Dinuclear zinc complexes of phenol-based "end-off" compartmental ligands: Synthesis, structures and phosphatase-like activity

Article abstract of DOI:10.1246/bcsj.74.85

The phenol-based compartmental ligands of the "end-off" type, 2,6-bis{N-[2-(dimethylamino)ethyl]iminomethyl})-4-methylphenol (HL¹), 2-{N-[2-(dimethylamino)ethyl]iminomethyl}-6-{N-methyl-N-[2-(dimethylamino) ethyl]aminomethyl}-4-bromophenol (HL²), 2,6-bis{2-[(2-pyridyl)ethyl]iminomethyl}-4-methylphenol (HL³) and 2-[N,N-di(2-pyridylmethyl)aminomethyl]-6-{N-[2-(dimethylamino)ethyl] iminomethyl}-4-methylphenol (HL⁴), have formed dinuclear zinc complexes: [Zn₂(L¹)(AcO)₂]PF₆ (1), [Zn₂(L¹)(NCS)₃] (2), [Zn₂(L²)(AcO)₂]PF₆ (3), [Zn₂(L²)(NCS)₃] (4), [Zn₂(L³)-(AcO)₂]PF₆ (5), [Zn₂(L³)(NCS)₃] (6), [Zn₂(L⁴)(AcO)₂]C104 (7), [Zn₂(L⁴)(AcO)(NCS)₂] (8) and [Zn₂(L⁴)(NCS)₃] (9). The crystal structures of 1, 5·(DMF)_0.5(2-PrOH)_0.5, 7·CHCl₃, 8·(2-PrOH) and 9·3CHCl₃ have been determined. Complexes 1 and 5·(DMF)_0.5(2-PrOH)_0.5 have a di-μ-acetato-μ-phenolato-dizinc(II) core comprised of two square-pyramidal Zn centers. 7·CHCl₃ has a similar dinuclear core, but it is comprised of one square-pyramidal Zn and one pseudo-octahedral Zn. 8·(2-PrOH) has a μ-acetato-μ-phenolato-dizinc(II) core with a unidentate thiocyanato-N group on each Zn. 9·3CHCl₃ exists in two different crystals: one has a μ-thiocyanato-N-μ-phenolato-dizinc(II) core, whereas the other has a μ-phenolato-dizinc(II) core. The diacetato complexes, 1, 3, 5 and 7, are stable in solution. Hydrolytic activities of the complexes toward tris(p-nitrophenyl) phosphate (TNP) have been studied in aqueous DMF by means of UV-visible spectroscopic and ³¹P NMR methods. Complexes 1, 3 and 5 have an activity to hydrolyze TNP into bis(p-nitrophenyl) hydrogenphosphate (HBNP) in aqueous DMF. In contrast, 7 showed little hydrolytic activity toward TNP in aqueous DMF.

Full text of DOI:10.1246/bcsj.74.85

© 2001 The Chemical Society of Japan
85
Bull. Chem. Soc. Jpn., 74, 85–95 (2001)
Dinuclear Zinc Complexes of Phenol-Based “End-off” Compartmental
Ligands: Synthesis, Structures and Phosphatase-Like Activity
Ko-ji Abe, Jun Izumi, Masaaki Ohba, Takusi Yokoyama, and Hisashi Okawa*
Department of Chemistry, Faculty of Sciences, Kyushu University,
Hakozaki 6-10-1, Higashiku, Fukuoka 812-8581
(Received August 21, 2000)
The phenol-based compartmental ligands of the “end-off” type, 2,6-bis{N-[2-(dimethylamino)ethyl]iminomethyl}-
4-methylphenol (HL1), 2-{N-[2-(dimethylamino)ethyl]iminomethyl}-6-{N-methyl-N-[2-(dimethylamino)ethyl]amino-
methyl}-4-bromophenol (HL2), 2,6-bis{2-[(2-pyridyl)ethyl]iminomethyl}-4-methylphenol (HL3) and 2-[N,N-di(2-py-
ridylmethyl)aminomethyl]-6-{N-[2-(dimethylamino)ethyl]iminomethyl}-4-methylphenol (HL4), have formed dinuclear
zinc complexes: [Zn2(L1)(AcO)2]PF6 (1), [Zn2(L1)(NCS)3] (2), [Zn2(L2)(AcO)2]PF6 (3), [Zn2(L2)(NCS)3] (4), [Zn2(L3)-
(AcO)2]PF6 (5), [Zn2(L3)(NCS)3] (6), [Zn2(L4)(AcO)2]ClO4 (7), [Zn2(L4)(AcO)(NCS)2] (8) and [Zn2(L4)(NCS)3] (9).
The crystal structures of 1, 5•(DMF)0.5(2-PrOH)0.5, 7•CHCl3, 8•(2-PrOH) and 9•3CHCl3 have been determined. Complex-
es 1 and 5•(DMF)0.5(2-PrOH)0.5 have a di-µ-acetato-µ-phenolato-dizinc(II) core comprised of two square-pyramidal Zn
centers. 7•CHCl3 has a similar dinuclear core, but it is comprised of one square-pyramidal Zn and one pseudo-octahedral
Zn. 8•(2-PrOH) has a µ-acetato-µ-phenolato-dizinc(II) core with a unidentate thiocyanato-N group on each Zn.
9•3CHCl3 exists in two different crystals: one has a µ-thiocyanato-N-µ-phenolato-dizinc(II) core, whereas the other has a
µ-phenolato-dizinc(II) core. The diacetato complexes, 1, 3, 5 and 7, are stable in solution. Hydrolytic activities of the
complexes toward tris(p-nitrophenyl) phosphate (TNP) have been studied in aqueous DMF by means of UV-visible spec-
troscopic and 31P NMR methods. Complexes 1, 3 and 5 have an activity to hydrolyze TNP into bis(p-nitrophenyl) hydro-
genphosphate (HBNP) in aqueous DMF. In contrast, 7 showed little hydrolytic activity toward TNP in aqueous DMF.
Bimetallic cores exist at the active sites of many
metalloenzymes1 and play essential roles required in biological
systems. Dinuclear Zn cores are found in hydroxylases such as
alkaline phosphatase,2 phospho-lipase C,3 P1 nuclease,4 and
leucine aminopeptidase.5 Recent X-ray crystallographic stud-
ies have indicated that the active sites of most hydroxylases are
asymmetric with respect to the two Zn centers. It is thought
that hydroxylases employ such an asymmetric dinuclear core
to facilitate the concerted binding of a substrate on one Zn cen-
ter and the nucleophilic attack of hydroxide or activated water
at the adjacent Zn center.6 Some model studies have been car-
ried out to mimic the hydroxylase functions using dinuclear Zn
complexes.7
In this work, the “end-off” compartmental ligands
(L1)––(L4)– (Chart 1) were used to synthesize dinuclear zinc(II)
complexes, with the hope of providing functional models of
phosphatases. The ligands (L1)––(L3)– have two bidentate
Phenol-based “end-off” compartmental ligands, having pen-
dant arms attached to the 2 and 6 positions of the phenolic ring,
have often been used to model bimetallic biosites.8–11 Di-µ-car-
boxylato-µ-phenolato-dimanganese(II) complexes derived
from such ligands show Mn catalase-like activity to dispropor-
tionate hydrogen peroxide into dioxygen and water.8 Urea ad-
ducts of dinuclear nickel(II) complexes were derived as struc-
tural models of urease,9 and chemical conversion of urea into
cyanate ion was achieved on dinuclear nickel(II) complexes.10
Dioxygen adducts of dinuclear cobalt(II), iron(II) and cop-
per(I) complexes of such “end-off” compartmental ligands
were extensively studied as models for oxygen-carriers and ox-
ygenases.11
Chart 1. Chemical structures of phenol-based “end-off”
compartmental ligands (L1)−– (L4)−.

