**Abstract**

The computational study of some s-block metal nitrophenolate complexes, [Ca(THEEN)(PIC)]<sup>+</sup> (**1**), [Ca(THPEN)(H2O)2] 2+ (**2**), Ba(THPEN)(PIC)2 (**3**) [Na(THPEN)]2 2+ (**4**), [Sr(THPEN)(H2O)2]2 2+ (**5**) and [Ba(THPEN)(H2O)2]2 2+ (**6**) (where THEEN (N,N,N<sup>0</sup> ,N<sup>0</sup> -Tetrakis(2-hydroxyethyl)ethylenediamine) and THPEN (N,N,N<sup>0</sup> ,N<sup>0</sup> -Tetrakis(2-hydroxypropyl)ethylenediamine) are tetrapodal ligands and PIC� is 2,4,6-trinitrophenolate anion), is presented here using density functional theory (DFT) in its hybrid form B3LYP. The geometries of the title complexes are described by the quantum-chemical approach using input coordinates obtained from the previously synthesized and X-ray characterized diffraction data of [Ca(THEEN)(PIC)](PIC), [Ca(THPEN)(H2O)2](PIC)2, Ba(THPEN)(PIC)2, [Na(THPEN)]2(PIC)2, [Sr(THPEN)(H2O)2]2(DNP)4 and [Ba(THPEN) (H2O)2]2(DNP)4 (where DNP is 3,5-dinitrophenolate). Only the primary coordination sphere of complexes (**1–6**) is optimized in the gaseous phase. Calculations of the energy gaps of frontier orbitals (HOMO-LUMO), 13C-NMR shifts and vibrational bands are carried out using B3LYP/6-31 g + (d,p)/LANL2DZ level of theory. The calculated geometric and spectral parameters reproduced the experimental data with a well agreement.

**Keywords:** DFT, s-block metal complexes, nitrophenolates, tetrapodal ligands

## **1. Introduction**

The alkali and alkaline earth metal cations have inert gas electronic structures and are not expected to show any stereochemical requirements in their complex formation as do transition metal cations. They may be considered spherical even in the complex state. Their complexation is thus treated as recognition of spherical cations by organic ligands [1]. Depending upon the nature of the organic ligand and the anion, the metal ions can be separated as solvated ions, solvent separate, loose and tight ion pairs.

Alkali and alkaline earth metal ions form a large number of solid complexes with podands [2–6]. The podands are inherently flexible because the two ends of the molecule are not tied simultaneously. Polypodal ligands are acyclic multidentate ligands containing more than three arms. They form an unlimited family of

structures which finally give rise to dendrimers. A predominant 1:1 complexation has also been observed in alkali and alkaline earth metal complexes of the tetra- and pentapodands. The stability constants of the terapodands are generally lower than those of the corresponding tripodands because of more severe steric hindrance to complexation [7]. Vögtle and coworkers have indicated that the ligands resembling tetrapodands are capable of forming 1:1 complexes with s-block metal ions [8, 9].

The s-block elements present a usual challenge in the molecular modeling, because the metal-ligand interactions in both cases are principally electrostatic. The types of alkali and alkaline earth metal complexes subjected to molecular modeling can be divided into five categories: crown ethers [10–16], cryptands [17, 18], spherands [19, 20], podands and other biologically important ligands, such as ionophores and cyclic antibiotics [21–24] . The present work has been undertaken with the aim to computationally characterize the structure and nature of complexes of s-block metal ions with the tetrapodands THEEN and THPEN. Recently the computational studies of these tetrapodal ligands with Cu(II), Ag(I) and La(III) have been reported. Recently, synthesis, crystal structure and biological properties of [Co(edtp)Cl]�NO3�H2O complex was also determined, where edtp is N,N,N<sup>0</sup> , N0 -Tetrakis(2-hydroxypropyl) ethylenediamine in which Co2+ ion is coordinated by the N,N<sup>0</sup> ,O,O<sup>0</sup> ,O″-pentadentate edtp ligand and a chloride to generate a distorted CoClN2O3 octahedron [25–28].

