Phosphane copper(I) formate complexes stabilized by formic acid and acetic acid through H?O?H bridges

Article abstract of DOI:10.1016/j.ica.2007.06.028

The formate copper(I) complex [(P(C₆H₂CH₂NMe₂-2)₃)CuO₂CH] (3) is accessible by the reaction of equimolar amounts of P(C₆H₂CH₂NMe₂-2)₃

Full text of DOI:10.1016/j.ica.2007.06.028

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 95–102
www.elsevier.com/locate/ica
Phosphane copper(I) formate complexes stabilized by formic acid
and acetic acid through Hꢀ ꢀ ꢀOꢀ ꢀ ꢀH bridges
*
Heinrich Lang , Yingzhong Shen, Tobias Ruffer, Bernhard Walfort
¨
Technische Universita¨t Chemnitz, Fakulta¨t fu¨r Naturwissenschaften, Institut fu¨r Chemie, Lehrstuhl fu¨r Anorganische Chemie,
Straße der Nationen 62, 09111 Chemnitz, Germany
Received 20 April 2007; received in revised form 8 June 2007; accepted 17 June 2007
Available online 30 June 2007
Abstract
The formate copper(I) complex [(P(C6H2CH2NMe2-2)3)CuO2CH] (3) is accessible by the reaction of equimolar amounts of
P(C6H2CH2NMe2-2)3 (1) with [CuO2CH] (2). When 3 is treated with HO2CH (4) or HO2CMe (6), molecules [(P(C6H2CH2NMe2-
2)3)CuO2CH Æ 2HO2CH] (5) and [(P(C6H2CH2NMe2-2)3)CuO2CH Æ HO2CMe] (7), respectively, are formed.
In 3, 5, and 7 the phosphane unit is acting as a tripodal PN2 ligand as it could be shown by 1H NMR spectroscopy. IR studies showed
that the formate building block in 3 and in its solvated form in 5 and 7 is r-bonded by one oxygen atom to Cu(I). The thermal decom-
position behavior of 3 is discussed.
The solid state structure of 5 is reported. The crystal structure consists of two chemical identical crystallographic independent mol-
ecules. In 5 a four-coordinated copper(I) ion is present with the P(C6H4CH2NMe2-2)3 ligand occupying three of the coordination sites,
while the 4th site is occupied by the formate anion. One of the two formic acid molecules in 5 is thereby hydrogen-bonded to the
CuO2CH entity, while the second HCO2H molecule forms a Nꢀ ꢀ ꢀH hydrogen bridge with the non-coordinating ortho-substituent
Me2NCH2.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Copper(I) formate; Formic acid; Acetic acid; Phosphane; Hydrogen-bonding; Molecular recognition; X-ray structure analysis; Thermolysis
1. Introduction
However, only less is known about the solid state structure
of the latter molecules [1–5]. More recently, copper(I) and
silver(I) carboxylates have gained an inherent interest, since
such complexes play an important role, for example, as cat-
alysts in organic transfer reactions and in the isomerization
of olefines [2,3]. In addition, these species can successfully
be used as precursors in the deposition of metal films on
(structured) oxidized silicon wafers by applying chemical
vapor deposition (CVD), atomic layer deposition (ALD),
or spin-coating processes [6–8]. Decomposition studies both
in the solid state and in the gas phase were carried out [9].
As the simplest carboxylate ligand, the formate ion
HCOꢁ2 is of importance in metal–organic chemistry, since
copper(I) formats are of interest with respect to some
important industrial reactions involving the synthesis and
selective partial oxidation of methanol, which may be car-
ried out over copper and silver catalysts [10]. Also, carbox-
Copper(I) carboxylates are known since quite some time
and have prooved to be very useful as reagents in organic,
organometallic and metal–organic synthesis [1–3]. In gen-
eral, copper(I) carboxylates are highly aggregated species
in which the carboxylic units are l-bridging the respective
copper(I) ions. Complexes of higher nuclearity can be
transferred to lower aggregated assemblies on addition of
Lewis-bases L (L = neutral or ionic 2-electron donor)
[4,5]. Depending on the ratio of L, cubane- or staircase-like
(1:1), dimeric (1:2) or monomeric (1:3) [LnCuO2R] com-
plexes (R = singly-bonded organic ligand, H; n = 1, 2, 3;
L = phosphane, phosphate, alkyne, alkene) are formed.
*
Corresponding author.
E-mail address: heinrich.lang@chemie.tu-chemnitz.de (H. Lang).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.06.028

96
H. Lang et al. / Inorganica Chimica Acta 361 (2008) 95–102
ylic- and formate-functionalized metal complexes can be
used as precursors for the preparation of self-assembled
monolayers [11]. Considering these topics, it is of interest
to study Lewis-base copper(I) formates involving coordi-
nated formic acid or other carboxylic acids, since
[CuO2CH] in its non-coordinated form is very sensitive to
moisture, oxygen and temperature.
