Inorganica Chimica Acta 376 (2011) 549–556

Contents lists available at SciVerse ScienceDirect

Inorganica Chimica Acta

journal homepage: www.elsevier .com/locate / ica

Synthesis, characterization, crystal structures and photophysical properties ofcopper(I) complexes containing 1,10-bis(diphenylphosphino)ferrocene (B-dppf)in doubly-bridged mode

Manoj Trivedi a,⇑, R. Nagarajan a, Abhinav Kumar b, Nigam P. Rath c,⇑⇑, Pedro Valerga d,⇑⇑a Department of Chemistry, University of Delhi, Delhi 110007, Indiab Department of Chemistry, University of Lucknow, Lucknow 226007, Indiac Department of Chemistry & Biochemistry and Centre for Nanoscience, University of Missouri-St. Louis, One University Boulevard, St. Louis, MO 63121-4499, USAd Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, 11510 Puerto Real, Cádiz, Spain

a r t i c l e i n f o a b s t r a c t

Article history:Received 24 September 2010Received in revised form 13 July 2011Accepted 15 July 2011Available online 23 July 2011

Dedicated to Professor Josef Michl

Keywords:Copper(I) complexesBis(diphenylphosphino)ferrocene (B-dppf)X-ray crystal structuresLuminescenceTD-DFT

0020-1693/$ - see front matter � 2011 Elsevier B.V. Adoi:10.1016/j.ica.2011.07.024

⇑ Corresponding author. Tel.: + 91(0) 9811730475 (⇑⇑ Corresponding authors. Tel.: +1 314 516 5333(P. Valerga) (for crystallographic correspondence).

E-mail addresses: manojtri@gmail.com (M. Trivedi)pedro.valerga@uca.es (P. Valerga).

Five copper(I) complexes having general formula [Cu2(l-X)2(j2-P,P-B-dppf)2] (X = Cl(1), Br(2), I(3), CN(4),and SCN(5)) were prepared starting with CuX and B-dppf in 1:1 molar ratio in DCM-MeOH (50:50 V/V) atroom temperature. The complexes have been characterized by elemental analyses, IR, 1H NMR, 31P NMRand electronic spectral studies. Molecular structures for 1, 2 and 4 were determined crystallographically.Complexes 1, 2 and 4 exist as centrosymmetric dimers in which the two copper atoms are bonded to twobridging B-dppf ligands and two bridging (pseudo-)halide groups in a l-g1 bonding mode to generatenearly planar Cu2(l-g1-X)2 framework. Both bridging B-dppf ligands are arranged in antiperiplanar stag-gered conformation in 1 and 2 (mean value 56.40–56.76�), and twisted from the eclipsed conformation(mean value 78.19�) in 4. The U angle value in 4 is relatively larger as compared to 1 and 2. This seemsto indicate that the molecular core [Cu2(l-g1-X)2] in 4 is a sterically demanding system that forces theB-dppf ligand to adopt a relatively strained conformation in comparison to less strained system in 1 and2. All the complexes exhibit moderately strong luminescence properties in the solution state at ambienttemperature.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction

1,10-Bis(diphenylphosphino)ferrocene (B-dppf)-based com-plexes have drawn much attention due to their increasing role inindustry, materials chemistry, biology and applications in catalysis[1–10]. This is attributed to its stability and the ease with which ititself incorporates into more complex structures. Because of theseproperties, B-dppf has become a versatile building block for the syn-thesis of compounds with tailor made properties [1,11–13].Although B-dppf synthesized more than four decades ago, has re-ceived considerable attention recently because of its chemicaluniqueness and industrial importance [11]. The unique ability ofthis metalloligand is to modify its steric bite angle as per the geo-metric requirement of the metal to which it is attached. This isaccomplished through appropriate ring twisting or tilting andthereby lead to the stabilization of not only the usual chelates whichis the predominant character in most of the homo- and heteropoly-

ll rights reserved.

for general correspondence).(N.P. Rath), +34 956 016340

, rathn@umsl.edu (N.P. Rath),

nuclear complexes known today [14–39] but also the open [40–42],double [43] and quasi-closed bridging systems [44]. The ‘double’and ‘quasi-closed bridge’ mode are relatively rare in the literature(Scheme 1;a). The binding modes found in bimetallic complexesare of two types: g1,g1-intrabridging and g1,g1-interbridging(Scheme 1;b) [45]. Recently another incentive to study bis(diphen-ylphosphino)ferrocene copper(I) complexes has emerged from thefinding that little has been defined in respect of the structural formof its complexes with simple salts, particularly copper(I) and theirapplication in catalysis (C–C or C–O bond formation) [46–48]. Previ-ous report of simple CuX:B-dppf (1:1) adducts comprise: CuX:B-dppf (1:1) (X = Cl [49], I [50], SCN [51], (NO3)2 [52], HCO2 [52]), ofthe form [Cu2(l-X)2(j2-P,P-B-dppf)2] but no structural report hasbeen published till date dealing with CuX:dppf (1:1) (X = Br, CN).Similar adducts for AgX:B-dppf (1:1) (X = Cl, Br, I, SCN, OCN, CN,NO3, O2CCH3) were reported by Pettinari and co-workers [50]. Dur-ing the course of our current study concerning interaction of differ-ent CuX with B-dppf, to assist our understanding of the Cu(I) speciespresent in solid and solution, herein, we report the synthesis, spec-troscopic characterization and photophysical properties of five cop-per(I) complexes [Cu2(l-X)2(j2-P,P-B-dppf)2] (X = Cl(1), Br(2), I(3),CN(4), SCN(5)) and X-ray crystal structure for the complexes 1, 2and 4.

Scheme 1. (a) Coordination modes of B-dppf and (b) binding modes in bimetalliccomplexes.

550 M. Trivedi et al. / Inorganica Chimica Acta 376 (2011) 549–556

2. Experimental

2.1. Materials and physical measurements

All the synthetic manipulations were performed under oxygenfree nitrogen atmosphere. The solvents were purified and dried be-fore use by adopting the standard procedures [53]. Copper(I) chlo-ride, copper(I) bromide, copper(I) iodide, copper(I) cyanide,copper(I) thiocyanate and 1,10-bis(diphenylphosphino)ferrocene(all Aldrich) were used as received.