## **2. Computational details**

From the last 3 decades density functional theory has been the dominant method for the quantum mechanical simulation of periodic systems. In recent years it has also been adopted by quantum chemists and is now very widely used for the simulation of energy surfaces in molecules. The quantum-chemical calculations (DFT calculations) giving molecular geometries of minimum energies, molecular orbitals (HOMO-LUMO), 13C-NMR and vibrational spectra were performed using the Gaussian 09 [29]. Molecular orbitals were visualized using "Gauss view". The method used was Becke's three-parameter hybrid-exchange functional, the nonlocal correlation provided by the Lee, Yang and Parr expression, and the Vosko, Wilk, and Nuair 1980 local correlation functional (III) (B3LYP) [30, 31]. The 6-31 g + (d,p) basis set was used for C, N and O. The LANL2DZ basis set [32] and pseudopotentials of Hay and Wadt were used for Ca, Sr, Ba and Na metal atoms [33, 34]. DFT calculations were performed in the gaseous phase and the input coordinates were obtained from and then compared with crystal structure data of already reported complexes: [Ca(THEEN)(PIC)](PIC),[Ca(THPEN)(H2O)2](PIC)2, Ba(THPEN)(PIC)2, [Na (THPEN)]2(PIC)2, [Sr(THPEN)(H2O)2]2(DNP)4 and [Ba(THPEN)(H2O)2]2(DNP)4 (where DNP is 3,5-dinitrophenolate) [35]. The structural parameters were adjusted until an optimal agreement between calculated and experimental structure obtained throughout the entire range of available structures. HOMO-LUMO analyses and spectroscopic calculations were performed on the optimized geometries of the title complexes (**1**–**6**) using B3LYP/6-31 g + (d,p)/LANL2DZ level of theory.

M-Ligand bond lengths (Å) of complexes (**1–3**) and (**4**–**6**), respectively. The picrates and dinitrophenolates that are excluded from the primary coordination spheres of metal atoms in the crystallographic determinations, are not optimized in the computed structures. **Tables 3** and **4** represent comparison of calculated and experimental torsion angles of ligand in complexes (**1–3**) and (**4**–**6**) respectively.

*Comparison of experimental and calculated M-ligand bond lengths (Å) of complexes (4–6).*

The coordination number of Ca(II) ion is eight with distorted cube geometry in the optimized geometry of cationic complex (**1**) (**Figure 1**). THEEN is interacting with Ca(II) ion through all the six potential donor atoms. The seventh and eighth coordination sites of Ca(II) are occupied by picrate anion through phenolic oxygen

**Complex 1 (M = Ca) Complex 2 (M = Ca) Complex 3 (M = Ba) Theo. Exp. Dev. Theo. Exp. Dev. Theo. Exp. Dev.**

M-O1 2.450 2.410 0.040 2.389 2.341 0.048 2.720 2.722 0.002 M-O2 2.450 2.380 0.070 2.495 2.498 0.003 2.807 2.812 0.006 M-O3 2.410 2.480 0.070 2.753 2.753 0.000 M-O4 2.410 2.370 0.040 2.812 2.816 0.004 M-O5 2.681 2.687 0.006 M-O6 3.127 3.135 0.008 M-O12 2.310 2.30 0.01 2.728 2.735 0.007

*Quantum Computational Chemistry: Modeling and Calculation of S-Block Metal Ion Complexes*

M-O18 2.977 2.990 0.013

M-N1 2.824 2.591 0.233 2.601 2.603 0.002 3.038 3.042 0.004 M-N2 2.738 2.658 0.08 3.026 3.032 0.006

M-O1 2.412 2.416 0.004 2.617 2.628 0.011 2.736 2.743 0.007 M-O2 2.393 2.396 0.003 2.611 2.618 0.007 2.763 2.767 0.004 M-O3 2.505 2.508 0.003 2.506 2.516 0.010 2.756 2.762 0.006 M-O4 2.628 2.632 0.004 2.618 2.626 0.008 2.658 2.668 0.010 M-O1W 2.701 2.711 0.010 2.880 2.884 0.004 M-O2W 2.699 2.705 0.006 2.988 2.995 0.007

M-N1 2.835 2.842 0.007 3.009 3.008 0.001 M-N2 2.849 2.857 0.008 3.010 3.010 0.000

**Complex 4 (M = Na) Complex 5 (M = Sr) Complex 6 (M = Ba) Theo. Exp. Dev. Theo. Exp. Dev. Theo. Exp. Dev.**

*Comparison of experimental and calculated M-ligand bond lengths (Å) of complexes (1–3).*

M-O1W 2.440 2.442 0.002

M-O2WA 2.726 2.732 0.006

*3.1.1 [Ca(THEEN)(PIC)]<sup>+</sup> (1)*

M-O13 2.470 2.73 0.26

*DOI: http://dx.doi.org/10.5772/intechopen.90531*

M-O2W

**Table 1.**

**Table 2.**

**15**

#### **3. Geometrical structures**

#### **3.1 Results and discussion**

Complexes (**1**–**6**) were successfully modeled by using the input coordinates of crystal data. **Tables 1** and **2** represent comparison of calculated and experimental

