Synthesis, characterization and X-ray structural studies of novel dinuclear silver(I) complexes of poly(azolyl)borate ligands

Article abstract of DOI:10.1016/S0020-1693(00)00211-5

A series of Ag(I) complexes of tris- and tetrakis-(pyrazolyl)hydroborates, tetrakis(imidazol-1-yl)borate, and hydrotris(3-methyl-1-imidazolyl-2-thione)borate, namely the previously recorded [Ag{HB(pz)₃}]₂, [Ag{HB(3,5-Me₂pz)₃}]₂, [Ag{B(pz)₄}](n), together with [Ag{HB(4-Brpz)₃}]₂, [Ag{B(3-Mepz)₄}](n), [Ag[(im)₄}](n) (Him = imidazole) and [Ag{Tm}]₂ (Tm = hydrotris(3,methyl-2-thioxo-1-imidazolyl)borate) have been synthesized and further characterized by elemental analysis, IR, Far-IR, ¹H, ¹³C NMR spectroscopy, and in the case of [Ag{Tm}]₂, also by a single-crystal X-ray study. Variable-temperature ¹H NMR spectra indicate that [Ag{HB(3,5-Me2pz)₃}]₂, [Ag{HB(4-Brpz)₃}]₂, and [Ag{B(pz)₄}](n) are fluxional, with a pyrazolyl ring exchange process occurring rapidly at 293 but not at 193 K, whereas [Ag{HB(pz)₃}]₂ and the Crystalline form of [Ag{HB(3,5-Me₂pZ)₃}]₂ are not fluxional, even at room temperature. The reactions between K[HB(pz)₃], K[HB(3,5-Me₂pz)₃], K[B(pz)₄] or K[Tm] and AgNO₃ in presence of N-and S-donor, unidentate or bidentate ligands such as pyrazole, imidazole, 1-10-phenanthroline and 1-methylimidazoline(2,3H)thione (Hmimt) were investigated. We also report the results of positive ion FAB MS studies carried Out for selected derivatives. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00211-5

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Inorganica Chimica Acta 308 (2000) 65–72
Synthesis, characterization and X-ray structural studies of novel
dinuclear silver(I) complexes of poly(azolyl)borate ligands
Effendy a,b, Giancarlo Gioia Lobbia a,c, Claudio Pettinari c,*, Carlo Santini c,
Brian W. Skelton b, Allan H. White b
a Department of Chemistry, The Uni6ersity of Western Australia, Nedlands, Western Australia 6907, Australia
b Jurusan Kimia, Uni6ersitas Negeri Malang, Jalan Surabaya 6, Malang 65145, Indonesia
c Dipartimento di Scienze Chimiche, Uni6ersita` degli Studi di Camerino, 6ia S. Agostino 1, 62032 Camerino MC, Italy
Received 11 February 2000; accepted 5 May 2000
Abstract
A series of Ag(I) complexes of tris- and tetrakis-(pyrazolyl)hydroborates, tetrakis(imidazol-1-yl)borate, and hydrotris(3-methyl-
1-imidazolyl-2-thione)borate, namely the previously recorded [Ag{HB(pz)3}]2, [Ag{HB(3,5-Me2pz)3}]2, [Ag{B(pz)4}]n, together
with [Ag{HB(4-Brpz)3}]2, [Ag{B(3-Mepz)4}]n, [Ag{B(im)4}]n (Him=imidazole) and [Ag{Tm}]2 (Tm=hydrotris(3-methyl-2-thi-
oxo-1-imidazolyl)borate) have been synthesized and further characterized by elemental analysis, IR, Far–IR, 1H, 13C NMR
1
spectroscopy, and in the case of [Ag{Tm}]2, also by a single-crystal X-ray study. Variable-temperature H NMR spectra indicate
that [Ag{HB(3,5-Me2pz)3}]2, [Ag{HB(4-Brpz)3}]2, and [Ag{B(pz)4}]n are fluxional, with a pyrazolyl ring exchange process
occurring rapidly at 293 but not at 193 K, whereas [Ag{HB(pz)3}]2 and the crystalline form of [Ag{HB(3,5-Me2pz)3}]2 are not
fluxional, even at room temperature. The reactions between K[HB(pz)3], K[HB(3,5-Me2pz)3], K[B(pz)4] or K[Tm] and AgNO3 in
presence of N-and S-donor, unidentate or bidentate ligands such as pyrazole, imidazole, 1-10-phenanthroline and 1-methylimida-
zoline(2,3H)thione (Hmimt) were investigated. We also report the results of positive ion FAB MS studies carried out for selected
derivatives. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Silver complexes; Poly(azolyl)borate complexes
1. Introduction
interesting to view the crystal structures of the
[Cu{HB(pz)3}]2 complexes as representatives of inter-
mediate structures that lie along the potential energy
surface of the pyrazolyl ring exchange pathway [6].
