[Cr(bpym)(C2O4)2]- in designing heterometallic complexes. Crystal structures and magnetic properties of PPh4[Cr(bpym)(C2O4)2]·H 2O and [Ag(bpym)][Cr(C2O4)2](H2O) 2]·2H2O (bpym=2,2′-bipyrimidine)

Article abstract of DOI:10.1016/S0020-1693(02)00880-0

The preparation, crystal structure and magnetic properties of PPh₄[Cr(bpym)(C₂O₄)₂]·H ₂O (1) and [Ag(bpym)][Cr(C₂O₄)₂(H₂O) ₂]·2H₂O (2) (C₂O₄^2-=oxalate dianion, bpym=2,2′-bipyrimidine and PPh₄⁺=tetraphenylphosphonium cation) are described. The structure of 1 is made up of discrete (2,2′-bipyrimidine)bis(oxalato)chromate(III) anions, teraphenylphosphonium cations and uncoordinated water molecules. The structure of 2 consists chains of univalent silver cations bridged by bis-chelating 2,2′-bypyrimidine, cis-diaquabis(oxalato)chromate(III) anions and crystallisation water molecules. The chromium atom in 1 and 2 has a slightly distorted octahedral geometry with two bidentate oxalate groups (1 and 2), and one bidentate bpym ligand (1) or two cis-coordinated water molecules (2). The Cr-O(ox) bonds are in the ranges 1.951(3)-1.981(3) A? (1) and 1.9575(12)-1.9585(14) A? (2), values which are shorter than the Cr-O(w) bonds in 2 [1.9999(16) A?]. The Cr-N(bpym) bond lengths are 2.064(4) and 2.090(4) A? for 1. The silver atom in 2 is disordered with two different four-coordinated environments from two bpym groups. One of these environments can be defined as a flattened tetrahedron with Ag-N(bpym) distances of 2.331(2) A? (x2) and 2.360(2) A? (x2) and the second one is distorted with values of the Ag-N(bpym) bonds in the range 2.132(18) and 2.59(2) A?. The silver-silver separation across bridging bpym is 6.1854(8) A?. Magnetic susceptibility measurements of 1 and 2 in the temperature range 1.9-290 K reveal the occurrence of weak antiferromagnetic interactions together with zero-field splitting effects. The use of the [Cr(bpym)(C₂O₄)₂]^- unit of 1 as a ligand towards different univalent and divalent metal ions is discussed in the light of the available structural information.

Full text of DOI:10.1016/S0020-1693(02)00880-0

Inorganica Chimica Acta 336 (2002) 46ꢃ54
/
www.elsevier.com/locate/ica
[Cr(bpym)(C2O4)2]ꢀ in designing heterometallic complexes. Crystal
structures and magnetic properties of PPh4[Cr(bpym)(C2O4)2]×H2O
and [Ag(bpym)][Cr(C2O4)2](H2O)2]×2H2O (bpymꢁ2,2?-bipyrimidine)
/
/
/
Gabriela Marinescu a, Rodrigue Lescouezec b, Donatella Armentano c, Giovanni De
¨
Munno c, Marius Andruh a, Santiago Uriel d, Rosa Llusar d, Francesc Lloret b,
Miguel Julve b,*
a Inorganic Chemistry Laboratory, Chemistry Faculty, University of Bucharest, Str. Dumbrava Rosie nr. 23, 70254 Bucharest, Romania
b Departament de Qu´ımica Inorga`nica/Instituto de Ciencia Molecular, Facultat de Qu´ımica de la Universitat de Vale`ncia, Dr. Moliner 50, 46100
Burjassot, Vale`ncia, Spain
c Dipartimento di Chimica della Universita` degli Studi della Calabria, 87030 Arcavacata di Rende, Cosenza, Italy
d Departament de Cie`ncies Experimentals, Campus Riu Sec de la Universitat Jaume I, POB 224, 12080 Castello´, Spain
Received 2 December 2001; accepted 26 February 2002
Abstract
The preparation, crystal structure and magnetic properties of PPh4[Cr(bpym)(C2O4)2]×
/
H2O (1) and [Ag(bpym)]-
[Cr(C2O4)2(H2O)2]× oxalate dianion, bpymꢁ tetraphenylphosphonium cation)
/
2H2O (2) (C2O42ꢀ ꢁ 2,2?-bipyrimidine and PPh4ꢂ ꢁ
/
/
/
are described. The structure of 1 is made up of discrete (2,2?-bipyrimidine)bis(oxalato)chromate(III) anions, teraphenylpho-
sphonium cations and uncoordinated water molecules. The structure of 2 consists chains of univalent silver cations bridged by bis-
chelating 2,2?-bypyrimidine, cis-diaquabis(oxalato)chromate(III) anions and crystallisation water molecules. The chromium atom in
1 and 2 has a slightly distorted octahedral geometry with two bidentate oxalate groups (1 and 2), and one bidentate bpym ligand (1)
˚
or two cis-coordinated water molecules (2). The Crꢀ
/
O(ox) bonds are in the ranges 1.951(3)ꢃ
/
1.981(3) A (1) and 1.9575(12)ꢃ
/
˚
˚
1.9585(14) A (2), values which are shorter than the Crꢀ
/
O(w) bonds in 2 [1.9999(16) A]. The Crꢀ
/N(bpym) bond lengths are 2.064(4)
˚
and 2.090(4) A for 1. The silver atom in 2 is disordered with two different four-coordinated environments from two bpym groups.
