Supramolecular aspects of metal (M) dipicolinate anionic frameworks [M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)]

The role of dipicolinic acid is to aid in the thermal resistance of bacterial endospores by creating a highly impermeable barrier [3]. The reaction of dipicolinic acid with (NH4)2Ce(NO3)6 and BaCl2 led to the following coordination complexes with similar stoichiometry but different network structures [48].

Fig. 1.4: Different coordination modes in dipicolinate complexes

Heterometallic polymeric complexes of dipicolinic acid with transition metals and lanthanides

In lattice, it comprises a series of [Co(dipic)]∞ chains bridged by 4,4´-bipyridine molecules to give a 2D structure (Fig. 1.15c). The octahedral geometry of Fe(II) is completed by four carboxylate O atoms and two water molecules (Fig. 1.17a).

Water clusters in Lanthanum-dipicolinates

Stabilization of a hydrogen-bonded octameric water cluster in the crystal lattice of cerium dipicolinate complex Ce(dipic)2(H2O)3·4H2O was reported by Rajasekharan and colleagues [65]. The four lattice water molecules available in the asymmetric unit are assembled into a centrosymmetric octamer (Fig. 1.18b).

Fig. 1.18: (a) 1D infinite chair network of octameric water cluster stabilized by cerium dipicolinates, and (b) Close view of hydrogen bonded octameric cluster

Supramolecular chemistry metal dipicolinate complexes

Inorganic-organic hybrid materials of [M(dipic) 2 ] complex with imidazolium or 2-methylimidazolium cation
Inorganic-organic hybrid materials of [M(dipic) 2 ] complex with pyridine-2,6- diammonium cation ( pyda)
Inorganic-organic hybrid materials of [M(dipic) 2 ] complex with cations of guanidine (G) and creatinine (creat)
Inorganic-organic hybrid materials of [M(dipic) 2 ] complex with piperazinium cations (pipzH 2 )
Inorganic-organic hybrid materials of M(dipic) 2 ] complex with cation of 1,3- propanediamine (pn)

In the complex (GH)3[Ce(dipic)3]·3H2O, Ce(III) shows the usual coordination number of nine, which is bound by three (dipic)2-ligands [92]. The complex (GH)[Zn(dipic)(dipicH)]·(dipicH2)·4H2O shows the presence of doubly ionized, (dipic)2- and singly ionized (dipicH)- and neutral dipicolinic acid molecules in the crystal structure [94].

Fig. 1.23: (a) Synthetic scheme of M(II) dipicolinate imidazole/2-methylimidazole complexes, (b) Crystal packing, layered structure and hydrogen bonds for [(2-methylimidazolium) 2 ][Ni(dipic) 2 ] (left) and [(imidazolium) 2 ][Ni(dipic)

Scope of the present work

Although similar study to construct layered structures by dipicolinate has been undertaken earlier, there is no systematic approach to understand the nature of the layers controlled by anions or cations. In addition, the studies on the role of different cations will help to understand the ion exchange processes.

Fig. 1.26: (a) Overview inorganic–organic hybrid assemblies based on LDH, and (b) Schematic structure of cefazolin (antibiotics) in the interlayer of LDH as a drug delivery system

Layered inorganic–organic hybrid materials of Ni(II), Cu(II) or Zn(II) dipicolinates and organic ammonium cations

Inorganic-organic hybrid materials of Ni(II), Cu(II) or Zn(II) dipicolinate complex with ethylenediammonium cation

The diammonium cation (enH2)2+ is strongly hydrogen-bonded to the carboxylate oxygen atom [CuL2]2- and water molecules in the lattice. Coordinated water molecules [Cu(en)2(H2O)2]2+. In the lattice, each of the complex anions or dications is surrounded by five oppositely charged species via ammonium-carboxylate hydrogen bonds (Figure 2.4.1a).

Fig. 2.2.1: (a) Ammonium-carboxylate interactions in 2.1, (b) Layered packing diagram of 2.1, (enH 2

Inorganic-organic hybrid materials of Ni(II), Cu(II) or Zn(II) dipicolinate complex with mono cation of 4-aminobenzylamine

These weak interactions cause the bam cations to lie perpendicularly, resulting in greater interlayer separation. Interlayer separation complex cations (Å). Reported earlier) Since most of the complexes are isostructural with respect to a particular amine, changing the metal ion does not cause any significant structural changes, as well as separation of the interlayers.