It has been reported that coordination number, geo-
metry and CuꢀN distances within this class of com-
pounds are strongly dependent on the size of the ligand
substituents. For example in [Cu{HB(3-Butpz)3}]2 [3]
the copper is two-coordinate with a linear geometry
whereas in [Cu{HB(pz)3}]2 [4,5] one pyrazolyl ring
adopts a bridging binding mode with the copper ion
four-coordinated. Very recently it has also been ob-
served that in the sterically encumbered [Cu{HB(3-But-
5-Mepz)3}]2 [7] an inverted disposition of the
hydrotris(pyrazolyl)borate ligand permits close contact
between the Cu (coordinated exclusively by two pyra-
zolyl moieties) and the HꢀB center. The crystal struc-
ture determination of the binary silver complex
[Ag2{HB(3,5-Me2pz)3}2] was first reported in 1999 [8].
The coordination chemistry of poly(pyrazolyl)borate
ligands [HxB(pz)4−x] has been extensively developed
over the last few decades [1]. This family of N-donors is
able not only to control the steric and electronic envi-
ronment about a metal center by modification of the
pyrazolyl substituents, but also to give multimetallic
transition metal complexes maintaining the metal cen-
ters in close proximity. This is a very interesting feature
because of the potential role of this kind of derivative
in multimetal-centered catalysis in both biological and
industrial reactions [2]. For example the dimers
[Cu{HB(pz)3}]2 have been found to be useful as starting
materials for bioinorganic modeling studies [3–5]. It is
* Corresponding author. Tel.: +39-0737-402 217; fax: +39-0737-
637 345.
E-mail address: pettinar@camserv.unicam.it (C. Pettinari).
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00211-5

66
Effendy et al. / Inorganica Chimica Acta 308 (2000) 65–72
As part of a continuing study on the coordination
aluminum foil. Concentration was always carried out in
vacuo (water aspirator). The samples for microanalysis
were dried in vacuo to constant weight (20°C, ca. 0.1
Torr). Elemental analyses (C,H,N) were performed in
house with a Carlo-Erba model 1106 instrument. IR
spectra were recorded from 4000 to 100 cm−1 with a
Perkin–Elmer System 2000 FT–IR instrument. The
electrical conductance of the dichloromethane solutions
was measured with a Crison CDTM 522 conductimeter
at room temperature (r.t.). 1H and 13C spectra were
recorded on a VXR-300 Varian spectrometer operating
chemistry of poly(azolyl)borate ligands we have re-
cently initiated an investigation into the coordination
chemistry of anionic poly(pyrazolyl)borate ligands to-
gether with analogous systems obtained by attempting
to replace the hard N-donor pyrazole ring, with the
softer S-donor 1-methylimidazoline-2(3H)-thione ring,
with silver(I) and a variety of phosphine coligands. The
compounds obtained show an interesting, and in some
cases unpredictable, structural variety, both in the local
coordination environment and in the overall geometry.
We were especially interested in exploring the factors
causing these variations, detailed investigation of which
suggests that they are determined primarily by the steric
demands of the poly(pyrazolyl)borate and only mar-
ginally by the steric demands of the phosphine ligands
[9].
Recently, Dias et al. [10] have reported the synthesis
of several poly(pyrazolyl)borate systems containing per-
fluorinated substituents, and their copper(I) and sil-
ver(I) chemistry. These studies indicate that fluoro sub-
stituents on the pyrazole rings can exert a significant
effect on the electronic properties of the metal center.
Silver(I) complexes of tris(triazolyl)borate [11] and
tris(pyrazolyl)methane [12] ligands have also attracted
some current interest [13].
1
at r.t. (300 MHz for H and 75 MHz for 13C). FAB
mass spectra were obtained on a Finnigan-MAT
TSQ70 triple stage quadrupole instrument equipped
with an Ion Tech (Teddington, UK) atom gun using Xe
as bombarding gas. The emission current was typically
set at 2 mA with an accelerating voltage of 8 keV. For
all experiments, the source was kept at r.t., using CsI
for mass calibration. Samples were directly dissolved in
a 3-nitrobenzyl alcohol matrix.
2.2. Syntheses
The proligands K[HB(pz)3], K[HB(4-Brpz)3] [15],
K[HB(3,5-Me2pz)3], K[B(pz)4] [16], K[Tm] [9a],
Na[B(im)4] [17] and K[B(3-Mepz)4] [18] were prepared
in accordance with procedures reported in the litera-
ture. KBH4, NaBH4, Hpz (pyrazole), Him (imidazole),
4-BrpzH (4-Br-pyrazole), 3,5-Me2pzH (3,5-Me2-pyra-
zole), Hmimt (1-methylimidazolyl-2-thione) were pur-
chased (Aldrich) and used as received.
Despite the importance and the wide utility of
poly(azolyl)borate complexes of group 11 metals(I) the
chemistry of silver(I) complexes with this family of
donors, in the absence of stabilizing coligands such as
PR3 or CNR, is largely unexplored except for the
pioneering studies of [14].
