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Crystals, Volume 4, Issue 1 (March 2014), Pages 1-73

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Editorial

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Open AccessEditorial Acknowledgement to Reviewers of Crystals in 2013
Crystals 2014, 4(1), 11; doi:10.3390/cryst4010011
Received: 24 February 2014 / Accepted: 24 February 2014 / Published: 24 February 2014
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Abstract The editors of Crystals would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2013. [...] Full article

Research

Jump to: Editorial

Open AccessArticle Synthesis and Crystal Structures of 1,1′-Methylene-bis(imidazolidine-2,4-dione) and Alkali Metal Salts
Crystals 2014, 4(1), 1-10; doi:10.3390/cryst4010001
Received: 22 October 2013 / Revised: 22 November 2013 / Accepted: 31 December 2013 / Published: 8 January 2014
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Abstract Single-crystal structures of 1,1′-methylenebis(imidazolidine-2,4-dione) and its sodium and dipotassium salts were determined. Powder X-ray diffraction was also employed to characterize the bulk materials and those phases which did not yield single-crystals. These compounds are of interest for intumescent coatings. Full article
Open AccessArticle σ-Hole Interactions of Covalently-Bonded Nitrogen, Phosphorus and Arsenic: A Survey of Crystal Structures
Crystals 2014, 4(1), 12-31; doi:10.3390/cryst4010012
Received: 15 January 2014 / Revised: 24 January 2014 / Accepted: 6 February 2014 / Published: 26 February 2014
Cited by 65 | PDF Full-text (655 KB) | HTML Full-text | XML Full-text
Abstract
Covalently-bonded atoms of Groups IV–VII tend to have anisotropic charge distributions, the electronic densities being less on the extensions of the bonds (σ-holes) than in the intervening regions. These σ-holes often give rise to positive electrostatic potentials through which the atom can interact
[...] Read more.
Covalently-bonded atoms of Groups IV–VII tend to have anisotropic charge distributions, the electronic densities being less on the extensions of the bonds (σ-holes) than in the intervening regions. These σ-holes often give rise to positive electrostatic potentials through which the atom can interact attractively and highly directionally with negative sites (e.g., lone pairs, π electrons and anions), forming noncovalent complexes. For Group VII this is called “halogen bonding” and has been widely studied both computationally and experimentally. For Groups IV–VI, it is only since 2007 that positive σ-holes have been recognized as explaining many noncovalent interactions that have in some instances long been known experimentally. There is considerable experimental evidence for such interactions involving groups IV and VI, particularly in the form of surveys of crystal structures. However we have found less extensive evidence for Group V. Accordingly we have now conducted a survey of the Cambridge Structural Database for crystalline close contacts of trivalent nitrogen, phosphorus and arsenic with six different types of electronegative atoms in neighboring molecules. We have found numerous close contacts that fit the criteria for σ-hole interactions. Some of these are discussed in detail; in two instances, computed molecular electrostatic potentials are presented. Full article
(This article belongs to the Special Issue Crystal Engineering Involving Weak Bonds)
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Open AccessArticle Dimensionality Variation in Dinuclear Cu(II) Complexes of a Heterotritopic Pyrazolate Ligand
Crystals 2014, 4(1), 32-41; doi:10.3390/cryst4010032
Received: 21 January 2014 / Revised: 6 February 2014 / Accepted: 10 February 2014 / Published: 26 February 2014
Cited by 3 | PDF Full-text (523 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Two new Cu(II) complexes of the ligand 3-carboxy-5-(2-pyridyl)-1H-pyrazole, H2L1, have been prepared and structurally characterized and found to be comprised of a similar [M2L2] dimer motif. Subtle variation in the synthetic conditions allowed isolation
[...] Read more.