Elemental analyses were performed on a Carlo Erba Model EA-1108 elemental analyzer and data of C, H and N is within ±0.4% ofcalculated values. Infrared spectra were recorded using Perkin-El-mer FT-IR spectrophotometer. Electronic and emission spectra ofthe complexes were obtained on a Perkin Elmer Lambda-35 andHoriba Jobin Yvon Fluorolog 3 spectrofluorometer, respectively.1H and 31P{1H} NMR spectra were recorded on a JEOL AL-300FTNMR instrument using tetramethylsilane and phosphoric acidas an internal standard, respectively.

2.2. Syntheses

2.2.1. [Cu2(l-Cl)2(j2-P,P-B-dppf)2] (1)1,10-Bis(diphenylphosphino)ferrocene (B-dppf) (0.554 g, 1.0 mmol)

was added to a solution of copper(I) chloride (0.099 g, 1.0 mmol) in30 mL CH3OH:CH2Cl2 (50:50 V/V) mixture at room temperature. Theresulting mixture was stirred at room temperature for 24 h. Slowly,the color of the solution changed from orange to yellow. The resultingsolution was evaporated to dryness to give a yellow solid which wasthen extracted with dichloromethane (50 mL). The addition of diethylether (100 mL) to this solution led to yellow needle shaped diffractionquality crystals. These were separated and washed with diethyl etherand dried. Yield: (0.522 g, 80%). Anal. Calc. for C68H56Cl2P4Cu2Fe2: C,62.48; H, 4.29. Found: C, 62.62; H, 4.35%. IR (cm�1, KBr):m = 3448,3046, 1636, 1586, 1480, 1434, 1383, 1305, 1183, 1163, 1095, 1070,1029, 998, 889, 820, 743, 695, 634, 531, 487. 1H NMR (d ppm,300 MHz, CDCl3, 298 K): 7.72–7.35 (m, 40H, Ph), 4.37 (s, 8H, C5H4),4.20 (s, 8H, C5H4). 31P{1H}: d �17.78 (s) (sharp). UV–Vis: kmax

(e[dm3 mol�1 cm�1]) = 275 (10 458), 451 (21 203).

2.2.2. [Cu2(l-Br)2(j2-P,P-B-dppf)2] (2)This complex was prepared by similar method (Complex 1)

except copper(I) bromide (0.143 g, 1.0 mmol) was used in place

of copper(I) chloride. The resulting orange yellow solution wasevaporated to dryness to give a yellowish orange solid whichwas then extracted with 50 mL dichloromethane and methanol(50:50 V/V) mixture and left for slow crystallization at room tem-perature. The complex separated as yellow-orange needle shapedcrystals. These were separated and air dried. Yield: (0.488 g,70%). Anal. Calc. for C68H56Br2P4Cu2Fe2: C, 58.49; H, 4.01. Found:C, 58.72; H, 4.32%. IR (cm�1, nujol):m = 3447, 3051, 2923, 2852,1653, 1636, 1480, 1434, 1384, 1165, 1120, 1096, 1029, 997, 838,821, 743, 695, 632, 530, 495. 1H NMR (d ppm, 300 MHz, DMSO-d6, 298 K): 7.46–7.67 (m, 40H, Ph), 4.46 (s, 8H, C5H4), 4.28 (s, 8H,C5H4). 31P{1H}: d �15.58 (s) (sharp). UV–Vis: kmax

(e[dm3 mol�1 cm�1]) = 274 (68 020), 449 (27 038).

2.2.3. [Cu2(l-I)2(j2-P,P-B-dppf)2] (3)This complex was synthesized by using the same method as

mentioned for 1, using copper(I) iodide (0.190 g, 1.0 mmol). Theresulting yellow solution was evaporated to dryness to give a yel-low solid which was then extracted with dichloromethane (50 mL).The addition of hexane (100 mL) to this solution led to golden yel-low needle shaped crystals. These were separated and washed withdiethyl ether. Yield: (0.596 g, 80%). Anal. Calc. for C68H56I2P4Cu2Fe2:C, 54.80; H, 3.76. Found: C, 54.94; H, 3.80%. IR (cm�1, nu-jol):m = 3448, 3069, 2924, 2853, 1636, 1571, 1480, 1435, 1384,1310, 1170, 1097, 1068, 1027, 998, 837, 817, 744, 694, 626, 481,458, 428. 1H NMR (d ppm, 300 MHz, CDCl3, 298 K): 7.76–7.34 (m,40H, Ph), 4.36 (s, 8H, C5H4), 4.21 (s, 8H, C5H4),. 31P{1H}: d �19.36(s) (sharp). UV–Vis: kmax (e[dm3 mol�1 cm�1]) = 273 (10 510), 451(14 133).

2.2.4. [Cu2(l-CN)2(j2-P,P-B-dppf)2] (4)The same method as mentioned for 1, was used for the synthesis

of 4, using copper cyanide (0.089 g, 1.0 mmol). The resulting orangeyellow solution was evaporated to dryness to give a solid residuewhich was washed with diethyl ether, and dried under vacuo. Or-ange color crystals suitable for X-ray studies were grown by slowdiffusion of diethyl ether into a solution of CH3CN after 2 weeks.Yield: (0.516 g, 80%). Anal. Calc. for C70H56N2P4Cu2Fe2: C, 65.66; H,4.53; N, 2.36. Found: C, 65.32; H, 4.35; N, 2.18%. IR (cm�1, nu-jol):m = 3442, 3051, 2925, 2112 (CN), 1961, 1896, 1655, 1580,1479, 1432, 1311, 1165, 1158, 1094, 1088, 1028, 897, 818, 743,695, 629, 495. 1H NMR (d ppm, 300 MHz, CDCl3, 298 K): 7.62–8.02(m, 40H, J = 7.5 Hz, Ph), 4.53 (s, 4H, C5H4), 4.64 (s, 4H, C5H4), 4.67(s, 4H, C5H4), 4.88 (s, 4H, C5H4). 31P{1H}: d �15.88 (s) (sharp). UV–Vis: kmax (e[dm3 mol�1 cm�1]) = 457 (8777), 259 (31 675).

