Synthesis, characterization and crystal structure of manganese (IV) complex derived from salicylic acid

Article abstract of DOI:10.1016/j.ica.2004.11.044

The binuclear manganese (IV) [Mn₂(Hsal)₄(OH)₄] (H₂sal = salicylic acid) complex has been obtained from a complex reaction mixture in methanol consisting of Mn(II)(OAc)₂ · 4H₂O, GS ( a reagent obtained by refluxing glycine and salicylaldehyde in 1:1 molar ratio in methanol), monosodium salicylate and pyridine. The compound contains a distorted octahedral MnO₆ coordination unit of potential importance to high oxidation state manganese bimolecules.

Full text of DOI:10.1016/j.ica.2004.11.044

Inorganica Chimica Acta 359 (2006) 3105–3110
www.elsevier.com/locate/ica
Synthesis, characterization and crystal structure of manganese
(IV) complex derived from salicylic acid
a,
b
a
b
Ram A. Lal *, Samhita Bhaumik , Aka Lemtur , Mahesh K. Singh ,
a
a
b
Debjani Basumatari , Sanjesh Choudhury , Arjun De , Arvind Kumar
c
a
Department of Chemistry, North-Eastern Hill University, Shillong 793022, Meghalaya, India
b
Department of Chemistry, Tripura University, Suryamaninagar 799130, Tripura, India
c
Department of Chemistry, Rice University, 1600 Main Street, MS-60, Houston, TX 77005, USA
Received 20 May 2004; received in revised form 19 November 2004; accepted 28 November 2004
Available online 24 April 2006
Abstract
The binuclear manganese (IV) [Mn2(Hsal)4(OH)4] (H2sal = salicylic acid ) complex has been obtained from a complex reaction
mixture in methanol consisting of Mn(II)(OAc)2 Æ 4H2O, GS ( a reagent obtained by refluxing glycine and salicylaldehyde in 1:1
molar ratio in methanol), monosodium salicylate and pyridine. The compound contains a distorted octahedral MnO6 coordination
unit of potential importance to high oxidation state manganese bimolecules.
ꢀ 2006 Published by Elsevier B.V.
Keywords: Maganese (IV) complex; Salicylic acid; Crystal structure; Spectroscopic data
1. Introduction
the manganese cofactor of photosystem II has been pre-
pared that makes use of manganese catechol complexes
as template for the preparation of O–O bond.
It is essential that four manganese ions are necessary
for high rates of oxygen evolution [10]. It has been
shown by EXAFS studies and further by XANES stud-
ies that these four ions are arranged in two [11] or per-
haps three [12] in equivalent binuclear environments
with two distinct Mnꢀ ꢀ ꢀMn separations. Manganese
atoms in one set are separated by a short distance of
The chemistry of manganese is the subject of much
current interest owing to its involvement in a number
of biological systems, e.g., superoxide dismutase [1]
and an azide sensitive catalase [2]. The role of manga-
nese in the oxygen evolving complex (OEC) of photosys-
tem II (PS II) is of great importance [3–8]. Manganese
appears to serve as an electron transfer agent in the
charge accumulation center of the water oxidizing sys-
tem in reaction with PS II. It is proposed that in PS
II, manganese functions as template to bring the oxygen
atoms of two water molecules into close proximity to
form an O–O bond [9]. Quinones are not effective li-
gands for transition metal ions, although they are pres-
ent in significant quantities in chloroplasts. A model for
˚
ca. 2.7 A bridged by a l2-oxo system, while in the other
˚
set by a longer distance of ca. 3.3 A which is most prob-
ably bridged by a carboxylate group.
Thus, synthesis and characterization of manganese-
hydroxy aromatic aldehyde and ketone complexes con-
stitute an active area of research that promise to yield
complexes that may act as effective models for the man-
ganese cofactor of photosystem-II and for manganese
superoxide dismutase. One ligand that finds much utility
in this regard is salicylic acid (2-hydroxy benzoic acid,
*
Corresponding author. Tel.: +91 03642722616; fax: +91
03642551634.
E-mail address: ramashraylal@rediffmail.com (R.A. Lal).