Here we report further synthetic and spectroscopic
studies, extending our knowledge of those previously
recorded in [14], encompassing as well [Ag{HB(4-
Brpz)3}]2, [Ag{B(3-Mepz)4}]n, [Ag{B(im)4}]n, and,
finally, of hydrotris(3-methyl-1-imidazolyl-2-thione)-
borate, [Ag{Tm}]2 with its crystal structure determina-
tion. Here we also report on the interaction between
M[HxB(pz)4−x] (M=Na or K) and K[Tm] with
AgNO3 in the presence of equimolar quantities of
unidentate (pyrazole or imidazole) or bidentate (1,10-
phenanthroline) N-donor or unidentate S-donor (1-
methylimidazoline(2,3H)thione) ligands.
2.2.1. [Ag(Tm)]2 (1)
This complex was prepared in methanol following
literature methods [9a]. Its analytical and spectral data
are in accordance with those reported in the literature
[9a]. X-ray quality crystals of 1 were obtained from
CHCl3–CH3CN at 0°C as the bis(chloroform) solvate.
\
(CH2Cl2)=1.0 V−1 cm2 mol−1. MS, FAB: m/z
M
1027 [M+Ag]+ (60%) 917 [M+H]+ (3%) 788
[M’2pzH+Ag]+ (70%) 567 [M−Tm]+ (100%) (all
peaks are at the center of an isotopic cluster).
2.2.2. [Ag{HB(pz)3}]2 (2)
Compound 2 was prepared following the method of
[14]. To a stirred methanol solution (30 ml) of
Na[HB(pz)3] (0.236 g, 1 mmol) was added AgNO3
(0.170 g, 1 mmol) at r.t. The mixture was stirred for 2
h and the solid obtained was then filtered off, washed
with methanol, and shown to be compound 2 (yield
94%). m.p. (dec.): 163°C (lit. 162−165°C [14]). 1H
NMR (DMSO, 293 K): l 6.22 (s br, 3H, 4-CH), 7.53 (s
br, 3H, 5-CH), 7.80 (s br, 3H, 3-CH). 1H NMR
(CDCl3, 293 K): l 6.25 (s br, 2H, 4-CH), 6.38 (pt, 1H,
5-CH), 7.42 (s br, 2H, 5-CH), 7.62 (pd, 1H, 3-CH),
7.80 (s br, 2H, 3-CH). \M (CH2Cl2)=0.5 V−1 cm2
2. Experimental
2.1. General procedures
All reactions were carried out under an atmosphere
of dry oxygen-free dinitrogen, using standard Schlenk
techniques. Solvents were freshly distilled over an ap-
propriate drying agent and further degassed before use
where necessary. In some cases the reactions were pro-
tected from light by covering reaction vessels with
mol−1
.

Effendy et al. / Inorganica Chimica Acta 308 (2000) 65–72
67
1
IR (Nujol, cm−1): 3124 w (CꢀH), 2429 m, 2397 m, 2379
sh (BꢀH), 1544 w, 1502 m (C···C, C···N), 355 m, 321
mbr, 279 m. Anal. Calc. for C9H10AgBN6; C, 33.8; H,
3.1; N, 26.3; Found: C, 33.4, H, 3.3; N, 26.1%. MS,
FAB: m/z 747 [M+Ag]+ (80%), 641 [M+H]+ (3%),
429 [M−HB(pz)3]+ (100%) (all peaks are at the center
of an isotopic cluster).
Et2O (1:1) (yield 98%). m.p. (dec.): 258°C. H NMR
(CDCl3, 293 K): l 6.21 (s br, 4H, 4-CH), 7.04 (s br, 4H,
5-CH), 7.42 (s br, 4H, 3-CH). H NMR (CDCl3, 193
1
K): l 5.16 (s, 2H, 4-CH), 5.30 (s, 4H, 4-CH), 7.51 (s,
6H, 5-CH), 7.68 (s, 6H, 3-CH). 13C NMR (CDCl3, 293
K): l 105.5 (s, 4-CH), 135.5 (s, 5-CH), 143.0 (s, 3-CH).
\
M
(CH2Cl2)=0.4 V−1 cm2 mol−1. IR (Nujol, cm−1):
3132 vw, 3093 vw (CꢀH), 1504 w (C···C,C···N), 368 m,
350 m, 331 w, 311 w, 261 m. Anal. Calc. for
C12H12AgBN8; C, 37.3, H; 3.1; N, 29.0; Found: C, 37.0;
H, 3.1; N, 28.9%. MS, FAB: m/z 1651 [4M+Ag]+
(30%), 1545 [4M+H]+ (25%), 1275 [3M+Ag]+ (45%),
883 [2M+Ag]+ (20%), 495 [2M−B(pz)4]+ (100%), 426
[2M+H−pzH−B(pz)4]+ (60%), 319 [M−Ag−pz−
B(pz)4]+ (90%), (all peaks are at the center of an
isotopic cluster).