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Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Dinuclear Zn Complexes of End-Off Type Ligands
M
–1 cm–1)]: 391 (10700) in DMF. Selected IR (KBr) data: 2090,
chelating arms. The ligands (L1)– and (L3)– are symmetric with
respect to the two chelating arms, whereas (L2)– is asymmetric
with respect to the aminic and iminic nature of the articular ni-
trogens of the bidentate arms. The ligand (L4)– has bidentate
and tridentate chelating arms and can provide a dinuclear core
in a coordination number asymmetry. The following dinuclear
Zn complexes have been obtained: [Zn2(L1)(AcO)2]PF6 (1),
[Zn2(L1)(NCS)3] (2), [Zn2(L2)(AcO)2]PF6 (3), [Zn2(L2)(NCS)3]
(4), [Zn2(L3)(AcO)2]PF6 (5), [Zn2(L3)(NCS)3] (6), [Zn2(L4)-
(AcO)2]ClO4 (7), [Zn2(L4)(AcO)(NCS)2] (8) and [Zn2(L4)-
(NCS)3] (9). The crystal structures of 1, 5•(DMF)0.5(2-PrOH)0.5
(5′), 7•CHCl3 (7′), 8•(2-PrOH) (8′) and 9•3CHCl3 (9′) have
been determined by X-ray crystallography, and the solution
structures of 1–9 in DMF have been examined by 1H NMR and
visible spectra. A focus is placed on phosphatase-like activity
of the diacetato complexes 1, 3, 5 and 7 toward tris(p-nitrophen-
yl) phosphate (TNP) in aqueous DMF.
1992, 1650, 819, 488, 462, 410 cm–1.
[Zn2(L2)(AcO)2]PF6 (3). The ligand HL2 was prepared in situ
by reacting 5-bromo-3-{N-[2-(dimethylamino)ethyl]-N-meth-
yl}aminomethylsalicylaldehyde (157 mg, 0.5 mmol) and N,N-
dimethylethylenediamine (44 mg, 0.5 mmol) in methanol (10 cm3)
at the boiling temperature. To this solution was added zinc(II) ace-
tate tetrahydrate (220 mg, 1.0 mmol), and the mixture was stirred
at 60 °C for 20 min. A methanol solution (10 cm3) of ammonium
hexafluorophosphate (82 mg, 1 mmol) was then added, and the
mixture was concentrated to ca. 10 cm3 to give yellow microcrys-
tals. The yield was 300 mg (77%). Found: C, 32.41; H, 4.40; N,
7.20; Zn, 16.8%. Calcd. for BrC21F6H34N4O5PZn2: C, 32.54; H,
4.46; N, 7.18; Zn, 16.6%. FAB MS m/z 633 for {Zn2(L2)(AcO)2}+.
Molar conductance [ΛM/S cm2 mol–1]: 61 in DMF. UV-vis [λmax
/
nm (ε/M–1 cm–1)]: 365 (6200) in DMF. Selected IR (KBr) data:
1648, 1600, 1446, 844, 558 cm–1.
[Zn2(L2)(NCS)3] (4). This was obtained as yellow microcrys-
tals by the reaction of HL2 and Zn(NCS)2 in methanol. Yield:
86%. Found: C, 35.12; H, 4.17; N, 14.20; Zn, 18.9%. Calcd. for
BrC20H28N7OS3Zn2: C, 34.85; H, 4.09; N, 14.22; Zn, 19.0%. Mo-
lar conductance [ΛM/S cm2 mol–1]: 48 in DMF. UV-vis [λmax/nm
(ε/M–1 cm–1)]: 374 (6700) in DMF. Selected IR (KBr) data: 2078,
2024, 1644, 826, 752, 482, 461, 412 cm–1.
Experimental
Physical Measurements. Elemental analyses of C, H, and N
were obtained at the Elemental Analysis Service Center of Kyushu
University. Analyses of Zn were obtained using a Shimadzu AA-
660 atomic absorption/flame emission spectrometer. Infrared
spectra were recorded on a Perkin Elmer BX FT-IR system using
KBr disks. Molar conductances in DMF were measured with a
DKK AOL-10 conductivity meter at room temperature. Electronic
spectra were recorded using a Shimadzu UV-3100PC spectrome-
ter. 1H-NMR spectra (270 MHz) were recorded on a JEOL JNM-
GX 400 using tetramethylsilane as the internal standard. 31P-
NMR spectra were recorded on the same spectrometer using
H3PO4 (85%) as the external reference. Positive ion fast atom
bombardment (FAB) mass spectra were recorded on a JEOL JMS-
SX 102A BE/BE four-sector type tandem mass spectrometer using
m-nitrobenzyl alcohol as the matrix.
Preparation. 2,6-Diformyl-4-methylphenol was prepared by
the method of Denton and Suschitzky.12 The proligands, 5-bromo-
3-{N-[2-(dimethylamino)ethyl]- N -methyl}aminomethylsalicyl-
aldehyde13 and 3-[N,N-di(2-pyridylmethyl)aminomethyl]-5-meth-
ylsalicylaldehyde,8d,8e were prepared by the methods in our previ-
ous papers. Other chemicals were of reagent grade and were used
as purchased.
[Zn2(L3)(AcO)2]PF6 (5). The ligand HL3 was prepared in situ
by reacting 2,6-diformyl-4-methylphenol (164 mg, 0.5 mmol) and
2-(2-pyridyl)ethylamine (122 mg, 1.0 mmol) in methanol (20
cm3). To this solution was added zinc(II) acetate tetrahydrate (220
mg, 1.0 mmol), and the mixture was stirred at 60 °C for 20 min. A
solution of ammonium hexafluorophosphate (82 mg, 1.0 mmol) in
methanol (10 cm3) was then added, and the mixture was concen-
trated to ca. 10 cm3 to result in the precipitation of yellow microc-
rystals. Yield: 335 mg (86%). Found: C, 43.31; H, 4.41; N, 7.99;
Zn, 17.4%. Calcd. for C27F6H29N4O5PZn2: C, 43.31; H, 4.42; N,
7.61; Zn, 17.0%. FAB MS m/z 621.1 for {Zn2(L3)(AcO)2}+. Mo-
lar conductance [ΛM/S cm2 mol–1]: 61 in DMF. UV-vis [λmax/nm
(ε/M–1 cm–1)]: 390 (10800) in DMF. Selected IR (KBr) data:
1649, 1633, 1596, 1571, 1552, 1490, 1444, 1414, 843, 558 cm–1.
Single crystals of [Zn2(L3)(AcO)2]PF6•(DMF)0.5(2-PrOH)0.5
(5′) suitable for X-ray crystallography were grown when a DMF
solution of 5 was diffused with 2-propanol (2-PrOH).
[Zn2(L3)(NCS)3] (6). This was obtained as yellow microcrys-
tals by the reaction of HL3 and Zn(NCS)2 in methanol. Yield:
32%. Found: C, 46.35; H, 3.40; N, 14.45; Zn, 16.8%. Calcd. for
C26H23N7OS3Zn2: C, 46.16; H, 3.43; N, 14.49; Zn, 19.3%. Molar
conductance [ΛM/ S cm2 mol–1]: 58 in DMF. UV-vis [λmax/nm (ε/
M–1 cm–1)]: 397 (9300) in DMF. Selected IR (KBr) data: 2077,
2030, 1649, 1630, 1608, 1554, 816, 712, 701, 478, 466, 418 cm–1.
