Crystallographic curiosities: polymorphism and structures with Z′ > 1

Polymorphs often have different values of Z′, the number of independent molecules in the asymmetric unit of the crystal structure. Structures with Z′ > 1 are a small minority, particularly so for Z′ > 2, and many are associated with packing problems, disorder and weak intermolecular interactions. These phenomena are fascinating and have important practical implications.

A new tool for finding approximate symmetry

A new method for identifying and visualizing approximate symmetry in mol­ecular crystals is discussed.

A simple graphical method to pinpoint local pseudosymmetries in Z′ > 1 cases

An intuitive method is presented for detecting pseudosymmetries in Z′ > 1 cases as a complement to well-proven strategies already available in the literature. It is based on the simple idea that the mid-points between equivalent atoms in symmetrically related mol­ecules are disposed according to simple well-known patterns, which are easily recognizable by optical inspection.

Crystal structure and pseudosymmetry analysis of the triclinic prodrug cloxazolam (Z′ = 4)

There are four independent mol­ecules in the P asymmetric unit of cloxazolam, related by a striking pseudosymmetry. The identical mol­ecules consist of four rings linked in a rather rigid fashion. Even in the absence of strong hydrogen-bond inter­actions, the structure presents an unusual compactness (Kitaigorodskii packing index ≃ 0.71).

Preparation, characterization and luminescence-sensing properties of two Zn^II MOFs with mixed 5-amino-2,4,6-tri­bromo­isophthalic acid and bi­pyridyl-type ligands

The luminescence quenching of two Zn^II MOFs with mixed 5-amino-2,4,6-tri­bromo­isophthalic acid and bipyridyl-type ligands by NAEs have been investigated.

Regioselective synthesis and characterization of monovanadium-substituted β-octa­molybdate [VMo₇O₂₆]⁵⁻

The monovanadium-substituted β-octa­molybdate [VMo₇O₂₆]⁵⁻ was prepared by a one-pot approach using peroxido complexes of vanadium. ⁵¹V NMR spectroscopy confirmed the high selectivity of the synthesis.

Nickel(II) cluster-based mixed-cation coordination polymer synthesized from 2-mercapto­benzoic acid and its application

A new nickel(II) cluster-based coordination polymer featuring high-nuclearity nickel(II) secondary building units was successfully prepared, and a tightly packed nanocomposite with extra-long cycling stability (>5000 cycles) was formed by sinter­ing the coordination precursor. This structure and composite have rarely been investigated in significant detail.

K₃Eu₅(PO₄)₆: hydro­thermal synthesis, crystal structure and photoluminescence properties

A new phosphate, K₃Eu₅(PO₄)₆, with a three-dimensional open framework of [Eu₅(PO₄)₆]_∞, is reported. Under near-UV light excitation, it shows a strong red emission due to the characteristic 4f→4f transition of the Eu³⁺ ion.

Design and synthesis of methyl 2-{[4-phenyl-5-(pyridin-2-yl)-4H-1,2,4-triazol-3-yl]sulfanyl}­acetate (phpy2NS) as a ligand for complexes of Group 12 elements: structural assessment and hydrogen-bonded supra­molecular assembly analysis

The crystal structures of Group 12 complexes and their precursor, 4-phenyl-5-(pyridin-2-yl)-2,4-dihydro-3H-1,2,4-triazole-3-thione, were studied. The role of hydrogen bonding and other weak interactions in crystal packing was analyzed.

A new crystalline form of αβ-D-lactose prepared by oven drying a concentrated aqueous solution of D-lactose

A monoclinic polymorph of αβ-D-lactose has been identified from crystalline phase mixtures obtained by oven drying concentrated aqueous solutions of D-lactose. This is the second crystalline form of αβ-D-lactose to be identified and it has a high degree of structural three-dimensional similarity to the previously identified triclinic form.

The first silver bis­muth borate, AgBi₂B₅O₁₁

The first silver bis­muth borate, AgBi₂B₅O₁₁, has been prepared via glass crystallization. Its acentric structure is derived from that of centrosymmetric Bi₃B₅O₁₂ by ordered substitution of one Ag⁺ ion for Bi³⁺.

Tuning the energy level of TAPC: crystal structure and photophysical and electrochemical properties of 4,4′-(cyclo­hexane-1,1-di­yl)bis­[N,N-bis­(4-meth­oxy­phen­yl)aniline]

The crystal structure of 4,4′-(cyclo­hexane-1,1-di­yl)bis­[N,N-bis­(4-meth­oxy­phen­yl)aniline] was determined and its photophysical and electrochemical properties investigated. It is expected that the compound will be a good candidate for a hole-transporting material in electronic devices.

Synthesis, structure and bioactivity of Ni²⁺ and Cu²⁺ acyl­hydrazone complexes

Mononuclear [Ni(L)₂] and dinuclear [Cu(L)(μ_1,1-N₃)]₂ types of complexes were obtained from N,N′,O-donor acyl­hydrazone ligand HL. The two complexes show potent urease inhibitory activity and suitable binding affinity to BSA.

Coordination polymers of Cd^II and Pb^II with croconate show remarkable differences in coordination patterns: a structural and spectroscopic study

The X-ray structures of Cd^II–croconate versus Pb^II–croconate coordination polymers present one-dimensional coordination patterns with a planar configuration for Cd^II and a nonplanar hemidirected geometry for Pb^II.

Enhanced π-back-donation resulting in the trans labilization of a pyridine ligand in an N-heterocyclic carbene (NHC) Pd^II precatalyst: a case study

The mol­ecular structure of a PEPPSI precatalyst, as well as general remarks about PEPPSI complexes compared to NHC complexes, is presented using quantum chemical computations and CSD searches highlighting the importance of π-back-donation in PEPPSI complexes.

