π-Donor/Acceptor Effect on Lindqvist Type Polyoxomolibdates Because of Various Multiple-Bonded Nitrogenous Ligands

Theoretical investigation of the mechanism of primary amines reacting with hexamolybdate: an insight into the organoimido functionalization and related reactions of polyoxometalates

The functionalization of polyoxometalates (POMs), especially with an amino group to yield organonitrogenous derivatives of POMs, is an efficient approach to the enrichment of their structures and the diversification of their properties for various applications. The mechanism for the formation of organonitrogenous-derivatized hexamolybdates was explored by investigating the monofunctionalization of the [Mo(6)O(19)](2-) ion with methylamine using the density functional theory (DFT) method. The calculations show that the direct imidoylization of hexamolybdate with methylamine is both kinetically and thermodynamically unfavorable. However, this imidoylization was found to take place readily in the presence of dimethylcarbodiimide (DMC), for which the free-energy barrier was calculated to be +32.5 kcal mol(-1) in acetonitrile. Moreover, various factors controlling the efficiency of the imidoylization were examined. The calculations show that [W(5)MoO(19)](2-) has a relatively lower reactivity than [Mo(6)O(19)](2-), and that the imidoylization of [W(6)O(19)](2-) is an unfavorable process. With respect to the effect of carbodiimides, it is found that the catalytic activity is directly proportional to the electron-withdrawing effects of the substituents. As to the reactivity of R-NH(2) , the computation results indicate that the free-energy barriers of the substitution reactions are linearly correlated with the basicity constants (pK(b)) of the amino groups. It is noteworthy that the introduction of the proton dramatically decreases the free-energy barrier of the imidoylization of [Mo(6)O(19)](2-) catalyzed by DMC to 24.3 kcal mol(-1) in acetonitrile.

A DFT study on the electronic and redox properties of [X8V14O50]n– (X = SiIV, GeIV, PV, and AsV)

The electronic and redox properties of the title polyanions have been calculated by means of density functional theory (DFT). These were unrestricted open-shell systems with electronic configuration of d1 of V. In this behalf, energies and compositions of α-LUMO, β-LUMO, α-HOMO, and β-HOMO were also analyzed. First of all, electronic and redox properties of vanadosilicate [Si8V14O50]12– (system 1) were calculated and then SiIV was substituted with GeIV, PV, and AsV for further investigations of systems 2, 3, and 4, respectively. The substitution greatly modifies the electronic properties as α-LUMOs are quite different in all the studied systems. The α-LUMO is mainly composed of V and O in system 1, V and Ge in system 2, V and O in system 3, and As, O, and V in system 4. The alpha HOMO–LUMO energy gaps are greatly reduced in systems 2, 3, and 4 as compared with system 1. The system 4 [As8V14O50]4– has minimal value of total bonding energy, whereas system 2 [Ge8V14O50]12– has maximal, so energetically system 4 is more favourable than the others. After the first reduction, α-LUMO in [Si8V14O50]14– is made up of V and Si, β-LUMO in [Ge8V14O50]13– is concentrated on V and Ge, β-LUMO in [P8V14O50]5– is composed of V only, whereas β-LUMO in [As8V14O50]5– is delocalized over V, O, and As with almost the same contribution of all three atoms.

Prediction of remarkably large second-order nonlinear optical properties of organoimido-substituted hexamolybdates

The dipole polarizabilities, dipole moments, density of states, and second-order nonlinear optical (NLO) properties of organoimido derivatives of hexamolybdates have been investigated by using time-dependent density functional response theory. This class of organic-inorganic hybrid compounds possesses remarkably large and eye-catching molecular second-order NLO response, especially [Mo(6)O(17)(NC(16)H(12)NO(2))(FeNC(10)H(9))](2-) (7) and [Mo(6)O(17)(NC(16)H(12)NO(2))(NC(6)H(2)(NH(2))(3))](2-) (6) with static second-order polarizability (beta(vec)) computed to be 15766.27 x 10(-30) esu and 6299.59 x 10(-30) esu, respectively. Thus, these systems have the possibility to be excellent second-order nonlinear optical materials. Analysis of the major contributions to the beta(vec) value suggests that the charge transfer (CT) from polyanion to organic segment (D-A) along the z-axis plays the key role in NLO response; the polyanion acts as a donor (D) whereas organoimido acts as an acceptor (A) in all the studied systems. The computed beta(vec) values increase by incorporation of an electron acceptor (-NO(2)) at the end of the phenyl ring of the organoimido segment. Furthermore, substitution of amino (-NH(2)) or ferrocenyl (-FeC(10)H(9)) at the outer side of polyanion and an electron acceptor (-NO(2)) at the end of the phenyl ring in organoimido segment simultaneously is more important to enhance the optical nonlinearity. Orbital analysis shows that the degree of CT between the polyanion and organoimido segments was increased when ferrocenyl donor was introduced. The present investigation provides important insight into the remarkably large NLO properties of organoimido-substituted hexamolybdates.