[Zn2(L4)(AcO)2]ClO4 (7). A solution of HL4 was prepared in
situ by reacting 3-[N,N-di(2-pyridylmethyl)aminomethyl]-5-me-
thyl-salicylaldehyde (157 mg, 0.5 mmol) with N,N-dimethylethyl-
enediamine (44 mg, 0.5 mmol) in methanol (5 cm3) at the boiling
temperature. To this solution was added zinc(II) acetate tetrahy-
drate (210 mg, 1.0 mmol), and the mixture was stirred at 60 °C for
30 min. A methanol solution (10 cm3) of sodium perchlorate (120
mg, 1.0 mmol) was then added, and the mixture was diffused with
ether to give yellow microcrystals. The yield was 222 mg (58%).
Found: C, 45.56; H, 4.73; N, 9.12; Zn, 17.1%. Calcd. for
C29ClH36N5O9Zn2: C, 45.58; H, 4.87; N, 9.14; Zn, 17.0%. FAB
MS: m/z 664 for {Zn2(L4)(AcO)2}+. Molar conductance [ΛM/S
cm2 mol–1]: 49 in DMF, 32 in DMSO. UV-vis [λmax/nm (ε/
M–1 cm–1)]: 367 (6100) in DMF. Selected IR (KBr) data: 3436,
[Zn2(L1)(AcO)2]PF6 (1). The ligand HL1 was prepared in
situ by reacting 2,6-diformyl-4-methylphenol (164 mg, 0.5 mmol)
and N,N-dimethylethylenediamine (88 mg, 1.0 mmol) in methanol
(10 cm3) at the boiling temperature. To the ligand solution was
added zinc(II) acetate tetrahydrate (220 mg, 1.0 mmol), and the
mixture was stirred at 60 °C for 20 min. A methanol solution (10
cm3) of ammonium hexafluorophosphate (82 mg, 1.0 mmol) was
then added, and the solution was concentrated to ca. 10 cm3 to
form yellow crystals. The yield was 523 mg (75%). Found: C,
35.64; H, 4.89; N, 8.05; Zn, 18.3%. Calcd. for C21H33F6N4O5PZn2:
C, 36.17; H, 4.77; N, 8.07; Zn, 18.8%. Molar conductance [ΛM/S
cm2 mol–1]: 61 in DMF. UV-vis [λmax/nm (ε/M–1 cm–1)]: 390
(10400) in DMF. Selected IR data (KBr) 1655, 1640, 1598, 1549,
1449, 842, 557 cm–1.
[Zn2(L1)(NCS)3] (2). This was obtained as yellow microcrys-
tals by the reaction of HL1 and Zn(NCS)2 in methanol. Yield:
23%. Found: C, 39.60; H, 4.50; N, 15.87; Zn, 21.0%. Calcd. for
C20H27N7OS3Zn2: C, 39.48; H, 4.47; N, 16.11; Zn, 21.5%. Molar
conductance [ΛM /S cm2 mol–1]: 47 in DMF. UV-vis [λmax/nm (ε/

K. Abe et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
1519, 1345, 1243, 1207, 1108 cm–1.
87
2926, 1637, 1604, 1464, 1431, 1311, 1092, 1022, 775, 624 cm–1.
Single crystals of [Zn2(L4)(AcO)2]ClO4•CHCl3 (7′) suitable for
X-ray crystallography were grown by recrystallization from a
chloroform/hexane mixture.
[Zn2(L2)(bnp)2]ClO4 (11). This was obtained as yellow crys-
tals in a way similar to that for 10. Yield: 60%. Found: C, 38.35;
H, 3.46; N, 8.67; Zn, 9.7%. Calcd. for BrC41ClH44N8O21P2Zn2: C,
38.09; H, 3.43; N, 8.67; Zn, 10.1%. Molar conductance [ΛM/S
cm2 mol–1]: 86 in DMF. UV-vis [λmax/nm (ε/M–1 cm–1)]: 384
(9100) in DMF. Selected IR (KBr) data: 1648, 1521, 1348, 1297,
1250, 1220, 1108 cm–1.
[Zn2(L4)(AcO)(NCS)2] (8). A methanol solution HL4 (0.5
mmol) was prepared as described for 7. To this was added zinc(II)
acetate tetrahydrate (210 mg, 1.0 mmol), and the mixture was
stirred for 30 min. Sodium thiocyanate (81 mg, 1.0 mmol) was
then added, and the mixture was stirred for 30 min and allowed to
stand at room temperature to provide yellow crystals. The yield
was 234 mg (64%). Found: C, 48.16; H, 4.59; N, 13.57; Zn,
18.1%. Calcd. for C29H35N7O3S2Zn2: C, 48.07; H, 4.87; N, 13.53;
Zn, 18.0%. FAB MS: m/z 655 for {Zn2(L4)(AcO)(NCS)}+. Molar
conductance [ΛM/S cm2 mol–1]: 71 in DMF, 50 in DMSO. UV-vis
[λmax/nm (ε/M–1 cm–1)]: 370 (5700) in DMF. Selected IR (KBr)
data: 3469, 2915, 2081, 1641, 1577, 1463, 1434, 1303, 1017, 765
cm–1.
[Zn2(L3)(bnp)2]ClO4 (12). This was obtained as yellow crys-
tals in a way similar to that for 10. Yield: 50%. Found: C, 44.17;
H, 3.03; N, 8.81; Zn, 10.2%. Calcd. for C41ClH39N8O21P2Zn2: C,
44.10; H, 3.07; N, 8.75; Zn, 10.2%. Molar conductance [ΛM/S
cm2 mol–1]: 85 in DMF. UV-vis [λmax/nm (ε/M–1 cm–1)]: 387
(8800) in DMF. Selected IR (KBr) data: 1650, 1520, 1347, 1238,
1227, 1207, 1108 cm–1.
Crystal Structure Analyses. Crystal structures of [Cu2(L1)-
(AcO)2]PF6 (1), [Zn2(L3)(AcO)2]PF6•(DMF)0.5(2-PrOH)0.5 (5′),
[Zn2(L4)(AcO)2]ClO4•CHCl3 (7′), [Zn2(L4)(AcO)(NCS)2]•(2-
PrOH) (8′) and [Zn2(L4)(NCS)3]•3CHCl3 (9′) were determined by
X-ray crystallography. Each single crystal was mounted on a glass
fiber and used for X-ray structural measurements. Intensities and
lattice parameters were obtained on a Rigaku AFC-7R automated
four-circle diffractometer, using graphite-monochromated Mo-Ka
radiation (λ = 0.71069 Å) and a 12 kW rotating anode generator at
23 1 °C. The cell parameters were determined by 25 reflections
in the 2θ range of 29.8° < 2θ < 30.0°. For the intensity data collec-
tions, the ω – 2θ scan mode was used to a maximum 2θ value of
55.0° at the scan rate of 16° min–1. The weak reflections (I <
10.0σ (I)) were rescanned (maximum of 4 scans), and the counts
were accumulated to ensure good counting statistics. Stationary
background counts were recorded on each side of the reflection.