Reaction of 2-[(2-amino­eth­yl)amino]­ethanol with pyridine-2-carbaldehyde and complexation of the products with Cu^II and Cd^II along with docking studies

The reaction between 2-[2-(amino­eth­yl)amino]­ethanol and pyridine-2-carbaldehyde in a 1:2 molar ratio affords a mixture containing 2-({2-[(pyridin-2-yl­methyl­idene)amino]­eth­yl}amino)­ethanol (PMAE) and 2-[2-(pyridin-2-yl)oxazolidin-3-yl]-N-(pyridin-2-yl­methyl­idene)ethanamine (POPME). Treatment of this mixture with copper(II) chloride or cadmium(II) chloride gave [Cu(HPMAE)Cl₃]·H₂O, 1, and [CdCl₂(POPME)], 2. The ability of PMAE, POPME and 1 to inter­act with ten selected biomolecules (BRAF kinase, CatB, DNA gyrase, HDAC7, rHA, RNR, TrxR, TS, Top II and B-DNA) was investigated by docking studies and compared with doxorubicin.

Construction of (3,8)-connected three-dimensional cobalt(II) and copper(II) coordination polymers with 1,3-bis­[(1,2,4-triazol-4-yl)meth­yl]benzene and benzene-1,3,5-tri­carboxyl­ate ligands

Two (3,8)-coordinated three-dimensional networks based on a tetra­nuclear hy­droxide cobalt(II) cluster or with a tetra­nuclear hy­droxide copper(II) cluster, 1,3-bis­[(1,2,4-triazol-4-yl)meth­yl]benzene and benzene-1,3,5-tri­carboxyl­ate were synthesized. The compounds exhibit good photocatalytic degradation of the organic dyes methyl­ene blue (MB) and rhodamine B (RhB) under visible-light irradiation.

Porous ZnO/Co₃O₄/N-doped carbon nanocages synthesized via pyrolysis of complex metal–organic framework (MOF) hybrids as an advanced lithium-ion battery anode

ZnO-Co₃O₄ nanocomposites embedded in N-doped carbon (ZnO-Co₃O₄@N-C) nanocages with hollow dodeca­hedral shapes were successfully prepared by the simple carbonizing and oxidizing of metal–organic frameworks (MOFs). Benefiting from the advantages of structural features, the as-prepared ZnO-Co₃O₄@N-C nanocages display enhanced electrochemical performance when employed as anode materials for Li-ions batteries, which show a discharge capacity of 2373 mAh g⁻¹ for the first cycle and exhibit a retention capacity of 1305 mAh g⁻¹ even after 300 cycles at 0.1 A g⁻¹.

A threefold inter­penetrating two-dimensional zinc(II) coordination polymer: synthesis, crystal structure and selective luminescence sensing properties

A zinc(II) com­pound, prepared by the reaction of Zn(NO₃)₂·6H₂O with 4,4′-sulfonyldi­benzoic acid and 4,4′-bis­(2-methyl­imidazol-1-yl)diphenyl ether in H₂O, possesses a threefold inter­penetrating two-dimensional 4⁴-sql network and exhibits a highly selective and sensitive sensing for Fe³⁺ ions in aqueous solution.

Luminescence properties and optimized structural conformations of the S₀, S₁ and T₁ states of a tetra­nuclear formamidinate complex based on Au^I and Ag^I metal ions

A novel Au^I/Ag^I tetra­nuclear formamidinate complex consisting of a disordered potential derived from six unique metal complexes is reported. DFT calculations were performed to investigate the optimized structures of the individual unique metal complexes and the electronic and luminescence properties of the structure.

A new three-dimensional cobalt(II) coordination polymer based on V-shaped 3,4′-oxydibenzoate: synthesis, crystal structure and magnetic properties

A new coordination polymer formulated as [Co(3,4′-obb)(4,4′-bipy)]_n (3,4′-obb²⁻ is 3,4′-oxydibenzoate and 4,4′-bipy is 4,4′-bi­pyridine) was prepared by the self-assembly of Co(NO₃)₂·6H₂O with the rarely used 3,4′-obbH₂ ligand and 4,4′-bipy under solvothermal conditions, and has been structurally characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography and powder X-ray diffraction.

The heteroscorpionate ligand 2,2-bis­(3,5-di­methyl­pyrazol-1-yl)-1,1-di­phenyl­ethanol and an easy preparation of its tungsten complex

A simple and straightforward synthesis of a heteroscorpionate tungsten complex has been developed. The crystal structures of the tungsten complex and the heteroscorpionate mol­ecule have been analysed. he Hirshfeld surface analysis shows a change of the inter­molecular contacts due to the coordination of the WO₂Cl unit with the ligand mol­ecule.

Synthesis, crystal structure and biological properties of Cd and Zn coordination polymers based on a flexible tripodal ligand

Two isostructural Cd^II/Zn^II coordination polymers containing a flexible tripodal ligand were synthesized and characterized. The anti­oxidant activities against DPPH and the anti­diabetic activities against α-amylase were evaluated in vitro.

Synthesis, crystal structure and studies on the inter­action with albumin of a new silver(I) complex based on 2-(4-nitro­benzene­sulfonamido)­benzoic acid

The silver(I) complex of 2-(4-nitro­benzene­sulfonamido)­benzoic acid (HL) was analyzed by IR and NMR spectroscopies, and single-crystal X-ray crystallography. The Ag⋯Ag inter­action shows an OOOCAg⋯AgOOOC environment in the polymeric complex. The human serum albumin (HSA) inter­actions were analyzed by stead-state fluorescence, where the complex AgL–HSA presented an inter­action 20-times stronger compared to the HL–HSA inter­action.