Cation exchange of the complexes

Depending on the nature and size or geometry of the organic amines (small or large alkyl and aryl substituents), the cation layer varies considerably. The structure of the polymeric complex 2.13 consists of complex anions [CuL2]2- that bind Na+ ions through their free oxygen of carbonyl groups.

Fig. 2.6.1: ORTEP of complex (a) {[Na(H 2 O) 2 ] 2 [CuL 2 ]·2H 2 O} n (2.13 ), (b) {[K 2 (H 2 O) 7 ][CuL 2 ]} n

Conclusion

In packing, the complexes do not form a well-defined layer, regardless of dinuclear or polymer complexes. Organic cation exchange resulted in dinuclear or polymeric complexes where the carbonyl oxygen atoms of the complex anion hold the aqueous metal cations.

Experimental section

Complex [bamH] 2 [NiL 2 ]·5H 2 O (2.10), [bamH] 2 [CuL 2 ]·5H 2 O (2.11) and [bamH] 2

The weak interactions that drive the packing pattern in these complexes also affect interlayer separation. In addition to organic substituents, metals also act as exchangeable components in these complexes. Thermal analysis: ~ 70-90 ºC (loss of water molecule of crystallization); further decomposition occurs at ~ 140-160 ºC (loss of two coordinated water molecules).

These complexes were prepared in a similar manner by reacting dipicolinic acid (2.0 mmol) with respective metal salts (1.0 mmol) followed by treatment with 1,8-diaminooctane (0.144 g, 1.0 mmol). These complexes were synthesized by a similar method as discussed previously; only difference is the use of 4-aminobenzylamine (226.0 µL, 2.0 mmol) as the organic amine.

Crystallographic data and refinement parameters for the complexes 2.1-2.16

Intercalation of protonated amino acids in layers of cobalt(II) or copper(II) dipicolinates

Synthesis, characterization and intercalation of dication of L-histidine in layers of Co(II) or Cu(II) dipicolinate complexes
Synthesis, characterization and intercalation of dication of L-ornithine in layers of Co(II) or Cu(II) dipicolinate complexes
Optical activity of the complexes
Conclusion
Experimental section

Synthesis and characterization of [L-hisH 2 ][CoL 2 ]·3H 2 O (3.1) and [L-hisH 2 ] [CuL 2 ]·5H 2 O (3.2)

Crystallographic data and refinement parameters for the complexes 3.1-3.4

In the Cu(II) dipicolinate complex, two dipicolinate ligands are meridionally coordinated to Cu(II) ion via tridentate chelation mode. Although both complexes 3.1 and 3.2 form layered structures, the arrangement of the indication in the lattice is different. The recurring units in the self-assembly of the complexes have the cations and anions in a 2:2 ratio.

It is clear from the table that the specific rotations are lower in the complexes than the parent amino acids. This is attributed to the flexible nature of amino acids resulting from electrostatic ammonium-carboxylate interactions in the crystal lattice.

Fig. 3.1.1: Schematic representations of Cu(II)-histidine complex

Intercalation of nucleobases by metal dipicolinates

Synthesis, characterization and intercalation of protonated adenine by Mn(II) / Cu(II) dipicolinates

These two non-equivalent aggregates of adenium cations via hydrogen bonding lead to a 1D zigzag ribbon interlaced in the Cu(II) dipicolinate anionic frameworks (Fig. 4.1.2b). Recently, stabilizations of the 1H,9H-adeninium cation have been observed in Cu(II) oxalate complexes with adenine, (1H,9H-ade)2. Isostructural complexes with other metal ions such as Co(II) and Zn(II) showed the formation of 3H,7H-adeninium cation in the complex.

Similarly, 1D assemblies of 1H,9H-adeninium cation in the form of cationic ribbon in Cu(II) malonate complexes were established by the same group of colleagues [28]. The other complexes with Co(II) or Ni(II) showed coordinated as well as adeninium cation outside the coordination sphere.

