Charge-density distribution and electrostatic flexibility of ZIF-8 based on high-resolution X-ray diffraction data and periodic calculations.

The electron-density distribution in a prototypical porous coordination polymer ZIF-8 has been obtained in an approach combining high-resolution X-ray diffraction data and Invariom refinement. In addition, the periodic quantum-chemical calculation has been used to describe the theoretical density features of ZIF-8 in the same geometry (m1) and also in a "high-pressure" form of ZIF-8 (m2) characterized by conformational change with respect to the methylimidazolate linker. A thorough comparison of the electronic and electrostatic properties in two limiting structural forms of ZIF-8 proposes additional aspects on diffusion and adsorption processes occurring within the framework. The dimensions of the four-membered (FM) and six-membered (SM) apertures of the ß cage are reliably determined from the total electron-density distribution. The analysis shows that FM in m2 becomes competitive in size to the SM aperture and should be considered for the diffusion of small molecules and cations. Bader's topological analysis (quantum theory of atoms in molecules) shows similar properties of both ZIF-8 forms. On the other hand, analysis of their electrostatic properties reveals tremendous differences. The study suggests exceptional electrostatic flexibility of the ZIF-8 framework, where small conformational changes lead to a significantly different electrostatic potential (EP) distribution, a feature that could be important for the function and dynamics of the ZIF-8 framework. The cavity surface in m1 contains 38 distinct regions with moderately positive, negative, or neutral EP and weakly positive EP in the cavity volume. In contrast to m1, the m2 form displays only two regions of different EP, with the positive one taking the whole cavity surface and the strong negative one localized entirely in the FM apertures. The EP in the cavity volume is also more positive than that in m1. A pronounced influence of the linker reorientation on the EP of the ZIF-8 forms is related to the high symmetry of the system and to an amplification of the electrostatic properties by cooperative effects of the proximally arranged structural fragments.

Crystal structure of tetra-aqua-(5,5'-dimethyl-2,2'-bipyridyl-κ(2) N,N')iron(II) sulfate.

In the title compound, [Fe(C12H12N2)(H2O)4]SO4, the central Fe(II) ion is coordinated by two N atoms from the 5,5'-dimethyl-2,2'-bi-pyridine ligand and four water O atoms in a distorted octa-hedral geometry. The Fe-O coordination bond lengths vary from 2.080 (3) to 2.110 (3) Å, while the two Fe-N coordination bonds have practically identical lengths [2.175 (3) and 2.177 (3) Å]. The chelating N-Fe-N angle of 75.6 (1)° shows the largest deviation from an ideal octa-hedral geometry; the other coordination angles deviate from ideal values by 0.1 (1) to 9.1 (1)°. O-H⋯O hydrogen bonding between the four aqua ligands of the cationic complex and four O-atom acceptors of the anion leads to the formation of layers parallel to the ab plane. Neighbouring layers further inter-act by means of C-H⋯O and π-π inter-actions involving the laterally positioned bi-pyridine rings. The perpen-dicular distance between π-π inter-acting rings is 3.365 (2) Å, with a centroid-centroid distance of 3.702 (3) Å.

(E)-4-[(2-carbamoylhydrazinylidene)methyl]-3-hydroxy-5-hydroxymethyl-2-methylpyridin-1-ium nitrate.

The title compound, C9H13N4O3(+)·NO3(-), is the first structurally characterized Schiff base derived from semicarbazide and pyridoxal. Unusually for an unsubstituted semicarbazone, the compound adopts a syn conformation, in which the carbonyl O atom is in a cis disposition relative to the azomethine N atom. This arrangement is supported by a pair of hydrogen bonds between the organic cation and the nitrate anion. The cation is essentially planar, with only a hydroxymethyl O atom deviating significantly from the mean plane of the remaining atoms (r.m.s. deviation of the remaining non-H atoms = 0.01 Å). The molecules are linked into flat layers by N-H···O and C-H···O hydrogen bonds. O-H···O hydrogen bonds involving the hydroxymethyl group as a donor interconnect the layers into a three-dimensional structure.

4-[(4-Methyl-phen-yl)sulfan-yl]butan-2-one.

In the title compound, C11H14OS, all non-H atoms are essentially coplanar, with a mean deviation of 0.023 Å. In the crystal, centrosymmetrically related mol-ecules are weakly connected into dimers by pairs of C-H⋯O inter-actions. The dimers are further linked along the a axis by weak C-H⋯π and C-H⋯S inter-actions.

