**5.2 Electronic spectra**

*Stability and Applications of Coordination Compounds*

this band is observed in the 1618–1626 cm<sup>−</sup><sup>1</sup>

occurrence of band around 1500 cm<sup>−</sup><sup>1</sup>

552–573 cm<sup>−</sup><sup>1</sup>

appearing around 1640 cm<sup>−</sup><sup>1</sup>

appears around 740 cm<sup>−</sup><sup>1</sup>

strong band in the region 1185–1221 in free ligand of chalcones due to *υ* (C—O). The shifts of this band were observed to move to lower wave numbers indicates bonding of phenolic oxygen atom to metal center via deprotonation. The band in the region

*ν* (V—O) [23]. In addition the compound exhibit a strong band in the 952–983 cm<sup>−</sup><sup>1</sup> range due to the terminal V〓O stretching and this value is close to the majority of oxovanadium(IV) complexes [24]. In the IR spectra of all the ligands an intense band

wave number indicates coordination through oxygen of (C〓O) group. The band

can be assigned to the stretching modes of the metal to ligand bonds,

is attributed [25] to (C〓O) group. In the complexes

in chloro complex indicating presence of C—Cl bond. The

**<sup>C</sup>**〓**<sup>O</sup> <sup>C</sup>**〓**<sup>C</sup> <sup>C</sup>**〓**<sup>O</sup> <sup>C</sup>**〓**CH(Aro) <sup>V</sup>**—**<sup>O</sup>** —**NO2 <sup>C</sup>**—**Cl <sup>V</sup>**〓**<sup>O</sup>**

L1 2921 1640 1503 1221 2858 — — VL1 3029 1626 — 1198 2964 552 — — 963 L2 3242 1639 1588 1221 2987 — — VL2 3174 1621 1404 1205 3018 561 — — 952 L3 3390 1635 1513 1190 2921 — 1520 — VL3 3353 1623 1406 1168 3018 556 1490 — 983 L4 3527 1635 1567 1185 2920 — 738 — VL4 3190 1618 1583 1162 3020 573 — 742 976

*) of the complexes.*

range. The shifting of band to lower

in VL3 complex is due to *ν* (C—NO2) mode.

**74**

**Table 2.**

**Figure 2.**

*Structure of vanadium complex.*

**Compound OH** 

*Important IR spectral bands (cm<sup>−</sup><sup>1</sup>*

**group**

Electronic absorption spectral study is an important tool used [26] to determine the geometry around a central metal atom. The electronic spectra (**Figure 3**) of the metal complexes in DMF (10**<sup>−</sup><sup>3</sup>** M) were recorded on Shimadzu UV-VIS spectrophotometer in the range 200–950 nm. The Vanadium chalcone complexes show absorption band in 380–770 nm region (**Table 5**). Most of the VO(II) complexes are green in colour. The electronic absorption spectra of VO(II) complexes showed three bands at 13,015–13,305, 17,455–17,632 and 25,755–25,930 cm<sup>−</sup><sup>1</sup> , with 17,455–17,632 cm<sup>−</sup><sup>1</sup> representing 10 Dq. These bands are assigned to the transitions 2 B2 → [2]E(dxy → dxz,dyz),<sup>2</sup> B2 → <sup>2</sup> B1 (dxy → dx<sup>2</sup> -y [2]), and <sup>2</sup> B2 → [2]A1 (dxy → dz 2 ) respectively. From these electronic absorption bands and paramagnetic nature, square pyramidal geometry suggested for VO(II) chalcone complexes. As these oxovanadium(IV) belong to the 3d1 system, there is no interelectronic repulsion in the metal ion so B0 value of V4+ is not available. Therefore calculation of Racah parameter is not possible for these vanadium complexes (**Table 3**).

**Figure 3.** *Electronic spectra of V(IV) complexes.*


#### **Table 3.**

*Electronic spectral data for vanadium metal complexes.*


#### **Table 4.**

*Magnetic moment values of the vanadium (IV) chalcone complexes.*
