**5. Synthesis by slow evaporation at room temperature**

It is the simplest method, but it is suitable only for certain materials. The preparation protocol consists in weighing the reagents in the desired proportion and adding water or an organic base in a ratio that should be determined experimentally. Then the solution must be heated to reach the saturation.

This method takes a few hours to obtain crystals as in the synthesis of NH4H2AsO4 or NH4H2PO4, and for other materials, it needs a few days. The condensation of ions

**17**

**Figure 11.**

*location of the alkali metal cations [34].*

*Synthesis Methods in Solid-State Chemistry DOI: http://dx.doi.org/10.5772/intechopen.93337*

the laboratory.

by different types of oxygenated bridges, HO−

in aqueous solution forms entities in which cations, identical or different, are linked

The following phosphate KCdHP2O7.2H2O (**Figure 11**) [34] has been obtained by slowly evaporation at room temperature. The method consists in the preparation of a saturated solution containing the reagents in the desired proportion. The reagents are dissolved in water then heated at 100°C for a few minutes to have a saturated solution. The solution obtained is transferred into a petri dish and left in a corner in

The hybrid materials (organic base+ salt) may be synthesized by slow evaporation at room temperature. The best solvent can be used is the water. It is possible to add other solvent with water such as alcohol like in the preparation of (C7H7N2)2[CuCl4].2H2O [35]. In this type of materials, the organic part and the inorganic part are linked via hydrogen bond and π▬π bond as shown in **Figure 12**. Another example may be sited in this section, the synthesis and the crystal structure of (C3H6N3)4Bi2Cl10 [36] which was grown by a slow evaporation of an aqueous solution of bismuth chloride (BiCl3) and 3-aminopyrazole (C3H5N3) in molar amount (1: 2) with a small excess of hydrochloric acid (HCl). The single

Many organic compounds also have been crystallize by slow evaporation at room

temperature such as alkyl-2-(2-imino-4-oxothiazolidin-5-ylidene) acetate [37], 3,4-*cis*-disubstituted pyrrolidin-2-ones [38] ethyl 2-(4-chlorophenyl)-3-cyclopentyl-4-oxo-1-propylimidazolidine-5-carboxylate (C20H27ClN2O) [39]. The obtaining

*Perspective view of the structure of KCdHP2O7.2H2O showing the hydrogen bonds (dashed lines) and the* 

crystals were obtained after 7 months of slow evaporation (**Figure 13**).

important factor in this method. In fact, the choice of pH must be chosen to coprecipitate the various reagents simultaneously. For example, in the ternary system H2O-NH3-As2O5, the adjusting of the pH at 4.3 allows the formation of NH4H2AsO4, and for a basic value of pH, the preparation gives a second phase: (NH4)2HAsO4.

or O2−. Thus, the value of pH is a very

#### **Figure 10.** *Structures of olivine-, Na2CrO4-, and spinel-like LiCoXO4 (X = P, As) [29].*

#### *Synthesis Methods in Solid-State Chemistry DOI: http://dx.doi.org/10.5772/intechopen.93337*

*Synthesis Methods and Crystallization*

dral 8a sites [29] (**Figure 10**).

chemical properties.

from the hexagonal close packing into the cubic close packing of the spinel structure [29]. Upon high pressure conditions (6 GPa, 1173 K) olivine-like LiMAsO4

randomly occupy 16d octahedral positions and the As+5 cations occupy the tetrahe-

Since 2006, the prediction of the structure at high pressures became an area of intense activity thanks to the development of the new computer program USPEX [30] by Oganov et al. The code was used with success to predict many new crystal structures, and the results were confirmed by the synthesis of same predicted materials such as Na-Cl system: Na3Cl, Na2Cl, Na3Cl2, Na4Cl3, NaCl3, and NaCl7 [31] and H-Cl system: H2Cl, H3Cl, H5Cl, and H4Cl7 [32, 33]. This result allows the discovery of new generation of materials where the core electrons can participate in the formation of chemical bonds. Thus, obviously, we will have very interesting physical and

It is the simplest method, but it is suitable only for certain materials. The preparation protocol consists in weighing the reagents in the desired proportion and adding water or an organic base in a ratio that should be determined experimentally.

This method takes a few hours to obtain crystals as in the synthesis of NH4H2AsO4 or NH4H2PO4, and for other materials, it needs a few days. The condensation of ions

and M+2 ions

(M = Fe, Co, Ni) transforms to spinel-like compounds where Li+

**5. Synthesis by slow evaporation at room temperature**

Then the solution must be heated to reach the saturation.

*Structures of olivine-, Na2CrO4-, and spinel-like LiCoXO4 (X = P, As) [29].*

**16**

**Figure 10.**

in aqueous solution forms entities in which cations, identical or different, are linked by different types of oxygenated bridges, HO− or O2−. Thus, the value of pH is a very important factor in this method. In fact, the choice of pH must be chosen to coprecipitate the various reagents simultaneously. For example, in the ternary system H2O-NH3-As2O5, the adjusting of the pH at 4.3 allows the formation of NH4H2AsO4, and for a basic value of pH, the preparation gives a second phase: (NH4)2HAsO4.