2.2.3. [Ag{HB(3,5-Me2pz)3}]2 (3)
3 was prepared following the methods of [14], and as
for 2 above, by using AgNO3 (0.170 g, 1 mmol) and
K[HB(3,5-Me2pz)3] (0.336 g, 1 mmol) in methanol (50
ml) at 298 K. Compound 3 was recrystallized from
CHCl3–Et2O (1:1) (yield 90%). X-ray quality crystals of
this molecule were obtained from ethyl acetate–CHCl3
at r.t. m.p. (dec.): 200°C (lit. dec. \190° [14]). 1H NMR
(CDCl3, 293 K): l 1.92 (s, 9H, 5-CH3), 2.31 (s, 9H,
3-CH3), 5.77 (s, 3H, 4-CH). \M (CH2Cl2)=0.1 V−1
2.2.6. [Ag{B(3-Mepz)4}]n (6)
1
cm2 mol−1. H NMR of solution of crystals (CDCl3,
Compound 6 was prepared similarly to compound 2,
by using AgNO3 (0.170 g, 1 mmol) and K[B(3-Mepz)4]
(0.374 g, 1 mmol) in methanol (50 ml) at 298 K (yield
293 K): l 1.91 (s, 6H, 5-CH3), 2.24 (s, 6H, 3-CH3), 2.27
(s, 2H, 3- or 5-CH3), 2.30 (s, 2H, 3- or 5-CH3), 5.76 (s,
1
1
2H, 4-CH), 5.83 (s, 1H, 4-CH). H NMR (CDCl3, 193
97%). m.p. (dec.): 220°C. H NMR (DMSO, 293 K): l
K): l 1.87 (s, 18H, 5-CH3), 2.30 (s, 18H, 3-CH3), 5.72
(s, 6H, 4-CH). 13C NMR (CDCl3, 293 K): l 13.9 (s,
CH3), 14.8 (s, CH3), 105.3 (s, 4-CH), 146.8 (s, 5-CCH3),
150.0 (s, 3-CCH3). IR (Nujol, cm−1): 3118 vw (CꢀH),
2509 w (BꢀH), 1538 m (C···C,C···N), 553 w, 473 m, 456
s, 359 m, 349 w, 327 w, 303 w, 255 s. Anal. Calc. for
C15H22AgBN6; C, 44.6; H, 5.5; N, 20.8; Found: C, 44.2;
H, 5.6; N, 20.6%. MS, FAB: m/z 917 [M+Ag]+
(100%), 809 [M+H]+ (3%), 714 [M+H−pzH]+
(10%), 606 [M+H−pzH+Ag]+ (30%), 512 [M+
2H−2pzH+Ag]+ (10%), 403 [M−HB(3,5-Me2pz)3]+
(15%) (all peaks are at the center of an isotopic cluster).
2.08 (s br, 12H, 3-CH3), 5.92 (d, 4H, 5-CH), 6.70 (d,
4H, 3-CH). IR (Nujol, cm−1): 3126 vw, 3107 w (CꢀH),
1519 m (C···C,C···N), 423 m, 413 m, 405 s, 393 m, 253
s. Anal. Calc. for C16H20AgBN8; C, 43.5; H, 4.6; N,
25.3; Found: C, 43.4; H, 4.6; N, 25.0%. MS, FAB: m/z
993 [M+Ag]+ (10%), 912 [M+Ag+H-pzH]+ (10%),
739 [M+H+Ag−B(3-Mepz)3]+ (40%), 550 [M−B-
(3-Mepz)4]+ (50%), 468 [M+H−3-MepzH−B(3-
Mepz)4]+ (38%), 363 [M−Ag−3-Mepz−B(3-
Mepz)4]+ (100%), (all peaks are at the center of an
isotopic cluster).
2.2.7. [Ag{B(im)4}n] (7)
2.2.4. [Ag{HB(4-Brpz)3}]2 (4)
Compound 7 was prepared similarly to compound 2,
by using AgNO3 (0.170 g, 1 mmol) and Na[B(im)4]
(0.302 g, 1 mmol) in methanol (50 ml) at 298 K (yield
93%); 2 is insoluble in all common organic solvents.
m.p. (dec.): 250°C. IR (Nujol, cm−1): 3140 w, 3112 w
(CꢀH), 1559 w (C···C, C···N), 374 w, 332 w, 240 w. Anal.
Calc. for C12H12AgBN8; C, 37.3; H, 3.1; N, 29.0; Found:
C, 37.0; H, 3.2; N, 28.7%.
Compound 4 was prepared similarly to compound 2,
by using AgNO3 (0.170 g, 1 mmol) and K[HB(4-Brpz)3]
(0.480 g, 1 mmol) in methanol (50 ml) at 298 K.