2.2.5. [Cu2(l-SCN)2(j2-P,P-B-dppf)2] (5)Complex 5 was synthesized similar method mentioned for 1,

using copper(I) thiocyanate. The resulting orange yellow solutionwas evaporated to dryness to give a yellowish orange solid whichwas then extracted with 50 mL dichloromethane and methanol(50:50 V/V) and left for slow crystallization at room temperature.Slowly, orange needle shaped crystals appeared. These were sepa-rated and air dried. The crystals turned opaque in air. Yield:(0.457 g, 70%). Anal. Calc. for C70H56N2S2P4Cu2Fe2: C, 62.18; H,4.15; N, 2.07; S, 4.74. Found: C, 62.39; H, 4.35; N, 2.28; S, 4.80%.IR (cm�1, nujol):m = 3442, 2108 (SCN), 1632, 1433, 1386, 1164,1091, 1024, 899, 811, 741, 695, 529, 484. 1H NMR (d ppm,300 MHz, DMSO-d6, 298 K): 7.47–7.53 (m, 40H, J = 7.5 Hz, Ph),4.35 (s, 8H, C5H4), 4.13 (s, 8H, C5H4). 31P{1H}: d �16.81 (s) (broad).UV–Vis: kmax (e[dm3 mol�1 cm�1]) = 451 (28 643), 264 (13 593).

2.3. X-ray crystallographic study

Intensity data for 1, 2 and 4 were collected on X-calibur S oxfordand Bruker APEXII CCD area detector diffractometers using graph-

M. Trivedi et al. / Inorganica Chimica Acta 376 (2011) 549–556 551

ite monochromatized Mo Ka radiation at 293(2) K (1 and 2) and100(2) K (4). SMART and SAINT software packages [54] were used fordata collection and data integration for 1, 2 and 4. Structure solutionand refinement were carried out using the SHELXTL-PLUS software pack-age [55,56]. The non-hydrogen atoms were refined with anisotropythermal parameters. All the hydrogen atoms were treated usingappropriate riding models. The computer programme PLATON wasused for analyzing the interaction and stacking distances [55,56].

2.4. Computational details

In order to ascertain the nature of the electronic absorptionbands, the density functional theory (DFT) calculations were per-formed on the complex 4 calculated using the B3LYP exchange-correlation functional [57,58]. 6-31G⁄⁄ basis set was used for C,H, N atoms, whilst TZVP basis set was employed for Fe and Cuatoms. The energies and intensities of the 60 lowest-energy spinallowed electronic excitations were calculated using the TD-DFTby employing the single crystal X-ray geometry of the complexusing polarized continuum model (PCM) [59]. The solvent param-eters were those of the dichloromethane. All calculations were per-formed using GAUSSIAN 03 program [60]. Molecular orbital diagramwere constructed by MOLDEN program [61].

3. Results and discussion

3.1. Synthesis

The reactions of CuX (X = Cl, Br, I, CN, SCN) with 1,10-bis(diphen-ylphosphino)ferrocene (B-dppf) ligand in a dichloromethane:methanol mixture (50:50 V/V) in equimolar ratio under stirringconditions at room temperature gave neutral bimetallic complexeswith the formulations [Cu2(l-X)2(j2-P,P-B-dppf)2] (X = Cl(1), Br(2),I(3), CN(4), SCN(5)) in good yield (Scheme 2).

3.2. Characterization

The complexes are air-stable, non-hygroscopic solids and solu-ble in dimethylformamide, dimethylsulfoxide and halogenated sol-vents but insoluble in petroleum ether and diethyl ether. Thecomplexes were fully characterized by IR, UV–Vis, 1H, and 31PNMR spectroscopies.

Infra-red spectrum of complex 4 exhibited characteristic bandcorresponding to mC„N of the bridging cyanide group at2112 cm�1 (see F-1 supporting material). However, only one mC„N

band agrees well with the presence of only one type of cyanidebridge between copper(I) atom [62,63]. The band associated withbridging SCN group appeared at 2108 cm�1 in 5 (see F-2 supportingmaterial) which is in accordance with those reported in literaturefor bridging pseudohalide groups [64,65].

Scheme 2. Synthetic rout

1H and 31P{1H} NMR spectral data of the complexes are recordedin the experimental section along with other data. In 1HNMR spectraof the complexes 1, 2, 3 and 5, g5-C5H4 protons of B-dppf ligands res-onated as a two singlets in the range of d 4.13–4.46 ppm and in 4 asfour singlets at d 4.53–4.88 ppm. The phenyl ring protons of B-dppfligands resonated as a multiplets at d 8.02–7.34 ppm. In the 31P{1H}NMR spectra of the complexes 1–5 showed a single resonance (d�17.78(1), �15.58(2), �19.36(3), �15.88(4), �16.81(5) ppm) forB-dppf ligands indicating that all the phosphorus atoms were chem-ically equivalent. These chemical shifts are within the range and arecomparable to copper(I) complexes containing chelating B-dppf li-gands [49,52,66,67].

All the complexes exhibit two bands at 449–457 and 259–275 nm in dichloromethane solution (see F-3 supporting material).The lower-energy band in the range of 449–457 nm can be assignedto the d–d transition. The higher-energy band at 259–275 nm hasbeen assigned to intraligand charge transfer. As a representative,the observed electronic absorption band for complex 4 has been as-signed with the help of time dependent density functional theory(TD-DFT) calculations. Since each absorption line in a TD-DFT spec-trum is composed from several single excitations, a description ofthe transition character is generally not straightforward. However,approximate assignments have been made, although they providea simplified representation of the transitions. The TD-DFT calcula-tion of 4 indicates that the low energy band (calculated at 461 nmwith oscillator strength of 0.0009) is due to the d–d transition andis attributed to the electron transfer from the dz2 orbital of the Featom of the ferrocenyl entity. The next band calculated at�260 nm is ascribed to the intraligand charge transfer. Additionally,the absorptions calculated at 354 and 287 nm with oscillatorsstrengths of 0.0165 and 0.0062, respectively indicates metal to li-gand (MLCT) charge transfer transitions from the Cu atom to the aro-matic rings of the phosphine entity (see Fig. 1).

3.3. Molecular structure determination

Details about the data collection, solution and refinement arepresented in Table 1. The molecular structures of complexes 1, 2and 4 with atomic numbering scheme are shown in Fig. 2 andimportant geometrical parameters are tabulated in Table 2. Struc-tural parameters relevant for the characterization of the Cu(I) coor-dination spheres of these tetranuclear systems are given in Table 3.Complex 1, 2 and 4 crystallized in monoclinic system with C2/cspace group. The molecular structure of 1 and 2 revealed a centro-symmetrical dimeric unit with the two chlorine/bromine atomsbridging the two copper atoms. The structure of the dichlorometh-ane solvate of 1 was already reported by Pinto [67] and Gimenoand co-workers [30]. The tetrahedral coordination of the copperatoms is achieved by two P atoms of the chelating B-dppf ligand[Cu–P bond length for 1 = 2.2675(9) and 2.2702(10) Å and Cu–P

es to complexes 1–5.