0020-1693/$ - see front matter ꢀ 2006 Published by Elsevier B.V.
doi:10.1016/j.ica.2004.11.044

3106
R.A. Lal et al. / Inorganica Chimica Acta 359 (2006) 3105–3110
Table 2
Atomic coordinates (·104) and equivalent isotropic displacement
parameters (A · 10 ) for the compound
H2sal) whose phenolic and carboxylic acid functions are
being used as convenient substitutes for the amino acid
site groups of tyrosine and aspartic acid/glutamic acid,
respectively [13].
2
3
˚
x
y
z
Ueq
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
Mn(1)
5926(6)
6677(7)
6808(9)
7520(11)
8166(10)
8061(9)
7312(8)
4980(6)
5343(6)
5671(7)
6072(8)
6106(9)
5766(8)
5383(7)
5802(5)
5442(5)
4802(5)
5063(5)
7909(5)
2286(5)
5101(5)
7233(7)
5071(1)
2979(4)
2529(4)
1416(4)
975(6)
7398(4)
8222(4)
8343(4)
9102(5)
9762(5)
9688(4)
8914(4)
4196(4)
3383(3)
2670(4)
1926(4)
1883(4)
2582(4)
3316(4)
7300(3)
6744(3)
4847(2)
3996(3)
5754(3)
5974(3)
5756(3)
8866(3)
5875(1)
46(1)
47(1)
64(2)
82(2)
83(2)
73(2)
57(2)
45(1)
40(1)
49(1)
60(2)
66(2)
57(2)
46(1)
60(1)
57(1)
51(1)
56(1)
55(1)
60(1)
57(1)
78(1)
42(1)
2. Results and discussion
1640(7)
2748(6)
3206(5)
3295(4)
2757(3)
3359(4)
2862(5)
1739(5)
1130(4)
1615(4)
4014(3)
2407(3)
2724(2)
976(2)
The crystal data showed that the general formula of
the compound obtained is [Mn2(Hsal)4(OH)4]. The com-
pound is assumed to result from redox reaction in the
presence of the reagent GS and pyridine.
The X-ray crystallographic data are listed in Table 1.
Fractional coordinates are listed in Table 2 and selected
bond distances and angles in Table 3.
The compound crystallizes in the monoclinic space
group P21/a. The ORTEP diagram of compound is gi-
ven in Fig. 1. There are two dimeric units in the unit cell
(see Table 4, Fig. 2).
The complex is composed of two symmetry related
pseudo six-coordinate Mn(IV) centers. Bidentate chelat-
ing and bridging Hsalꢁ (HOC6H4COOꢁ) ligands asym-
metrically coordinate each manganese.
4038(3)
4125(3)
5695(3)
4296(4)
3971(1)
Ueq is defined as one third of the trace of the orthogonalized Uij tensor.
Table 1
Crystal data for [Mn2(Hsal)4(OH)4]
The dimer consists of two Mn(IV) atoms which are
bridged by carboxylato oxygen atoms (O3, O4, O3a
and O4a) from salicylate group in syn–syn fashion of
bidentate salicylate anion. Each Mn(IV) is further
chelated by two oxygen atoms of carboxylato oxygen
atoms of another bidentate salicylate anion. The six
coordination around the metal center is completed
by hydroxyl (OHꢁ) group that does not take part in
coordination. The deposition of the ligands is such
as to produce a dimer of C2 symmetry. The Mn2O4
bridging unit is almost planar. The Mn(IV) ions are
in a highly distorted octahedral environment with
elongation of the three Mn–O bonds in the equatorial
Formula
M
C28H24Mn2O16
726.35
Crystal system
Space group
Unit cell dimensions
monoclinic
P21/a
˚
a (A)
7.631(5)
12.320(5)
15.623(5)
96.560(5)
1459.2(12)
2
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z
Dcalc (mg/m3)
F(000)
1.653
740
Crystal size (mm)
˚
0.3 · 0.2 · 0.2
0.71069
2776
k(Mo Ka) (A)
˚
direction, i.e., Mn–O(1) = 2.234(4) A, Mn–O(2) =
Number of collected reflections
Number of unique reflections [Rint
Data/restraints/parameters
Absorption correction
˚
2.356(4) A and Mn–O(3) = 2.215(3) A except fourth
˚
]
2562 [0.0463]
2562/4/225
w-scan
˚
Mn–O(4) = 2.133(3) A which is shorter than the axial
˚
Mn–O(5) = 2.197(4) and Mn–O(6) = 2.157(4) A.
Although d3 system is not subjected to Jahn–Teller
distortion, even then the structure is highly distorted.