Compound 4 was recrystallized from CHCl3/Et2O (1:1)
(yield 91%). m.p. (dec.): 170°C. H NMR (CDCl3, 293
K): l 6.90 (s, 6H, 3-CH), 6.60 (s, 6H, 5-CH). H NMR
(CDCl3, 193 K): l 5.18 (s, 1H), 5.30 (s, 2H), 6.83 (s, 3H,
3-CH), 6.58 (s, 3H, 5-CH), 7.51 (s, 6H), 7.53 (s, 3H),
7.68 (s, 6H). 13C NMR (CDCl3, 293 K): l 94.1 (s,
1
1
2.2.8. [(Hmimt)Ag{B(3-Mepz)4}] (8)
4-CBr), 134.7 (s, 5-CH), 142.6 (s, 3-CH).
\
To a stirred diethyl ether suspension (20 ml) of 6
(0.442 g, 1 mmol) was added Hmimt (0.114 g, 1 mmol)
at r.t. The mixture was stirred for 4 h and the solid
obtained was then filtered off, washed with diethyl
ether, and shown to be compound 8 (yield 90%). m.p.
M
(CH2Cl2)=0.8 V−1 cm2 mol−1. IR (Nujol, cm−1):
3125 vw (CꢀH), 2374 m (BꢀH), 1518 w (C···C,C···N),
419 w, 331 m, 285 w. Anal. Calc. for C9H7AgBBr3N6; C,
19.4; H, 1.3; N, 15.1; Found: C, 19.2; H, 1.2; N, 15.2%.
1
(dec.): 230°C. H NMR (CDCl3, 293 K): l 2.19 (s br,
2.2.5. [Ag{B(pz)4}]n (5)
12H, 3-CH3), 3.62 (s, 3H, N-CH3), 6.00 (d, 4H, 5-CH),
6.59 (d, 1H, 4- or 5-CH), 6.68 (d, 4- or 5-CH), 7.11 (d,
4H, 3-CH). 13C NMR (CDCl3, 293 K): l 13.9 (s,
3-CH3), 34.7 (s, N-CH3), 104.4 (s, 4-CH), 117.7 (br,
C=S), 119.8 (s, 3-CCH3), 134.8 (s, 4- or 5-CH), 136.5
Compound 5 was prepared following the method for
compound 2 and [14] by using AgNO3 (0.170 g, 1 mmol)
and K[B(pz)4] (0.318 g, 1 mmol) in methanol (50 ml) at
298 K. Compound 5 was recrystallized from CHCl3/

68
Effendy et al. / Inorganica Chimica Acta 308 (2000) 65–72
(s, 5-CH), 143.0 (s, 3-CH), 150.1 (s, 4- or 5-CH). \M
(CH2Cl2)=0.1 V−1 cm2 mol−1. IR (Nujol, cm−1):
3110 vw (C−H), 1581 w, 1517 m (C···C,C···N), 518 m,
419 m, 411 m, 397 s, 352 w, 308 w, 279 m, 247 m. Anal.
Calc. for C20H26AgBN10S; C, 41.8; H, 4.9; N, 24.3;
Found: C, 41.9; H; 4.8, N, 24.6%.
dimer)=1.737
g
cm−3
;
F(000)=576. vMo=15.7
cm−1; specimen: 0.10×0.32×0.29 mm; Tmin,
=
max
−3
,
0.70, 0.86. ny=313, ꢀDzmaxꢀ=1.09 e A
.
Comment — ‘Thermal motion’ on the solvent chlo-
rine atoms was high, possibly a foil for unresolved
disorder. Site occupancies were set at unity after trial
refinement.
2.2.9. [(phen)Ag{B(3-Mepz)4}] (9)
To a stirred diethyl ether suspension (20 ml) of 6
(0.442 g, 1 mmol) was added 1,10-phenanthroline
(phen) (0.180 g, 1 mmol) at r.t. The mixture was stirred
for 4 h and the yellow solid obtained was then filtered
off, washed with diethyl ether, and shown to be com-
pound 9 (yield 95%). m.p. (dec.): 280°C. 1H NMR
(CDCl3, 293 K): l 2.08 (s br, 12H, 3-CH3), 5.90 (br,
4H, 5-CH), 6.90 (br, 4H, 3-CH), 7.67 (m, 2H, CH),
7.86 (s, 2H, CH), 8.34 (dd, 2H, CH), 9.02 (d, 2H, CH).
13C NMR (CDCl3, 293 K): l 14.3 (s, 3-CH3), 103.9 (s,
4-CH), 123.2 (s, CH), 126.6 (s, CH), 128.7 (s, 3-CCH3),
136.1 (s, CH), 136.4 (s, 5-CH), 150.4 (s, CH). \M
(CH2Cl2)=1.0 V−1 cm2 mol−1. IR (Nujol, cm−1):
1588 w, 1565 w, 1505 m (C···C,C···N), 417 m, 410 m,
396 m, 388 m, 341 w, 324 w, 304 w, 279 w, 256 m, 247
m. Anal. Calc. for C28H28AgBN10; C, 54.0; H, 4.5; N,
22.5; Found: C, 54.5; H, 4.5; N, 22.7%.