Fig. 1. Selected orbital transitions for the complex 4 (orbital contour value 0.05).

552 M. Trivedi et al. / Inorganica Chimica Acta 376 (2011) 549–556

bond length for 2 = 2.2707(12) and 2.2696(13) Å] and two chlorine/bromine atoms of the halogen groups. The P1–Cu–P2 bite angle forthe complexes 1 and 2 are 111.24(4)� and 111.58(5)�, of the chelatingB-dppf is very close to the expected value for this coordination. Theother coordination bond angles in 1 and 2 are rather distorted

Table 1Crystallographic data for complexes 1, 2 and 4.

1

Empirical formula C68H56Cl2P4Fe2Cu2Fw 1306.69Crystal system monoclinicSpace group C2/ca (Å) 24.7407(4)b (Å) 13.3773(2)c (Å) 18.6910(3)a (�) 90b (�) 93.6754(17)c (�) 90V (Å3) 6173.33(19)Z 4Dcalc (g cm�3) 1.406l (mm�1) 1.371T (K) 293(2)R1 all 0.0875R1 [I > 2r(I)] 0.0650wR2 0.2148wR2 [I > 2r(I)] 0.2077GOF on F2 1.486

[P(2)–Cu(1)–Cl(1) = 118.67(4), P(2)–Cu(1)–Cl(1)#1 = 116.02(4), P(1)–Cu(1)–Cl(1) = 99.24(4), P(1)–Cu(1)–Cl(1)#1 = 114.10(4), Cl(1)#1–Cu(1)–Cl(1) = 95.77(3); P(2)–Cu(1)–Br(1) = 119.14(4), P(2)–Cu(1)–Br(1)#1 =116.63(4), P(1)–Cu(1)–Br(1) = 98.61(4), P(1)–Cu(1)–Br(1)#1 =111.77(4), Br(1)#1–Cu(1)–Br(1) = 97.11(2)], because of the four-membered Cu2Cl2/Cu2Br2 ring and of the steric hindrance of theB-dppf ligand. The two Cu–Cl as well as Cu–Br bond lengths areasymmetrical, [2.3557(10) and 2.4419(10) Å for 1 and 2.5545(7)and 2.4766(7) Å for 2]. The plane of the bridge defined in 1 bythe two copper centers and the two chlorine atoms is almost per-pendicular to the plane defined by the four phosphorus atoms. Thedihedral angle between these two planes (b) is 83.4(1)�. TheCu����Cu distance in 1 is of 3.216(2) Å. Bond distances and anglesin 1 agree with those previously observed in dichloromethane sol-vate of 1 [30,67], while in 2, the plane of the bridge defined by thetwo copper centers and the two bromine atoms is almost perpen-dicular to the plane defined by the four phosphorus atoms. Thedihedral angle between these two planes (b) is 83.5�. The Cu����Cudistance in 2 is of 3.331 Å. The bond distances and angles in 2 agreewith those reported for other Cu(I) B-dppf complexes [30,50–52,67]. The two substituted Cp rings in the B-dppf ligand in 1and 2 adopt the antiperiplanar staggered conformation [Cp(cen-troid)����Fe����Cp(centroid) = 178.60–178.62�], which determinesthe conformational chirality of the Cp2Fe fragment. The iron cen-ters in 1 and 2 are located ±0.444–0.570 Å above and below ofthe least squares plane determined by the two copper atoms andtwo halogen bridges. The deviations of similar magnitudes werefound for the other related complexes (Table 3). This geometricarrangement leads to almost constant intermolecular Fe����Cu dis-tances (ca. 4.0 Å) for all complexes. The molecular structure of 4closely resembles to 1 and 2, except that a cyano group is bridgedto each copper center through the carbon atom. The disorder fortwo phenyl rings has been partly solved. This is probably due tomore than two orientations of phenyl rings. 4 consists of a centro-symmetrical dimeric unit with two copper(I) centers doublybridged by two synclinal eclipsed B-dppf ligands. Stabilization ofthe 14e� P–Cu(I)–P fragment is achieved by the two angular bridg-ing cyano groups which are less common than linear mode but arealso known for several metals, including copper [49,68,69]. Thedistorted tetrahedral coordination of the copper atoms [internalangles range = 107.83(12)–115.85(3)�] is achieved by two P atomsof the chelating B-dppf ligand and two carbon atoms of the cyanogroups [Cu–C bond lengths = 2.141(4) and 2.154(4) Å]. The Cu–P

2 4

C68H56P4Br2Fe2Cu2 C70H58N2P4Fe2Cu2

1395.61 1289.84monoclinic monoclinicC2/c C2/c24.6932(5) 13.6399(15)13.5819(2) 18.133(2)18.8723(3) 23.385(2)90 9093.2431(16) 92.991(3)90 906319.27(19) 5775.9(11)4 41.467 1.4832.519 1.375293(2) 100(2)0.0726 0.06050.0432 0.04390.1749 0.11470.1677 0.10361.113 1.040

Fig. 2. Molecular structures for (a) 1, (b) 2 and (c) 4.

M. Trivedi et al. / Inorganica Chimica Acta 376 (2011) 549–556 553

distances [Cu–P bond lengths = 2.2912(9) and 2.2829(10) Å] areslightly longer than those reported for polynuclear copper(I) com-plexes with B-dppf bridging ligand [30,35,52,67,70–74] but smalleras compared to [Cu2(l2-g1-C„CC6H4CH3-4)2(l-B-dppf)2] [49] and