*Quantum Computational Chemistry: Modeling and Calculation of S-Block Metal Ion Complexes DOI: http://dx.doi.org/10.5772/intechopen.90531*


#### **Table 1.**

,

structures which finally give rise to dendrimers. A predominant 1:1 complexation has also been observed in alkali and alkaline earth metal complexes of the tetra- and pentapodands. The stability constants of the terapodands are generally lower than those of the corresponding tripodands because of more severe steric hindrance to complexation [7]. Vögtle and coworkers have indicated that the ligands resembling tetrapodands are capable of forming 1:1 complexes with s-block metal ions [8, 9]. The s-block elements present a usual challenge in the molecular modeling, because the metal-ligand interactions in both cases are principally electrostatic. The types of alkali and alkaline earth metal complexes subjected to molecular modeling can be divided into five categories: crown ethers [10–16], cryptands [17, 18], spherands [19, 20], podands and other biologically important ligands, such as ionophores and cyclic antibiotics [21–24] . The present work has been undertaken with the aim to computationally characterize the structure and nature of complexes of s-block metal ions with the tetrapodands THEEN and THPEN. Recently the computational studies of these tetrapodal ligands with Cu(II), Ag(I) and La(III) have been reported. Recently, synthesis, crystal structure and biological properties of [Co(edtp)Cl]�NO3�H2O complex was also determined, where edtp is N,N,N<sup>0</sup>


From the last 3 decades density functional theory has been the dominant method for the quantum mechanical simulation of periodic systems. In recent years it has also been adopted by quantum chemists and is now very widely used for the simulation of energy surfaces in molecules. The quantum-chemical calculations (DFT calculations) giving molecular geometries of minimum energies, molecular orbitals (HOMO-LUMO), 13C-NMR and vibrational spectra were performed using the Gaussian 09 [29]. Molecular orbitals were visualized using "Gauss view". The method used was Becke's three-parameter hybrid-exchange functional, the nonlocal correlation provided by the Lee, Yang and Parr expression, and the Vosko, Wilk, and Nuair 1980 local correlation functional (III) (B3LYP) [30, 31]. The 6-31 g + (d,p) basis set was used for C, N and O. The LANL2DZ basis set [32] and pseudopotentials of Hay and Wadt were used for Ca, Sr, Ba and Na metal atoms [33, 34]. DFT calculations were performed in the gaseous phase and the input coordinates were obtained from and then compared with crystal structure data of already reported complexes: [Ca(THEEN)(PIC)](PIC),[Ca(THPEN)(H2O)2](PIC)2, Ba(THPEN)(PIC)2, [Na (THPEN)]2(PIC)2, [Sr(THPEN)(H2O)2]2(DNP)4 and [Ba(THPEN)(H2O)2]2(DNP)4 (where DNP is 3,5-dinitrophenolate) [35]. The structural parameters were adjusted until an optimal agreement between calculated and experimental structure obtained throughout the entire range of available structures. HOMO-LUMO analyses and spectroscopic calculations were performed on the optimized geometries of the title

complexes (**1**–**6**) using B3LYP/6-31 g + (d,p)/LANL2DZ level of theory.

Complexes (**1**–**6**) were successfully modeled by using the input coordinates of crystal data. **Tables 1** and **2** represent comparison of calculated and experimental

,O″-pentadentate edtp ligand and a chloride to generate a distorted

N0

by the N,N<sup>0</sup>

,O,O<sup>0</sup>

**2. Computational details**

**3. Geometrical structures**

**3.1 Results and discussion**

**14**

CoClN2O3 octahedron [25–28].

*Density Functional Theory Calculations*

*Comparison of experimental and calculated M-ligand bond lengths (Å) of complexes (1–3).*


#### **Table 2.**

*Comparison of experimental and calculated M-ligand bond lengths (Å) of complexes (4–6).*

M-Ligand bond lengths (Å) of complexes (**1–3**) and (**4**–**6**), respectively. The picrates and dinitrophenolates that are excluded from the primary coordination spheres of metal atoms in the crystallographic determinations, are not optimized in the computed structures. **Tables 3** and **4** represent comparison of calculated and experimental torsion angles of ligand in complexes (**1–3**) and (**4**–**6**) respectively.
