Syntheses and Studies of Mononuclear, Dinuclear, and Hexanuclear Metal Complexes with the H2bphany and H2bpyany Ligands
Date Issued
2005
Date
2005
Author(s)
Chien, Chih-Hsien
DOI
zh-TW
Abstract
We report here novel ligands, 2,7-Bis(α-phenylamino)-1,8-naphthyridine
(H2bphany) and 2,7-Bis(α-pyridylamino)-1,8-naphthyridine (H2bpyany).
H2bphany (or H2bpyany) was synthesized by palladium-catalyzed crosscoupling
of treatment of 2,7-Dichloronaphthyridine with aniline (or 2-Aminopyridine). The
ligand H2bphany has been used to synthesize the dinuclear molybdenum(II)
complexes, [Mo2(Hbphany)3(O2C(R))] (R = CH3,CF3) and a tetranuclear nickel(II)
complex, [Ni4(µ4-bphany)4](1). Unfortunately, the crystals of complex (1) have
not been good enough for X-ray structural determination until now. The
coordination chemistry of the other ligand, H2bpyany, is rich and was
found that the H2bpyany ligand can bind metal ions at least in three conformations,
the anti-anti form I, the anti-anti-syn-anti-anti form II , and the all syn form III.
In I the ligand is bidentate and coordinates to a metal ion through one nitrogen
atom of pyridine and of naphthyridine to form [Co(H2bpyany)(NCS)2] (2) and
[Ni(H2bpyany)(NCS)2(H2O)] (3). In II the ligand can bind two metal ions, and
the complex [Cu2(µ-H2bpyany)(µ-Cl)(µ-OH)Cl2] (4) was obtained. The
coordination geometry about each Cu(II) ion is closer to a trigonal bipyramid.
Complex 4 has a slight longer Cu(II)…Cu(II) distance of 3.022(1) Å and exhibits
ferromagneitc interaction (J = 63.3 cm-1) from magnetic studies. In the last form
III, the ligands have been deprotonated to act as hexadentate ones and were
helically wrapped the metal ions to form a hexanuclear metal string, structurally
similar to previous reports. We have successfully prepared the novel hexametal
string complex , [Ni6(µ6-bpyany)4(X)2]n+ (X= NCS– : n=2 (5), n=1 (6);X = Cl–:
n=2 (7), n=1 (8)) and [Co6(µ6-bpyany)4(X)2]n+ (X= NCS– : n = 1 (9), n=2 (10); X =
OTf –: n=1 (11), n=2 (12)). Ni6 complexes have linear cores of metal
arrangements, Ni(1)…Ni(2)…Ni(3)…Ni(4)…Ni(5)…Ni(6), with D4 symmetry
without considering axial ligands. For complex (5) and (7), the terminal nickel(II)
ions, Ni(1) and Ni(6), are in high-spin states (S = 1) and the inner four ones are
in low-spin states (S = 0). The coupling constant (J16) of Ni6 metal string is –4
~ –5 cm–1. The The complex (5) has a redox couple at E1/2 = – 0.19 V and would
6
be easily reduced by chemical methods. One-electron reduction of complex (7)
produces complex (8). Ni(3)–Ni(4) distance is slight shorter 0.08 Å from 2.281(2)
Å to 2.201(3) Å with respect to complex (7) and (8). Ni(3)–Npy(av) distance is
obviously becoming longer 0.106 Å from 1.903(8) Å to 2.009(4) Å. We propose
reduction was occurred at one unit of Ni(3) and Ni(4).The arrangement of the
nickel charge are Ni+2…Ni+2…Ni+1.5…Ni+1.5…Ni+2…Ni+2.
In cobalt systems, one-electron reduced complexes (9) and (11) are
stable in the air. One-electron oxidation of complex (9) and (11) generate
complex (10) and (12). Complex [Co6(µ6-bpyany)4(NCS)2](PF6) (9) has +1.83
averaged oxidation state of cobalt and exhibits magnetic moment as 1.80 µB.
(300 K) which reveals S = 1/2 electronic configuration. The electrochemistry of
the complex (9) displays four redox couples at −0.55 V, +0.38 V, +0.91 V
and+1.18 V. One-electron oxidized form, complex
[Co6(µ6-bpyany)4(NCS)2](PF6)2 (10) has an unusual magnetic behavior with
gradually increasing magnetic moment from 0.80 µB (2 K) to 2.79 µB (300 K).
EHMO calculation is consistent with S = 1 electronic configuration at high
temperature. These two unpaired electrons fill in SOMO orbitals, namely σ*(4)
and δ*(6).
Subjects
二苯胺萘
啶
二吡
啶胺萘
六核金屬錯合物
H2bphany
H2bpyany
Hexanuclear Metal Complexes
Type
thesis