This is most probably due to steric crowding around
manganese centers due to bridged and chelated salicy-
lato ligands.
Maximum and minimum
transmission
Refinement method
0.9921 and 0.5477
full-matrix least-squares
on F2
2.11–25.00
h Range for data collection (ꢁ)
Limiting indices
0 6 h 6 9, 0 6 k 6 14,
ꢁ18 6 l 6 18
Although angles at the metal subtended by trans-
ligand atoms and a pair of angles subtended by cisoid
ligands are reasonably close to the theoretical value
for an octahedron (180ꢁ and 90ꢁ, respectively), yet pair
of angles subtended by cisoid ligands differ widely from
the theoretical value of 90ꢁ. Thus, the widely differing ci-
soid bond angles O1–Mn–O2 and O3–Mn–O4 are 56.27ꢁ
Completeness to h = 5.00
Goodness-of-fit on F2
Final R indices [I > 2r (I)]
R indices (all data)
99.6%
0.947
R1 = 0.0573, wR2 = 0.1404
R1 = 0.1079, wR2 = 0.1592
0.0005(13)
Extinction coefficient
Largest difference in peak
0.508 and ꢁ0.569
ꢁ3
˚
and hole (e A
)

R.A. Lal et al. / Inorganica Chimica Acta 359 (2006) 3105–3110
3107
Table 3
and 128.95ꢁ, while the reasonably close cisoid bond an-
gles O2–Mn–O3 and O1–Mn–O4 are 81.14ꢁ and 93.39ꢁ.
The larger deviations in cisoid bond angles are attrib-
uted to the asymmetry in the bridging and chelating re-
gion as clearly visible in Fig. 1.
For the chelating salicylato group, the Mn–O bond
length is longer than those due to bridging salicylate
group, arising from the steric crowding imposed by the
neighboring bridging salicylate group. Thus, in the com-
pound, the carboxylate functions of salicylate group
(Hsalꢁ) form bond by means of bridging and chelating
mode. The compound is quite stable in solid state due
to the H-bonding between the phenolic-H atoms and
chelating oxygen atom, coordinated hydroxyl-H atom
and chelating oxygen atom.
A neutral manganese (IV) salicylate complex has been
well characterized by Christou and coworkers [14], but to
the best of our knowledge the present compound is the
only dinuclear manganese (IV) salicylate complex con-
taining bridging as well as chelating carboxylate functions
of salicylato group. The structure may have some impor-
tant implication in Lippardꢀs ꢁCarboxylate Shiftꢀ phenom-
enon that relates to the structure, function and kinetics of
carboxylate containing metalloproteins [15].
˚
Selected interatomic distances (A) and bond angles (ꢁ) for the
compound
Manganese environment
O(1)–Mn(1)
O(3)–Mn(1)
O(6)–Mn(1)
2.234(4)
2.215(3)
2.157(4)
O(2)–Mn(1)
O(5)–Mn(1)
O(7)–Mn(1)
2.356(4)
2.197(4)
2.133(3)
C(1)–O(1)–Mn(1)
C(8)–O(3)–Mn(1)
Mn(1)–O(5)–H(50)
C(8)#1–O(7)–Mn(1)
O(7)–Mn(1)–O(6)
O(6)–Mn(1)–O(5)
O(6)–Mn(1)–O(3)
O(7)–Mn(1)–O(1)
O(5)–Mn(1)–O(1)
O(7)–Mn(1)–O(2)
O(5)–Mn(1)–O(2)
O(1)–Mn(1)–O(2)
95.8(3)
100.9(3)
122(3)
C(1)–O(2)–Mn(1)
C(14)–O(4)–H(40)
Mn(1)–O(6)–H(60)
C(7)–O(8)–H(80)
O(7)–Mn(1)–O(5)
O(7)–Mn(1)–O(3)
O(5)–Mn(1)–O(3)
O(6)–Mn(1)–O(1)
O(3)–Mn(1)–O(1)
O(6)–Mn(1)–O(2)
O(3)–Mn(1)–O(2)
90.8(3)
110(2)
124(3)
93(4)
170.5(4)
86.52(14)
172.75(13)
95.90(15)
93.39(14)
87.02(15)
149.66(16)
91.46(13)
56.27(13)
6.23(13)
128.95(15)
88.56(14)
93.55(16)
137.00(13)
94.87(13)
81.14(15)
Salicylate chelate environment
C(1)–O(2)
C(7)–O(8)
O(2)–C(1)–O(1)
1.262(6)
1.345(7)
116.6(5)
C(1)–O(1)
C(1)–C(2)
1.286(6)
1.458(8)
Salicylate bridge environment
C(8)–O(7)#1
C(8)–C(9)
O(7)#1–C(8)–O(3)
1.248(5)
1.486(7)
119.9(5)
C(8)–O(3)
C(14)–O(4)
1.256(6)
1.367(6)
The compound is different from that of Christou and
coworkersꢀ [14] monomeric MnIV compound [Mn(sal)2
(bipy)]. The complex has no crystallographically im-
posed symmetry but does approach C2 symmetry. Two
salicylato groups and one bipyridyl group, salicylato
ligand functions as a chelating bidentate ligand through
phenoxide and one-carboxylato oxygen atoms, coordi-
nate manganese atom. The phenoxide oxygen atoms
are cis and carboxylato oxygen atoms are trans about
the manganese.