[Cu(CNtBu)2(j2-P,P-B-dppf)][BF4] [30]. The two cyano ligands,which are C-bonded to the two copper atoms, form nearly planarCu2(l-g1-CN)2 framework, with Cu–C distances 2.141(4)–2.154(4) Å and C–N distances 0.974(7)–1.048(6) Å. The C–N dis-tances are somewhat smaller than reported for copper(I) complexeswith B-dppf bridging ligand [30], which may be due to steric hin-drance of the bulky B-dppf ligand. The two Cu–C bond lengths in 4are comparable to those of other copper(I) B-dppf complexes [49].The Cu–Cu distance is 2.5298(8) Å and comparable to the analogousdicopper(I) derivatives and within range reported for polynuclearcomplexes. The structure of complex 4 also shows the ability ofthe B-dppf ligand to adapt its conformation to the steric demandsof the dicopper(I) fragment to which it is bonded. It is apparent thatthe skeletal flexibility of B-dppf is also able to stabilize nearly planarsystem [Cu2(l-g1-CN)2(l-B-dppf)2]. In this respect the followingstructural features are significant: (a) the angleU formed by the pro-jection of the Cp���Cp axis of B-dppf onto the Cu���Cu vector (mean va-lue 46.57�); (b) the angle x by which the two Cp rings of a given B-dppf are twisted from the eclipsed position (mean value 78.19�); (c)the angle a Cipso(Cp)–P–Cu of 117.36� (average). Structural data ofdinuclear copper(I) are within range with values reported for cop-per, rhenium and silver complexes with bridging B-dppf ligand[45,50,51]. It is interesting to note that the anglesx anda in complex4 are similar to the [Cu2(l-g1-C„CC6H4CH3-4)2(l-B-dppf)2]. Thisseems to indicate that the [Cu2(l-g1-CN)2(l-B-dppf)2] core in 4 isthe most sterically demanding system, forcing the B-dppf ligand toadopt a relatively strained conformation. Crystal packing in 1, 2and 4 are stabilized by inter- and intra-molecular C–H���X (X = Cl,Br), C–H���p and p���p interactions. An interesting feature of the crys-tal packing in 1 and 4 are single helical motif resulting from C–H���pand p���p interactions, while no such motif is present in 2 (see F-4supporting material). The contact distances for C–H���p and p���pinteractions are in the range of 2.240–2.872 and 3.333–3.374 Å,respectively. These distances are within the range reported by otherworkers [75–77]. The complex 1 and 2 show C–H���Cl type of intra-molecular and C–H���Br intra-and intermolecular interaction be-tween bridging Cl/Br group and adjacent hydrogen atom attachedto the phenyl rings (B-dppf) (see F-5 supporting material). Theself-assembling of 1, 2 and 4 contain solvent accessible voids inthe crystal 3D lattice (see F-6 supporting material).

3.4. Photophysical properties

All the complexes were found to show photoluminescent at roomtemperature in dichloromethane solution (Fig. 3). The complexesupon excitation at their respective lowest energy band maximum(449–457 nm) exhibit a moderately strong emission (518–524 nm). Consistent with these previously reported complexes ofcopper(I) [78–83], we tentatively assigned the emission of theseCu(I) complexes as being a combination of a metal-centered statemodified by the Cu����Cu interaction and a MLCT or XLCT state dueto their broad emission spectra as B-dppf ligands do not show lumi-nescence in the range of 460–700 nm. The emission peaks for thecomplexes 1–5 are similar, which is in agreement with their similarCu2X2 inorganic subunits. For complexes 1–5, which have similarstructures only with a different X, the emission maximum from518 (1, CuCl type) to 520 (2, CuBr type) and 523 (3, CuI type) canbe ascribed to the electron donating ability of X because the energiesof the HOMO or LUMO of the systems would certainly depend on theextent of mixing due to the XLCT [79]. However, in the case of com-plex 4 and 5, the CN� and SCN� anions may be play a similar role ashalogen in other Cu(I) compounds. However, XLCT, CC, and LC tran-sitions may be ruled out since metal-metal bonding is negligible andcyanide and thiocyanide has a fairly large band gap. Pike et al. [82]reported that the emission band at 392 nm for CuCN should be as-cribed to invoke MC transitions of the type 3d ? (4p, 4s). They also

Table 2Selected bond lengths (Å) and bond angles (�) for complexes 1, 2 and 4.

Complex 1 Complex 2 Complex 4

Cu(1)–P(2) 2.2675(9) Cu(1)–P(2) 2.2707(12) Cu(1)–C(35) 2.141(4)Cu(1)–P(1) 2.2702(10) Cu(1)–P(1) 2.2696(13) Cu(1)–C(36) 2.154(4)Cu(1)–Cl(1)#1 2.3557(10) Cu(1)–Br(1)#1 2.4766(7) Cu(1)–P(2) 2.2829(10)Cu(1)–Cl(1) 2.4419(10) Br(1)–Cu(1) 2.5545(7) Cu(1)–P(1) 2.2912(9)Fe(1)–C(1) 2.023(4) Fe(1)–C(1) 2.029(5) Cu(1)–Cu(1)#1 2.5298(8)Fe(1)–C(2) 2.053(5) Fe(1)–C(2) 2.060(5) Fe(1)–C(1) 2.035(3)Fe(1)–C(3) 2.054(4) Fe(1)–C(3) 2.041(5) Fe(1)–C(2) 2.036(3)Fe(1)–C(4) 2.038(4) Fe(1)–C(4) 2.029(5) Fe(1)–C(3) 2.047(3)Fe(1)–C(5) 2.027(4) Fe(1)–C(5) 2.030(4) Fe(1)–C(4) 2.060(4)Fe(1)–C(6) 2.049(4) Fe(1)–C(6) 2.071(5) Fe(1)–C(5) 2.050(3)Fe(1)–C(7) 2.039(4) Fe(1)–C(7) 2.046(4) Fe(1)–C(6) 2.045(3)Fe(1)–C(8) 2.031(4) Fe(1)–C(8) 2.039(5) Fe(1)–C(7) 2.039(3)Fe(1)–C(9) 2.043(4) Fe(1)–C(9) 2.037(5) Fe(1)–C(8) 2.042(3)Fe(1)–C(10) 2.057(4) Fe(1)–C(10) 2.052(5) Fe(1)–C(9) 2.056(4)P(1)–C(5) 1.811(4) P(1)–C(5) 1.809(5) Fe(1)–C(10) 2.052(4)P(1)–C(17) 1.821(4) P(1)–C(11) 1.821(5) P(1)–C(7) 1.808(3)P(1)–C(11) 1.828(4) P(1)–C(17) 1.824(5) P(1)–C(11A) 1.833(4)Cl(1)–Cu(1)#1 2.3557(10) Br(1)–Cu(1)#1 2.4766(7) P(1)–C(11B) 1.868(4)P(2)–C(7) 1.821(4) P(2)–C(7) 1.813(4) P(1)–C(17) 1.834(3)P(2)–C(29) 1.826(4) P(2)–C(29) 1.831(5) P(2)–C(1)#1 1.820(3)P(2)–C(23) 1.828(4) P(2)–C(23) 1.822(5) P(2)–C(23) 1.832(3)P(2)–Cu(1)–P(1) 111.24(4) P(1)–Cu(1)–P(2) 111.58(5) P(2)–C(29A) 1.889(8)P(2)–Cu(1)–Cl(1)#1 116.02(4) P(2)–Cu(1)–Br(1)#1 116.63(4) N(1)–C(35) 1.048(6)P(1)–Cu(1)–Cl(1)#1 114.10(4) P(1)–Cu(1)–Br(1)#1 111.77(4) N(2)–C(36) 0.974(7)P(2)–Cu(1)–Cl(1) 118.67(4) P(2)–Cu(1)–Br(1) 119.14(4) C(35)–Cu(1)#1 2.141(4)P(1)–Cu(1)–Cl(1) 99.24(4) P(1)–Cu(1)–Br(1) 98.61(4)Cl(1)#1–Cu(1)–Cl(1) 95.77(3) Br(1)#1–Cu(1)–Br(1) 97.11(2)C(1)–Fe(1)–C(9) 177.85(19) C(1)–Fe(1)–C(9) 178.4(2)C(5)–Fe(1)–C(10) 176.00(18) C(5)–Fe(1)–C(10) 176.2(2)C(7)–Fe(1)–C(3) 176.06(19) C(3)–Fe(1)–C(7) 176.5(2)C(8)–Fe(1)–C(2) 177.32(19) C(8)–Fe(1)–C(2) 178.7(2)C(4)–Fe(1)–C(6) 175.16(16) C(4)–Fe(1)–C(6) 176.23(19)