The ratio of peak counting time to background counting time was
2:1. The diameter of the incident beam collimator was 1.0 mm,
the crystal-to-detector distance was 235 mm, and the computer-
controlled detector aperture was set to 9.0 × 13.0 mm (horizontal ×
vertical). Three standard reflections were monitored every 150 re-
flections. Over the course of the data collection, the standards de-
creased by 5.0% for 1, –4.6% for 7′, –1.14% for 8′ and 15.2% for
9′. A linear correction factor was applied to the data to account for
the phenomena. The linear absorption coefficient, µ, for Mo-Kα
radiation was 17.8 cm–1 for 1, 14.0 cm–1 for 5′, 15.6 cm–1 for 7′,
14.4 cm–1 for 8′ and 16.4 cm–1 for 9′. An empirical absorption cor-
rection based on azimuthal scans of several reflections was applied
which resulted in transmission factors ranging from 0.81 to 1.00
for 1, from 0.95 to 1.00 for 5′, from 0.42 to 1.00 for 7′, from 0.92
to 1.00 for 8′ and from 0.68 to 1.00 for 9′. The intensity data were
corrected for Lorentz and polarization factors. Pertinent crystallo-
graphic parameters are summarized in Table 1.
Single crystals of [Zn2(L4)(AcO)(NCS)2]•2(2-PrOH) (8′) suit-
able for X-ray crystallography were grown when a DMF solution
of 8 was diffused with 2-propanol.
[Zn2(L4)(NCS)3] (9). To a methanol solution HL4 (0.5 mmol)
was added zinc(II) thiocyanate (182 mg, 1.0 mmol), and the mix-
ture was stirred for 30 min. Sodium thiocyanate (42 mg, 0.5
mmol) was then added, and the mixture was allowed to stand at
room temperature to give yellow crystals. The yield was 202 mg
(64%). Found: C, 46.57; H, 4.11; N, 15.50; Zn, 18.0%. Calcd. for
C28H30N8OS3Zn2: C, 46.61; H, 4.19; N, 15.53; Zn, 18.1%. Molar
conductance [ΛM/S cm2 mol–1]: 73 in DMF. UV-vis [λmax/nm (ε/
M–1 cm–1)]: 379 (5300) in DMF. Selected IR (KBr) data: 3469,
2908, 2072, 1984, 1639, 1608, 1563, 1463, 1441, 1023, 762 cm–1.
Single crystals of [Zn2(L4)(NCS)3]•3CHCl3 (9′) suitable for X-
ray crystallography were grown when a chloroform solution of 9
was diffused with n-hexane.
Studies of Phosphatase-LikeActivity. The hydrolytic activi-
ty of the di-acetato complexes (1, 3, 5 and 7) toward tris(p-nitro-
phenyl) phosphate (TNP) was studied in aqueous DMF (H2O:
DMF = 0.3:99.7 in volume) at 25 °C by means of UV-visible and
31P NMR methods. A solution of a complex and TNP in aqueous
DMF (H2O:DMF = 0.3:99.7 in volume; [complex] = 5.0 × 10–4
M
and [TNP] = 5.0 × 10–4 M) was prepared and subjected to visible
spectral measurements (1 M = 1 mol dm–3). A complex solution of
5.0 × 10–4 M was used as the reference, and the hydrolysis of TNP
was followed by measuring the difference spectra. For 31P-NMR
spectroscopic studies, a solution of a complex and TNP in aqueous
DMF (H2O:DMF = 0.3:99.7; [complex] = 2.5 × 10–3 M and
[TNP] = 2.5 × 10–2 M) was prepared, and the hydrolysis of TNP
was followed by a decrease in the TNP signal near –16 ppm and by
observing a 31P signal arising from the hydrolysis of TNP.
For comparative studies, the following bnp (bnp = bis(p-nitro-
phenyl) phosphate) complexes, [Zn2(L)(bnp)2]ClO4 (L = L1, L2
and L3), were prepared.
The structures were solved by direct methods and expanded us-
ing Fourier techniques. Refinements were carried out by the full-
matrix least-squares method, where the function minimized is
w(|F0|–|Fc|)2 with w = 1/σ2(F0). Non-hydrogen atoms were re-
fined anisotropically. Hydrogen atoms were fixed at the calculated
positions and were not refined.
Neutral atom scattering factors were taken from Cromer and
Waber.14 Anomalous dispersion effects were included in Fcalc; the
values for ∆f′ and ∆f ′′ were those of Creagh and McAuley.15 The
values for the mass attenuation coefficients were those of Creagh
and Hubbel.16 All calculations were performed using the teXsan
crystallographic software package of Molecular Structure Corpo-
ration.17
[Zn2(L1)(bnp)2]ClO4 (10). To a methanol solution of HL1
(0.5 mmol) (prepared as described for complex 1) was added
zinc(II) perchlorate hexahydrate (372 mg, 1.0 mmol), and the mix-
ture was stirred at 60 °C for 20 min. A solution of di(p-nitrophe-
nyl) sodium phosphate (NaBNP) (362 mg, 1.0 mmol) in methanol
(120 cm3) was then added, and the mixture was concentrated to ca.
100 cm3 to give yellow microcrystals. Yield: 428 mg (70%).
Found: C, 40.77; H, 3.57; N, 9.28; Zn, 10.8%. Calcd. for
C41ClH43N8O21P2Zn2: C, 40.63; H, 3.58; N, 9.25; Zn, 10.8%. Mo-
lar conductance [ΛM/S cm2 mol–1]: 85 in DMF. UV-vis [λmax/nm
(ε/M–1 cm–1)]: 360 (7100) in DMF. Selected IR (KBr) data: 1661,
Crystallographic data have been deposited at the CCDC, 12

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Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Dinuclear Zn Complexes of End-Off Type Ligands
α
β
γ

K. Abe et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
89
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on request, free of charge, by quoting the publication citation and
the deposition numbers 151667–151671. The data are also depos-
ited as Document No. 74009 at the Office of the Editor of Bull.
Chem. Soc. Jpn.
Results and Discussions
Syntheses and General Properties. The “end-off” com-
partmental ligands, (L1)––(L4)–, combine two Zn ions to pro-
vide two types of dinuclear zinc complexes. One type is the di-
µ-acetato-µ-phenolato-dizinc(II) core complexes, [Zn2(L)-
(AcO)2]X (X– = PF6 or ClO4 ) (1, 3, 5 and 7), that were ob-
tained by the reaction of HL1–HL4 with zinc(II) acetate tet-
rahydrate in the presence of PF6– or ClO4– ion. They show the
νas(COO) and νs(COO) vibrations of the acetate group at
1610–1600 and 1450–1440 cm–1, respectively. Thesmallsepa-
ration between the two vibrations (< 200 cm–1) is in accord
with a bridging function of the acetate group,18 as demonstrat-
ed by X-ray crystallography for 1, 5′ and 7 (see below). The
complexes show an intense band at 365–390 nm that is attribut-
–
–
Fig. 1. An ORTEP view of the cationic part of 1 with the
atom numbering scheme.
