imidazolium]bis(iodide)} corrects discrepancies of up to 0.38 Angstrom between chemically similar hydrogen-bond distances. Wrongly identified atoms are corrected in theta-[bis(ethylenedithio)tetrathiafulvalene]2 (CsCd)(SCN)(4) and (purported) diaquadihydroxotetrakis (m-nitrobenzenesulfonate) discandium(III). The reported difference between the crystal structure of (CH3NH3)(4)YbCl7 and those of the other members of this family of (CH3NH3)(4)MX7 (M = In, Fe, V; X = Cl, Br) structures is pointed out in the context of possibly different N-H...Cl hydrogen bonding in the Yb structure

Binuclear platinum diphosphite complexes. Crystal structures of K4[Pt2(pop)4Br]·3H2O, a new linear chain semiconductor, and K4[Pt2(pop)4Cl2]·2H2O

The structures of crystals of K4[Pt2(pop)4Br]·3H2O (pop = (HO2P)2O2-), "Pt2Br", and K4[Pt2(pop)4Cl2]·2H2O, "Pt2Cl2", have been determined. The structure of "Pt2Br" features a symmetric Pt-Br-Pt unit in an infinite linear chain (Pt-Pt-Br-Pt-Pt-Br-; σ∥ = ∼10-4-10-3 Ω-1 cm-1) with d(Pt-Pt) = 2.793 (1) and d(Pt-Br) = 2.699 (1) Å; "Pt2Cl2" is a discrete binuclear ion, with d(Pt-Pt) = 2.695 (1) and d(Pt-Cl) = 2.407 (2) Å. Both Pt-Pt distances are shorter than those (2.925 (1) Å) in K4[Pt2(pop)4]·2H2O, "Pt2"; the order d("Pt2") > d ("Pt2Br") > d("Pt2Cl2") accords with an electronic structural model in which "Pt2" is (dσ)2(dσ*)2 "Pt2Br" is (dσ)2 (dσ*)1, and "Pt2Cl2" is (dσ)2. © 1983 American Chemical Society.link_to_subscribed_fulltex

Binuclear complexes of palladium(II) containing 1,8-diisocyano-p-menthane

Well-characterized binuclear isocyano complexes of palladium(II) are obtained with the bridging ligand 1,8-diisocyano-p-menthane (DMB). The ion [Pd2(DMB)4]4+ reacts with X (Cl- or Br-) to give [Pd2(DMB)4X]3+, where the X is positioned between the metal atoms, encapsulated in the complex. Reaction with I- leads to an entirely different product, Pd2(DMB)2I4, which has been characterized by X-ray crystallography: Pd2C24N4H36I4 crystallizes in the monoclinic space group P21/n with a = 11.766 (4) Å, b = 15.123 (8) Å, c = 9.703 (2) Å, β = 93.93 (2)°, and Z = 2. The Pd atoms are square-planar coordinated to two CN groups and two I atoms; the DMB ligands are disordered across a center of symmetry. The coordination planes of the Pd atoms are tilted 35° from the perpendicular to the Pd-Pd vector, and a fifth (axial) site is occupied by an I atom from the other half of the dimer. The Pd⋯Pd distance, 4.582 (1) Å, is such that the ion [Pd2(DMB)4]4+ can accommodate a Br- or Cl- ion between the Pd atoms. © 1984 American Chemical Society.link_to_subscribed_fulltex

Some 60 new space-group corrections

Some 60 examples of crystal structures are presented which can be better described in space groups of higher symmetry than used in the original publications. These are divided into three categories: (A) incorrect Laue group (33 examples), (B) omission of a center of symmetry (22 examples), (C) omission of a center of symmetry coupled with a failure to recognize systematic absences (nine examples). Category A errors do not lead to significant errors in molecular geometry, but these do accompany the two other types of error. There are 19 of the current set of examples which have publication dates of 1996 or later. Critical scrutiny on the part of authors, editors and referees is needed to eliminate such errors in order not to impair the role of crystal structure analysis as the chemical court of last resort