We report here on the synthesis and characterization of
the phosphane copper(I) formate [(P(C6H4CH2NMe2-2)3)-
CuO2CH] and its reaction behavior towards formic and
acetic acid.
M.p.: 197–199 ꢁC (decomp.). Elemental Anal. Calc. for
C28H37CuN3O2P (542.14): C, 62.03; H, 6.88; N, 7.75.
Found: C, 61.78; H, 6.75; N, 7.46%. IR (KBr) m [cmꢁ1]:
3053 (m), 2966 (m), 2939 (m), 2857 (m), 2818 (s), 2775 (s),
2709 (w), 1607 (s) (CO, asym.), 1458 (s), 1364 (m) (CO,
sym.), 1309 (m), 1264 (m), 1172 (m), 1124 (w), 1097 (w),
1028 (s), 1003 (m), 840 (m), 756 (s), 735 (s), 531 (w), 501
(w), 484 (w). 1H NMR (CDCl3): d 2.29 (s, 18H, CH3), 3.47
2
2
(d, JHH = 12.2 Hz, 3H, CH2), 3.82 (d, JHH = 12.2 Hz,
3
4
3H, CH2), 6.76 (dd, JHH = 7.7 Hz, JPH = 7.7 Hz, 3H,
C6H4), 7.17–7.36 (m, 9H, C6H4), 8.42 (s, 1H, CH).
3
13C{1H} NMR (CDCl3): d 47.3 (CH3), 65.3 (d, JPC
=
2. Experimental
36.8 Hz, CH2), 128.5 (d, JPC = 4.3 Hz, C6H4), 130.2
(C6H4), 131.7 (d, JPC = 25.2 Hz, C6H4), 132.3 (d, JPC
=
2.1. General methods
8.2 Hz, C6H4), 133.9 (C6H4), 142.1 (d, JPC = 18.1 Hz,
iC/C6H4), 168.5 (CO2H). 31P{1H} NMR (CDCl3): d ꢁ33.1.
All reactions were carried out under an atmosphere of
purified nitrogen (O2 traces: CuO catalyst, BASF AG, Lud-
wigshafen; H2O: molecular sieve 4 A, Aldrich) using stan-
3.2. Synthesis of [(P(C6H4CH2NMe2- 2)3)CuOC(O)H Æ
2HOC(O)H] (5)
˚
dard Schlenk techniques. Diethyl ether was purified by
distillation from sodium/benzophenone ketyl and acetoni-
trile by distillation from calcium hydride. Infrared spectra
were recorded with a Perkin–Elmer FT-IR 1000 spectrome-
ter. 1H, 13C{1H} and 31P{1H} NMR spectra were recorded
with a Bruker Advance 250 spectrometer operating in the
Formic acid (4) (0.184 g, 4.0 mmol) dissolved in 10 mL
of
dichloromethane
was
drop-wise
added
to
[(P(C6H4CH2NMe2-2)3)CuO2CH] (3) (1.08 g, 2.0 mmol)
dissolved in 20 mL of dichloromethane at 0 ꢁC. After 1 h
of stirring at this temperature, the reaction solution was fil-
tered through a pad of Celite. Evaporation of all volatiles
in oil-pump vacuum afforded 5 as a yellow solid. Yield:
1.05 g (1.66 mmol, 83% based on 1). Single crystals of 5
suitable for X-ray structure determination could be
obtained by slowly cooling a dichloromethane solution
containing 5 to ꢁ20 ꢁC.
1
Fourier transform mode. H NMR spectra were recorded
at 250.130 MHz (internal standard, relative to CDCl3, d
7.26); 13C{1H} NMR spectra were recorded at 67.890
MHz (internal standard, relative to CDCl3, d 77.16);
31P{1H} NMR spectra were recorded at 101.202 MHz in
CDCl3 with P(OMe)3 as external standard (d 139.0, relative
to 85% H3PO4, d 0.00). Chemical shifts are reported in d
units (ppm) downfield from tetramethylsilane (d = 0.0) with
the solvent as the reference signal. Melting points were
determined using sealed nitrogen purged capillaries on a
M.p.: 105–106 ꢁC (decomp.). Elemental Anal. Calc. for
C30H41CuN3O6P (634.19): C, 56.82; H, 6.52; N, 6.63.
Found: C, 56.38; H, 6.46; N, 6.51%. IR (KBr) m [cmꢁ1]:
3453 (m), 3060 (m), 2997 (m), 2959 (s), 2924 (s), 2778 (s),
2834 (s), 2777 (m), 2703 (m), 2679 (m), 1692 (s) (CO asym.,
formic acid), 1598 (vs) (CO asym., formate), 1496 (s), 1443
(m), 1377 (m) (CO sym., formate), 1327 (m), 1309 (m), 1268
(m), 1207 (s) (CO, sym., formic acid), 1172 (m), 1148 (m),
1129 (m), 1108 (m), 1076 (m), 1029 (m), 992 (m), 966 (m),
883 (m), 837 (m), 757 (vs), 735 (m), 701 (m), 531 (m), 504
Buchi MP 510 melting point apparatus. Microanalyses were
¨
performed by the Institute of Organic Chemistry, Chemnitz,
Technical University.