˚ ˚
N(bpym) distances of 2.331(2) A (x2) and 2.360(2) A
One of these environments can be defined as a flattened tetrahedron with Agꢀ
(x2) and the second one is distorted with values of the AgꢀN(bpym) bonds in the range 2.132(18) and 2.59(2) A. The silverꢃ
separation across bridging bpym is 6.1854(8) A. Magnetic susceptibility measurements of 1 and 2 in the temperature range 1.9ꢃ
/
˚
/
/silver
˚
/
290
K reveal the occurrence of weak antiferromagnetic interactions together with zero-field splitting effects. The use of the
[Cr(bpym)(C2O4)2]ꢀ unit of 1 as a ligand towards different univalent and divalent metal ions is discussed in the light of the
available structural information. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Magnetic properties; Chromium complexes; Silver complexes; Oxalato complexes
1. Introduction
anionic precursors are commonly referred to as building
blocks and examples such as the bis(oxamidato)cop-
A well known strategy in designing heteropolynuclear
species in the field of molecular magnetism consists of
using stable anionic mononuclear species as complexes
towards coordinatively unsaturated metal ions. These
per(II) [1,2], tris(oxalato)chromate(III) [3ꢃ
hexacyanometallate species [9ꢃ11] are among the most
rewarding ones. In the case of the [Cr(ox)3]3ꢀ complex
(oxꢁoxalate), two- and three-dimensional oxalate-
/
8] and several
/
/
bridged bimetallic compounds have been reported,
some of them exhibiting magnetic ordering at low
temperatures [3,4,5a,5b,5d,6,7b]. The recent control of
the optical activity in the three-dimensional family
enhances the interest in this type of compounds [7].
* Corresponding author. Tel.: ꢂ
4322
E-mail address: miguel.julve@uv.es (M. Julve).
/
34-96-386-4856; fax: ꢂ34-96-386-
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 8 8 0 - 0

G. Marinescu et al. / Inorganica Chimica Acta 336 (2002) 46ꢃ
/
54
47
Focusing on the homoleptic [Cr(ox)3]3ꢀ unit, the
replacement of one or more oxalate groups by bidentate
or potentially bridging polydentate ligands would mod-
ify its overall charge and its behaviour as a ligand. So
the preparation of new heterometallic extended mag-
netic systems using these new precursors as ligands
appears as a new challenge. With this respect, the
availability of the mononuclear complexes of formula
bipyrimidine (1 mmol) and sodium oxalate (2 mmol)
was refluxed with continuous stirring until the green
colour turned reddish violet (ca. 1 h). After the addition
of tetraphenylphosphonium chloride (1 mmol) dissolved
in the minimum amount of water, the resulting solution
is left to slow evaporation at room temperature (r.t.).
Violet needles of 1 separate from the mother liquor in a
few days. Yield: 80%. Anal. Calc. for C36H28N4O9PCr
(1): C, 58.16; H, 3.77; N, 7.53. Found: C, 57.96; H, 3.68;
N, 7.45%.
[Cr(AA)(ox)2]ꢀ with AAꢁ
1,10-phenanthroline (phen) [12ꢃ
/
2,2?-bipyridine (bipy) [12],
/
14] and 2,2?-dipyridyla-
mine (dpa) [15] moved us to carry out a systematic study
concerning their use as ligands towards univalent and
divalent metal ions. The richness of this chemistry is well
illustrated by the variety of structural motifs obtained:
2.2.2. [Ag(bpym)][Cr(C2O4)2(H2O)2]×
/
2H2O (2)
Silver(I) perchlorate (0.5 mmol) dissolved in a mini-
mum amount of water is added to a concentrated
aqueous solution of 1 (0.5 mmol) with continuous
stirring. The white solid of tetraphenylphosphonium
perchlorate which separates is removed by filtration and
the resulting violet solution is left to evaporate at r.t. in
the darkness. Red prisms of 2 which were suitable for X-
ray diffraction and green needles which did not diffract
appeared in a few days. This last product was not
investigated further. The yield of 2 is approximately
40%. Anal. Calc. for C12H14N4O12AgCr (2): C, 25.46;
H, 2.47; N, 9.90. Found: C, 25.34; H, 2.40; N, 9.85%.
