4
Tetrahedron
ions. After coordination, the charges of copper ion changes from
ACCEPTED MANUSCRIPT
1.000 to 0.611, which is due to the electrons transfer from
coordinated atoms to copper ions. Additionally, the negative
charges of N and O increase after coordination. For example, the
charges of N(11), O(30), N(58) and N(97) increase from -0.250, -
0.581, -0.086 and -0.142 to -0.356, -0.610, -0.167 and -0.172,
respectively. At the same time, the positive charges of their
adjacent atoms such as N(12), C(25), N(57) and N(96) increase,
and the charges values change from -0.150, 0.747, -0.268 and -
0.256 to -0.086, 0.766, -0.230 and -0.222. It can be concluded
that parts of their electrons transfer to coordinated atoms O and
N, which increase their negative charges and strengthen the
coordination interaction. Therefore, the copper complex becomes
more stable.
In conclusion, a new tripodal fluorescent receptor derived from
naturally occurring coumarin was developed. It was highly
sensitive and selective for Cu2+ ion with a 2.87 µM detection
limit. The resulted 1·Cu2+ complex shows a selective recognition
Scheme 2. Proposed mechanism for the recognition behaviour of
-
tripodal 1 for Cu2+ and H2PO4 ions.
-
ability toward H2PO4 by metal displacement approach.
Acknowledgements
We gratefully acknowledge the financial support from the
National Science Foundation of China (21403122, 41406090)
and High-level Science Foundation of Qingdao Agricultural
University (6631405, 631302).
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mechanism, a computational study was performed. The structure
of tripodal 1 is fully optimized by B3LYP method with the
Gaussian 09 program23 (Fig. 7a, S8). For C, O, N, and H, the 6-
31+ G(d, p) basis set was used. For Cu, the Lanl2DZ basis set
with effective core potential (ECP) was used. The optimized
structure shows that the copper ion is coordinated by three
nitrogen atoms of triazole groups and one oxygen atom to form a
four-coordinated complex (Fig. 7b). The bond length of three Cu-
N is 2.1092, 2.0619 and 2.1343 Å respectively and the
corresponding bond order is 0.2632, 0.2927 and 0.2720. The
bond length of Cu-O is 1.3119 Å and its bond order is 0.1842.
The values of bond order prove the formation of coordination
bond. The dihedral angles of N(11)-Cu(128)-N(17)-O(30),
N(11)-Cu(128)-N(97)-N(58) and N(97)-Cu(128)-N(58)-O(30)
are 145.9o, 132.2o and 105.1o respectively, which means the
copper atom is surrounded on all sides by four coordination
atoms.
The Natural Bond Orbital (NBO) charges of tripodal 1 and
1·Cu2+ complex are shown in table S1. It is revealed that all the
oxygen and nitrogen atoms coordinating with copper ion carry
negative charges. So they are easy to coordinate with the copper
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