3. General remarks
1
P(C6H4CH2NMe2-2)3 (1) [12] and [CuO2CH] (2) [13]
were prepared by published procedures. All other chemi-
cals were purchased from commercial providers and were
used as received.
(m), 483 (m), 465 (m), 440 (m). H NMR (CDCl3): d 2.50
2
(s, 18H, CH3), 3.43 (d, JHH = 10.2 Hz, 3H, CH2), 4.13
2
3
(d, JHH = 10.2 Hz, 3H, CH2), 6.77 (dd, JHH = 9.6 Hz,
4JPH = 9.6 Hz, 3H, C6H4), 7.26–7.55 (m, 9H, C6H4),
12.24 (s, 2H, CO2H), 8.38 (s, 2H, HO2CH). 13C{1H}
NMR (CDCl3): d 46.5 (CH3), 63.8 (d, JCP = 10.6 Hz,
3.1. Synthesis of [(P(C6H4CH2NMe2-2)3)CuOC(O)H]
(3)
CH2), 129.8 (d, JPC = 4.3 Hz, C6H4), 130.6 (d, JPC =
24.2 Hz, C6H4), 131.2 (C6H4), 133.0 (d, JPC = 7.7 Hz,
i
P(C6H4CH2NMe2-2)3 (1) (0.88 g, 2.0 mmol) was dis-
solved in 20 mL of dichloromethane, and [CuO2CH] (2)
(0.22 g, 2.0 mmol) suspended in 20 mL of dichloromethane
was slowly added at ꢁ20 ꢁC. After 2 h of stirring at this
temperature, the reaction solution was filtered through a
pad of Celite. Evaporation of all volatile materials in oil-
pump vacuum gave the title compound as a yellow solid.
Yield: 0.94 g (1.7 mmol, 87% based on 1).
C6H4), 133.5 (C6H4), 139.6 (d, JPC = 19.1 Hz, C/C6H4),
168.5 (HC O2), 162.3 (HCO2H). 31P{1H} NMR (CDCl3):
d ꢁ40.1.
3.3. Structure determination and refinement of 5
X-ray structure measurement was performed with a
BRUKER SMART CCD 1K diffractometer. Crystal data,

H. Lang et al. / Inorganica Chimica Acta 361 (2008) 95–102
97
data collection and refinement parameters for 5 are given in
Table 1. The unit cell was determined with the program
SMART [14]. For data integration and refinement of the unit
cell, the program SAINT [14] was used. Space group determi-
nation was done with XPREP [14]. The structure was solved
with direct methods using SHELX-97 [15], the structure
refinement was based on least-square methods based on
F2 with SHELX-97 [15]. All non-hydrogen atoms were fully
refined in the calculated positions. The hydrogen atoms
of the formate ion and of the formic acid building blocks
were taken from the electron density difference map and
refined freely. All other hydrogen atoms were positioned
as riding on their neighboring atoms.
Found: C, 59.54; H, 6.58; N, 6.74%. IR (KBr) m [cmꢁ1]:
3433 (w), 3054 (m), 2964 (s), 2936 (m), 2857 (s), 2812 (s),
2764 (s), 2711 (m), 1613 (s) (CO asym., acetic acid), 1583
(s) (CO asym., formate), 1457 (s), 1440 (s), 1365 (s) (CO
sym., formate), 1306 (m), 1264 (s) (CO asym., acetic acid),
1171 (m), 1125 (w), 1097 (w), 1025 (s), 1001 (m), 880 (w),
840 (s), 754 (s), 730 (s), 702 (w), 673 (w), 531 (w), 500
(w), 488 (w). 1H NMR (CDCl3): d 2.07 (s, 3H, CH3),
2
2.40 (s, 18H, CH3), 3.45 (d, JHH = 10.2 Hz, 3H, CH2),
2
3
4.01 (d, JHH = 10.2 Hz, 3H, CH2), 6.76 (dd, JHH
=
4
7.8 Hz, JPH = 7.8 Hz, 3H, C6H4), 7.20–7.41 (m, 9H,
C6H4), 8.40 (s, 1 H, CHCO2), 12.98 (s, 1H, MeCO2H).
13C{1H} NMR (CDCl3): d 23.4 (MeCO2H), 47.1 (Me2N),
3
64.5 (d, JPC = 36.8 Hz, CH2), 129.0 (d, JPC = 4.3 Hz,
3.4. Synthesis of [(P(C6H4CH2NMe2- 2)3)CuOC(O)H Æ
HOC(O)Me] (7)
C6H4), 130.7 (C6H4), 132.6 (d, JPC = 8.0 Hz, C6H4), 133.7
I
(C6H4), 141.1 (d, JPC = 18.3 Hz, C/C6H4), 168.9 (HCO2),
176.8 (MeCO2H). 31P{1H} NMR (CDCl3): d ꢁ31.7.