Two new Cu(II) complexes of the ligand 3-carboxy-5-(2-pyridyl)-1H-pyrazole, H2L1, have been prepared and structurally characterized and found to be comprised of a similar [M2L2] dimer motif. Subtle variation in the synthetic conditions allowed isolation of two metal complexes: [Cu2L12(MeOH)2], 1, a discrete dimer linked by hydrogen bonding interactions in the solid state, and poly-[Cu2L12], 2, a polymeric material where the dimer motif is linked by carboxylate bridges to give an extended two-dimensional sheet. The selective isolation of each phase by careful synthetic control highlights the subtlety and importance of the underlying synthetic conditions. Full article
(This article belongs to the Special Issue Crystal Engineering Involving Weak Bonds)
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Open AccessArticle Structural Variation in Polyoxomolybdate Hybrid Crystals Comprising Ionic-Liquid Surfactants
Crystals 2014, 4(1), 42-52; doi:10.3390/cryst4010042
Received: 10 January 2014 / Revised: 11 February 2014 / Accepted: 20 February 2014 / Published: 4 March 2014
Cited by 3 | PDF Full-text (683 KB) | HTML Full-text | XML Full-text
Abstract
Polyoxomolybdate inorganic-organic hybrid crystals were synthesized with 1-decyl-3-methylimidazolium and 1-dodecyl-3-methylimidazolium as ionic-liquid surfactants. Both hybrid crystals possessed alternate stacking of surfactant layers and octamolybdate (Mo8) monolayers, while the molecular structures of Mo8 were different depending on the surfactants and solvents
[...] Read more.
Polyoxomolybdate inorganic-organic hybrid crystals were synthesized with 1-decyl-3-methylimidazolium and 1-dodecyl-3-methylimidazolium as ionic-liquid surfactants. Both hybrid crystals possessed alternate stacking of surfactant layers and octamolybdate (Mo8) monolayers, while the molecular structures of Mo8 were different depending on the surfactants and solvents employed for crystallization. Each Mo8 anion was connected by two sodium cations to form infinite one-dimensional chain. The surfactant chains in these crystals were arranged in a complicatedly bent manner, which will be induced by the weak C–H···O hydrogen bonds between the Mo8 anions and ionic-liquid surfactants. Full article
(This article belongs to the Special Issue Crystal Engineering Involving Weak Bonds)
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Open AccessArticle Hydrogen-Bonding Motifs in Piperazinediium Salts
Crystals 2014, 4(1), 53-63; doi:10.3390/cryst4010053
Received: 14 January 2014 / Revised: 5 February 2014 / Accepted: 18 February 2014 / Published: 4 March 2014
Cited by 1 | PDF Full-text (652 KB) | HTML Full-text | XML Full-text
Abstract Four novel organic salts of piperazine and 2-methylpiperazine with p-toluenesulfonic acid and chloroacetic acid have been synthesized and structurally characterized. The hydrogen-bonding ring synthons that exist between the cation/anion pairs are compared and contrasted alongside database results. Full article
(This article belongs to the Special Issue Crystal Engineering Involving Weak Bonds)
Open AccessArticle Polyoxotungstates in Molecular Boxes of Purine Bases
Crystals 2014, 4(1), 64-73; doi:10.3390/cryst4010064
Received: 31 December 2013 / Revised: 17 February 2014 / Accepted: 20 February 2014 / Published: 12 March 2014
Cited by 1 | PDF Full-text (631 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Three new compounds, (GuaH)4[W10O32](H2O)4 (1), (ThbH)3(H3O)[(W10O32](H2O)7.5 (2) and (ThbH)2[W6O19](H2O)2 (
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Three new compounds, (GuaH)4[W10O32](H2O)4 (1), (ThbH)3(H3O)[(W10O32](H2O)7.5 (2) and (ThbH)2[W6O19](H2O)2 (3) (GuaH = guaninium, thbH = theobrominium) were synthesized in acidified acetonitrile solutions. The polyoxotungstates in all of these compounds are surrounded by an organic matrix consisting of protonated purine bases and water molecules. The distinctive structural arrangement of the aromatic organic cations around the polyoxoanions parallel to their faces is reminiscent of nanosized boxes. The results of IR spectroscopy are consistent with previously reported results for polyoxotungstates and neat organic compounds. The polyoxoanions are reduced to tungsten(IV) oxide upon heating over 400 °C in an intramolecular redox reaction. Full article
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