*
ed to the π–π transition associated with the azomethine link-
age.19,20
˚
Table 2. Selected Bond Distances (A) and Angles (deg)
for [Zn2(L1)(AcO)2]ClO4 (1)
The other type is [Zn2(L)(NCS)3] (2, 4, 6 and 9) that was
prepared by the reaction of HL1–HL4 and Zn(NCS)2. Complex
2 shows two ν(CN) vibrations at 2080 and 1995 cm–1. Similar-
ly,4, 6 and 9 each show two ν(CN)vibrations. Evidently,there
are two bonding modes of NCS– group in these complexes. X-
ray structural studies for analogous [Ni2(L2)(NCS)3(MeOH)]9
have indicated a µ-thiocyanato-N-µ-phenolato-dinickel(II)
core with a terminal thiocyanato nitrogen on each Ni. A simi-
lar dinuclear core structure is supposed for the present thiocy-
anato complexes. Molar conductances for the complexes at 1 ×
10–3 M in DMF (ΛM: 47–73 S cm2 mol–1) indicate that they be-
have as 1:1 electrolytes in DMF. Electronic spectra of the
Zn(1) O(1)
Zn(1) O(4)
Zn(1) N(2)
Zn(2) O(3)
Zn(2) N(3)
2.093(3) Zn(1) O(2)
1.975(3) Zn(1) N(1)
2.192(4) Zn(2) O(1)
1.983(3) Zn(2) O(5)
2.017(4) Zn(2) N(4)
1.971(3)
2.035(4)
2.098(3)
1.967(3)
2.218(4)
O(1) Zn(1) O(2) 95.2(1)
O(1) Zn(1) N(1) 87.2(1)
O(2) Zn(1) O(4) 114.1(2)
O(2) Zn(1) N(2) 86.9(2)
O(4) Zn(1) N(2) 96.5(2)
O(1) Zn(2) O(3) 96.4(1)
O(1) Zn(2) N(3) 88.5(2)
O(3) Zn(2) O(5) 111.7(2)
O(3) Zn(2) N(4) 92.7(2)
O(5) Zn(2) N(4) 88.9(2)
O(1) Zn(1) O(4) 97.3(1)
O(1) Zn(1) N(2) 163.8(2)
O(2) Zn(1) N(1) 136.1(2)
O(4) Zn(1) N(1) 108.9(2)
N(1) Zn(1) N(2) 80.2(2)
O(1) Zn(2) O(5) 94.8(1)
O(1) Zn(2) N(4) 168.1(1)
O(3) Zn(2) N(3) 109.6(2)
O(5) Zn(2) N(3) 137.9(2)
O(3) Zn(2) N(4) 81.3(2)
*
complexes show the π–π transition band in the region of
374–397 nm.
The asymmetric ligand (L4)– exhibits versatility in complex-
ation to form another type of complex, [Zn2(L4)(AcO)(NCS)2]
(8). It shows the νas(COO) and νs(COO) modes of the acetate
group at 1577 and 1434 cm–1, respectively, and one ν(CN) vi-
bration at 2081 cm–1.
O5−Zn2−N3 is 359.2°.
[Zn2(L3)(AcO)2]PF
6 (DMF)0.5(2-PrOH)0.5 (5′). An ORTEP
•
Crystal Structures.
[
Zn2(L1)(AcO)2]PF6 (1). An ORTEP21
view is shown in Fig. 2 together with the numbering scheme.
The selected bond distances and angles are summarized in
Table 3.
view of the cationic part of 1 is shown in Fig. 1, together with
the numbering scheme. The selected bond distances and an-
gles are given in Table 2.
The dinuclear core of 5′ is essentially the same as that of 1.
The two Zn ions are bridged by the phenolic oxygen of (L3)–
and two acetate groups in the syn-syn mode, in the Zn1–Zn2
interatomic separation of 3.297(2) Å. The two Zn ions have a
similar trigonal-bipyramidal geometry with the phenolic oxy-
gen O1 and the terminal nitrogen N2 (N4) at the axial sites and
with the imino nitrogen N1 (N3) and the two acetate oxygens
O2 and O4 (O3 and O5) on the trigonal base. The O1−Zn1−N2
angle is 179.1°. The sum of the N1−Zn1−O2, O2−Zn1−O4
and O4−Zn1−N1 angles are 359.8°. The O1−Zn2−N4 angle is
174.6° and the sum of the N3−Zn2−O3, O3−Zn2−O5 and
O5−Zn2−N3 angles is 359.7°
It has a di-µ-acetato-µ-phenolato-dizinc(II) core with a
Zn1–Zn2 interatomic separation of 3.237(4) Å. The environ-
ments about Zn1 and Zn2 are similar but not equivalent. The
geometry about Zn1 and Zn2 can be regarded as trigonal-bi-
pyramid (the parameter τ22 is 0.461 for Zn1 and 0.503 for
Zn2), with the phenolic oxygen O1 and the terminal nitrogen
N2 (N4) at the axial sites and with the imino nitrogen N1 (N3)
and the two acetate oxygens O2 and O4 (O3 and O5) on the
trigonal plane. The O1−Zn1−N2 angle is 163.8° and the
O1−Zn2− N4 angle is 168.1°. The sum of the angles of
N1−Zn1−O2, O2−Zn1−O4 and O4−Zn1−N1 is 359.1°, and the
sum of the angles of N3−Zn2−O3, O3−Zn2−O5 and
[Zn2(L4)(AcO)2]ClO4•CHCl3 (7′). An ORTEP view of 7′

90
Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Dinuclear Zn Complexes of End-Off Type Ligands
Fig. 2. An ORTEP view of 5ꢀ with the atom numbering
scheme.
Fig. 3. An ORTEP view of 7ꢀ with the atom numbering
scheme.
Table 3. Selected Bond Distances (Å) and Angles (deg)
for [Zn2(L3)(AcO)2]ClO4•(DMF)0.5•(2-PrOH)0.5 (5ꢀ)
Zn(1) O(1)
2.120(5) Zn(1) O(2)
1.978(5) Zn(1) N(1)
2.197(6) Zn(2) O(1)
1.970(5) Zn(2) O(5)
2.011(6) Zn(2) N(4)
1.988(5)
2.018(8)
2.115(5)
1.983(5)
2.202(6)
Table 4. Selected Bond Distances (Å) and Angles (deg)
[Zn2(L4)(AcO)2]ClO4•CHCl3 (7ꢀ)
Zn(1) O(4)
Zn(1) N(2)
Zn(2) O(3)
Zn(2) N(3)
Zn(1) O(1)
Zn(1) O(4)
Zn(1) N(2)
Zn(2) O(3)
Zn(2) N(3)
Zn(2) N(5)
2.026(5) Zn(1) O(2)
1.976(6) Zn(1) N(1)
2.177(7) Zn(2) O(1)
2.019(5) Zn(2) O(5)
2.194(6) Zn(2) N(4)
2.215(6)
1.986(5)
2.078(7)
2.080(5)
2.116(5)
2.151(6)
O(1) Zn(1) O(2) 92.8(2)
O(1) Zn(1) N(1) 88.0(3)
O(2) Zn(1) O(4) 114.9(2)
O(2) Zn(1) N(2) 87.5(2)
O(4) Zn(1) N(2) 85.6(2)
O(1) Zn(2) O(3) 94.7(2)
O(1) Zn(2) N(3) 88.5(2)
O(3) Zn(2) O(5) 118.4(2)
O(3) Zn(2) N(4) 90.4(2)
O(5) Zn(2) N(4) 83.8(2)
O(2) Zn(1) O(4) 95.0(2)
O(1) Zn(1) N(2) 179.1(2)
O(2) Zn(1) N(1) 123.4(4)
O(4) Zn(1) N(1) 121.4(4)
N(1) Zn(1) N(2) 91.1(3)
O(1) Zn(2) O(5) 92.3(2)
O(1) Zn(2) N(4) 174.6(2)
O(3) Zn(2) N(3) 117.7(3)
O(5) Zn(2) N(3) 123.6(2)
N(3) Zn(2) N(4) 90.5(3)
O(1) Zn(1) O(2) 103.0(2)
O(1) Zn(1) N(1) 86.9(2)
O(2) Zn(1) O(4) 113.1(2)
O(2) Zn(1) N(2) 92.4(2)
O(4) Zn(1) N(2) 90.1(3)
O(1) Zn(2) O(3) 101.7(2)
O(1) Zn(2) N(3) 89.9(2)
O(1) Zn(2) N(5) 91.8(2)
O(3) Zn(2) N(3) 164.3(2)
O(3) Zn(2) N(5) 90.9(2)
O(5) Zn(2) N(4) 84.1(2)
N(3) Zn(2) N(4) 77.4(2)
N(4) Zn(2) N(5) 96.7(2)
O(2) Zn(1) O(4) 93.0(2)
O(1) Zn(1) N(2) 161.6(2)
O(2) Zn(1) N(1) 103.8(2)
O(4) Zn(1) N(1) 142.1(2)
N(1) Zn(1) N(2) 79.6(3)
O(1) Zn(2) O(5) 84.9(2)
O(1) Zn(2) N(4) 162.8(2)
O(3) Zn(2) O(5) 99.5(2)
O(3) Zn(2) N(4) 93.1(2)
O(5) Zn(2) N(3) 92.0(2)
O(5) Zn(2) N(5) 169.6(2)
N(3) Zn(2) N(5) 78.1(2)
is given in Fig. 3, together with the atom numbering scheme.