the trinuclear {M(H2O)2[Cr(bipy)(ox)2]2}×
Cu(II) (nꢁ1.5) and Co(II) (nꢁ1) [16,17] and tetra-
nuclear {Ag(H2O)2[Cr(bipy)(ox)2]}2 [16] and {[Mn2(bi-
py)2(H2O)2(ox)] [Cr(phen)(ox)2]2}×6H2O [18] complexes,
the double zigzag chains {Mn[Cr(bipy)(ox)2]2}n [17] and
{Sr[Cr(dpa)(ox)2]2×8H2O}n [15], the sheetl-ike polymers
{Na(H2O)[Cr(bipy)(ox)2]×2H2O}n [19], {Na(H2O)[Cr-
(phen)(ox)2]×2H2O}n [13,18] and {K(dmf)[Cr(phen)-
(ox)2]×1/2H2O}n (dmfꢁdimethylformamide) [13] and
the three-dimensional compound {Ba(H2O)[Cr(bipy)-
(ox)2]2×H2O}n [17]. In the present contribution, we
/
nH2O [Mꢁ
/
/
/
/
/
/
/
/
/
/
discuss the synthetic possibilities offered by the mono-
nuclear complex [Cr(bpym)(ox)2]ꢀ (bpym is the poten-
tially bis-chelating 2,2?-bipyrimidine ligand) when acting
as a ligand. The structure of this anion has been
previously described as tetraphenylarsonium, sodium
and potassium salts [20,21]. The preparation, structural
characterization and magnetic investigation of the
2.3. Physical measurements
IR spectra (4000ꢃ
Bruker IF S55 spectrometer with samples prepared as
KBr pellets. Variable temperature (1.9ꢃ290 K) magnetic
/
400 cmꢀ1) were recorded with on a
/
susceptibility measurements were carried out with a
Quantum Design SQUID magnetometer operating at
complexes
[Ag(bpym)][Cr(C2O4)2(H2O)2]×
of this work.
PPh4[Cr(bpym)(ox)2]×
/
H2O
(1)
and
2H2O (2) are the subject
0.1 T. It was calibrated with (NH4)2Mn(SO4)2×
Diamagnetic corrections of the constituent atoms were
estimated from Pascal’s constants [22] as ꢀ405ꢄ
10ꢀ6
(1) and ꢀ234ꢄ
10ꢀ6 (2) cm3 molꢀ1
/
12H2O.
/
/
/
/
/
.
2. Experimental
2.4. Crystal structure determination and refinement
2.1. Materials
Diffraction data on single crystals of 1 and 2 were
collected on Siemens R3m/V automatic (1) and Bruker
Smart CCD (2) diffractometers by using graphite-
2,2?-Bipyrimidine was purchased from Lancaster and
used without further purification. All other chemicals
were reagent grade and used as received. Elemental
analysis (C, H, N) were performed by the Microanaly-
tical Service of the Universidad Auto´noma de Madrid.
The value of the P:Cr (1) and Ag:Cr (2) molar ratio (1:1
for 1 and 2) was determined by electron microscopy at
the Servicio Interdepartamental de Investigacio´n of the
University of Valencia.
monochromated Mo Ka radiation with the v ꢃ
/2u
technique. A nominal crystal to detector distance of 4
cm is used in the case of 2. Accurate cell dimensions and
orientation matrices (1) were obtained by least-squares
refinements of 25 accurately centred reflections with
15B
/
u B308. Examination of three standard reflections
/
(1) monitored after every 50 reflections, showed no sign
of crystal deterioration. Lorentz polarization (Lp) and
c-scan absorption (1) corrections [23] were applied to
the intensity data. A hemisphere of data (2) was
2.2. Preparation of compounds
collected based on three v-scan runs (starting vꢁ
at values of fꢁ0, 90, and 1808 with the detector at
2uꢁ308. At each of these runs, frames (606, 435, and
230, respectively) were collected at 0.38 intervals and 15
/
308)
2.2.1. PPh4[Cr(bpym)(ox)2]×
/
H2O (1)
A concentrated aqueous solution (40 cm3) containing
/
/
chromium(III) chloride hexahydrate (1 mmol), 2,2?-

48
G. Marinescu et al. / Inorganica Chimica Acta 336 (2002) 46ꢃ54
/
s per frame. The diffraction frames were integrated
using the SAINT package [24] and corrected for absorp-
tion with SADABS [25]. The maximum and minimum
transmission factors were 0.9234 and 0.8997 for 1 and
1.95 and 1.26 for 2. Pertinent details for the structure
determination and refinement of 1 and 2 are sum-
marised in Table 1.
The structures of 1 and 2 were solved by direct
methods through the SHELXTL NT [26] program package
and subsequently refined by Fourier recycling. All non-
hydrogen atoms of 1 and 2 were refined anisotropically.
In the structure of compound 2, the chromium atom was
found on a twofold axis and the silver atom disordered
in two positions: one on a twofold axis [Ag(1)] and the
other one on a general position [Ag(2)]. The refinement
of the occupancy of Ag(1) and Ag(2) led to convergence
with 0.26(3) and 0.23(3) occupancy factors, respectively;
these values (sum 0.50) are in agreement with stoichio-
metry. The hydrogen atoms of the water molecule of 1
were located on a DF map and refined with restraints
whereas those of the bpym ligand were set in calculated
positions and refined as riding atoms. In the case of 2,
all the hydrogen atoms were found in a difference
Fourier map and refined isotropically. The final full-
matrix least-squares refinement on F2, minimising the
function a w(½Fo½ꢀ
½Fc½)2, reached convergence at the
/
values of the discrepancy indices listed in Table 1. The
final geometrical calculations and graphical manipula-
tions were carried out with the PARST program [27] and
the XP utility of the SHELXTL NT systems. Selected bond
distances and angles are gathered in Table 2 (1) and
Table 3 (2).