4. Results and discussion
Complex 7 was synthesized in the same manner as 5 (see
above). Thus, HO2CMe (6) (0.12 g, 2.0 mmol) was added
to [(P(C6H4CH2NMe2-2)3)CuO2CH] (3) (1.08 g, 2.0 mmol).
After appropriate work-up, complex 7 was obtained as a yel-
low solid. Yield: 1.0 g (1.7 mmol, 83% based on 3).
4.1. Synthesis
M.p.: 193–195 ꢁC (decomp.). Elemental Anal. Calc. for
C30H41CuN3O4P (602.19): C, 59.84; H, 6.86; N, 6.98.
The phosphane copper(I) formate [(P(C6H4CH2NMe2-
2)3)CuOC(O)H] (3) is accessible by treatment of
P(C6H4CH2NMe2-2)3 (1) with 1 equiv. of [CuO2CH] (2)
in dichloromethane or tetrahydrofuran as solvent at
ꢁ20 ꢁC (Eq. (1)). After appropriate work-up, complex 3
could be isolated as a yellow solid in 87% yield (Section 2).
Table 1
Crystal data, collection and refinement parameters for 5
Formula
C30H41O6PN3
Formula weight
Crystal dimensions (mm)
Crystal system
634.17
N
P
0.45 · 0.35 · 0.25
monoclinic
P2(1)/c
18.357(4)
19.577(4)
17.684(3)
90.776(16)
6355(2)
O
N
[CuO2CH]
+
Cu
O C
P(
N)3
Space group
H
˚
N
a (A)
˚
b (A)
ð1Þ
˚
c (A)
1
2
3
b (ꢁ)
3
˚
V (A )
Z
8
N
=
Dcalc (g/cm3)
Index ranges
1.326
Me2N
ꢁ22 6 h 6 22, ꢁ24 6 k 6 24,
ꢁ21 6 l 6 21
2672
7.82
k = 0.71073
223(2)
52.00
12486
10416
F(000)
l (Mo Ka) (cmꢁ1
Radiation, Mo Ka (A)
Temperature (K)
2hmax (ꢁ)
Number of reflections measured
Independent reflections observed
[I > 2r(I)]
Complex 3 is obtained in solvent free form and hence, is
)
the first example in copper(I) formate chemistry without a
solvent molecule attached to copper(I). All other so far
synthesized Lewis-base copper(I) formats include at least
half of a solvent molecule, i.e. EtOH, which forms a
Hꢀ ꢀ ꢀOꢀ ꢀ ꢀH hydrogen bridge with the CuOC(O)H core
[16]. The stability of 3 is related to phosphane 1, since this
ligand acts as a multipodal protecting group and stabilizes
the copper(I) formate. The phosphorus atom and two of
the three Me2NCH2 ortho-substituents are datively-bonded
to the Cu(I) ion [1]. Due to this bonding motif, the group-
11 metal ion possesses coordination number 4 and hence,
counts to 18-valence electrons.
˚
Number of refined parameters
R1 [I > 2r(I)]a
779
0.0530/0.0429
0.1384/0.1325
1.060
2.607
0.392
wR2 [I > 2r(I)]b
Goodness-of-fit on F2c
˚
Dqmax (eAꢁ3
)
˚
Dqmin (eAꢁ3
(D/r)max
)
0.083
h
i
1=2
P
P
P
P
2
a
R ¼ ðkF oj ꢁ jF ckÞ= jF oj; wR2 ¼
ðwðF 2o ꢁ F 2c Þ Þ= ðwF o4Þ
.
While 3 is fairly stable to oxygen and moisture, even
more stable molecules can be obtained, when 3 is subse-
quently reacted with formic acid (4) (Eq. (2)) and acetic
acid (6) (Eq. (3)), respectively.
2
b
c
w ¼ 1=½r2ðF o2Þ þ ð0:0835PÞ þ 4:1728Pꢂ; P ¼ ðF o2 þ 2F 2cÞ=3.
h
i
P
2
1=2
S ¼
wðF 2o ꢁ F 2c Þ =ðn ꢁ pÞ
(n = number of reflections, p =
parameters used).

98
H. Lang et al. / Inorganica Chimica Acta 361 (2008) 95–102
Treatment of 3 with an excess of HCO2H (4) in dichlo-
N
P
romethane as solvent produced [(P(C6H4CH2NMe2-2)3)-
CuOC(O)H Æ 2HOC(O)H] (5) which is the solvated form
of 3 at room temperature. Complex 5 could be isolated in
the form of yellow crystals after crystallization from
dichloromethane at room temperature.