The following phosphate KCdHP2O7.2H2O (**Figure 11**) [34] has been obtained by slowly evaporation at room temperature. The method consists in the preparation of a saturated solution containing the reagents in the desired proportion. The reagents are dissolved in water then heated at 100°C for a few minutes to have a saturated solution. The solution obtained is transferred into a petri dish and left in a corner in the laboratory.

The hybrid materials (organic base+ salt) may be synthesized by slow evaporation at room temperature. The best solvent can be used is the water. It is possible to add other solvent with water such as alcohol like in the preparation of (C7H7N2)2[CuCl4].2H2O [35]. In this type of materials, the organic part and the inorganic part are linked via hydrogen bond and π▬π bond as shown in **Figure 12**.

Another example may be sited in this section, the synthesis and the crystal structure of (C3H6N3)4Bi2Cl10 [36] which was grown by a slow evaporation of an aqueous solution of bismuth chloride (BiCl3) and 3-aminopyrazole (C3H5N3) in molar amount (1: 2) with a small excess of hydrochloric acid (HCl). The single crystals were obtained after 7 months of slow evaporation (**Figure 13**).

Many organic compounds also have been crystallize by slow evaporation at room temperature such as alkyl-2-(2-imino-4-oxothiazolidin-5-ylidene) acetate [37], 3,4-*cis*-disubstituted pyrrolidin-2-ones [38] ethyl 2-(4-chlorophenyl)-3-cyclopentyl-4-oxo-1-propylimidazolidine-5-carboxylate (C20H27ClN2O) [39]. The obtaining

#### **Figure 11.**

*Perspective view of the structure of KCdHP2O7.2H2O showing the hydrogen bonds (dashed lines) and the location of the alkali metal cations [34].*

#### **Figure 12.**

*Projection of the structure of (C7H7N2)2[CuCl4].2H2O showing the alternating stacking of the organic and inorganic layers connected through hydrogen bonds. The face-to-face π▬π stacking between parallel organic molecules is noteworthy with a centroid-centroid distance of 3.968 (3) [35].*

**Figure 13.** *Bi2Cl10 octahedron surrounded by aminopyrazolium entities, showing the H-Cl contacts [36].*

**19**

*Synthesis Methods in Solid-State Chemistry DOI: http://dx.doi.org/10.5772/intechopen.93337*

the hottest region to the coldest region.

**6. Flux method**

**7. Crystal growth**

of single crystals depends in the case on the nature of the organic compounds and solvent. The presence of heterocyclic group in the organic molecule promotes the

Usually, the flux method is used to grow materials as single crystals [40]. The main objective of this method is to decrease the crystallization temperature. This technique has been used to grow high melting phosphate crystals, arsenates, oxides, minerals, and ceramic crystals which cannot be obtained by the conventional solid-state method (Section 1). In this growth technique, the basic materials (solute precursors to crystallize) are reduced to a liquid form in an appropriate flow and the growth process starts when the solution reaches critical supersaturation. The resulting supersaturation and crystal growth are achieved by flow evaporation, solution cooling, or a transport process in which the solute is caused to flow from

The understanding of the phase information about the materials is indispensable to optimize the crystal growth of multi-component system. Practically, binary or other above compositional systems can be easily described using the phase diagram. The phase diagram shows the crystallization or solidification within a material as a function of the material composition (% elements) and material temperature. The solvent can be a single element, compound, or combination of chemical compounds. The solute is an element or a compound with a melting point generally higher than that of the solvent but in principle it is quite possible to grow crystals

from eutectic systems in which the "solvent" has a higher melting point.

lites connect to each other, and the size increases [41–43].

may proceed in the light of several different ways:

1.Vapor-solid (condensation)

2.Solution-solid (precipitation)

4.Solid A-Solid B (transformation)

3.Melt-solid (freezing)

For more clarification, taking the example of LiPr(PO3)4 [40]. The material has been synthesized as a single crystal by the means of flux method. A mixture of Li2CO3 and Pr6O11 with stoichiometric ratio was dissolved in an excess of phosphoric acid H3PO4 (85%). The mixture was heated to 200°C for 12 h, then to 325°C for 5 days. Finally, the mixture was cooled slowly to room temperature. The single crystal was separated from the excess phosphoric acid by washing in boiling water [40].

When a solid is heated, some physical and chemical changes sintering, melting, and thermal decomposition can be observed. Sintering process results from crystal growth at the contact area between adjacent crystallites. As to conclude, the crystal-

In high temperatures, as a result of ion movements, melting occurs. The ordered lattice array is replaced by the short-range order of the liquid state. Crystallization

crystallization by the formation of hydrogen and π▬π bond.

of single crystals depends in the case on the nature of the organic compounds and solvent. The presence of heterocyclic group in the organic molecule promotes the crystallization by the formation of hydrogen and π▬π bond.