Benzyl 2-(benzylsulfanyl)benzoate.

In the title compound, C(21)H(18)O(2)S, the central aromatic ring makes dihedral angles of 5.86 (12) and 72.02 (6)° with the rings of the terminal O-benzyl and S-benzyl groups, respectively. The dihedral angle between the peripheral phenyl rings is 66.16 (6)°. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds, forming inversion dimers. These dimers are linked via C-H⋯π inter-actions, forming a three-dimensional network.

4-Di-chloro-methyl-4-methyl-5-(nitro-meth-yl)cyclo-hex-2-enone.

In the title compound, C9H11Cl2NO3, the six-membered ring adopts a screw-chair conformation. In the crystal, two different C-H⋯O hydrogen bonds involving the same acceptor atom connect the mol-ecules into a chain extending along the c-axis direction.

4-Eth-oxy-3-meth-oxy-benzaldehyde.

In the title compound, C10H12O3, all non-H atoms are approximately coplanar, with an r.m.s. deviation of 0.046 Å. In the crystal, very weak C-H⋯O inter-actions link the mol-ecules into sheets parallel to (101).

A new polymorph of 1-ferrocenyl-3-(3-nitroanilino)propan-1-one.

Recrystallization of the title compound, [Fe(C(5)H(5))(C(14)H(13)N(2)O(3))], from a mixture of n-hexane and dichloromethane gave the new polymorph, denoted (I), which crystallizes in the same space group (P1) as the previously reported structure, denoted (II). The Fe-C distances in (I) range from 2.015 (3) to 2.048 (2) Å and the average value of the C-C bond lengths in the two cyclopentadienyl (Cp) rings is 1.403 (13) Å. As indicated by the smallest C-Cg1-Cg2-C torsion angle of 1.4° (Cg1 and Cg2 are the centroids of the two Cp rings), the orientation of the Cp rings in (I) is more eclipsed than in the case of (II), for which the value was 15.3°. Despite the pronounced conformational similarity between (I) and (II), the formation of self-complementary N-H···O hydrogen-bonded dimers represents the only structural motif common to the two polymorphs. In the extended structure, molecules of (I) utilize C-H···O hydrogen bonds and, unlike (II), an extensive set of intermolecular C-H···π interactions. Fingerprint plots based on Hirshfeld surfaces are used to compare the packing of the two polymorphs.

3-(3-Acetyl-anilino)-1-ferrocenylpropan-1-one.

The title ferrocene-containing Mannich base, [Fe(C(5)H(5))(C(16)H(16)NO(2))], crystallizes with two independent mol-ecules (A and B) in the asymmetric unit. Mol-ecules A and B have similar conformations. The dihedral angles between the best planes of the benzene and substituted cyclo-penta-dienyl rings are 88.59 (9) and 84.39 (10)° in A and B, respectively. In the crystal, the independent mol-ecules form centrosymmetric dimers via corresponding N-H⋯O hydrogen bonds. The dimers further arrange via C-H⋯π and C-H⋯O inter-actions. There are no significant inter-actions between the A and B mol-ecules.

1-Ferrocenyl-3-(2-methyl-anilino)propan-1-one.

In the ferrocene-containing Mannich base, [Fe(C(5)H(5))(C(15)H(16)NO)], the dihedral angle between the mean planes of the benzene ring and the substituted cyclo-penta-dienyl ring is 84.63 (7)°. The conformation of the title compound significantly differs from those found in corresponding m-tolyl-amino and p-tolyl-amino derivatives. In the crystal, C-H⋯O inter-actions connect the mol-ecules into chains, which further inter-act by means of C-H⋯π inter-actions. It is noteworthy that the amino H atom is shielded and is not involved in hydrogen bonding.

3-Anilino-1-ferrocenylpropan-1-one.

In the title ferrocene derivative, [Fe(C(5)H(5))(C(14)H(14)NO)], the dihedral angle between the mean planes of the phenyl ring and the substituted cyclo-penta-dienyl ring is 84.4 (1)°. The mol-ecules are connected into centrosymmetric dimers via N-H⋯O hydrogen bonds. In addition, C-H⋯O and C-H⋯N contacts stabilize the crystal packing.

1-Ferrocenyl-3-(4-methyl-anilino)propan-1-one.