3. Results and discussion
3.1. Synthesis
The interaction between silver(I) nitrate and potas-
sium or sodium salts of tris- and tetrakis-(azol-1-
yl)borates [HxB(Az)4−x] (HAz=1-methylimidazoline-
(3H)-thione, pyrazole, 3-methylpyrazole, 3,5-dimethyl-
pyrazole, 4-bromopyrazole or imidazole) in methanol at
r.t., readily gives the complexes 1–7 in high yield, in
accordance with the following equation:
CH OH/r.t.
3
AgNO3+M[HxB(Az)4−x]ꢀꢀꢀꢀꢀꢀꢁ [Ag{HxB(Az)4−x}]n
+MNO3
(x=0 or 1, M=K or Na)
(1)
On the basis of literature data [8], X-ray structural
studies and MS FAB (see below) a dinuclear structure
can be plausibly assigned to compounds 1–4, three
different coordination modes being possible for the
tris(pyrazolyl)borates (Fig. 1), whereas poly- or oligo-
nuclear structures, containing bridging poly(pyra-
zolyl)borates [20], appear more likely for the poorly
soluble derivatives 5–7, it not being possible to obtain
good quality crystals suitable for X-ray studies for 5–7,
so that we are unable to confirm this hypothesis. All the
colorless compounds 1–7 decompose without melting.
They are stable to air and somewhat light-sensitive,
poorly soluble in chlorinated solvents, acetone and
DMSO. They are generally non-electrolytes in CH2Cl2
(\m in the range 0.1–1.0 V−1 mol2 cm−1) and insolu-
ble in acetonitrile, water, ethyl acetate, methanol, etha-
nol, and benzene. In chloroform solution the silver(I)
tris(pyrazol-1-yl)borate complexes 2–4 often darken,
even with strict exclusion of oxygen and light: this is
due to the strong reducing power of the borate anion
retaining one hydrogen which immediately converts the
complex into metallic silver, in accordance with the
following equation:
2.3. Attempted reactions
The reactions between complexes 1, 2, 3 or 5 and
Hpz, Him, Hmimt and phen have been carried out
similarly, but no products were obtained, the starting
material being always recovered. The reaction between
compound 6 and Hpz or Him was always unsuccessful,
the starting material being recovered.
2.4. Single crystal X-ray study
For [Ag(Tm)]2·2CHCl3 (1) a unique room-tempera-
ture single counter diffractometer data set was mea-
sured (T ca. 295 K; monochromatic Mo Ka radiation,
,
u=0.71073 A; 2qmax=50°) yielding 3884 independent
reflections, 2744 with I\3|(I) being used in the refine-
ment after gaussian absorption correction. Full-matrix
least-squares refinement was employed, anisotropic
thermal parameter forms being refined for the non-hy-
drogen atoms, together with (x,y,z,Uiso)H. Conventional
residuals R, Rw (statistical weights) were 0.051, 0.054 at
convergence; neutral atom complex scattering factors
were employed within the context of the Xtal 3.4
program system [19].
[AgHB(pz)3]2“H2+2Ag+[B(pz)3]2
(2)
2.4.1. Crystal/refinement data
[Ag(Tm)]2·2CHCl3 (1). C26H34Ag2B2Cl6N12S6, M=
1157.1. Triclinic, space group P1 (Ci , No.2) a=
11.067(5) b=10.338(5) c=9.729(5) A, h=86.72(4)
A similar decomposition has been previously reported
for mercury derivatives containing HB(pz)3 [21].
The reaction between compounds 1, 2, 3 or 5 and
uni- or bidentate, N- or S-donor ligands was always
unsuccessful, the starting material being always recov-
1
(
,
3
,
i=86.53(3) k=85.66(4)°, V=1106 A . Dcalc (Z=1

Effendy et al. / Inorganica Chimica Acta 308 (2000) 65–72
69
ered, even when the reaction was carried out under
forcing conditions, i.e. large excess of the neutral ligand
and refluxing solvent, whereas the reaction between
and Hg(II) derivatives [23]. In particular the absorp-
tions at 150 and 130 cm−1 are assigned, in accordance
with literature data, to the bridging w(AgꢀS) modes
[23a].
compound
(Hmimt) or 1,10-phenanthroline (phen) yielded the 1:1
adducts [(Hmimt)Ag{B(3-Mepz)4}] (8) and
6
and 1-methylimidazoline(3H)-thione
In addition to several absorptions characteristic of
the azole ring system and of the starting silver(I) deriva-
tives, there are some bands at ca. 350–250 cm−1
,
[(phen)Ag{B(3-Mepz)4}] (9) respectively. It is worth to
noting that to date this is the only procedure that
allows the synthesis of this kind of complex containing
both anionic and neutral azole-type ligands.
similar to those described in the literature [24] for some
metal(I) azolato derivatives, tentatively assigned to
w(AgꢀN) vibrations.
