Shabbir Muhammad

Quantum mechanical design and structure of the Li@B10H14 basket with a remarkably enhanced electro-optical response.

An innovative type of lithium decahydroborate (Li@B(10)H(14)) complex with a basketlike complexant of decaborane (B(10)H(14)) has been designed using quantum mechanical methods. As Li atom binds in a handle fashion to terminal electrophilic boron atoms of the decaborane basket, its NBO charge q (Li) is found to be 0.876, close to +1. This shows that the Li atom has been ionized to form a cation and an anion at the open end of B(10)H(14). The most fascinating feature of this Li doping is its loosely bound valence electron, which has been pulled into the cavity of the B(10)H(14) basket and become diffuse by the electron-deficient morphological features of the open end of the B(10)H(14) basket. Strikingly, the first hyperpolarizability (beta(0)) of Li@B(10)H(14) is about 340 times larger than that of B(10)H(14), computed to be 23,075 au (199 x 10(-30) esu) and 68 au, respectively. Besides this, the intercalation of the Li atom to the B(10)H(14) basket brings some distinctive changes in its Raman, (11)B NMR, and UV-vis spectra along with its other electronic properties that might be used by the experimentalists to identify this novel kind of Li@B(10)H(14) complex with a large electro-optical response. This study may evoke the possibility to explore a new thriving area, i.e., alkali metal-boranes for NLO application.

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.

Capturing a synergistic effect of a conical push and an inward pull in fluoro derivatives of Li@B10H14 basket: toward a higher vertical ionization potential and nonlinear optical response.

We present the design of fluoro derivatives of B(10)H(14) and Li@B(10)H(14) baskets. A synergistic effect of conical push and inward pull (reported independently in previous lithium nonlinear optical (NLO) complexes) has been explored in these derivatives to achieve a robustly large NLO response and a higher vertical ionization potential. Li@1,3,6,9-F(4)B(10)H(10), Li@6,9-F(2)B(10)H(12), and Li@2,4,6,9-F(4)B(10)H(10) exhibit first hyperpolarizability (β(0)) values as large as 181 624, 133 199, and 32 314 au; their vertical ionization potentials are 6.45, 6.30, and 6.78 eV, respectively. These values are significantly higher than those previously reported in Li-doped fluorocarbon chains at the same MP2/6-31+G* level of theory (Xu, H. L.; Li, Z. R.; Wu, D.; Wang, B. Q.; Li, Y.; Gu, F. L.; Aoki, Y. J. Am. Chem. Soc. 2007, 129, 2967). They also exceed those from our earlier designed Li@B(10)H(14) basket (Muhammad, S.; Xu, H. L.; Liao, Y.; Kan, Y. H.; Su , Z. M. J. Am. Chem. Soc. 2009, 131, 2967). In addition, new quantum chemical calculations of enthalpies of reaction (Δ(r)H°) at 298 K for B(10)H(14) and its lithium/fluoro derivatives highlight the changes in their thermodynamical aspects. The calculated enthalpies of lithiation reactions are -10.04, -11.29, and -13.18 kcal/mol for B(10)H(14), 6,9-F(2)B(10)H(12), and 2,4-F(2)B(10)H(12), respectively, demonstrating a higher probability of fluoro decaboranes for reaction with lithium. The obtained results not only explain the effect of position and number dependence of substituted fluoro atom(s) in B(10)H(14) and Li@B(10)H(14) but also elucidate a synergistic behavior to polarize a lithium excess electron for high NLO responses and vertical ionization potentials.

Halide Ion Complexes of Decaborane (B10H14) and Their Derivatives: Noncovalent Charge Transfer Effect on Second-Order Nonlinear Optical Properties

Quantum molecular engineering has been performed to determine the second-order nonlinear optical (NLO) properties in different halo complexes of decaborane (B(10)H(14)) and their derivatives using the density functional theory (DFT) method. These decaborane halo complexes of X(-)@B(10)H(14) (X = F, Cl, Br, and I) are found to possess noncovalent charge transfer interactions. The static polarizability (α(0)) and first hyperpolarizability (β(0)) among these complexes increase by moving down the group from F to I, partly due to the increase in size of their anionic radii and the decrease in their electron affinities. A two-level approximation has been employed to investigate the origin of β(0) values in these halo complexes, which show very consistent results with those by the finite-field method. Furthermore, in the same line, two experimentally existing complexes, I(-)@B(10)H(14) and I(-)@2,4-I(2)B(10)H(12), are found to have considerably large β(0) values of 2859 and 3092 a.u., respectively, which are about three times larger than a prototypical second-order NLO molecule of p-nitroaniline, as reported by Soscun et al. [Int. J. Quantum Chem.2006, 106, 1130-1137]. Besides this, the special effects of solvent, counterion, and bottom substitutions have also been investigated. Interestingly, 2,4-alkali metal-substituted decaborane iodide complexes show remarkably large second-order NLO response with β(0) amplitude as large as 62436 a.u. for I(-)@2,4-K(2)B(10)H(12) complex, which are explained in terms of their transition energies, frontier molecular orbitals and electron density difference plots. Thus, the present investigation provides several new comparative insights into the second-order NLO properties of halo complexes of decaborane, which possess not only large first hyperpolarizabilities, but also high tunability to get a robustly large second-order NLO response by alkali metal substitution effects.