3. Results and discussion
3.1. Crystal structures
Table 1
Crystal data and structure refinement parameters for complexes 1 and
2
3.1.1. Description of PPh4[Cr(bpym)(ox)2]×
/
H2O (1)
The structure of 1 consists of discrete [Cr(bpym)-
(ox)2]ꢀ anions (Fig. 1), tetraphenylphosphonium ca-
tions and uncoordinated water molecules which are
linked by electrostatic forces, hydrogen-bonds and Van
der Waals interactions (see below). Each chromium
atom is six-coordinated with two bpym-nitrogen and
four oxalate-oxygen atoms building a distorted octahe-
dral environment. The main distortions of the ideal
octahedral geometry are due to the short bite of the
Compound
Formula
M
1
2
36H28CrN4O9P C12H14AgCrN4O12
C
743.59
566.14
monoclinic
C2/c
Crystal system
Space group
Crystal size (mm)
monoclinic
P21/c
0.24ꢄ0.20-
ꢄ0.18
0.38ꢄ0.27ꢄ0.18
˚
a (A)
14.628(4)
13.787(4)
18.084(5)
112.46(2)
3370.5(16)
4
18.0827(16)
10.9385(13)
12.3648(14)
95.209(2)
1896.9(4)
4
˚
b (A)
˚
c (A)
b (8)
Volume (A )
bidentate bpym [77.5(1)8 for N(1)ꢀ
oxalate ligands [82.7(1) and 83.0(1)8 for O(1)ꢀ
O(2) and O(5)ꢀCr(1)ꢀO(6), respectively]. The mean
/
Cr(1)ꢀ
/
N(4)] and
3
˚
/
Cr(1)ꢀ
/
Z
T (K)
rcalc (g cmꢀ3
/
/
293(2)
1.465
293(2)
1.982
)
˚
l (Mo Ka) (A)
0.71073
0.450
1532
0.71073
1.678
1124
Table 2
Main interatomic bond distances (A) and angles with e.s.d.s in
parentheses for complex 1
m (mmꢀ1
F(000)
)
˚
uRange (8)
Index ranges
1.91ꢃ
/
25.22
2.36ꢃ26.37
ꢀ175h 517,
ꢀ115k 513,
ꢀ135l 515
5813
/
Bond lengths
ꢀ175h 515,
05k 516,
05l 521
6245
Cr(1)ꢀO(1)
Cr(1)ꢀO(5)
Cr(1)ꢀN(1)
1.952(3) Cr(1)ꢀO(2)
1.981(3) Cr(1)ꢀO(6)
2.090(4) Cr(1)ꢀN(4)
1.964(3)
1.951(3)
2.064(4)
Total data collected
Independent reflections 5863
1944
0.0199
full-matrix least- full-matrix least-squares
Bond angles
Rint
0.0240
O(1)ꢀCr(1)ꢀO(2)
82.7(1) O(1)ꢀCr(1)ꢀO(5) 96.4(1)
Refinement method
O(1)ꢀCr(1)ꢀN(4) 169.8(1) O(1)ꢀCr(1)ꢀN(1) 94.3(1)
O(1)ꢀCr(1)ꢀO(6) 95.1(1) O(2)ꢀCr(1)ꢀN(4) 91.2(1)
O(2)ꢀCr(1)ꢀO(5) 178.8(1) O(2)ꢀCr(1)ꢀN(1) 91.4(1)
O(2)ꢀCr(1)ꢀO(6) 96.2(1) O(5)ꢀCr(1)ꢀN(4) 89.7(1)
O(5)ꢀCr(1)ꢀN(1) 89.5(1) O(5)ꢀCr(1)ꢀO(6) 83.0(1)
N(4)ꢀCr(1)ꢀN(1) 77.5(1) N(4)ꢀCr(1)ꢀO(6) 93.7(1)
a,b
Hydrogen bonds
squares on F2
on F2
Data/restraints/para-
meters
Goodness-of-fit on F2
5863/3/466
1944/0/175
1.067
0.909
R indices [I ꢀ2s(I)]
R1ꢁ0.0573;
wR2ꢁ0.1294
R1ꢁ0.1029;
wR2ꢁ0.1661
R1ꢁ0.0233;
wR2ꢁ0.0534
R1ꢁ0.0326;
wR2ꢁ0.0551
a
a
R indices (all data)
A
D
H
AÁ Á ÁD
AÁ Á ÁHꢀD
Largest difference peak 0.302 and
ꢀ3
0.227 and ꢀ0.357
˚
and hole (e A
)
ꢀ0.337
O(8)
O(3a)
O(9)
O(9)
H(1w)
H2w)
2.918(6) 155(4)
2.936(6) 167(4)
a
R1ꢁS(½Fo½ꢀ½Fc½)/S½Fo½,
wR2ꢁ{S[w(Fo2ꢀFc2)2]/[Sw(Fo2)2]}1/2
and wꢁ1/[s2(Fo2)ꢂ(aP)2ꢂbP] with Pꢁ[Fo2ꢂ2Fc2]/3, aꢁ0.0672
(1) and 0.0314 (2) and bꢁ1.7817 (1) and 0.0000 (2).
a
Symmetry code: (a) ꢀx, yꢀ1/2, ꢀzꢂ3/2.
