10 mL of ethanolic solution of furfural (1 mL, 0.01 mol) were added to 5 mL of aqueous solution of nicotinic acid hydrazide (1.37 g, 0.01 mol) and stirred well for an hour in the presence of hydrochloric acid to form a white precipitate. The reaction mixture was maintained at room temperature and the colourless solid was obtained. The solid was separated and filtered under suction, washed with ice-cold water. The precipitate was washed with water and filtered and again washed with petroleum ether (40-60%) and dried over in a vacuum desicator then the product was recrystallized from hot ethanol.

The optimized bond parameters of F2CNH was carried out using DFT/B3LYP/6-311++G(d,p) basis set and are listed in Table 1. The optimized structure is shown in Figure 1. The title molecule consist of pyridin and furan ring linked by hydrazone linkage. The hydrazone linkage plays an important role in F2CNH. The electronic coupling between the amino hydrogen (N12-H13), carbonyl (C14=O15) lone pairs electrons and the (C14-C16) pyridine ring π-system creates phenyl N, O conjugations. This conjugations bring about intra-molecular charge (ICT) transfer. In the ICT state, the nπ interactions are substantially decreased, and thereby an electronic decoupling occurs from the ring π-system 22, which causes the differences in bond lengths of C9=N11 (1.282Å), C14-N12 (1.385Å) and also the variation of bond angles of C14-C16-C17 (117.59°) and C14-C16-C18 (123.59°). The bond distance of C14-N12 is well below the single bond distance which indicates the electron delocalization over the region of the molecule and it is supported by literature 22.

The bond angle of O₁₅=C₁₄-C₁₆ is calculated at 121.24°, which is in agreement with literature value 122.15 and also finds support from literature Song and Fan, (2009) 23. In hydrazone linkage, the angle for C₉=N₁₁-N₁₂ was calculated about 116.86° whereas the literature value is 116.43° 22. The bond angles of C₁₆-C₁₇-H₂₀ (119.09°) is negatively ~2.8° deviated from C₁₉-C₁₇-H₂₀ (121.96°), which is due to the presence of O₁₅ atom next to H₂₀ atom. The furan ring moiety is planar [C₃-C₂-C₉-N₁₁ = -0.20° and O₁-C₂-C₉-N₁₁ = 179.75°] with hydrazone linkage, while phenyl ring is not planar [C₁₇-C₁₆-C₁₄-N₁₂ = -154.58° and C₁₈-C₁₆-C₁₄-N₁₂ = 28.13°]. Most of the calculated bond parameters are comparable with XRD values and also find support from the literature values of related structure [24, 25].

The fundamental vibrations of a non-linear molecule which contains N atoms is equal to (3N-6), apart from three translational and three rotational degrees of freedom 2627. The F2CNH molecule belongs to Cs point group symmetry and has 25 atoms; hence 69 normal modes of vibrations are possible. The fundamental modes are distributed as: Гvib = 47A′ + 22A′′. All vibrations are active in both IR and Raman absorption. The harmonic wavenumbers were calculated using DFT/B3LYP/6-311++G(d,p) basis set and are listed in Table 2. The vibrational assignments were made by visual inspection of modes animated by using the Gauss view 17 program and are also justified with the help of TED analysis. The combined vibrational spectra of F2CNH are shown in Figure 2 and Figure 3.

The molecular electronic dipole moment and molecular first hyperpolarizability of F2CNH were calculated using B3LYP level and the obtained results were given in Table 3. The dipole moment was calculated as 0.9722 Debye which is comparatively closer to standard urea. The first order hyperpolarizability (β₀)was calculated as 2.0918x10^-30 esu, which is six times greater than that of the value of the urea. Hence this molecule has considerable NLO activity.

The NBO analysis has been carried out with B3LYP/6-311++G(d,p) level of basis set. The Lewis and non-Lewis NBO’s of the F2CNH are given in Table 4. The strong intra-molecular hyper conjucative interaction of the π and σ electrons of C-C to the anti C-C bond of the rings lead to stabilization of some part of the rings. The intra-molecular hyper cnjucative interaction of π(C₂-C₃)→π*(C₉-N₁₁), π(C₉-N₁₁)→π*(C₂-C₃) and π(N₂₁-C₂₃)→π*(C₁₆-C₁₈) leading to stabilization of 75.48, 41.17 and 113.09 KJ/mol, respectively. On the other hand the σ(C₂-C₃)→σ*(C₂-C₉), σ(C₉-N₁₁)→σ*(N₁₂-C₁₄) and σ(C₁₇-C₁₉)→σ*(C₁₆-C₁₇) transition stabilize lesser energy 17.87, 9.46 and 12.01 KJ/mol, respectively. In such a way that the molecule F2CNH delivers maximum delocalization energy during π-π* transition whereas the electron density of the donor (Lewis) bond decreases with increasing of electron density of acceptor (Non-Lewis) bonds. The maximum energy transfer during the intra-molecular interaction between (π-π*) (C₁₇-C₁₉) and (N₂₁-C₂₃) is about 122.13 KJ/mol. This may be due to the hyperconjucative interaction between C₁₇-C₁₉ donor and C₂₃-N₂₁ acceptor bonds. It is evident from Table 4, the π(C₁₇-C₁₉) hyperconjucative interactions transfer more energy (122.13 KJ/mol) to the acceptor bond π*(N₂₁-C₂₃) in pyridine ring. Hence the strong delocalization in pyridine is mainly due to the presence of C=N-C. Based on the fact, that the ν(C₂₃-N₂₁) modes appear at higher frequency (1542 cm^-1) on comparing with ν(C₁₈-N₂₁/1240 cm^-1 mode. In F2CNH, the π-π* interaction appear with maximum delocalization energy which leads the molecule become highly active. The lone pair of oxygen and nitrogen atoms play greater role in the molecule F2CNH: LPO₁→C₄-C₅ (114.47), LPO₁₅→N₁₂-C₁₄ (118.41) and LPN₁₂→C₁₄-O₁₅ (190.62 KJ/mol), respectively. These charge transfer interactions of F2CNH are responsible for more stabilization, medicinal and biological properties.