O
H
Δ
T
N
N
Cu
O C
[CuO2CH]
Δ
T
-P(
N)3
-CO2
-1/2H2
3
Cu
O
C
N
O
N
H
Δ
T
P
P
-1/2H2
N)3
N
H
O
Δ
T
N
P
N
Cu
O C
-P(
Cu
H
N
-CO 2
O
HO2CH(exc.) (4)
H
N
N
N
P
N
Cu
O C
O
H
O
O
N
N
H
3
C
C H
Cu
O
H
Scheme 1. Thermolysis of 3 (P(\N)3 = P(C6H4CH2NMe2-2)3).
3
5
ð2Þ
In 5, one HCO2H molecule solvates the copper(I) for-
mate entity [CuOC(O)H], while the second formic acid is
hydrogen-bonded to the free MeNCH2 ortho-substituent
through Hꢀ ꢀ ꢀOꢀ ꢀ ꢀH bond formation.
cene-stabilized copper(I) organyls {[Ti](l-r,p-C „ CR)2}-
CuR0 [18]. Another favoured decomposition route for 3
is the elimination of the phosphine P(C6H4CH2NMe2-2)3
to yield copper formate [CuO2CH] which subsequently
eliminates CO2 and H2 to give Cu(0) (Scheme 1). This
decomposition path is also possible [17], although we could
not isolate [(P(C6H4CH2NMe2-2)3)CuH].
Decarboxylation and dehydrogenation of 3 is also
observed, when 3 is refluxed in toluene or mesitylene,
whereby elemental copper deposited at the Schlenk walls.
On cooling such solutions to room temperature, colorless
crystals of 1 precipitated.
When acetic acid (6) is used, [(P(C6H4CH2NMe2-2)3)-
CuOC(O)H Æ HOC(O)Me] (7) is formed in which one
MeCO2H molecule is hydrogen-bonded to the keto-oxygen
atom of the copper formate building block (Eq. (3)). The
yield is 83% (Section 2). This differs from 5, where two car-
boxylic acids are coordinated to the phosphane copper(I)
formate core (vide supra). However, a compound similar
to 5 in which one of the three Me2NCH2 units is hydro-
gen-bridged by a carboxylic acid could not be isolated for
7 even, when 3 is reacted with an excess of MeCO2H.
4.2. Characterization
N
N
Complexes 3, 5, and 7 gave satisfactory elemental anal-
P
P
1
yses. They were characterized by FT-IR, H, 13C{1H} and
O
O
H
O
O
MeCO2H (6)
N
N
N
N
C
C Me
Cu
O
C
Cu
O
31P{1H} NMR spectroscopy (Section 2). The solid state
structure of 5 was established by single X-ray structure
determination.
H
H
3
7
ð3Þ
After appropriate work-up, complexes 3, 5, and 7 could
be isolated as yellow crystalline materials. They are soluble
in most common polar organic solvents such as tetrahydro-
furan, diethyl ether, and dichloromethane.
In the IR spectra of 3, 5, and 7, characteristic absorp-
tions are found between 1200 and 1700 cmꢁ1 for the for-
mate, formic acid and acetic acid groups (Table 2).
Distinct m(CO2) frequencies for the copper formate unit
in 3, 5, and 7 are found at 1607 and 1364 cmꢁ1 for 3, 1598
and 1377 cmꢁ1 for 5 and 1583 and 1365 cmꢁ1 for 7,
whereby the frequencies at ca. 1600 cmꢁ1 can be assigned
to the asymmetric and those at ca. 1360 cmꢁ1 to the sym-
metric O–C–O stretching modes of the coordinated CO2Hꢁ
A further method for the preparation of a phosphine
copper formate is the insertion of carbon dioxide into a
Cu–H bond in, for example, hexanuclear [(Ph3P)CuH]6
[5,17]. This prompted us to study the thermolysis of, e.g.
3. On heating 3 to temperatures around 200 ꢁC, gas evolu-
tion was observed and yellow colored 3 darkend to give
P(C6H4CH2NMe2-2)3 (1) along with elemental copper
(Scheme 1). This shows that most probably 3 decarboxy-
lates to give [(P(C6H4CH2NMe2-2)3)CuH] which then elim-
inates H2 to produce copper along with 1. The latter
decomposition is also favoured in, for example, heterobi-
metallic organometallic p-tweezer chemistry. Here it was
found that on heating {[Ti](l-r,p-C „ CR)2}CuO2CR0
[Ti] = (g5-C5H4SiMe3)2Ti; (R, R0 = singly-bonded organic
group), CO2 is eliminated to give the bis(alkynyl)titano-
Table 2
Characteristic IR spectral frequencies for 3, 5, and 7 [cmꢁ1 a
]
Compound
Formate
Formic/acetic acid
mas(CO2)
ms(CO2)
mas(CO2)
ms(CO2)
3
5
7
a
1607
1598
1583
1364
1377
1365
1692
1613
1207
1264
D = mas ꢁ ms; as = asymmetric, s = symmetric.