1
The H and 13C NMR spectra were obtained using
3.2. Spectroscopy
chloroform or DMSO as a solvent. They support the
formulae proposed and show that our [HxB(Az)4−x
donors have not undergone any structural change upon
coordination.
]
In the infrared spectra of derivatives 1–7 (the most
remarkable bands are reported in Section 2) recorded in
Nujol mull w(CꢀH) for the heterocyclic ring is found
above 3100 cm−1, the ‘breathing’ of the heterocyclic
rings [22] at ca. 1540–1500 cm−1 and finally the BꢀN
stretching vibration as a band of medium intensity at
The generally significant Z values (Z is the difference
in chemical shift of a given magnetically equivalent
nucleus in the anionic ligand of the alkali metal salt
with respect to its silver(I) derivative) suggest the persis-
tence of the complexes in weak donor solvents such as
the chlorinated ones.
ca. 1400 cm−1
.
In 3 the BꢀH stretch appears as a single peak at ca.
2509 cm−1, whereas a closer examination of the spec-
trum of the derivative of [HB(pz)3] shows a medium
absorption at ca. 2450 cm−1 and the presence of a
second weaker absorption at ca. 2400 cm−1. These
bands are not significantly shifted upon co-ordination.
The IR spectrum of the complex 1 shows w(CꢀN)
shifted to higher frequencies with respect to the
analogous bands in the potassium salts of Tm. In the
Far-IR region several bands due to w(CꢀS) coupled
with w(AgꢀS) bands at ca. 280 cm−1 are also found
which suggest ligand thione S-donation. The absorp-
tions found in the 200–150 cm−1 region are analogous
to those reported for dinuclear S-bridged Cu(I), Ag(I)
1
In the H NMR spectra, as previously found in other
poly(azol-1-yl)borate derivatives [9], upfield resonances
in the case of H(3) and H(4), and downfield ones in the
1
case of H(5), were detected. In the H NMR spectra
(r.t.) of derivatives 3, 4 and 5, only one set of signals is
found for the pyrazolyl groups, suggesting highly flux-
ional species likely due to a complete dissociation and
reassociation of the pyrazolyl nitrogens throughout a
‘pinwheel’ mechanism [3] which does not occur at lower
temperatures: in fact, on cooling the CDCl3 solutions of
3–5 to 193 K, additional pyrazole ring signals
appeared.
Fig. 1. Molecular structures proposed for compounds 2–4.

70
Effendy et al. / Inorganica Chimica Acta 308 (2000) 65–72
cated, it is of interest to note that frequently the
disposition of a species in the crystal is often indicative
of the form predominant in solution at low
temperature.
The positive fast atom bombardment mass spectra of
silver(I) complexes 1, 3, 5, and 6 (the most relevant data
are reported in the Experimental section) indicated that
these derivatives undergo a sequential loss of ligands; in
particular, decomposition of the silver(I) complexes fol-
lowed two fragmentation routes: those in which the
parent molecular ion sequentially lost pyrazole, and
which included direct cleavage of the BꢀN bonds, and
those corresponding to loss of tetrakis- or tris-(azol-1-
yl)borate groups or their fragments, which included
breaking of the AgꢀN bond. The first route was confi-
rmed by the detection of peaks consistent with either
[M−pzH]+ or [M+nH−npzH]+ (with n=2 or 3),
whereas the second route was confirmed by the exis-
tence of fragments corresponding to the loss of
[HxB(pz)4–x] (x=0–2) species. However, the predomi-
nant peaks, corresponding to ions containing silver, are
those which undergo addition of the Ag+ ion with the
probable formation of trinuclear or polynuclear species
such as that identified by single crystal X-ray diffrac-
tion methods [25].
The presence of peaks due to trinuclear and tetranu-
clear fragments in the spectrum of 5, further support
the hypothesized oligo- or poly-nuclear structure for
the tetrakis(pyrazolyl)borate derivatives.
3.3. Structure determinations
The results of the single crystal X-ray structure study
shows [Ag(Tm)]2·2CHCl3 (1) to be binuclear accompa-
nied by a pair of chloroform solvent molecules. One
half of the dimer, (together with one solvent molecule)
comprises the asymmetric unit of the structure of 1, the
dimer being disposed about a crystallographic center of
symmetry.
Fig. 2. Two projections showing the dimer 1; 20% thermal ellipsoids
are shown for the non-hydrogen atoms, hydrogen atoms having
The dimer 1 is depicted in two projections in Fig. 2.
The core of the dimer is a four-membered Ag(m-S)2Ag
ring, the sulfur atom of ring 1 bridging the two silver
atoms somewhat unsymmetrically (AgꢀS 2.857(2)
,
arbitrary radii of 0.1 A.