Symmetry transformations used to generate equivalent atoms: #1
ꢁx + 1,ꢁy + 1,ꢁz + 1.
2.1. Magnetic moment
The room temperature magnetic moment of a pow-
dered sample of the compound (lB = 6.45 BM at
25 ꢁC) is slightly lower than the spin-only magnetic mo-
ment expected for a dimeric d3 ion (ls = 6.90 BM). This
indicates either no interaction or a very weak interaction
between metal ions in the solid state of the compound.
2.2. EPR spectra
Fig. 1. ORTEP diagram of the compound.
The X-band EPR spectra of the complex were exam-
ined in polycrystalline phase (300 and 77 K) as well as in
DMF glass (77 K). In the polycrystalline phase, two
broad resonances are observed: a strong one near g @ 2
and a weak one near g @ 4. In the magnetically dilute
glassy state, the 55Mn hyperfine structure is well resolved
for the resonance near g @ 2.
Table 4
˚
Hydrogen bonds for the compound (A) and (ꢁ)
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA) d(Dꢀ ꢀ ꢀA) \(DHA)
O(5)–H(50)ꢀ ꢀ ꢀO(4)#2 0.9500(12) 1.899(7)
2.847(5)
2.550(5)
175(5)
145(3)
166(5)
169(7)
O(4)–H(40)ꢀ ꢀ ꢀO(3)
0.9500(11) 1.72(2)
O(6)–H(60)ꢀ ꢀ ꢀO(4)#3 0.9499(11) 1.973(13) 2.904(5)
O(8)–H(80)ꢀ ꢀ ꢀO(1)
0.9500(11) 1.646(14) 2.585(7)
Interestingly, 55Mn hyperfine coupling constant for
the g @ 2.0 signal is equal to 75G which is close to the
values observed for Mn (IV) complexes. Depending on
Symmetry transformations used to generate equivalent atoms: #1
ꢁx + 1, ꢁy + 1, ꢁz + 1 #2 ꢁx + 3/2, y + 1/2, ꢁz + 1 #3 ꢁx + 1/2,
y + 1/2, ꢁz + 1.

3108
R.A. Lal et al. / Inorganica Chimica Acta 359 (2006) 3105–3110
Fig. 2. ORTEP diagram of the unit cell.
the nature and extent of distortion of the ligand field
from Oh symmetry, the frozen-solution EPR spectra of
a 3d3 ion can assume different forms [16–18]. The form
observed here (strong g ꢂ 2 and weak g ꢂ 4 resonances)
is characteristic of small axial distortion: 2D ꢃ hm,
where D is the axial zero field splitting parameter and
hm is the microwave quantum (0.31 cmꢁ1 at X-band).
When D is small, rhombic splitting is necessarily very
small, since D/E P 3, where E is the rhombic splitting
parameter whereas the large distortion case 2D ꢄ hm
occurs in a number of complexes [19–21], the 2D ꢃ hm
situation for Mn(IV) has been documented in tris-
(dithiocarbamate) [22] and in tris(thiohydroxamates)
[18]. The spectral features observed in the present study
(strong g ꢂ 2 and weak g ꢂ 4 resonances ) are charac-
teristic of small axial distortion, 2d ꢃ hm. Interestingly,
the 55Mn hyperfine splitting constant for the g ꢂ 2 sig-
nal lies close to 78G for the known 2D ꢃ hm manganese
(IV) species.
as phenyl ring [23]. In the complex, the mas(COO) and
ms(COO) appear at 1600s and 1402s cmꢁ1, respectively.
