Matthew D. Smith

Formation Principles for Vanadium Selenites: The Role of pH on Product Composition

A series of organically templated vanadium selenites has been prepared under mild hydrothermal conditions. Single crystals of [C5H14N2][(VO)3(SeO3)2(HSeO3)4], [C5H14N2][VO(SeO3)2], [(R)-C5H14N2][(VO)3(SeO3)2(HSeO3)4], and [(S)-C5H14N2][(VO)3(SeO3)2(HSeO3)4] were grown from VOSO4, SeO2, and 2-methylpiperazine. Controlling the initial pH of the reaction mixture allows for one to select between the compounds found in the VOSO4/SeO2/2-methylpiperazine system, as the solution pH directly affects the relative ratio of the HSeO3(-) and SeO3(2-) concentrations. Moreover, partial resolution of racemic 2-methylpiperazine is observed in [C5H14N2][(VO)3(SeO3)2(HSeO3)4], which is understood through the use of a one-dimensional Ising model. The use of enantiomerically pure 2-methylpiperazine results in fully ordered and fully resolved structures.

Role of Noncovalent Interactions in Vanadium Tellurite Chain Connectivities

Structural differences in [V2Te2O10]n(2n-) chain metrics are directly ascribed to variations in noncovalent interactions in a series of organically templated vanadium tellurites, including [C6H17N3][V2Te2O10]·H2O, [C5H16N2][V2Te2O10], and [C4H14N2][V2Te2O10]. The noncovalent interaction (NCI) method was used to locate, quantify, and visualize intermolecular interactions in [C4H14N2][V2Te2O10] and [C5H16N2][V2Te2O10]. Variations in the van der Waals attractions between [1,4-diaminobutaneH2](2+) and [1,5-diaminopentaneH2](2+) result in divergent packing motifs for these cations, which causes a reorganization of N-H···O hydrogen bonding and variances in the [V2Te2O10]n(2n-) chain metrics. The application of the NCI method to this type of solid-state structure provides a direct method to elucidate the structural effects of weak noncovalent interactions.

EQeq+C: An Empirical Bond-Order-Corrected Extended Charge Equilibration Method.

The extended charge equilibration (EQeq) scheme computes atomic partial charges using the experimentally measured ionization potentials and electron affinities of atoms. However, EQeq erroneously predicts constant (environment independent) charges for high-oxidation-state transition metals in amine-templated metal oxide (ATMO) compounds, contrary to the variation observed in iterative Hirshfeld (Hirshfeld-I) charges, bond-valence sum calculations, and formal oxidation state calculations. To fix this problem, we present a simple, noniterative empirical pairwise correction based on the Pauling bond-order/distance relationship, which we denote EQeq+C. We parametrized the corrections to reproduce the Hirshfeld-I charges of ATMO compounds and REPEAT charges of metal organic framework (MOF) compounds. The EQeq+C correction fixes the metal charge problem and significantly improves the partial atomic charges compared to EQeq. We demonstrate the transferability of the parametrization by applying it to a set of unrelated dipeptides. After an initial parametrization, the EQeq+C correction requires minimal computational overhead, making it suitable for treating large unit cell solids and performing large-scale computational materials screening.

Understanding structural adaptability: a reactant informatics approach to experiment design

The structural and electronic adaptability ranges of a [VO(SeO3)(HSeO3)] framework found in organically templated vanadium selenites were determined using a three step approach, informed by cheminformatics descriptors, involving (i) the extraction of the most important reaction parameters from historical reaction data, (ii) a fractional factorial design on those parameters to better explore chemical space and (iii) decision tree construction on organic molecular properties to determine the factors governing framework formation. This process enabled the elucidation of both the structural and electronic adaptability ranges and provided the context to extract chemical understanding from the structural features that give rise to these respective ranges. This work resulted in the synthesis and structural determination of five new compounds.

Inducing polarity in [VO{sub 3}]{sub n}{sup n-} chain compounds using asymmetric hydrogen-bonding networks

Abstract 1,4-Bis(3-aminopropyl)piperazine, (R)-3-aminopiperidine and (S)-3-aminopiperidine were used in the syntheses of [C10H26N4][VO3]2·2H2O, [(R)-C5H14N2][VO3]2 and [(S)–C5H14N2][VO3]2, which all contain similar [VO3]nn− chains. Inversion symmetry within the 1,4-bis(3-aminopropyl)piperazine allows for crystallization of [C10H26N4][VO3]2·2H2O in a centrosymmetric space group, while the use of enantiomerically pure sources of either (R)-3-aminopiperidine or (S)-3-aminopiperidine forces crystallographic noncentrosymmetry. Moreover, asymmetry in the hydrogen-bonding networks between the metavanadate chains and either [(R)-3-aminopiperidineH2]2+ or [(S)-3-aminopiperidineH2]2+ cations directs alignment of the chains and crystallization in a polar space group (C2, no. 5). Component and net dipole moments were calculated using iterative-Hirshfeld partial atomic charges. [(R)-C5H14N2][VO3]2 and [(S)-C5H14N2][VO3]2 both display type 1 phase-matching capabilities and exhibit second harmonic generation activities of ∼140×α-SiO2.