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How Inert, Perturbing or Interacting Are Cryogenic Matrices? A Combined Spectroscopic (Infrared, Electronic and X-ray Absorption) and DFT Investigation of Matrix Isolated Iron, Cobalt, Nickel and Zinc Dibromides Owen M. Wilkin, Neil Harris, John F. Rooms, Emma L. Dixon, Adam J. Bridgeman, and Nigel Andrew Young J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b09734 • Publication Date (Web): 28 Dec 2017 Downloaded from http://pubs.acs.org on December 30, 2017
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The Journal of Physical Chemistry
How Inert, Perturbing or Interacting are Cryogenic Matrices? A Combined
Spectroscopic
(Infrared,
Electronic
and
X-ray
Absorption) and DFT Investigation of Matrix Isolated Iron, Cobalt, Nickel and Zinc Dibromides. Owen M. Wilkin,(a) Neil Harris,(a) John F. Rooms,(a) Emma L. Dixon,(a) Adam J. Bridgeman,(b) and Nigel A. Young(a)* a
Department of Chemistry, The University of Hull, Kingston upon Hull, HU6 7RX, UK. Fax:
44 1482 466410; Tel: 44 1482 465442; E-mail:
[email protected] b
School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia
email:
[email protected] 1 ACS Paragon Plus Environment
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Abstract The interaction of FeBr2, CoBr2, NiBr2 and ZnBr2 with Ne, Ar, Kr, Xe, CH4 and N2 matrices has been investigated using IR, electronic absorption and X-ray absorption spectroscopies, as well as DFT calculations. ZnBr2 is linear in all the matrices. NiBr2 is linear in all but N2 matrices where it is severely bent. For FeBr2 and CoBr2 there is a more gradual change, with evidence of non-linearity in Xe and CH4 matrices as well as N2. In the N2 matrices the presence of νNN modes blue shifted from the “free” N2 values indicates the presence of physisorbed species, and the magnitude of the blue-shift correlates with the shift in the ν3 mode of the metal dibromide. In the case of NiCl2 and NiBr2 chemisorbed species are formed after photolysis, but only if deposition takes place below 10 K. There was no evidence for chemisorbed species for NiF2 and FeBr2 and in the case of CoBr2 the evidence was not strong.
2 ACS Paragon Plus Environment
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The Journal of Physical Chemistry
Introduction Whilst the notion that the spectroscopic data obtained from species trapped in (noble) gas matrices are always directly comparable to their vapor phase counterparts has been acknowledged as naïve, the need to identify and understand how matrices can affect the geometric and electronic structures of the trapped species remains. The matrix isolation literature is replete with asides and comments about site effects, matrix splittings etc., usually invoked to explain some spectral artefact. For example PdCO is found in two sites in Ar1 as is CO2,2 and SiH4.3-6 In the case of PdCO more recent calculations indicate the possible formation of Ar-PdCO.7 However, in the related NiCO case the computational work8,
9
indicated the possible presence of Ar-NiCO, but the experimentalists disputed this.10, 11 The ability of "inert" matrices to affect the structure of the trapped species has been demonstrated by Beattie et al. for both actinide tetrahalides and hexafluorometallates. ThCl4 and UCl4 are tetrahedral in neon, but have a distorted C2v geometry in argon.12,
13
The alkali metal
hexafluorouranates are C3v in solid argon, but C2v in nitrogen matrices.14 The alkali metal hexafluoroniobates15 have a tridentate coordination in neon and argon matrices, but a bidentate coordination mode in nitrogen and carbon monoxide matrices. Using CsClO4 as a probe molecule they showed that the order of host-guest interaction with the matrix was Ne