2.4. Electronic spectra
The electronic spectrum of the compound in metha-
nol shows a weak band in the visible region with strong
absorbance in the ultraviolet region. Mn(IV) exhibits
two absorption bands due to d–d electronic transitions
4
4
(from the octahedral approximation A2g ! T2g and
4
4A2g ! T1g) [24]. The compound shows a weak absorp-
tion
band
at
)
k
max = 450 nm
(emax = 0.71 ·
102 l molꢁ1 cmꢁ1
and 530 nm (emax = 0.332 · 102
l molꢁ1 cmꢁ1). These transitions are of low intensity
4
4
and are attributed to arise due to A2g ! T2g and
4A2g ! T1g transitions, in excellent agreement with
4
those reported for tris(thiohydroxamato)manganese(IV)
[18] and the mononuclear tris(glucarate), tris(gluconato)
and tris(sorbitolato)manganese (IV) complexes [25,26].
2.3. Infrared spectra
3. Experimental
Infrared spectroscopy provides a means of distin-
guishing the mode of coordination of salicylato groups
to the MnIV center. The IR spectrum of the compound
has been interpreted by comparing the spectrum with
that of sodium salicylate (NaHsal). The compound
shows a split strong band in the region 3200–
2300 cmꢁ1. The band in this region is attributed to
m(OH) of uncoordinated phenolic-OH group and coor-
dinated hydroxyl group. The essential features of the
band in this region indicate the presence of hydrogen
bond involving phenolic-OH and coordinated OH
groups, with carboxyl oxygen atom of coordinated carb-
oxylato oxygen atoms.
3.1. Physical measurements
Infrared spectra were recorded on FT-IR Perkin–
Elmer 983 spectrophotometer in the range 4000–
450 cmꢁ1 in KBr discs. The electronic spectra were
recorded on a UV-2600 Double beam UV–Vis spectro-
photometer. Room temperature magnetic susceptibility
measurement was carried out on a vibrating sample
magnetometer. Experimental magnetic susceptibility
values have been corrected for diamagnetism by the pro-
cedures given by Figgis and Lewis [27] and Earnshaw
[28]. The EPR spectra of the compound in powdered
form and DMF solution at RT and LNT were recorded
at X-band frequency on a Variance E-112X/2 band
spectrometer, DPPH was used as an internal field mar-
ker. The molar conductance of the complex at 10ꢁ3 M
The band observed at 1381 cmꢁ1 in the free salicy-
late ion is attributed to ms(COO) vibration of carboxy-
lato function, while that at 1593 cmꢁ1 is attributed to
mas(COO) vibrations of carboxylato function as well

R.A. Lal et al. / Inorganica Chimica Acta 359 (2006) 3105–3110
3109
dilution in methanol solution was measured on a Direct
Reading conductivity meter-303 with a dip type conduc-
tivity cell at room temperature.
diffraction study were chosen and mounted on glass fi-
bers and transferred to an Enraf-Nonius XCAD4 dif-
fractometer equipped with a graphite-monochromated
˚
Mo Ka X-ray source (k = 0.71069 A). The unit cell
parameters were determined using the method of short
vectors followed by least-squares refinement of 25
well-centered reflections. Data were collected at 293 K
using x < 2h scan technique. Intensities of two standard
reflections monitored every 1 h showed 0% variation
during the data collection time. An empirical absorption
correction [29] based on w-scans was also applied for the
compound. All the calculations were performed using a
software package ꢁXCAD4 (WINGX)ꢀ adapted on a Mi-
cro VAX 3100 computer.
Space groups were assigned on the basis of systematic
absences and crystallographic E-statistics. Atomic scat-
tering factors for neutral atoms Mn, O, C and H were
taken from [30]. Anomalous dispersion was taken into
account. The structure was solved by using ꢁSIR92
4. Synthesis of [Mn2(Hsal)4(H2O)4]
All manipulations were carried out under aerobic
conditions. Mn(OAc)2 Æ 4H2O, glycine, salicylaldehyde,
salicylic acid, NaOH, pyridine and other solvents were
E-Merk grade reagents, which were employed in the
preparation of the complex as received. The reagent
GS was prepared by refluxing glycine and salicylalde-
hyde in 1:1 molar ratio in 90% ethanol (30 mL) as
follows:
Glycine (0.5 g, 6.67 mmol) in hot water (5 mL) was
added to salicylaldehyde (6.72 mmol) in hot ethanol
(20 mL). The resulting solution was refluxed for 1 h
and then cooled. The precipitate was filtered and washed
with ethanol. It was again dissolved in 90% ethanol –
soln1.