A, acceptor; D, donor.
b

G. Marinescu et al. / Inorganica Chimica Acta 336 (2002) 46ꢃ
/
54
49
Table 3
Main interatomic bond distances (A) and angles with e.s.d.s in parentheses for complex 2
a
˚
Bond lengths
Cr(1)ꢀO(1)
Cr(1)ꢀO(3)
Ag(1)ꢀN(2)
Ag(2)ꢀN(2)
Ag(2)ꢀN(2c)
1.9999(16)
1.9585(14)
2.331(2)
Cr(1)ꢀO(2)
1.9575(12)
2.360(2)
2.178(17)
2.59(2)
Ag(1)ꢀN(1a)
Ag(2)ꢀN(1a)
Ag(2)ꢀN(1b)
2.58(2)
2.132(18)
Bond angles
O(1)ꢀCr(1)ꢀO(1c)
O(1)ꢀCr(1)ꢀO(3c)
O(1)ꢀCr(1)ꢀO(2c)
O(3)ꢀCr(1)ꢀO(2)
O(2)ꢀCr(1)ꢀO(2c)
N(2)ꢀAg(1)ꢀN(2c)
N(2c)ꢀAg(1)ꢀN(1b)
N(2)ꢀAg(2)ꢀN(1b)
N(2)ꢀAg(2)ꢀN(1a)
N(1a)ꢀAg(2)ꢀN(1b)
91.19(10)
179.13(7)
95.75(7)
83.50(6)
172.53(9)
160.0(3)
70.72(6)
99.4(11)
69.0(4)
O(1)ꢀCr(1)ꢀO(3)
O(1)ꢀCr(1)ꢀO(2)
O(3)ꢀCr(1)ꢀO(3c)
O(3)ꢀCr(1)ꢀO(2c)
N(2)ꢀAg(1)ꢀN(1a)
N(2)ꢀAg(1)ꢀN(1b)
N(1a)ꢀAg(1)ꢀN(1b)
N(2)ꢀAg(2)ꢀN(2c)
N(1a)ꢀAg(2)ꢀN(2c)
N(2c)ꢀAg(2)ꢀN(1b)
88.36(7)
89.48(7)
92.10(9)
91.31(6)
70.72(6)
114.33(6)
152.8(3)
153.9(9)
132.3(16)
69.4(4)
148.4(8)
Hydrogen bonds
A
D
H
AÁ Á ÁD
AÁ Á ÁH-D
O(10)
O(5f)
O(4g)
O(4h)
O(5h)
O(1)
O(1)
H(1A)
H(1B)
2.599(3)
2.664(2)
2.789(3)
2.908(3)
3.044(3)
169(3)
170(3)
153(4)
142(3)
145(3)
O(10)
O(10)
O(10)
H(10A)
H(10B)
H(10B)
a
Symmetry code: (a) ꢀxꢂ1, ꢀy, ꢀz; (b) x, ꢀy, zꢂ1/2; (c) ꢀxꢂ1, y, ꢀzꢂ1/2; (f) ꢀxꢂ1, ꢀyꢂ1, ꢀz; (g) ꢀxꢂ3/2, yꢂ1/2, ꢀzꢂ1/2; (h) x,
ꢀyꢂ1, zꢂ1/2.
˚
1.95(1) A] [19]. The bpym molecule as a whole is planar
and it forms dihedral angles of 88.7(1) and 86.6(1)8 with
values of the Crꢀ
/
N and Crꢀ
/
O bond distances are
˚
2.077(4) and 1.952(3) A, respectively. These values are
practically identical to those observed in the isostruc-
tural complex AsPh4[Cr(bpym)(ox)2] [2.075(6) and
the oxalate mean planes. Two sets of carbonꢀ
oxalate bond distances are observed, the shorter values
belonging to the peripheral CꢀO bonds in agreement
with their greater double bond character [the ranges of
the values for peripheral and inner CꢀO bonds are
1.220(6)ꢃ1.232(6) and 1.313(6)ꢃ1.294(6) A, respec-
tively].
/oxygen
/
˚
1.945(6) A] [20]. They are also close to previous values
reported for mononuclear chromium(III) complexes
containing either bidentate bpym or oxalate ligands
/
˚
/
/
such as NEt4[Cr(bpym)(NCS)4] [av. Crꢀ
/
N(bpym)ꢁ
H2O with AAꢁ
1.944 (6) A] [14], dpa [av. Crꢀ
1.97(1) A] [15] and bipy [av. CrꢀO(ox)ꢁ
/
˚
2.072(3) A] [28], PPh4[Cr(AA)(ox)2]×
/
/
In the overall crystal packing of 1, there are distinct
domains dealing with the anionic and cationic units.