In the title ferrocene derivative, [Fe(C(5)H(5))(C(15)H(16)NO)], the dihedral angle between the best planes of the benzene and the substituted cyclo-penta-dienyl ring is 83.4 (1)°. The presence of a methyl substituent in the para position of the aniline group does not alter the crystal packing compared to that of 3-anilino-1-ferrocenylpropan-1-one [Leka et al. (2012 ▶). Acta Cryst. E68, m229]. The molecules are connected into centro-symmetric dimers via N-H⋯O hydrogen bonds. In addition, C-H⋯O and C-H⋯N contacts stabilize the crystal packing.

1-Ferrocenyl-3-(3-fluoro-anilino)propan-1-one.

The title ferrocene derivative, [Fe(C(5)H(5))(C(14)H(13)FNO)], crystallizes in the same space group with similar unit-cell parameters as the derivatives 3-anilino-1-ferrocenylpropan-1-one [Leka et al. (2012 ▶). Acta Cryst. E68, m229] and 1-ferrocenyl-3-(4-methyl-anilino)propan-1-one [Leka et al. (2012 ▶). Acta Cryst. E68, m230]. The dihedral angle between the best planes of the benzene ring and the substituted cyclo-penta-dienyl ring is 83.4 (1)°. The presence of the electronegative fluoro substituent in the meta position of the aniline group does not alter the crystal packing compared to the other two derivatives. The molecules are connected into centrosymmetric dimers via N-H⋯O hydrogen bonds. In addition, C-H⋯O and C-H⋯N contacts stabilize the crystal packing.

4-[(2E)-2-(2-Hy-droxy-benzyl-idene)hydrazin-1-yl]benzonitrile.

The asymmetric unit of the title Schiff base, C(14)H(11)N(3)O, contains two independent mol-ecules which have similar conformations. The dihedral angles between the benzene rings are 4.19 (9) and 14.18 (9)° in the two mol-ecules. An intra-molecular O-H⋯N hydrogen bond stabilizes the mol-ecular conformation of each mol-ecules. The crystal packing is dominated by pairs of equivalent N-H⋯N and C-H⋯O hydrogen bonds which arrange the mol-ecules into layers parallel to (-111).

2-(1,3-Dioxoisoindolin-2-yl)acetic acid-N'-[(E)-4-meth-oxy-benzyl-idene]pyridine-4-carbohydrazide (2/1).

In the crystal structure of the title compound, 2C(10)H(7)NO(4)·C(14)H(13)N(3)O(2), the two independent acid mol-ecules are connected through strong O-H⋯N and O-H⋯O hydrogen bonds to the central mol-ecule of the anti-tubercular drug N'-[(E)-4-meth-oxy-benzyl-idene]pyridine-4-carbohydrazide. Two such trimolecular units related by an inversion centre inter-act through a pair of N-H⋯O hydrogen bonds, forming a 3 + 3 mol-ecular aggregate. The dihedral angle between the aromatic rings of the hydrazone mol-ecule is 1.99 (12)°. The crystal packing features weak C-H⋯O and π-π stacking inter-actions, with centroid-centroid distances of 3.8460 (19) and 3.8703 (13) Å.

Amino-(5-{2-[amino-(iminio)meth-yl]hydrazin-1-yl}-3,5-dimethyl-4,5-dihydro-1H-pyrazol-1-yl)methaniminium dinitrate.

The reaction of aqueous solutions of amino-guanidine hydrogennitrate and acetyl-acetone produces the title pyrazole salt, C(7)H(18)N(8) (2+)·2NO(3) (-). The crystal structure is stabilized by a complex N-H⋯O hydrogen-bonding network. The difference in the engagement of the two nitrate anions in hydrogen bonding is reflected in the variation of the corresponding N-O bond lengths.

Bis{N,N,N-trimethyl-2-oxo-2-[2-(2,3,4- trihydroxy-benzyl-idene)hydrazin-yl]ethanaminium} tetra-chlorido-zincate(II) methanol solvate.

The asymmetric unit of the title compound, (C(12)H(18)N(3)O(4))(2)[ZnCl(4)]·CH(3)OH, consists of two Girard reagent-based cations, a tetra-chlorido-zincate anion and a mol-ecule of methanol as solvate. These components are inter-connected in the crystal structure by an extensive network of O-H⋯O, N-H⋯O, C-H⋯O, O-H⋯N, O-H⋯Cl, N-H⋯Cl and C-H⋯Cl hydrogen bonds. The shortest inter-molecular inter-action is realized between the cation and anion [H⋯Cl = 2.29 (5) Å; O-H⋯Cl = 167 (3)°]. C-H⋯O inter-actions also play a important role in the inter-connection of the cations.