#1 The symmetry transformation used to generate equivalent atoms.

Table 3Molecular dimensions of dimeric Cu(I) B-dppf derivatives containing Cu–X bridges.

Distances (Å)Angles (�)

X = Cl�a X = Cl�a,⁄ X = Cl�a,⁄⁄ X = I�b X = I�b,⁄ X = Br�c X = NO3�d X = HCO2

�e X = CN�f X = SCN�g

Distances (Å)Cu����Cu 3.216(2) 3.208 3.218 3.527 3.323 3.331 3.429 4.561 2.530 5.169Cu����Fe 4.060(1) 4.053 4.049 4.043 4.035 4.043 3.967 4.058 4.532 4.025Cu–P 2.277(2) 2.272(1) 2.253(9) 2.283(9) 2.271(13) 2.270(12) 2.259(6) 2.260(2) 2.287(9) 2.247(1),

2.289(1)Cu–X 2.400(2) 2.396(1) 2.398(10) 2.692(6) 2.6766(7) 2.515(7) 2.162(6) 2.083(4) 2.141(4),

2.154(4)2.013(3),2.383(1)

Angles (�)Cu–X–Cu 84.1(1) 84.0 84.2 81.8(2) 76.73(2) 82.89(2) 104.9(3) – 71.91(17),

72.42(16)88.24

X–Cu–X 95.9(1) 96.0(3) 95.7(3) 98.2(2) 103.28(2) 97.11(2) 72.6(3) 98.1(2) 107.83(12) 103.60(1)P–Cu–P 111.2(1) 111.26(4) 111.24(4) 111.2(4) 111.06(5) 111.58(5) 117.8(1) 110.8(1) 115.85(3) 112.13(4)X–Cu–P 99.7(1)–

118.8(1)99.65(4)–111.26(4)

99.24(4)–118.67(4)

100.5(4)–119.1(3)

101.55(4)–119.41(3)

98.61(4)–119.14(4)

100.3(3)–130.3(4)

108.0(1)–121.5(1)

101.49(5)–115.36(4)

97.80(1)–118.40(1)

a 42.7 41.8 42.1 41.8 39.97 41.5 45.1 37.6 71.9 43.7b 83.4(1) 83.2 82.8 85.9 87.67 83.5 78.5 85.3 90.0 84.8Ref. [67] [30] this work [52] [50] this work [52] [52] this work [51]

⁄, ⁄⁄, a-g Differenciate molecular dimensions of dimeric Cu(I) B-dppf derivatives containing different Cu-X Bridges.

554 M. Trivedi et al. / Inorganica Chimica Acta 376 (2011) 549–556

reported that the peak broadening for (CuCN)20(pip)7 (pip = pipera-zine), compared to that of CuCN, were due to the incorporation of pipligands and a heterogeneous array of copper(I) centers. Taking theposition and broad shape into account, the emission of 4 and 5may also be reasonable and consistent with the MC transitions influ-enced by the existence of B-dppf ligands.

4. Conclusion

In this work we report facile interaction between copper (pseu-do-)halide and B-dppf afford dinuclear species possessing B-dppfin doubly bridging mode, depending on the 1:1 stoichiometry of

the reactants. Also, we have presented tetrabridged dicoppercomplex [Cu2(l-g1-CN)2(l-B-dppf)2] containing two three-centertwo-electron system of two l-g1-cyano groups forming a typicalelectron deficient system of 3c–2e. This seems that B-dppf hasability to adapt to the electronic and/or steric requirements ofthe dicopper(I) fragment Cu2(l-g1CN)2. These complexes havebeen shown to exhibit luminescence properties, and the emis-sion wavelength was found to similar, which is in agreementwith their similar Cu2X2 inorganic subunits. Detailed study aboutthe reactivity of these complexes towards different isocyanidesand alkynes and their structural characterization is in progressin our laboratory.

Fig. 3. Emission spectra of the 1–5 complexes in CH2Cl2 at ambient temperature.

M. Trivedi et al. / Inorganica Chimica Acta 376 (2011) 549–556 555

Acknowledgments

We gratefully acknowledge financial support by the UniversityGrants Commission, New Delhi (Grant No. F.4–2/2006(BSR)/13–76/2008(BSR)). We thank Dr. S. Uma, the Head, Department of Chem-istry, University of Delhi, India, and Dr. Zdenek Havlas, The Direc-tor, Institute of Organic chemistry and Biochemistry, Prague, CzechRepublic for their kind encouragement. We acknowledge fundingfrom the National Science Foundation (CHE0420497) for the pur-chase of the APEX II diffractometer. Special thanks are due to TheDirector, USIC, University of Delhi, INDIA for providing Single Crys-tal X-ray Diffraction Facility.