Synthesis, characterization and intercalation of cytosine assemblies by metal dipicolinates

N+-H stretching frequencies in the range of 3370-2808 cm-1. The complex 4.3 shows intense –N+-H stretching frequencies spread over a broad range than 4.4 or 4.5, due to different N+-H stretching available in the cytosine compositions. In contrast, we observed two neutral and two protonated cytosine molecules in the Mn(II) dipicolinate complex, which formed tetrameric assembly. The locations of the hydrogen atoms in the protonated cytosine are justified by difference Fourier synthesis map.

It is also determined by the complementary interactions of hydrogen bonds between the cationic and neutral cytosine molecules in the crystal structure. In the lattice, the cytosine cation interacts with the adjacent crystallographically non-equivalent cation via hydrogen bonds –NH2 and –C=O.

Fig. 4.2.1: (a) Overlay FTIR spectra of complex 4.3 and 4.4, (b) Thermogram of complex 4.3

Intercalation of discrete adeninium or cytosinium cations in layers of polymeric metal quinolinates

However, we manage to synthesize cytosine complexes with flexible organic molecules such as adipic acid and citric acid. The complex of citric acid and cytosine shows the presence of partially ionized citric acid and protonated and neutral cytosine molecules in the crystal structure. A molecule of crystallized water is encapsulated within parallel layers of partially ionized citric acid and cytosinium clusters.

Thus, by correlating the patterns obtained with adipic acid and citric acid in this study with other assemblies available in the literature, it appears that cytosine prefers a dimeric triple hydrogen-bonded assembly in dicarboxylic acid complexes. Intercalations of dimeric and trimeric assemblies have been observed in flexible organic host molecules such as adipic acid and citric acid, respectively.

Fig. 4.3.1: (a) Hydrogen bond and -stacked adeninium cations in layers of Mn(II) quinolinates, (b) Hydrogen bonded cytosinium cations in layers of Cu(II) quinolinates

Experimental section

As a future prospectus, we are interested in other host molecules with different functional groups that can interact with guanine and thymine. The other interesting finding in this chapter was the intercalation of different types of hydrogen-bonded cytosine assemblies, such as discrete, dimeric, trimeric and tetrameric assemblies into layers of different host molecules. However, the assemblies can be predicted to depend on the central metal ions and the nature of the host molecules.

It may further contribute to the molecular recognition processes of cations of adenine or cytosine by these different artificial host molecules. A pale yellow (for manganese) or blue (for copper) precipitate obtained from the reaction mixture was filtered, dried and crystallized from Milli Q water.

Crystallographic data and refinement parameters for the complexes 4.1-4.5

Intercalation of drug related molecules, thiamine and quinolines

Metal dipicolinate complexes with thiamine as dication

Thiamine, obtained in the mono-protonated salt, is converted to a dicyclic form in the complex by protonation at the less sterically crowded nitrogen atom (N1 atom) of the pyrimidine ring. The hydroxyl group of the thiamine is also involved in hydrogen bonding with an oxygen atom of the coordinated carboxylate group of the complex anion. The 1HNMR spectra of the zinc complex show the peaks of thiamine which show its existence in the complex (Fig. 5.1.4a).

The intensity of the C-2 proton of the thiazole ring of the thiamine indication, which appears at 9.6 ppm, decreased significantly in the complex. A 2D spectrum (1H-COSY) was recorded to see the coupling of the proton (Fig. 5.1.4b), but it shows no coupling with the other available protons in the complex.

Fig. 5.1.1: Zn(thiamine)Cl 3 complex (Bencini et al)

Solvent-free synthesis of Ni(II) and Cu(II) dipicolinate complexes with protonated quinolines

The strong and broad absorption bands in the range 3413-3408 cm-1 are attributed to (OH) vibrations of water of crystallization. The absorption bands that appeared in the range 3318-2913 cm-1 are related to (-N+-H) vibrations of protonated quinoline bases. Due to the stacking ability, the cation exhibits extensive face-to-face interactions in the crystal lattice.

In the lattice of complex 5.6, the 5AQ cations lie between two [NiL2]2 units in such a way that they stack simultaneously with adjacent symmetry-independent cationic units as well as with the complex anion. Due to planar geometry of the cations, they can be easily integrated into the empty space created by the bulky complex anion through stacking interactions.