Different intermolecular interactions in azido[2-(diphenylphosphino)benzaldehyde semicarbazonato-kappa2P,N1,O]nickel(II).

The title compound, [Ni(C(20)H(17)N(3)OP)(N(3))], is the first complex with a semicarbazide-based ligand having a P atom as one of the donors. The influence of the P atom on the deformation of the coordination geometry of the Ni(II) ion is evident but less expressed than in the cases of complexes with analogous seleno- and thiosemicarbazide ligands. The torsion angles involving the two bonds formed by the P atom within the six-membered chelate ring have the largest values [C-P-Ni-N = 24.3 (2) degrees and C-C-P-Ni = -24.2 (4) degrees ], suggesting that the P atom considerably influences the conformation of the ring. Two types of N-H...N hydrogen bond connect the complex units into chains.

{4-[(Carbamimidoylhydrazono)methyl-kappa2N1,N4]-5-hydroxymethyl-2-methylpyridinium-3-olate-kappaO}(methanol-kappaO)copper(II) dinitrate.

The title compound, [Cu(C(9)H(13)N(5)O(2))(CH(4)O)](NO(3))(2), consists of square-planar cationic complex units where the Cu(II) centre is coordinated by an N,N',O-tridentate pyridoxal-aminoguanidine Schiff base adduct and a methanol molecule. The tridentate ligand is a zwitterion exhibiting an almost planar conformation. The dihedral angles between the mean planes of the pyridoxal ring and the six- and five-membered chelate rings are all less than 2.0 degrees. The charge on the complex cation is neutralized by two nitrate counter-ions. Extensive N-H...O and C-H...O hydrogen bonding connects these ionic species and leads to the formation of layers. The pyridoxal hydroxy groups are the only fragments that deviate significantly from the flat layer structure; these groups are involved in O-H...O hydrogen bonding, connecting the layers into a three-dimensional crystal structure.

First crystal structures of metal complexes with a 4-nitropyrazole-3-carboxylic acid ligand and the third crystal form of the ligand.

Pyrazole (pz)-derived ligands can, besides exhibiting a strong coordination ability toward different metal ions, exhibit a great diversity in their coordination geometry and nuclearity, which can be achieved by varying the type and position of the pz substituents. The present study reports the synthesis and crystal structure of two binuclear complexes, namely bis(µ-4-nitro-1H-imidazol-1-ide-5-carboxylato)-κ3N1,O:N2;κ3N2:N1,O-bis[aqua(dimethylformamide-κO)copper(II)], [Cu2(C4HN3O4)2(C3H7NO)2(H2O)2], (II), and bis(µ-4-nitro-1H-imidazol-1-ide-5-carboxylato)-κ2N1,O:N2;κ2N2:N1,O-bis[triaquacobalt(II)] dihydrate, [Co2(C4HN3O4)2(H2O)6]·2H2O, (III). These compounds represent rare examples of metal complexes comprising 3,4-substituted pz derivatives as a bridging ligand and also the first crystal structures of transition-metal complexes with ligands derived from 4-nitropyrazole-3-carboxylic acid. Recently, the crystal structures of the same ligand in the neutral and mixed neutral/anionic forms have been reported. We present here the third form of this ligand, where it is present in a fully deprotonated anionic form within a salt, i.e. ammonium 4-nitropyrazole-3-carboxylate, NH4+·C4H2N3O4-, (I). Single-crystal X-ray diffraction revealed that in the present complexes, the CuII and CoII centres adopt distorted square-pyramidal and octahedral geometries, respectively. In both cases, the N,N',O-coordinated pz ligand shows simultaneously chelating and bridging coordination modes, leading to the formation of a nearly planar six-membered M2N4 metallocycle. In all three crystal structures, the supramolecular arrangement is controlled by strong hydrogen bonds which primarily engage the carboxylate O atoms as acceptors, while the nitro group adopts the role of an acceptor only in structures with an increased number of donors, as is the case with CoII complex (III). The electrostatic potential, as a descriptor of reactivity, was also calculated in order to examine the changes in ligand electrostatic preferences upon coordination to metal ions.