(
WINGX)ꢀ [31] and refined by using ꢁSHELXL-97 (Sheld-
rick, 1997)ꢀ [32]. The molecular graphics was solved by
using the direct methods program ꢁORTEP3ꢀ [33] included
in WINGX [34] version. Atomic coordinates were refined
using anisotropic thermal parameters for all non-hydro-
gen atoms. Hydrogen atoms are located on a difference
Fourier map.
Sodium salicylate was prepared by adding a solution
of salicylic acid (1.18 g, 8.55 mmol) in methanol (20 mL)
to a solution of NaOH (0.34 g, 8.5 mmol) in methanol –
soln2.
To
a
solution of Mn(OAc)2 Æ 4H2O (0.70 g,
2.86 mmol) in methanol (25 mL), the reagent GS
(soln1) was added drop wise accompanied by gentle
stirring for 45 min at 40 ꢁC. To the resulting solution,
monosodium salicylate (soln2) was added drop wise
with constant stirring and the reaction mixture was
stirred for another 45 min at 40 ꢁC. Then, pyridine
(1.5 mL, 18.6 mmol) was added to the reaction medium
dropwise with constant stirring and it was stirred for
45 min at 40 ꢁC, followed by concentration to ca.
10 mL. On keeping the resulting deep reddish brown
solution for 10 days at room temperature, the complex
formed as deep brown colored crystals in 75% yield.
The compound was recrystallized from methanol to
yield deep brown colored block shaped monoclinic
crystal. Yield: 80%. Anal. Calc. for [Mn2(Hsal)4(OH)4]:
Mn, 15.14; C, 46.26; H, 3.30. Found: Mn, 15.40; C,
47.73; H, 3.35%. It is soluble in EtOH, MeOH,
CH3CN, DMF, and DMSO and insoluble in diethyl
ether, benzene, chloroform, dichloromethane and other
common organic solvents.
5. Supplementary data
Tables of anisotropic displacement parameters, all
bond lengths and angles for the compound (5 pages);
listing of calculated and observed structure factors (7
pages) in CIF form.
Acknowledgements
The authors are thankful to the authorities of Tri-
pura University, Suryamaninagar 799130, Tripura, In-
dia and North-Eastern Hill University, Shillong
793022, Meghalaya, India for providing facilities for
carrying out this work. They thank the Head, Regio-
nal Sophisticated Instrumentation Centre, IIT, Ma-
dras, Chennai, India for Crystallographic and EPR
spectral studies and the Head, Department of Inor-
ganic Chemistry, Indian Association for Cultivation
of Science, Jadavpur, Kolkata 32 for magnetic suscep-
tibility data.
IR (KBr): m/cmꢁ1(OH) 3200–2300sbr band with split-
ting into several bands, mas(CO2) 1600s and ms(CO2)
1348s. kM (in MeOH) = 26.3 ohmꢁ1 cm2 molꢁ1. Elec-
tronic spectrum (CH3OH) [kmax
,
nm (e/MnIV,
l molꢁ1 cmꢁ1)]: 450 (0.71 · 102) and 530 (0.332 · 102).
References
4.1. X-ray crystallography
[1] M.L. Ludwig, K.A. Pattridge, W.C. Stalings, Manganese in
Metabolism and Enzyme Function, Academic Press, New York,
1986 (Chapter 21).
Suitable crystals of [Mn2(Hsal)4(OH)4] were obtained
as described above. Crystals for single crystal X-ray

3110
R.A. Lal et al. / Inorganica Chimica Acta 359 (2006) 3105–3110
[2] W.F. Beyer, I. Findovich, Ref. [1], Chapter 12, p. 193.
[3] Photosynthetic Water Oxidation: J. Nugeni (Ed.), Special Dedi-
cated Issue: Biochim. Biophys. Acta: Bioenergy, 1503 (2001) pp.
1–259.
[20] D.T. Richens, D.T. Sawyer, J. Am. Chem. Soc. 101 (1979) 3681.
