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pH‐Dependent Interactions between Keggin Heteropolyanions in Dilute Solutions
Author(s) -
Antonio Mark R.,
Bera Mrinal K.
Publication year - 2019
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201801165
Subject(s) - chemistry , small angle x ray scattering , lacunary function , hydrogen bond , crystallography , ion , polyoxometalate , scattering , chemical physics , inorganic chemistry , molecule , catalysis , organic chemistry , physics , mathematics , pure mathematics , optics
Keggin phosphotungstate heteropolyanions (HPA), PW 12 O 40 3– , are known to interact via short‐range attraction and long‐range repulsion (SALR) at moderate and high solution concentrations and low‐pH (pH = 1). These interactions were identified through the observation of structure factor peaks in small‐angle X‐ray scattering (SAXS) data reported previously ( J. Phys. Chem. C 2016 , 120 , 1317). Here we describe the interactions between the same heteropolyanions with extremely low concentrations at low (pH = 0) and high pH (pH = 4.7) conditions. The solution chemistry of Keggin heteropolyanions at these two pH values provides a unique way to change the charge of the cluster anions without changing the structure (from the perspective of SAXS) and, at the same time, changing the hydrogen bonding interactions. The structure factors obtained from concentration dependent SAXS data reveal that the change in pH changes the nature of SALR interactions, consistent with the presence of the plenary PW 12 O 40 3− anion at pH = 0 and the monovacant lacunary PW 11 O 39 7– anion at pH = 4.7. At the low pH condition, the attractive interactions dominate to provide a peak near Q = 0 Å −1 momentum transfer in the structure factors, whereas at pH = 4.7 the repulsive interactions dominate, thereby eliminating the peak near Q = 0 Å −1 . The experimental results presented here are in agreement with the recent liquid state theory and computer simulation predictions on SALR interactions.