Appendix A. Supplementary material

CCDC 779382–779384 contain the supplementary crystallo-graphic data for this paper. These data can be obtained free ofcharge from The Cambridge Crystallographic Data Centre viawww.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-ated with this article can be found, in the online version, atdoi:10.1016/j.ica.2011.07.024.

References

[1] N.J. Long, Metallocenes: An Introduction to Sandwich Complexes, BlackwellScience, Inc., Cambridge, MA, 1998.

[2] A. Fihri, P. Meunier, J.-C. Hierso, Coord. Chem. Rev. 251 (2007) 2017.[3] D.R. van Staveren, N. Metzler-Nolte, Chem. Rev. 104 (2004) 5931.[4] T.J. Colacot, Chem. Rev. 103 (2003) 3101.[5] Štepnicka (Ed.), Ferrocenes: Ligands, Materials and Biomolecules, Wiley,

Chichester, 2008.[6] N. Jiang, A.J. Ragauskas, Tet. Lett. 47 (2006) 197.[7] L.-C. Song, Z.-Y. Yang, H.-Z. Bian, Y. Liu, H.-T. Wang, X.-F. Liu, Q.-M. Hu,

Organometallics 24 (2005) 6126.[8] C. Bianchini, W. Oberhauser, A. Orlandini, C. Giannelli, P. Frediani,

Organometallics 24 (2005) 3692.[9] S.Y. Ng, G. Fang, W.K. Leong, L.Y. Goh, M.V. Garland, Eur. J. Inorg. Chem. (2007)

452.[10] M. Raghunath, W. Gao, X. Zhang, Tetrahedron Asymmetr. 16 (2005) 3676.[11] A. Togni, T. Hayashi (Eds.), Ferrocenes: Homogeneous Catalysis, Organic

Synthesis and Materials Science, VCH, Weinheim, 1995 (and references citedtherein).

[12] N.J. Long, Angew. Chem., Int. Ed. Engl. 34 (1995) 21.[13] A. Togni, R.L. Halterman (Eds.), Metallocenes: Synthesis, Reactivity,

Applications, Wiley-VCH, Weinheim, 1998.[14] L.T. Phang, T.S. Hor, Z.Y. Zhou, T.C.W. Mak, J. Organomet. Chem. 469 (1994)

253.

[15] F. Canales, M.C. Gimeno, A. Laguna, P.G. Jones, J. Am. Chem. Soc. 118 (1996)4839.

[16] M.C. Gimeno, A. Laguna, Gold Bull. 32 (1999) 90.[17] O. Crespo, F. Canales, M.C. Gimeno, P.G. Jones, A. Laguna, Organometallics 18

(1999) 3142.[18] C.E. Housecroft, D.M. Dorn, L. Arnold, Polyhedron 18 (1999) 2415 (and

references therein).[19] S. Canales, O. Crespo, M.C. Gimeno, P.G. Jones, A. Laguna, F. Mendizabal,

Organometallics 19 (2000) 4985.[20] P.M.N. Low, Z.-Y. Zhang, T.C.W. Thomas, T.S.A. Hor, J. Organomet. Chem. 539

(1997) 45.[21] V.W.-W. Yam, K.-L. Cheung, E. C.-C. Cheng, N. Zhu, K.-K. Cheung, Dalton Trans.

(2003) 1830.[22] C. Jiang, Y.-S. Wem, L.-K. Ling, T.S.A. Hor, Y.-K. Yan, Organometallics 17 (1998)

173.[23] T.S.A. Hor, L.-T. Phang, A.C.G.C. Chem, Res. Commun. 2 (1994) 1.[24] K. Lee, J.R. Shapley, Organometallics 17 (1998) 3020.[25] D.S. Shephard, B.F.G. Johnson, A. Harrison, S. Parsons, S.P. Smit, L.J. Yellowlees,

D. Reed, J. Organomet. Chem. 563 (1998) 113.[26] J.-F. Mai, Y. Yamamoto, J. Organomet. Chem. 560 (1998) 223.[27] Y.-Y. Choi, W.-T. Wong, J. Organomet. Chem. 542 (1997) 121.[28] K.S.Y. Leung, Inorg. Chem. Commun. 2 (1999) 498.[29] J. Granifo, A. Vega, M.T. Garland, Polyhedron 17 (1998) 1729.[30] J. Dîez, M.P. Gamasa, J. Gimeno, M. Lanfranchi, A. Tiripicchio, J. Organomet.

Chem. 637–639 (2001) 677.[31] H. Kawano, Y. Nishimura, M. Onishi, Dalton Trans. (2003) 1808.[32] P. Teo, L.L. Koh, T.S. Andy Hor, Chem. Commun. (2007) 4221.[33] L.M. Scolaro, M.R. Plutino, A. Romeo, R. Romeo, G. Ricciardi, S. Belviso, A.

Albinati, Dalton Trans. (2006) 2551.[34] J. Albers, V. Cadierno, P. Crochet, S.E. Garcîa-Garrido, José Gimeno, J.

Organomet. Chem. 692 (2007) 5234.[35] S. Roy, B. Sarkar, D. Bubrin, M. Niemeyer, S. Záliš, G.K. Lahiri, W. Kaim, J. Am.

Chem. Soc. 130 (2008) 15230.[36] A. Listorti, G. Accorsi, Y. Rio, N. Armaroli, O. Moudam, A. Gégout, B. Delavaux-

Nicot, M. Holler, J.-F. Nierengarten, Inorg. Chem. 47 (2008) 6254.[37] S. Roy, M. Sieger, P. Singh, M. Niemeyer, J. Fiedler, C. Duboc, W. Kaim, Inorg.

Chim. Acta 361 (2008) 1699.[38] N. Armaroli, G. Accorsi, G. Bergamini, P. Ceroni, M. Holler, O. Moudam, C.

Duhayon, B. Delavaux-Nicot, J.-F. Nierengarten, Inorg. Chim. Acta 360 (2007)1032.

[39] P. Braunstein, D. Bubrin, B. Sarkar, Inorg. Chem. 48 (2009) 2534.[40] S. Onaka, A. Mizuno, S. Takagi, Chem. Lett. (1989) 2037.[41] T.S.A. Hor, L.-T. Phang, L.-K. Liu, Y.-S. Wen, J. Organomet. Chem. 397 (1990) 29.[42] D.T. Hill, G.R. Girard, F.L. McCabe, R.K. Johnson, P.D. Stupik, J.H. Zhang, W.M.