[21] M.W. Lynch, D.N. Hendrickson, B.J. Fitzgerald, C.G. Pierpont,
J. Am. Chem. Soc. 106 (1984) 2041.
[22] K.L. Brown, R.M. Golding, P.C. Healy, K.J. Jessop, W.C.
Tennant, Aust. J. Chem. 27 (1974) 2075.
[4] V.L. Pecororo, Manganese Redox Enzymes, VCH Publishers,
New York, 1992.
[23] Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, third ed., Wiley, New York, 1978, p.
232.
[5] J.E. Penner-Hahn, Struct. Bonding 90 (1998) 1.
[6] V.K. Yachandra, K. Sauer, M.P. Klein, Chem. Rev. 96 (1996)
2927.
[24] A.B.P. Lever, Inorganic Electronic Spectroscopy, second ed.,
Elsevier, Amsterdam, 1984, p. 431.
[7] W. Ruttinger, G.C. Dismukes, Chem. Rev. 97 (1997) 1.
[8] C. Tommos, G.T. Babcock, Acc. Chem. Res. 31 (1998) 18.
[9] G.L. Lawrence, D.T. Sawyer, Coord. Chem. Rev. 27 (1978) 173.
[10] M.R. Bermejo, A. Gercia-Deibe, J. Sanmartin, A. Sousa, N.
Aurangzeb, C.E. Hulme, C.A. McAuliffe, R.G. Pritchard, M.
Watkinson, J. Chem. Soc., Chem. Commun. (1994) 645.
[11] V.K. Yachandra, V.J. DeRose, M.J. Latimer, I. Mukerji, K.
Sauer, M.P. Klein, Science 260 (1993) 675.
[25] D.T. Richens, C.G. Smith, D.T. Sawyer, Inorg. Chem. 18 (1979)
706.
[26] M.E. Bodini, L.A. Willis, T.L. Riechel, D.T. Sawyer, Inorg.
Chem. 15 (1976) 1538.
[27] B.N. Figgis, J. Lewis, in: J. Lewis, R.G. Wilkins (Eds.), Mordern
Coordination Chemistry, Interscience, New York (1960) p. 403.
[28] A. Earnshaw, Introduction to Magnetochemistry, Academic
Press, London, 1968, p. 35.
[12] J.H. Robblee, J. Messinger, R.M. Cinco, K.L. McFarlane, C.
Fernadez, S.A. Pizzaro, K. Sauer, V.K. Yachandra, J. Am.
Chem. Soc. 124 (2002) 7459.
[29] C.T. North, D.C. Phillips, F.S. Mathews, Acta Crystallogr. A24
(1968) 351.
[13] J.B. Vincent, K. Folting, J.C. Huffman, G. Christou, Inorg.
Chem. 25 (1986) 996.
[30] D.T. Cromer, J.T. Waber, International Table for X-ray Crystal-
lography, vol. IV, Kynoch Press, Birmingham, UK, 1974, Table
2.2B.
[14] P.S. Pavacik, J.C. Huffman, G. Christou, J. Chem. Soc., Chem.
Commun. (1986) 43.
[31] A. Altomare, G. Cascarano, C. Giacovazzo, M.C. Burla, G.
Polidori, N.J. Camalli, Appl. Crystallogr. 24 (1994) 435.
[32] SHELXL-97: G.M. Sheldrick, A Computer Program for Refine-
ment of Crystal Structures, University of Gottingen.
[33] M.N. Burnett, C.K. Johnson, ORTEPIII: Oak Ridge Thermal
Ellipsoid Plot Program for Crystal Structure Illustrations. Oak
Ridge National Laboratory Report ORNL-6895, Oak Ridge
National Laboratory, TN, 1996.
[15] R.L. Rardin, A. Bino, P. Poganiuch, W.B. Tolman, S. Liu, S.J.
Lippard, Angew. Chem., Int. Ed. Engl. 29 (1990) 812.
[16] J.C. Hempel, L.O. Morgan, W.B. Lewis, Inorg. Chem. 9 (1970)
2064.K.
[17] E. Pedersen, H. Toftlund, Inorg. Chem. 13 (1974) 1603.
[18] S. Pal, P. Ghosh, A. Chakravorty, Inorg. Chem. 24 (1985) 3704.
[19] S.K. Chandra, P. Basu, D. Ray, S. Pal, A. Chakraborty, Inorg.
Chem. 29 (1990) 2423.
[34] L.J. Farrugia, J Appl. Crystallogr. 32 (1999) 837.