H. Lang et al. / Inorganica Chimica Acta 361 (2008) 95–102
99
ion [16]. These absorptions appear at values which are typ-
ical for r-bonded formates in transition metal chemistry.
The separation D (D = mas ꢁ msym; as = asymmetric, sym =
symmetric) allows to indicate if the formate unit is monod-
entate or bidentate bound to copper(I) [19], whereby the
monodentate binding increases D between the m(CO2) fre-
quencies relative to the values of the free formate taken
as those of the respective sodium (D = 241 cmꢁ1) [19] or
potassium salts (D = 233 cmꢁ1). [20,21] This is also found
for 3, 5, and 7 (D = 243 (3), D = 221 (5), D = 218 cmꢁ1
(7)) and is similar for, e.g. [(Ph3P)2CuO2CH] (D = 231
cmꢁ1) [5a,16,22].
The CO2 frequencies of the solvated formic acid mole-
cules in 5 are observed at 1692 and 1207 cmꢁ1, respectively.
The difference D (485 cmꢁ1) lies between the data charac-
teristic for free formic acid (671 cmꢁ1) [23] and, for exam-
ple, for Na[H(HCO2)2] (439 cmꢁ1), [24] but is typical to
values found in the H-bridged formic acid dimers
[HCO2H]2 (524 cmꢁ1) [25], [(PPh3)3CuOC(O)H Æ HCO2H]
[16] and [(PPh3)2AgOC(O)H Æ 2HCO2H] [16,26].
observed at d 162.3 and 168.5, which can be assigned to
the coordinated formate ion and the formic acid solvate
molecule. A similar behavior is found for 7. The 13C{1H}
NMR spectrum of the latter complex consists of two sharp
resonance signals at 168.9 ppm (for the coordinated for-
mate ion) and 176.8 ppm (for the sp2-hybridized carbon
atom) of the MeCO2H solvate molecule. The CH3 entity
is found at 23.4 ppm.
The coordination of P(C6H4CH2NMe2-2)3 to copper(I)
is nicely confirmed by 31P{1H} NMR spectroscopy. For 3
and 5 a singlet appears at ꢁ33.1 (3) and ꢁ31.7 ppm (5)
which is downfield-shifted (1: ꢁ37.2 ppm) compared with
the starting material 1 [12]. In contrast to this finding it
is of interest to note that for 7, a up-field shift is observed
(ꢁ40.1 ppm).
4.3. Solid state structure of 5
Single crystals of [(P(C6H4CH2NMe2-2)3)CuO2CH Æ
2(HOOCH)] (5) could be grown by slowly cooling a satu-
rated dichloromethane solution containing 5 to ꢁ20 ꢁC.
The result of the X-ray structure analysis of 5 is depicted
In the case of ‘‘weak’’ to ‘‘medium’’ H bonds of general
type A–Hꢀ ꢀ ꢀB (m(AH)), an absorption band between 2000
and 3500 cmꢁ1 occurs, while for ‘‘strong’’ to ‘‘very strong’’
hydrogen bonds, very broad absorptions are observed
below 1600 cmꢁ1 [27]. This is illustrated by the following
systems: in [HCO2H]2, a hydrogen-bonded Oꢀ ꢀ ꢀO distance
˚
in Fig. 1. Selected bond distances (A) and bond angles (ꢁ)
are given in Table 3. Crystal data as well as collection
and refinement parameters are summarized in Table 1
(Section 2).
ꢁ1
˚
of 2.703 A [28], m(OH) = 2570–3490 cm (with the maxi-
Complex 5 crystallizes in the monoclinic space group
P21/c. The asymmetric unit comprises two independent
molecules (5a and 5b). In 5, a four-coordinated copper(I)
mum at ca. 3100 cmꢁ1) is typical [26], while for K[H-
˚
(O2CH)2] an Oꢀ ꢀ ꢀO bond separation of 2.45 A and a broad
m(OH) vibration with a maximum at 1400 cmꢁ1 is found
[24,29]. A correlation of the m(OH) frequencies and the
Oꢀ ꢀ ꢀO bonds based on the above results, gives a predicted
position of the m(OH) mode in [(P(C6H4CH2NMe2-2)3)-
CuO2CH Æ 2(HCO2H)] (5) at 1469 cmꢁ1 and 1440 cmꢁ1
,
respectively. The same is true for [(P(C6H4CH2NMe2-2)3)-
CuO2CH Æ HOC(O)Me] (7). The very weak absorptions at
1974 cmꢁ1 (5) and 1964 (7) can be assigned to the m(OH)
vibration.