Fig. 5.2.1: Solid state visible spectra (left) of (a) H 2 [NiL 2 ] · 3H 2 O, (b) [HQ] [NiL 2 ] · 5H 2 O (5.4), (c) [H5AQ] [NiL 2 ] · xH 2 O (5.6); TG of complex 5.6 (right)

Nature of the complex with change of pH

The complete release of the cationic molecules from the metal dipicolinate complex occurs at pH ~ 8.0. Furthermore, the chemical composition of the released molecule is monitored by comparing FTIR spectra with the thiamine molecule and detected intake. For example, when the pH of the aqueous solution of the Co(II)-dipicolinate-thiamine complex (5.1) is raised by the addition of sodium hydroxide; in basic medium (pH > 8) the thiamin moiety is detached from the metal complex and leads to the formation of a mixed metal complex with a composition {[Na(H2O)2]2[CoL2]·2H2O}n.

This complex is a cation-coordinated complex similar to the analogous Cu(II)-dipicolinate complex described in Chapter 2. The cationic moiety is coordinated to the dipicolinate moiety via carbonyl oxygen of the anionic moiety, as shown in Fig.

Fig. 5.3.1: (a) The crystal structure of {[Na(H 2 O) 2 ] 2 [CoL 2 ]·2H 2 O} n (the hydrogen atoms of water molecules are not located), (b) The tetra-nuclear coordinated cation of the complex (water molecules of crystallization are omitted)

Conclusion

Experimental section

After slow evaporation of direct Q Millipore water, dark red (cobalt), blue (copper), and colorless (zinc) single crystals suitable for X-ray analysis were obtained after a period of 3-4 days.

Crystallographic data and refinement parameters for the complexes 5.1 - 5.3

Mono or polynuclear copper(II) dipicolinate complexes

Cu(II) dipicolinate complex with imidazole as ancillary ligand
Cu(II) dipicolinate complex with pyridine as ancillary ligand
Synthesis, characterization and structural features of Cu(II) dipicolinate complex with 2,2 -bipyridine as ancillary ligand
Synthesis, characterization and structural features of Cu(II) dipicolinate 1,10- phenanthroline complex
Conclusion
Crystal structure and refinement parameters of the complexes 6.1-6.4

The hydrogen atoms of the water of crystallization molecules in this complex could not be located in the X-ray crystal structure. The formation of the five-coordinate copper complex 6.2 is attributed to the extensive hydrogen bonding between the molecules. The crystal structure of 6.3 possesses nine water molecules as the crystallization solvent occupying the interstitial spaces of the complex.

The dinuclear assemblies in complexes 6.3 and 6.4 differ due to the nature of the two different aromatic ligands. Analytical as well as spectroscopic data are also listed along with each of the complexes.

Fig. 6.1.1a, has two crystallographically independent mononuclear complex molecules (Z = 2)

Metal dipicolinates stabilized hydrogen bonded water clusters

Infinite cyclic decameric water cluster in mixed ionic complex, [Co(phen) 2
Hexadecameric water cluster (H 2 O) 16 in complex, [Ni(phen) 2 (bpy)][CoL 2 ]·8H 2 O
Encapsulation of infinite water cluster (H 2 O) n in complex [Co(phen) 3 ][MnL 2 ]
Infinite water cluster with cyclic tetrameric core in [Ni(phen) 3 ][CoL 2 ]·9H 2 O and [Ni(phen) 3 ] 2 [ZnL 2 ] 2 ·20H 2 O
Thermogravimetric analysis
Conclusion
Crystallographic data and refinement parameters for the complexes 7.1 - 7.5 Compound
Table 7.1: Some (O-O) distances (Å) and (O-O-O) angles (º) for the infinite decameric water cluster in 7.1

Change in the ligand composition of the cationic part showed creation of both hydrophilic and hydrophobic environment in the complex. 7.1.1: (a) An image showing the 2D (H2O)10 cluster passing through [ZnL2]2 unit, (b) Perspective view of the cluster showing the H-bonding interactions with the anionic units, (c) Close-up of the cluster with chair conformation. The water molecules fill the voids formed during the packing of the bulky complex ions in the crystal lattice.

Each of the complexes contains a relatively large number of network water molecules in the crystal structure. Depending on the cationic environment, the number of water molecules in the network varies per molecule.