Self-assembled Transition Metal Coordination Frameworks of ...

Chapter 5
5.3.1. AIALDI MS spectral studies
For revealing the formation of rigid tetranuclear molecular structures of
Ni(H), MALDI MS spectra were found very successful. Mn(H) complexes are found
to be not so stable, however formation of molecular square complexes are indicative
by significant fragmentation species. Theoretical simulations of isotropic distribution
pattems of fragmentation peaks are found useful to confirm expected structural
formulae. The parent molecular ions are not always seen in a mass spectrum, and so
the molecular weight can be greater [28]. Analysis by mass spectrometry requires
compound to be in the gas phase, and many compounds cannot be vaporized without
considerable, adverse decomposition, and these include the majority of cluster
compounds [28]. The techniques applied to volatile species are not always useful, as
they require stable gas phase molecules. The less stable nature of Mn(H) coordination
squares compared to well stable Ni(H) molecular squares are also significant to
consider. MALDI mass spectra of all the complexes were taken in CHZCI2 as DCTB
mix on positive ion mode.
The complex 19 exhibits peaks of well defined isotropic patterns centered at
m/z 1758, 1557, 1468.2, 1451.9, 1260, 1171, 1068, 979.1, 932, 892, 740 671, 625,
490 etc as given in Fig. 5.1. Of these, peaks at 1468.2, 1451.9, 1068, 979.1, 740 and
490 are assigned as fragmentation species of possible tetramer [Mn2(HL2)L2]2Cl2. The
base peak at 979 is consistent with [Mn2(HL2)L2]+ (calc. 979), while peaks at 1468.2,
1451.9 and 1068 attributed to [1\/I113(HI.2)(L2)2]"“(calc. 1463), [Mn2(HL2)2(H2L2)Cl]+
(calc. 1451) and [Mn3(L2)2Cl]+ (calc. 1068) respectively are found characteristic.
These species are in well agreement with calculated isotropic distribution patterns as
given in Fig. 5.2.
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