Reiff, D.S. Eggleston, Inorg. Chem. 28 (1989) 3529.[43] P. Kalck, C. Randrianalimanana, M. Ridmy, A. Thorez, H. tomDieck, J. Ehlers,

New J. Chem. 12 (1988) 679.[44] S.T. Chacon, W.R. Cullen, M.I. Bruce, O.B. Shawkataly, F.W.B. Einstein, R.H.

Jones, A.C. Willis, Can. J. Chem. 68 (1990) 2001.[45] G. Bandoli, A. Dolmella, Coord. Chem. Rev. 209 (2000) 161.[46] M. Beaupérin, E. Fayad, R. Amardeil, H. Cattey, P. Richard, S. Brandès, P.

Meunier, J.-C. Hierso, Organometallics 27 (2008) 1506.[47] M. Beaupérin, A. Job, H. Cattey, S. Royer, P. Meunier, J.-C. Hierso,

Organometallics 29 (2010) 2815.[48] J.-C. Hierso, R. Smaliy, R. Amardeil, P. Meunier, Chem. Soc. Rev. 36 (2007) 1754.[49] J. Dîez, M.P. Gamasa, J. Gimeno, A. Aguírre, S. García-Granda, J. Holubova, L.R.

Falvello, Organometallics 18 (1999) 662.[50] C.D. Nicola, Inorg. Chim. Acta 358 (2005) 695.[51] D. Li, Y.-F. Luo, T. Wu, S.W. Ng, Acta Crystallogr., Sect. E 60 (2004) m927.[52] S.P. Neo, Z.-Y. Zhou, T.C.W. Mak, T.S.A. Hor, J. Chem. Soc., Dalton Trans. (1994)

3451.[53] B.S. Furniss, A.J. Hannaford, V. Rogers, P.W.G. Smith, A.R. Tatchell, Vogel’s

Textbook of Practical Organic Chemistry, fourth ed., Longman, London, 1978.[54] G.M. Sheldrick, Bruker Analytical X-ray Division, Madison, WI, 1998.[55] G.M. Sheldrick, SHELX-97, Programme for Refinement of Crystal Structures,

University of Gottingen, Gottingen, Germany, 1997.[56] PLATON, A.L. Spek, Acta Crystallogr., Sect. 46A (1990) C34.[57] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.[58] C.T. Lee, W.T. Yang, R.G. Parr, Rev. B: Condens. Matter Mater. Phys. 37 (1988)

785.[59] A.E. Reed, R.B. Weinstock, F. Weinhold, J. Chem. Phys. 83 (1985) 735.[60] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,

J.A. Montgomery, T. Vreven Jr., K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar,J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A.Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox,H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E.Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y.Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S.Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K.Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J.Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L.Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M.Challacombe, P.M.W. Gill, B. Johnson, W. Chen, W.M. Wong, C. Gonzalez, J.A.Pople, GAUSSIAN, Inc., Wallingford, CT, 2004.

[61] G. Schaftenaar, J.H. Noordik, J. Comput. Aided Mol. Des. 14 (2000) 123.

556 M. Trivedi et al. / Inorganica Chimica Acta 376 (2011) 549–556

[62] E. Colacio, J.M. Domínguez-Vera, F. Lloret, J.M.M. Sánchez, R. Kivekäs, A.Rodríguez, R. Sillanpää, Inorg. Chem. 42 (2003) 4209.

[63] X. He, C.-Z. Lu, C.-D. Wu, L.-J. Chen, Eur. J. Inorg. Chem. (2006) 2491.[64] J.S. Thayer, R. West, Adv. Organomet. Chem. 5 (1967) 169.[65] J.S. Thayer, D.P. Strommen, J. Organomet. Chem. 5 (1966) 383.[66] I.D. Salater, S.A. Williams, T. Adatia, Polyhedron 14 (1995) 2803.[67] P. Pinto, M.J. Calhorda, V. Félix, T. Avilés, M.G.B. Drew, Monatshefte für Chemie

131 (2000) 1253.[68] G.-C. Guo, T.C.W. Mak, Angew. Chem., Int. Ed. 37 (1998) 3183.[69] X.L. Lu, W.K. Leong, L.Y. Goh, T.S.A. Hor, Eur. J. Inorg. Chem. (2004) 2504.[70] G. Pilloni, B. Longato, G. Bandoli, Inorg. Chim. Acta 277 (1998) 163.[71] Y.-C. Liu, C.-I. Li, G.-H. Lee, S.-M. Peng, Inorg. Chim. Acta 359 (2006) 2361.[72] J. Vicente, P. González-Herrero, Y. García-Sánchez, P.G. Jones, D. Bautista, Eur. J.

Inorg. Chem. (2006) 115.

[73] W.-Y. Yeh, Y.-C. Liu, S.-M. Peng, G.-H. Lee, Inorg. Chim. Acta 358 (2005) 1987.[74] Y. Cai, Y. Song, H. Zheng, Y. Niu, C. Du, X. Xin, Chem. Lett. 5 (2002) 508.[75] D. Braga, F. Grepioni, E. Tedesco, Organometallics 17 (1998) 2669.[76] D. Braga, P.J. Dyson, F. Grepioni, B.F.G. Johnson, Chem. Rev. 94 (1994) 1585.[77] E.A. Meyer, R.K. Castellano, F. Diederich, Angew. Chem., Int. Ed. Engl. 42 (2003)

1210.[78] P.C. Ford, E. Cariati, J. Bourassa, Chem. Rev. 99 (1999) 3625.[79] A. Hiromi, T. Kiyoshi, S. Yoichi, I. Shoji, K. Noboru, Inorg. Chem. 44 (2005) 9667.[80] C. Kutal, Coord. Chem. Rev. 99 (1990) 213.[81] W.F. Fu, X. Gan, C.M. Che, Q.Y. Cao, Z.Y. Zhou, N.N.Y. Zhu, Chem. Eur. J. 10

(2004) 2228.[82] R.D. Pike, K.E. deKrafft, A.N. Ley, T.A. Tronic, Chem. Commun. (2007) 3732.[83] S. Hu, A.-J. Zhou, Y.-H. Zhang, S. Ding, M.-L. Tong, Cryst. Growth Des. 6 (2006)

2543.