The selected bond distances and bond angles are summarized
in Table 4.
The two Zn ions are bridged by the phenolic oxygen and two
acetate groups in the syn-syn mode. The Zn1–Zn2 interatomic
separation is 3.29(1) Å. The geometry about Zn1 bound to the
bidentate arm can be regarded as a distorted square-pyramid (τ
= 0.325) with the phenolic oxygen O1, the nitrogens N1 and
N2 of the bidentate arm and one acetate oxygen O4 on the
equatorial base and another acetate oxygen (O2) at the apex.
The Zn1-to-donor bond distances range from 1.976(6) to
2.177(7) Å. The Zn2 bound to the tridentate arm has a six-co-
ordinate geometry with larger Zn2-to-donor distances ranging
from 2.019(5) to 2.215(6) Å. One of the pyridyl nitrogens (N4)
is situated trans to the phenolic oxygen, and the other pyridyl
nitrogen (N5) is cis to the phenolic oxygen.
The complex has a µ-acetato-µ-phenolato-dizinc(II) dinu-
clear core in a Zn1–Zn2 interatomic separation of 3.524(1) Å.
The Zn1 bound to the bidentate arm has a square-pyramidal ge-
ometry with O1, N1 and N2 of (L4)– and O2 of the bridging
acetate group on the base and an isothiocyanate nitrogen at the
apex. The discrimination parameter (τ) is 0.045. The Zn1-to-
donor bond distances range from 1.998(5) to 2.177(6) Å. The
Zn2 bound to the tridentate arm has a six-coordinate geometry
together with O3 of the bridging acetate group and a thiocya-
nate nitrogen. The Zn2-to-donor bond distances range from
2.048(7) to 2.231(6) Å. One of the pyridyl nitrogens (N5) is
situated trans to the bridging phenolic oxygen, and the other
pyridyl nitrogen (N4) is situated cis to the phenolic oxygen.
The terminal thiocyanate group on Zn1 and that on Zn2 are sit-
[Zn2(L4)(AcO)(NCS)2]•(2-PrOH) (8′). An ORTEP view
for 8′ is given in Fig. 4, together with the atom numbering
scheme. The selected bond distances and bond angles are sum-
marized in Table 5.

K. Abe et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
91
Fig. 4. An ORTEP view of 8ꢀ with the atom numbering
scheme.
Table 5. Selected Bond Distances (Å) and Angles (deg)
for [Zn2(L4)(AcO)(NCS)2]•2-PrOH (8ꢁ)
Zn(1) O(1)
Zn(1) N(1)
Zn(1) N(6)
Zn(2) O(3)
Zn(2) N(4)
Zn(2) N(7)
2.016(5) Zn(1) O(2)
2.087(6) Zn(1) N(2)
2.011(7) Zn(2) O(1)
2.108(5) Zn(2) N(3)
2.168(6) Zn(2) N(5)
2.048(7)
1.998(5)
2.177(6)
2.107(5)
2.231(6)
2.213(6)
O(1) Zn(1) O(2) 93.1(2)
O(1) Zn(1) N(2) 151.3(2)
O(2) Zn(1) N(1) 154.0(2)
O(2) Zn(1) N(6) 103.8(3)
N(1) Zn(1) N(6) 101.5(3)
O(1) Zn(2) O(3) 86.7(2)
O(1) Zn(2) N(4) 88.7(2)
O(1) Zn(2) N(7) 104.2(2)
O(3) Zn(2) N(4) 171.6(2)
O(3) Zn(2) N(7) 94.9(2)
N(3) Zn(2) N(5) 75.0(5)
N(4) Zn(2) N(5) 96.6(2)
N(5) Zn(2) N(7) 95.3(3)
O(1) Zn(1) N(1) 84.7(2)
O(1) Zn(1) N(6) 108.7(2)
O(2) Zn(1) N(2) 90.6(2)
N(1) Zn(1) N(2) 79.8(3)
N(2) Zn(1) N(6) 97.9(3)
O(1) Zn(2) N(3) 86.9(2)
O(1) Zn(2) N(5) 159.6(2)
O(3) Zn(2) N(3) 94.8(2)
O(3) Zn(2) N(5) 85.4(2)
N(3) Zn(2) N(4) 78.0(2)
N(3) Zn(2) N(7) 165.7(2)
N(4) Zn(2) N(7) 93.0(3)
Fig. 5. An ORTEP view of 9ꢀ with the atom numbering
scheme.
coordination of a terminal thiocyanate nitrogen N8. The N8 is
situated trans to the bridging phenolic oxygen, and the two py-
ridiyl nitrogens are situated cis to the phenolic oxygen.
In molecule B, the two Zn ions are singly bridged by the en-
dogenous phenolic oxygen in a Zn–Zn intermetallic separation
of 3.543(5) Å. The Zn3 bound to the bidentate arm has a five-
coordinate environment together with two terminal thiocyanate
nitrogens. The geometry about the metal is regarded as a
square-pyramid with O2, N9 and N10 of (L4)– and a thiocyan-
ate nitrogen N14 on the base and another thiocyanate nitrogen
N15 at the apex. The discrimination parameter (t) is 0.068.
The Zn4 bound to the tridentate arm has a distorted five-coordi-
nate environment with further coordination of a thiocyanate ni-
trogen N16. The geometry about the metal is regarded as a
trigonal-bipyramid, with the articular nitrogen N12 and a thio-
cyanate nitrogen N16 at the axial sites and with the phenolic
oxygen O2 and the pyridyl nitrogens N11 and N13 on the trig-
onal base.
uated trans to each other with respect to the mean molecular
plane formed by Zn1, O1, Zn2 and the acetate bridge.
[Zn2(L4)(NCS)3]•3CHCl3 (9′). ORTEP views for 9′ are
given in Fig. 5, together with the atom numbering scheme. The
selected bond distances and bond angles are summarized in Ta-
ble 6.