Focusing on the tetraphenylphosphonium cations, they
form chains along the y direction (Fig. 2), each cation
being involved in two kinds of supramolecular interac-
tions: the sextuple phenyl embrace (SPE) in which three
phenyl rings from each unit gives rise to six edge-to-face
local arylÁ Á Áaryl interactions, and the offset face-to-face
(OFF) pattern [the two phenyl planes are separated by
˚
phen [av. Crꢀ
/
O(ox)ꢁ
/
/
˚
O(ox)ꢁ
/
/
/
˚
3.55(1) A]. The intrachain PÁ Á ÁP separations through the
SPE and OFF supramolecular motifs are 6.002(2) and
˚
8.072(2) A, respectively. This terminology was intro-
duced by Dance et al. through a careful examination
and analysis of the Cambridge Structural Database [29].
These authors have described the multiple phenyl
ꢂ
embrace involving pairs of PPh4 cations in crystals
and they have shown that these interactions are indeed
strong attractive concerted supramolecular motifs [30].
As far as the [Cr(bpym)(ox)2]ꢀ anions are concerned,
Fig. 1. Perspective drawing of the [Cr(bpym)(ox)2]ꢀ mononuclear unit
of 1 with the atom numbering. Thermal ellipsoids are drawn at the
30% probability level.

50
G. Marinescu et al. / Inorganica Chimica Acta 336 (2002) 46ꢃ54
/
Fig. 4. A perspective view of the structure of 2 with the atom
numbering. Thermal ellipsoids are drawn at the 50% probability level.
interactions through bpym groups occur along the z
direction, the two pyrimidyl planes being separated by
˚
3.51(1) A. Parallel sheets standing in the yz plane result
from these two interactions (Fig. 3). The chains formed
ꢂ
by the PPh4 cations separate these sheets as shown by
an overall view of the crystal packing of 1 (Fig. S1). The
Fig. 2. A view along the y axis showing the alternating SPE and OFF
ꢂ
shortest intermolecular chromiumꢃchromium separa-
/
interactions between the PPh4 cations of 1.
˚
tion is 7.242(2) A.
adjacent anions are linked through hydrogen bonds
involving the uncoordinated water molecule [O(9)] and
two oxalate-oxygen atoms [O(8) and O(3a)] (see end of
Table 2), leading to chains of chromium atoms which
grow along the y axis (Fig. 3). In addition, OFF
3.1.2. Description of [Ag(bpym)][Cr(C2O4)2(H2O)2]×
/
2H2O (2)
The structure of
2
is made up of discrete
[Cr(ox)2(H2O)2]ꢀ anions, bpym-bridged silver(I) catio-
Fig. 3. A view of the arrangement of the [Cr(bpym)(ox)2]ꢀ units of 1 showing the hydrogen bonding pattern (broken lines) and the OFF bpym-bpym
interactions along the y and z axis, respectively.

G. Marinescu et al. / Inorganica Chimica Acta 336 (2002) 46ꢃ
/
54
51
nic chains and uncoordinated water molecules (Fig. 4)
which are held together by electrostatic forces, hydro-
gen-bonds and Van der Waals interactions (see below).
Each chromium atom has a distorted octahedral sur-
rounding with two cis-coordinated water molecules and
four oxalate-oxygens from two bidentate oxalate li-
gands. The two water molecules are related by a twofold
axis, the mononuclear chromium unit belong to the C2
5) which run parallel to the c axis, the intrachain
chromiumꢃchromium separation being 6.363(1). These
anionic chains are linked through hydrogen-bonds
involving the crystallisation water molecules leading to
a three-dimensional anionic network whose holes are
filled by the cationic bpym-bridged silver(I) chains (Fig.
6).