The HOMO and LUMO are the main orbital’s that take part in chemical stability. The HOMO represents the ability to donate an electron, whereas the LUMO is an electron acceptor which represents the ability to obtain an electron. This also predicted that the nature of electrophiles and nucleophiles to an atom where the HOMO and LUMO are stronger. The energy gap of F2CNH was calculated using B3LYP/6-311++G(d,p) level and are listed in Table 5. In the present study, the HOMO part is located over the furan ring and hydrazone linkage and HOMO energy is calculated about -6.032 eV. Similarly, the LUMO is located over the entire molecule and especially on pyridine ring and LUMO energy is -1.956 eV. The energy gap between HOMO and LUMO is 4.076 eV, which leads the molecule becomes less stable and more reactive. The calculated energies of frontier molecular orbitals are listed in Table 6 and the frontier molecular orbitals are shown in Figure 4. The various frontier molecule orbitals of F2CNH and listed their corresponding orbital energies are in Table 6.

The nature of the electronic transitions in the observed UV-visible spectrum of the title compound F2CNH had been studied by the TD-DFT involving configuration interaction between the singly existed electronic states. The observed UV-vis spectrum was shown in Figure 5. The electronic transitions and the corresponding excitation energies were listed in Table 7. The calculated electronic transition is shown at 333 nm whereas, the experimental electronic transition observed at 360 nm. The difference in these two values may possibly be owing to solvent influence.

The molecular electrostatic potential (MEP) map was calculated using B3LYP/6-311++G(d,p) level of basis set. The 3D plot of MEP map of F2CNH is shown in Figure 6. In MEP map, the maximum positive/negative regions are preferred sites for nucleophilic/electrophilic attack and are represented by Blue/Red colour, respectively. The importance of MEP lies in the fact that it simultaneously displays molecular size, shape as well as positive, negative and neutral electrostatic potential regions in terms of color grading Figure 6 and is very useful in research of molecular structure with its physiochemical property relationship 4142.

The Potential increases in the order of red < orange < yellow < green < blue. The color code of this map is in the range between -6.471 a.u. (deepest red) to 6.471 a.u. (deepest blue) in F2CNH, where blue indicates the strongest attraction and red indicates the strongest repulsion. It can be seen from the MEP map of the F2CNH, the regions having the negative potential are over the carbonyl group while the regions having the positive potential are over all the hydrogen atoms.

Mulliken atomic charge calculation has an important role in the application of quantum chemical calculation to molecular system, since atomic charges affect the dipole moment, molecular polarizability, electronic structure and more a lot of properties of molecular systems. The Mulliken charges were calculated by DFT/B3LYP/6-311++G(d,p) basis set. The calculated Mulliken charge values are listed in Table 8 and are plotted in Figure 7 The carbonyl group has the most positive C₁₄: 0.440 and most negative charge O₁₅: -0.3255 and all the hydrogen atoms have positive charge.

The various thermodynamic parameters such as: total energies, zero-point energy etc were calculated using B3LYP/6-311++G(d,p) basis set are presented in Table 9. On the basis of vibrational analysis, the statistical thermodynamic functions heat capacity (C⁰_p,m)

entropy (S0m), and enthalpy changes (ΔH0m) for the F2CNH were obtained from the theoretical harmonic frequencies listed in Table 10. It can be seen from Table 10, the thermodynamic functions are increasing with temperature ranging from 100 to 1000 K due to the fact that the molecular vibrational intensities increase with temperature. The correlation equations between heat capacity, entropy, enthalpy changes and temperatures were fitted by quadratic formulas and the corresponding fitting factors (R2) for these thermodynamic properties is 0.99895, 0.99997 and 0.99946 respectively. The comparative thermodynamical graphs of F2CNH are shown in Figure 8. The corresponding fitting equations are as follows:

C⁰_p,m = 5.42703 + 0.02291T + 2.0243x10^-5 T² (R² = 0.99895)

S⁰_m = 1.24898 + 0.00527T + 4.65873x10^-5 T² (R² = 0.99997)

ΔH⁰_m = 3.05729 + 0.01291T + 1.14038x10^-5 T² (R² = 0.99946)

All the given thermodynamic data are the helpful information for further study on F2CNH. They can be used to compute the other thermodynamic energies according to relationships of thermodynamic functions and estimate directions of chemical reactions according to the second law of thermodynamics in thermochemical field 43. All the thermodynamic calculations were done in gas phase and they could not be used in solution.