There are two crystallographically-independent molecules
(A and B) in the crystal. In molecule A, the two Zn ions are
doubly bridged by the endogenous phenolic oxygen and an ex-
ogenous thiocyanate nitrogen, in the Zn–Zn separation of
3.245(9) Å. The Zn1 bound to the bidentate arm has a square-
pyramidal geometry with O1, N1 and N2 of (L4)– and the
bridging thiocyanate nitrogen N6 on the base and a terminal
thiocyanate nitrogen N7 at the axial site. The Zn2 bound to the
tridentate arm has a six-coordinate environment with further
Solution Structures. All the diacetato complexes (1, 3, 5
and 7) are stable in DMF, judged from the low dependence of
their conductances and absorption spectra upon complex con-

92
Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Dinuclear Zn Complexes of End-Off Type Ligands
Table 6. Selected Bond Distances (Å) and Angles (deg)
for [Zn2(L4)(NCS)3]•3CHCl3 (9ꢁ)
Zn(1) O(1)
Zn(1) N(2)
Zn(1) N(7)
Zn(2) N(3)
Zn(2) N(5)
Zn(2) N(8)
Zn(3) N(9)
Zn(3) N(14)
Zn(4) O(2)
Zn(4) N(12)
Zn(4) N(16)
2.052(5) Zn(1) N(1)
2.253(8) Zn(1) N(6)
1.994(8) Zn(2) O(1)
2.196(6) Zn(2) N(4)
2.136(7) Zn(2) N(6)
2.077(8) Zn(3) O(2)
2.111(7) Zn(3) N(10)
1.977(8) Zn(3) N(15)
1.982(5) Zn(4) N(11)
2.230(7) Zn(4) N(13)
2.004(9)
2.019(8)
2.116(7)
2.185(5)
2.127(7)
2.182(7)
2.084(5)
2.211(6)
1.999(7)
2.127(7)
2.094(7)
O(1) Zn(1) N(1)
O(1) Zn(1) N(6)
N(1) Zn(1) N(2)
87.9(3) O(1) Zn(1) N(2) 165.8(3)
83.3(2) O(1) Zn(1) N(7) 98.7(3)
82.5(3) N(1) Zn(1) N(6) 128.9(3)
94.7(3)
95.2(3) N(6) Zn(1) N(7) 109.2(3)
N(1) Zn(1) N(7) 121.9(3) N(2) Zn(1) N(6)
N(2) Zn(1) N(7)
O(1) Zn(2) N(3)
O(1) Zn(2) N(5)
87.9(2) O(1) Zn(2) N(4)
93.6(2) O(1) Zn(2) N(6)
86.3(2)
78.7(2)
78.8(3)
O(1) Zn(2) N(8) 172.9(2) N(3) Zn(2) N(4)
N(3) Zn(2) N(5)
N(3) Zn(2) N(8)
77.6(3) N(3) Zn(2) N(6) 165.6(2)
96.7(3) N(4) Zn(2) N(5) 156.3(3)
N(4) Zn(2) N(6) 105.5(3) N(4) Zn(2) N(8)
89.3(3)
92.6(3)
81.9(2)
N(5) Zn(2) N(6)
N(6) Zn(2) N(8)
97.7(3) N(5) Zn(2) N(8)
97.2(3) O(2) Zn(3) N(9)
O(2) Zn(3) N(10) 151.3(2) O(2) Zn(3) N(14) 94.8(3)
O(2) Zn(3) N(15) 106.0(2) N(9) Zn(3) N(10) 79.5(3)
N(9) Zn(3) N(14) 155.4(3) N(9) Zn(3) N(15) 99.2(3)
N(10) Zn(3) N(14) 93.2(3) N(10) Zn(3) N(15) 98.4(3)
N(14) Zn(3) N(15) 105.1(3) O(2) Zn(4) N(11) 121.9(3)
O(2) Zn(4) N(12) 90.3(2) O(2) Zn(4) N(13) 114.7(2)
O(2) Zn(4) N(16) 98.4(3) N(11) Zn(4) N(12) 77.0(3)
N(11) Zn(4) N(13) 117.9(3) N(11) Zn(4) N(16) 95.2(3)
N(12) Zn(4) N(13) 79.2(3) N(12) Zn(4) N(16) 170.5(3)
N(13) Zn(4) N(16) 100.2(4)
Fig. 6. 1H NMR spectra of (a) [Zn2(L1)(AcO)2]PF6 (1)
and (b) [Zn2(L4)(AcO)2]ClO4 (7) in d7-DMF.
though the phenol ring protons (6.87 and 8.06 ppm) and the
azomethine proton (8.38 ppm) are clearly resolved. The ethyl-
ene protons of the bidentate chain at 4.4–3.6 ppm are also
broadened. Such NMR spectral features suggest a slow molec-
ular inversion with respect to the mean molecular plane (see
Chart 2).
As discussed above, the tri(thiocyanato) complexes (2, 4, 6
and 9) act as 1:1 electrolytes in DMF, indicating that one NCS-
group is dissociated:
centration. Furthermore, the FAB mass spectra of the diacetato
complexes clearly showed a parent ion peak corresponding to
{Zn2(L)(AcO)2}+ (see Experimental Section). 1H NMR (400
MHz) spectra for 1 and 7 were measured in d7-DMF to exam-
ine their solution structures (Fig. 6). The NMR spectrum of 1
shows three singlets at 2.01, 2.24 and 2.49 ppm in a relative in-
tensity of 2:1:4, which are assigned to the acetate methyl, the
ring methyl and the N-methyl protons, respectively. The ring
proton and the azomethine proton appear as singlets at 7,51 and
8.67 ppm, respectively. The ethylene protons at 2.85 and 3.91
ppm show an A2B2 pattern. The results clearly indicate that 1
retains the di-µ-acetato-µ-phenolato-dizinc(II) core (Fig. 1), if
one assumes D2 symmetry in solution.
[Zn2(L)(NCS)3] ꢀ [Zn2(L)(NCS)2]+ + NCS−.
This is supported by a concentration-dependence of the elec-
*
tronic spectra. In general, the π-π transition band shifted to a
shorter wavelength with a concomitant increase in intensity
Based on X-ray crystallography, 7 is asymmetric with re-
spect to the two acetate bridges and the coordination modes of
the two pyridyl residues (Fig. 3). Furthermore, the two methyl
groups on the terminal amino nitrogens are not equivalent in
1
the crystal. In its H NMR spectrum (Fig. 6(b)), the methyl
groups on the terminal amino nitrogens appear as a singlet at
2.65 ppm. Notably, the acetate methyl groups are not resolved.
The pyridyl protons are also unresolved owing to broadening,
Chart 2. Molecular inversion of 7 in solution.

K. Abe et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
93
when the complex concentration was lowered. For example, 2
shows the band maximum at 402 nm (ε: 9100 M–1 cm–1) at the
concentration of 1 × 10 –3 M but at 394 nm (ε: 10500 M–1 cm–1)
at the concentration of 1 × 10–4 M.
1
The H NMR spectrum for 2 also supports the dissociation
of the complex in DMF. The spectrum at ca. 1 × 10–2 M has
two pairs of signals due to the ring and the azomethine protons,
a pair of sharp singlets at 7.48 and 7.31 ppm and another pair of
broad bands at 8.76 and 8.50 ppm. In addition to these, some
weaker singlets exist in the region of 8.5–7.2 ppm. The meth-
ylene protons next to the imine nitrogen appear as a sharp trip-
let at 3.74 ppm and a broad band at 3.92 ppm. The N-methyl
protons appear at 2.45 and 2.40 ppm as dominant peaks. The
result indicates that 2 exists in two or more different structures
in solution. The 1H NMR spectrum of 9 is much more compli-
cated. It has two singlets due to the methyl group on the phe-
nolic ring (2.05 and 2.10 ppm in an approximate ratio of 1:4)
and three or more signals due to the N-methyl group. Futher-
more, it showed many signals in the region 9.0–6.6 ppm. The
NMR spectral feature of 9 means that the molecules A and B
(see Fig. 5) and their dissociated species exist in solution.