/
point group symmetry. The Crꢀ
/
O(w) bond length
[1.9999(16) A] is somewhat longer than the CrꢀO(ox)
bonds [av. value 1.958(1) A]. As in 1, the short bite of
the chelating oxalate [83.50(6)8 for O(2)ꢀCr(1)ꢀO(3)]
3.2. IR spectra
˚
/
˚
The most relevant aspect of the infrared spectra of 1
and 2 concerns the possibility to distinguish between the
occurrence of chelating (1) and bis(chelating) (2) co-
ordination modes of bpym. In fact, the ring stretching
mode of bpym appears as a quasi-symmetric doublet at
1575m and 1545m cmꢀ1 for complex 1 whereas a single
peak at 1560s cmꢀ1 accompanied by two weak peaks at
1578 and 1540 cmꢀ1 are observed for 2. According to
previous data, these features are indicative of the
occurrence of bidentate [20,28,32] and bis-bidentate
[20,21,32] coordination modes of bpym in 1 and 2,
respectively. Dealing with the oxalate absorptions, the
pattern of the nas(OCO) [1710sh, 1700s and 1670s cmꢀ1
(1) and 1708s and 1685s,br cmꢀ1 (2)], ns(OCO) [triplet
centred at 1360 cmꢀ1 (1 and 2)] and d(OCO) [810m
cmꢀ1 (1 and 2)] vibrations support the presence of
/
/
accounts for the distortion of the ideal octahedral
geometry around the chromium atom. The value of
the dihedral angle between the planes of the two oxalate
ligands is 80.1(1)8. The disordered silver atoms [Ag(1)
and Ag(2)] are coordinated by four nitrogen atoms from
two bpym molecules. The Ag(1) atom is found on a
twofold axis and the four nitrogen atoms define a
regular metal environment with two independent
˚
N(bpym) distances of 2.331(2) and 2.360(2) A
Ag(1)ꢀ
/
for Ag(1)ꢀ
/
N(2) and Ag(1)ꢀ/N(1a), respectively. The
metal environment is almost halfway between tetrahe-
dral and square-planar as shown in Fig. 4, the value of
the dihedral angle between the mean plane of the two
bpym ligands coordinated to Ag(1) is 38.05(3)8. The
Ag(2) atom is found in a general position with a
distorted four-coordination metal environment with
chelating oxalate in both complexes [15,18ꢃ20]. The
/
out-of-plane bending vibrations of the phenyl rings of
the tetraphenylphosphonium cation (1) appear as three
two short bonds of 2.132(18) [Ag(2)ꢀ
/
N(2c)] and
sharp and strong peaks at 690, 720 and 760 cmꢀ1
.
˚
2.178(17) A [Ag(2)ꢀ
/
N(1a)] and two long ones of
˚
Finally, in the high frequency region, a strong and broad
absorption centred at 3450 cmꢀ1 for 2 and at 3500
cmꢀ1 (with two peaks at 3560 and 3480 cmꢀ1) for 1 is
consistent with the occurrence of water molecules
involved in an extensive network of hydrogen-bonds
for these species [33].
2.58(2) [Ag(2)ꢀ
/
N(2)] and 2.59(2) A [Ag(2)ꢀ
/
N(1b)].
Although the shorter bonds are close to the observed
ones in bi-coordinated silver(I) complexes with aromatic
heterocyclic amine ligands [31], the angle around Ag(2)
is far away of linearity (see Table 3). The bpym molecule
adopts bis-bidentate [Ag(1)] and bis-monodentate
[Ag(2)] coordination modes affording bpym-bridged
chains of silver(I) cations which run parallel to the c
3.3. Magnetic properties of complexes 1 and 2
axis (see Fig. S2). The silverꢃsilver separation across
/
˚
bis-bidentate bpym is 6.1854(1) A whereas the shortest
The temperature dependence of xMT for 1 and 2 [xM
is the magnetic susceptibility per mol of chromium(III)]
˚
interchain Ag(1)Á Á ÁAg(1) distance is 8.9159(7) A.
Hydrogen-bonds between the water molecules and
two peripheral oxalate-oxygen atoms (see end of Table
3) lead to uniform chains of chromium(III) atoms (Fig.
in the temperature range 1.9ꢃ100 K is shown in Fig. 7
/
(2) and Fig. S3 (1). At room temperature, the value of
xMT (ca. 1.86 cm3 molꢀ1 K) is practically identical for
Fig. 5. Hydrogen bonding interactions (broken lines) in 2 along the c axis.

52
G. Marinescu et al. / Inorganica Chimica Acta 336 (2002) 46ꢃ54
/
Fig. 6. A projection of the structure of 2 down the c axis showing the relative positions of the bpym-bridged silver(I) chains and the hydrogen
bonded mononuclear chromium(III) units.
local spin quartets or to both factors simultaneously.
Having in mind the mononuclear nature of the para-
magnetic chromium(III) unit in 1 and 2, we have
analysed their magnetic data through Eq. (1) [34] which
is derived from the Hamiltonian given by Eq. (4) (case of
an axial zero field splitting and Sꢁ3/2)
/
Nb2g2
xM ꢁ
(x ꢂ2xꢁ)
(1)
(2)
½½
3k(T ꢀ u)
1 ꢂ 9exp(ꢀ2D=kT)
x ꢁ
½½
4(1 ꢂ exp(ꢀ2D=kT))
4 ꢂ (3kT=D)[1 ꢀ exp(ꢀ2D=kT)]
xꢁ ꢁ
(3)
(4)
4[1 ꢂ 2exp(ꢀ2D=kT)]
ˆ
ˆ2
H ꢁD[SZ ꢀ1=3S(Sꢂ1)]
The parameters N, b, k and g in Eq. (1) have their usual
meanings. Least-squares fit of the xMT data of 1 and 2
through Eq. (1) leads to the following set of parameters:
Fig. 7. xMT versus T plot for complex 2: (k) experimental data; (---)
and (__
best-fit curves through Eq. (1) with uꢁ0 and u "0,
respectively (see text).