,
Compound 2 shows a different behavior: in DMSO
at r.t. only one set of signals is found for the protons of
the three pyrazolyl groups; in CDCl3 only the H4
resonance splits into two resonances with 2/1 integrated
intensity, indicating that this compound is not fluxional
at r.t. in the latter solvent. It is also of interest to note
2.552(2); Ag···Ag 3.215(1), S···S 4.361(3) A; SꢀAgꢀS,
107.30(6) AgꢀSꢀAg 72.70(5)°; deviations of Ag from
2
,
the C3N2S plane ( 64.7) −2.46(1), 0.55(2) A, with
CꢀSꢀAg 96.4(2), 115.6(2)°). A concomitant of this
mode of interaction, together with the disposition of
the rest of the ligand, is that the BH bridgehead is
disposed with the hydrogen atom projecting into the
Ag2S2 ring, with H···Ag 2.83(5), 2.45(5), H···S 2.88(5),
1
that the H NMR spectrum (293 K) of 3 recrystallized
from chloroform and ethyl acetate, is completely differ-
ent from the spectrum of the same derivative not re-
crystallized. In the crystalline form of 3, analogously to
compound 2, the H4 resonance splits into two reso-
nances with 2/1 integrated intensity, consistent with the
X-ray crystal structure data [8]. As previously indi-
,
,
3.17(5) A and H lying only 2.07(5) A out of the plane.
The Ag2S2/ring 1 interplanar dihedral angle is 80.3(1)°.
The sulfur atoms of the two remaining rings of each
ligand complete four-coordinate arrays about the silver
atoms, that from ring 2 coordinating to the original

Effendy et al. / Inorganica Chimica Acta 308 (2000) 65–72
71
t
silver and that from ring 3 to its inversion image, so
that the ligand straddles the pair of metal atoms (Ag···S
CO and BuNC [10f,g], but also for a number of the
more common crystallization solvents such as tetrahy-
drofuran (thf) and toluene [10f,g]. To date, no crystallo-
graphic characterization of Ag(HBpz3) 2 has been
reported; however, the form of [Ag{HB(3,5-Me2pz)3}]2
3 [8], as recorded elsewhere recently, and substantiated
by our own work, despite substitution, is not that of its
copper(I) homologue, with non-bridging pyrazolate
units and three-coordinate metal atoms, but, rather,
that of the unsubstituted parent [Cu(HBpz3)]2 with
N2M(m-N)2 metal atom environments, presumably a
consequence of greater flexibility contingent upon the
incorporation of the larger (silver) metal atom.
,
2.553(2), 2.524(2) A, SꢀAgꢀS 106.99(7)°) with associ-
ated silver atom deviations from the ring planes being
,
rather large (1.545(6), 1.00(2) A) suggesting some strain
in the array. This perception is reinforced by rather
large associated AgꢀSꢀC angles (116.2(2), 111.7(2)°) but
there are few other indicators to strongly support this
contention: for example NꢀBꢀN are closely arrayed
between 107.7(5)–110.5(5)°, while the boron atom devi-
,
ates from the ligand planes by a maximum of 0.21(1) A,
and the interplanar dihedral angles for the ligand rings
range between 58.3(2)–82.1(2)°. There is a strong inter-
action between the chloroform hydrogen atom and the
,
sulfur of ring 2 (H···S 2.69(8) A).
Adducts of the form M[HB(Az)3] (M=Cu, Ag and
Az=azolate) are now well known. For copper(I) the
structure of the parent Cu(HBpz3) has long been estab-
lished [4], its structure being binuclear, [Cu(HBpz3)]2,
with ligands bridging the two copper atoms in a very
similar manner to that found in [Ag(Tm)]2 1 above
except that the donor atoms are now ring nitrogens so
that the resulting structure, with four-coordinate
[N2Cu(m-N)2] metal atoms, is rather more compact
(Scheme 1).
4. Supplementary material
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Centre, CCDC 143505. Copies of this information
may be obtained free of charge from: The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.
uk or www: http://www.ccdc.cam.ac.uk).
By contrast, the copper complex of the ligand con-
taining 3,5-dimethyl-substituted rings, although still
binuclear (Scheme 2) presumably in consequence of
greater steric crowding, has lost the bridging function-
ality of that pyrazolate ring, so that the copper atoms
are now three coordinate, although Cu···Cu becomes
Acknowledgements
We thank the MURST and the University of
Camerino for financial help.
,
rather shorter (2.507(1) cf. 2.660(1) A) in the process;
both dimers are centrosymmetric. The bridging func-
tion may also be supplanted in the presence of other
appropriate donors, notably CO [10d], wherein the
complex reverts to a mononuclear array of the form
[(OC)M(HBpz3)] containing four-coordinate copper(I)
in an environment of C36 symmetry. The latter form
appears to be more readily achievable with M=Ag,
such complexes having being described and structurally
characterized not only for unidentate ligands such as
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