SAMPLE: DH07A-E (except B)
Formulas:
(A) [Mn4(anca)4(Hbzdea)2(bzdea)2]·MeCN
(B) [Mn4(anca)4(mdea)2(Hmdea)2]· 2CHCl3
This one not received (measured by WW, paper)
(C) [Mn4(β-naphth)4(Hmdea)2(mdea)2]·Et2O
(D) [Mn4(β-naphth)4(Hedea)2(edea)2]·MeCN,EtOH
(E) [Mn4(anca)4(Hedea)2(edea)2]·2CHCl3,EtOH
Short description: Mn4 di-cubans with
emissive ligands (fluoresence SMMs)
Synthesized for experiment: General study
Received: 1/13/2010
Shipped by: Chris Beedle (Davids’s student)
Attached documents: Email and data from Chris Beedle
Hi Enrique,
Sample A: I face indexed crystals of this complex, only to discover that
after 15 minutes they totally desolvate and decompose. However, there are
two morphologies of crystals present: long rectangles and small cubes.
You want the small cubes. They are nearly perfectly square and seem the
most stable out of solution.
Sample C: Again, these crystals did not fair well out of solution. They
do not appear nice, but diffract beautifully.
Samples D and E: The crystals could not be face indexed because they are
irregular in shape (i.e. they have no regular crystal faces). This is not
always the case, but it is relatively common in low symmetry systems. When
checking the unit cell for these samples I cut the crystals down.
I'm sorry that I can not provide you with orientation information. And the
crystals would not have survived the trip out of solution (in grease). As
we discussed in earlier emails, Sample E seems to be the most interesting
magnetically (please see ppt). Steve is getting ready to measure this
sample. He has also either measured A or C. His postdoc will return to
the lab this week and he will let me know which of the two samples was
measured.
Let me know If you need anything further.
Chris
Hi Enrique,
I hope this email finds you and your family well. Patrick and I are
currently writing our dissertations. It looks as though Patrick will
leave us in December, and will follow sometime in late January of
February. Though, I have still not found work, and unfortunately, this is
a bad time to be looking. Anyway, I have been working on 2 series of Mn4
dicubanes with emissive ligands (naphthoic acid and 9-anthracene
carboxylic acid) with diethanolamine ligands where the R group has been
changed (methyl, ethyl, nbutyl, nbenzyl etc...). Last year we published a
communication (see attached) with preliminary room temperature
fluorescence, UV-vis and magnetization data. I am currently working on
liquid nitrogen temperature fluorescence of both solutions and single
crystals of this series, and I hope to do liquid helium measurements as
well. We are interested in this series because we think we may be able to
use these molecules to do single molecule imaging through fluorescence
detection. Furthermore, if the fluorescent excited state can be coupled
to the magnetic moment of these SMMs below their blocking temperature, we
may be able to look at magnetization dynamics on the fluorescent time
scale 10(-9) to 10(-12). I have attached a power point presentation with
data from 5 of the molecules. Recently I sent Steve complexes A-D in the
presentation and one of his post-docs is currently collecting data. Though
I know that dicubanes have been looked at before, there are a number of
reasons that we feel that these complexes are different:
1) These complexes appear to have S = 8 or smaller ground states. Where
all but one of the previously reported complexes are S = 9.
2) S = 8 fits of XmT magnetization data yield a positive Mn(3) Mn(3)
interaction but a negative Mn(3) Mn(2) interaction. For all of the
previously reported dicubanes both interactions are positive. To look at
this, I tried fitting my data to a S =9 ground state. I can get good fits
with both J values positive. However, error surface plots (see last
couple of slide of the power point presentation) suggest that the S = 8
state gives a better fit. Furthermore, fits of variable field data give
good fits for S=8. Most of the complexes can be fit to all of the measured
fields (0.1-5T). Extrapolation of AC in-phase data yields ground states of
8 or less.
3) WW did hysteresis measurements on one of the complexes (complex B).
If you look at the dM/dH plot, the first step is exchange biased +0.03T
and is very small in magnitude. I have not seen this in other dicubanes.
I suspect it is due to weak intermolecular ferromagnetic interactions or
ferromagnetic ordering, but I have not done any heat capacity. Also,
there is a peak in dM/dH at 1.18T that does not coincide with a quantized
tunneling event. I think this is probably due to spin-spin cross
relaxation or something of that nature. Relaxation processes in these
complexes are not simple as noted in the cole-cole plots (see
presentation). I would greatly appreciate any comments you might have
regarding the exhibited exchange bias, or even if you think it is
something worth looking at?
4) There is an outlier in the series. Complex E in the presentation
exhibits a larger barrier to magnetization reversal than the other
complexes (see table on first slide), and a higher blocking temperature at
1000Hz than all of the other complexes by ~0.5K. It is the only complex
in the two series in which a peak is seen for all of the measured
frequencies. I have not determined an origin for this, and the data has
been collected for a number of fresh and old samples of this complex, from
different batches, and always yield the same results.
Would you be willing to look at some of these complexes? If so, let me
know which complexes you would like to look at, and I will send them ASAP.
Please do not feel obligated to take measurements if you do not think
they are of interest. I look forward to your thoughts and/or suggestions.
cheers, Chris
Chris sent a Powerpoint file with all the info about susceptibility and more.
(see summary below, first page of PPT file)
There is also a paper published with WW in complex B