Phosphatase-LikeActivity. From the above discussion,
we conclude that the diacetato complexes (1, 3, 5 and 7) retain
the di-µ-acetato-µ-phenolato-dizinc(II) core in DMF, whereas
the tri(thiocyanato) complexes (2, 4, 6 and 9) are dissociated
into [Zn2(L)(NCS)2]+ of unknown structure in DMF. For such
reasons, our studies on phosphatase-like activity are restricted
to the diacetato complexes 1, 3, 5 and 7. We have confirmed
that the 1H-NMR spectra of 1 and 7 in D2O–d6-DMF (0.3:99.7)
are essentially the same as those in d6-DMF. This fact means
the diacetato complexes to be stable in an aqueous DMF solu-
tion for the study of phosphatase-like activity discussed below.
In Fig. 7(a) are shown the difference-spectral changes with
time for a solution of 1 and TNP ([1] = 5 × 10–4 M and [TNP] =
5 × 10–4 M) in aqueous DMF (H2O:DMF = 0.3:99.7). The
band at 270 nm due to TNP diminished with time, with a con-
comitant increase at 315 nm (due to BNP) and 420 nm (p-nitro-
phenolate). This result clearly demonstrates the hydrolysis of
TNP by 1. Similarly, 3 and 5 hydrolyzed TNP (Fig. 7(b), (c)).
In these cases, the resulting p-nitrophenol predominantly exists
in the protonated form: p-nitrophenol itself has an absorption at
330 nm. In contrast, 7 showed little hydrolytic activity toward
TNP (Fig. 7(d)).
Fig. 7. Difference spectral changes with time for a solu-
tion of a complex and TNP in aqueous DMF at 25 C
(H2O : DMF = 0.3 : 99.7 in volume, [complex] =
5 × 10−4 M and [TNP] = 5 × 10−4 M): (a) for complex
1, (b) for 3, (c) for 5, and (d) for 7.
◦
In order to examine the hydrolytic reaction in more detail, a
solution of 1 and TNP ([1] : [TNP] = 1 : 10) in aqueous DMF
(H2O : DMF = 0.3 : 99.7) was subjected to 31P-NMR spectro-
scopic measurements (Fig. 8(a)). The solution showed two sig-
nals at –9.8 and –16.0 ppm after 12 hours. The signal at –16.0
ppm is ascribed to intact TNP and the signal at –9.8 ppm to a
BNP species arising from the hydrolysis of TNP. The intensity
ratio of the signal at –9.8 ppm to the signal at –16.0 ppm was
approximately 2 : 3, indicating that four molecules of TNP
were hydrolyzed by one complex after 12 hours. Similarly, 3
and 5 showed a hydrolytic activity toward TNP (Fig. 8(b) and
(c)). Based on the 31P spectra, 3.3 and 2.8 molecules of TNP
were hydrolyzed by 3 and 5, respectively, after 12 hours. For
the solution of TNP and 7, no appreciable 31P resonance due to
BNP was recognized after 12 hours.
In our recent study using a dinuclear ZnII(OH)PbII com-
plex,23 the hydrolysis of TNP into BNP proceeds by the con-
certed binding of TNP on the Pb center and the nucleophilic at-
tack of the hydroxide at adjacent Zn center. This reaction was
essentially stoichiometric owing to the formation of a stable
bnp intermediate. Such a stable bnp intermediate can be a
cause for the slow hydrolysis by 1, 3 and 5. As a promising
candidate for the intermediate, [Zn2(L)(bnp)2]ClO4 (L = L1
(10), L2 (11), L3 (12)) were derived; a corresponding bnp com-
plex of (L4)– could not be obtained in spite of our many efforts.
Complexes 10–12 may have a di-µ-bnp-µ-phenolato-dizinc(II)

94
Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
Dinuclear Zn Complexes of End-Off Type Ligands
core similar to the di-µ-acetato-µ-phenolato-dizinc(II) core of
1, 3 and 5. In contrast to our expectation, the di-bnp complex-
es, 10–12, were readily dissociated in DMF:
[Zn2(L)(bnp)2]+ ꢀ [Zn2(L)(bnp)]2+ + BNP−
ꢀ [Zn2(L)]3+ + 2BNP−.
This was evidenced by their molar conductances (85–86 S
cm2 mol–1 at 1 × 10–3 M in DMF) that are large for 1:1
electrolytes18 and increased to 120–130 S cm2 mol–1 at lowered
concentration of 1 × 10–4 M. Electronic spectra of the com-
plexes were also dependent upon the complex concentration.
*
In general, the π-π band of the azomethine linkage shifted to a
longer wavelength with a concomitant increase in intensity
when the complex concentration was lowered. The 31P NMR
spectra of 10, 11 and 12 showed a resonance at –8.3, –9.0 and
–8.7 ppm, respectively. The different 31P resonances for 10–12
may reflect the degree in the dissociation of the complexes. It
must be mentioned that bis(p-nitrophenyl) hydrogenphosphate
(HBNP) and bis(p-nitrophenyl) sodium phosphate (NaBNP)
show the 31P resonance at –11.2 and –7.8 ppm, respectively. In
the hydrolytic reaction of TNP by 1, 5 and 7, the resulting BNP
is moderately protonated, judged from the 31P resonance ap-
pearing at –9.8––9.5 ppm (see Fig. 8).
Thus, 1, 3 and 5 have a C2 symmetric di-µ-acetato-µ-pheno-
lato-dizinc(II) core consisting of two trigonal-bipyramidal Zn
ions and show a hydrolytic activity toward TNP. Complex 7
has no such activity because one of the Zn centers is coordina-
tively saturated. A likely mechanism of the TNP hydrolysis by
1, 3 and 5 is shown in Chart 3. The addition of water or TNP to
one Zn center of I affords [Zn(L)(AcO)2(H2O)]+ (IIa) or
[Zn(L)(AcO)2(TNP)]+ (IIb). We have shown that [Mn2(L)-
(AcO)2(NCS)] (L = L1 or L2), analogous to IIa and IIb, has a
Cs symmetric core with the cis arrangement of the thiocyanate-
N group on one Mn and the sixth vacant site of the adjacent Mn
Fig. 8. 31P NMR spectra for a solution of TNP and a
complex ([TNP]/[complex] = 10/1): (a) for complex
1, (b) for 3, (c) for 5, and (d) for 7.
Chart 3. Proposed mechanism of TNP hydrolysis by 1, 3 and 5 (R = p-nitrophenyl).

K. Abe et al.
Bull. Chem. Soc. Jpn., 74, No. 1 (2001)
95
with respect to the mean molecular plane.8–10 Such a Cs sym-
metric core results from the steric requirement of the ligands
when one metal center adopts a six-coordinate geometry. The
further addition of TNP to IIa or the addition of water to IIb
leads to the intermediate [Zn(L)(AcO)2(H2O)(TNP)]+ (III),
that allows a nucleophilic attack of the water (or hydroxide) to
the phosphorus nucleus of the adjacent TNP. The low hydro-
lytic activity of 1, 3 and 5 may relate to their D2 symmetric core
(I) that is distorted with difficulty into the Cs symmetric core
(II).
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This work was supported by a Grant-in-Aid for Scientific
Research (No. 09440231) from the Ministry of Education, Sci-
ence, Sports and Culture. Thanks are also due to the Daiwa
Anglo-Japanese Foundation and the British Council for the
support.
9
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K.Takahashi, andH. O kawa, Inorg. Chem., 37, 989 (1998).
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