1
The H NMR spectra of 3, 5, and 7 show well-resolved
resonance signals and are consistent with the empirical for-
mula [(P(C6H4CH2NMe2)3)CuO2CH(HOC(O)R)n] (5: n =
2, R = H; 7: n = 1, R = Me). Characteristic for 3 is the
appearance of a distinct signal at 8.42 ppm which can be
assigned to the formate CH hydrogen atom. This proton
can be detected at 8.38 ppm for 5 and at 8.40 ppm for 7.
1
The H NMR spectra of 5 and 7 show for their solvated
RCO2H entities (R = H, CH3), two typical signals at 8.40
(CH) and 12.24 ppm (HO) for 5 and at 2.57 (CH3) and
12.98 ppm (HO) for 7. In addition to the O2CH and
HO2CR protons, the resonance signals for the P(C6H4-
CH2NMe2-2)3 moiety are observed in the range character-
istic for this type of ligand [30].
In the 13C{1H} NMR spectra of 3, 5, and 7, the formate
building block gives rise to a very characteristic resonance
signal at ca. 168.5 ppm. In respect to the appropriate non-
coordinated formic acid (171.3 ppm), an up-field shift of
ca. 3 ppm is observed. For 5 two distinct resonances are
Fig. 1. ORTEP plot (50% probability level) of the molecular structure of
one (5a) of the two crystallographically independent molecules of 5
showing the atom numbering scheme.

100
H. Lang et al. / Inorganica Chimica Acta 361 (2008) 95–102
Table 3
The O1–Cu1–P1 and O7–Cu2–P2 angles with 130.82(6)
and 129.58(6)ꢁ are larger than those observed for [(Ph3P)3-
CuO2CH Æ HO2CH] (97.35(8)–109.77(9)ꢁ), reflecting the
different coordination mode (see Table 4).
˚
Selected bond distances (A) and angles (ꢁ) of the two independent
molecules of 5a
5a
5b
˚
Bond distances
Cu(1)–O(1)
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–P(1)
O(1)–C(28)
O(2)–C(28)
O(3)–C(29)
O(4)–C(29)
O(5)–C(30)
O(6)–C(30)
The Cu–P separations with 2.1839(8) and 2.1859(8) A
2.041(2)
2.127(2)
2.172(2)
2.1839(8)
1.254(3)
1.242(4)
1.294(4)
1.163(4)
1.235(4)
1.189(6)
Cu(2)–O(7)
Cu(2)–N(4)
Cu(2)–N(5)
Cu(2)–P(2)
O(7)–C(58)
O(8)–C(58)
O(9)–C(59)
O(10)–C(59)
O(11)–C(60)
O(12)–C(60)
2.043(2)
2.174(2)
2.151(2)
2.1859(8)
1.249(4)
1.242(4)
1.305(4)
1.184(4)
1.217(4)
1.217(4)
(Table 3) are shorter than those ones found in, for example,
˚
[(Ph3P)3CuO2CH Æ HO2CH] (2.315–2.332 A) and [(Ph3P)3-
˚
CuO2CH Æ 0.5EtOH] (2.332–2.341 A), respectively [16].
The Cu–N distances of 5 are located between 2.127(2)
˚
and 2.174(2) A, somewhat shorter than those characteristic
for, i.e. [(P(C6H4CH2NMe2-2)3)Cu2Br2] (N–Cu = 2.17(2)–
˚
2.32(2) A) [30]. However, they are almost identical with
the separations found in [(P(C6H4CH2NMe2-2)3)Cu2Cl2]
˚
(N–Cu = 2.103(5)-2.215(5) A) [30] and [(Ph3P)2Cu(2,3-
Bond angles
˚
Py(CO2)(COOH))] (N–Cu = 2.109(2) A) [31]. The Cu–O
O(1)–Cu(1)–P(1)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–P(1)
N(2)–Cu(1)–P(1)
C(1)–P(1)–C(10)
C(1)–P(1)–C(19)
C(19)–P(1)–C(10)
C(1)–P(1)–Cu(1)
C(10)–P(1)–Cu(1)
C(7)–N(1)–Cu(1)
C(16)–N(2)–Cu(1)
C(19)–P(1)–Cu(1)
C(28)–O(1)–Cu(1)
O(2)–C(28)–O(1)
O(4)–C(29)–O(3)
O(6)–C(30)–O(5)
a
130.82(6)
O(7)–Cu(2)–P(2)
O(7)–Cu(2)–N(4)
O(7)–Cu(2)–N(5)
N(4)–Cu(2)–N(5)
N(4)–Cu(2)–P(2)
N(5)–Cu(2)–P(2)
C(40)–P(2)–C(31)
C(40)–P(2)–C(49)
C(31)–P(2)–C(49)
C(40)–P(2)–Cu(2)
C(31)–P(2)–Cu(2)
C(37)–N(4)–Cu(2)
C(46)–N(5)–Cu(2)
C(49)–P(2)–Cu(2)
C(58)–O(7)–Cu(2)
O(8)–C(58)–O(7)
O(9)–C(59)–O(10)
O(11)–C(60)–O(12)
129.58(6)
˚
bond lengths are 2.041(2) and 2.043(2) A. Comparing the
102.18(9)
106.26(9)
121.66(9)
99.06(6)
99.08(7)
103.7(1)
104.8(1)
104.8(1)
109.80(8)
104.08(9)
111.4(2)
108.8(2)
127.35(8)
124.2(2)
127.0(3)
123.5(3)
127.5(5)
106.24(9)
104.53(9)
121.18(9)
99.37(6)
97.79(6)
103.0(1)
103.9(1)
104.2(1)
110.50(9)
104.07(8)
109.1(2)
111.9(2)
128.43(8)
121.2(2)
126.9(3)
125.6(3)
126.7(4)
observed bond distances of 5 with a unidentate and che-
late-bonded HCOꢁ2 ion confirms this finding. The cop-
˚
per–oxygen bond length decreases from 2.226(3) A for a
˚
bidentate formate ligand to 2.04–2.08 A for a r-coordi-
nated HCOꢁ2 anion [5a].