0.49 cmꢀ1, gꢁ
/
1.99, uꢁ
/
ꢀ
/
0.35 K and Rꢁ
/
2.0ꢄ
/
)
/
/
Dꢁ
10ꢀ6 for 1 and Dꢁ
and Rꢁ3.6ꢄ
10ꢀ6 for 2 (R is the agreement factor
defined as
/
/
1.0 cmꢀ1, gꢁ
/
1.99, uꢁ 0.80 K
/
ꢀ
/
/
/
both complexes and it is as expected for a magnetically
isolated spin quartet. This value remains constant when
cooling and it decreases smoothly in the lower tempera-
ture, attaining values of 1.55 (1) and 1.24 (2) cm3 molꢀ1
K at 1.9 K. No susceptibility maximum was observed in
the temperature range explored. This decrease of xMT at
lower temperatures may be attributed to the zero field
splitting (D) of the chromium(III), to weak antiferro-
magnetic intermolecular interactions (u) between the
ai[(xMT)obs(i)ꢀ
(xMT)calc(i)]2/ai[(xM-
/
T)obs(i)]2). The computed curves (solid lines in Fig. 7
and S3) match the magnetic data very well in both cases.
In order to check the reliability of these best-fit data, we
tried to simulate the magnetic data of 1 and 2 through
Eq. (1) with uꢁ
are Dꢁ
2.1 cmꢀ1, gꢁ
and Dꢁ
4.6 cmꢀ1, gꢁ
The computed curves (dashed lines in Fig. 7 and S3)
/
0. Best-fit parameters for this situation
1.98 and Rꢁ4.6ꢄ
10ꢀ5 for 1
1.98 and Rꢁ8.6ꢄ
10ꢀ5 for 2.
/
/
/
/
/
/
/
/

G. Marinescu et al. / Inorganica Chimica Acta 336 (2002) 46ꢃ
/
54
53
follow the magnetic data worse than in the previous fit.
Consequently, we will consider only the values of the
first fit in the subsequent discussion.
of the resulting species would preclude the formation of
crystals.
Accurate determination of the values of ½D½ would
require anisotropy magnetic measurements on single
crystals but this is far from the aim of the present work.
As far as the values of the intermolecular interactions
are concerned, both are antiferromagnetic and weak.
The small magnitude of the magnetic coupling in 1 and 2
is in agreement with their structures. In fact, the
hydrogen-bonds linking the chromium(III) mononuc-
lear units in 1 and 2 provide the exchange pathway. In
this respect, the somewhat larger antiferromagnetic
coupling in 2 when compared with that of 1 can be
understood by an inspection of Figs. 3 and 5. One can
see there that for compound 1, the uncoordinated water
molecule is hydrogen-bonded to two peripheral oxalate-
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 173965 (1) and 173966 (2).
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge, CB21EZ, UK (fax: ꢂ44-1233-336-033; e-
/
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk). Copies of Figures S1 (1), S2 (2)
and S3 (1) are available from the authors on request.
oxygens from two [Cr(bpym)(ox)2]ꢀ units (the
˚
chromiumꢃchromium separation being 7.242(2) A),
Acknowledgements
/
whereas in the case of 2, the coordinated water
molecules of a [Cr(ox)2(H2O)2]ꢀ unit are hydrogen-
bonded to the peripheral oxalate-oxygens from adjacent
Financial support from the Italian Ministero dell’Uni-
versita` e della Ricerca Scientifica e Tecnologica, the
Romanian Ministery of Education (Grants 30C/
CNCSIS and 1D/CNCSIS), the Spanish Ministry of
Science and Technology (Projects BQU2001-2928 and
PB98-1044) and the European Union (TMR Pro-
gramme, Contract ERBFMRXCT-980181) is acknowl-
edged.
chromium units [the chromiumꢃchromium distance
/
˚
being 6.363(1) A]. The hydrogen-bonding pattern in 2
is thus more efficient than that of 1.
3.4. On the complexing ability of the anionic building
block [Cr(bpym)(ox)2]ꢀ
We would like to finish this work with a brief
comment on the synthetic possibilities provided by the
heteroleptic complex [Cr(bpym)(ox)2]ꢀ. A priori, its
tris-chelating capability (through two bpym-nitrogens
and four oxalate-oxygen atoms) together with its
negative charge and inert character make this complex
very suitable for metal assembling in a controlled
manner. Its reaction with univalent cations such as
sodium(I) and potassium(I) led to neutral hexagonal [20]
and tetragonal [21] sheet-like polymers, respectively.
However, all the attempts we carried out using this
mononuclear complex as ligand towards first row
transition metal ions in aqueous solution were unsuc-
cessful. No crystals were obtained by slow evaporation
of these aqueous solutions, the existing species being
very soluble in this solvent. Only powder samples were
obtained to dryness. The structure of complex 2 in the
present work clarifies the situation. In fact, in the
presence of silver(I), the bpym ligand from the
[Cr(bpym)(ox)2]ꢀ unit is replaced by two water mole-
cules affording the anion [Cr(ox)2(H2O)2]ꢀ and the
silver(I) ions are complexed by the released bpym
yielding the unprecedented bpym-bridged silver(I)
chain. Thus, 2 is an ionic compound made up by
[Cr(ox)2(H2O)2]ꢀ anions and {[Ag(bpym)]ꢂ}n cations.
A similar dissociation of bpym may be envisaged when
using other transition metal ions, and the high solubility
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