One of the two formic acid molecules in 5 is hydrogen-
bonded to the formate anion to form an assembly that is
best described as a biformate anion [H(HCO2)2]ꢁ. This
anion is the simplest member of a class of hydrogen com-
plexes, involving carboxylic acids and carboxylate anions
[32]. Theoretical studies on this matter exist [27]. Hydrogen
bonds display an almost continuous distribution of Oꢀ ꢀ ꢀO
˚
separations between 2.36 and 3.69 A and have been sub-
divided into classes which are referred to us as ‘‘very
The estimated standard deviation(s) of the last significant digit are
shown in parentheses.
˚
˚
strong’’ (<2.5 A), ‘‘strong’’ (2.5–2.65 A), ‘‘medium’’ (2.65–
˚
˚
2.80 A), or ‘‘weak’’ (>2.80 A) [33]. For 5 the hydrogen bond
ꢁ
˚
of the [H(HCO2)2] unit with O2ꢀ ꢀ ꢀO3 = 2.552(3) A can be
considered as a ’’strong’’ interaction. This can be compared
with the hydrogen bond length observed for K[H(HCO2)2],
ion is present with the P(C6H4CH2NMe2-2)3 ligand occu-
pying three of the coordination sites (PNN) and the for-
mate anion binds through one oxygen atom to the 4th
site, forming a distorted tetrahedral environment around
copper. The range of the O–Cu–P angles are between
129.58(6) and 130.82(6)ꢁ (Table 3) which are larger than
that of the ideal tetrahedron angle, while the angles of
O–Cu–N (between 102.18(9) and 106.24(9)ꢁ) and N–Cu–
P (between 97.79(6) and 99.37(6)ꢁ) are smaller (Table 3).
˚
where a Oꢀ ꢀ ꢀO separation of 2.45 A is typical [29]. The
hydrogen bond distance for the respective [H(HCO2)2]ꢁ
entity in [(Ph3P)3CuO2CH Æ HO2CH] with Oꢀ ꢀ ꢀO =
˚
2.529(5) A is similar [16]. The second formic acid molecule
present in 5 is also hydrogen-bonded, however, to the free
nitrogen atom N3 of the P(C6H4CH2NMe2-2)3 ligand
˚
(Fig. 1). The N3ꢀ ꢀ ꢀO5 distance with 2.619(3) A indicates
that a strong hydrogen bond exists as well (vide supra).
The apparent reduction in hydrogen bond strength
compared to the free biformate ion ½HðHCOꢁ2 Þ2ꢂꢁ can
be explained by a competition of the formate ion electron
density between the copper(I) ion and the formic acid
molecule.
Table 4
˚
Selected bond distances (A) and angles (ꢁ) of the hydrogen bonds of
molecules 5a and 5b
D–Hꢀ ꢀ ꢀAa
Molecule 5a
D–H
Hꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
5. Supplementary material
CCDC 626529 contains the supplementary crystallo-
graphic data for 5. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
O(2)–H(2H)ꢀ ꢀ ꢀO(3)
1.13(7)
0.90(3)
1.43(7)
1.74(3)
2.551(3)
2.618(3)
168(7)
166(3)
N(3)–H(3N)ꢀ ꢀ ꢀO(5)
Molecule 5b
O(9)–H(9H)ꢀ ꢀ ꢀO(8)
N(6)–H(6N)ꢀ ꢀ ꢀO(11)
a
0.86(6)
1.01(3)
1.71(6)
1.64(3)
2.549(3)
2.637(3)
167(5)
166(3)
D = donor atom; A = acceptor atom.

H. Lang et al. / Inorganica Chimica Acta 361 (2008) 95–102
101
(h) A. Shaporenko, K. Ro¨ssler, H. Lang, M. Zharnikov, J. Phys.
Chem. B 110 (2006) 24621;
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