DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 1067–1075 1067 Novel Cu–Se clusters with Se–layer structures: [Cu32Se7(SenBu)18- (PiPr3)6], [Cu50Se20(SetBu)10(PiPr3)10], [Cu73Se35(SePh)3(PiPr3)21], [Cu140Se70(PEt3)34] and [Cu140Se70(PEt3)36] Nianyong Zhu and Dieter Fenske * Institut für Anorganische Chemie, Universität Karlsruhe, Engesserstr. Geb. Nr. 30.45, 76128 Karlsruhe, Germany. E-mail: dieter.fenske@chemie.uni-karlsruhe.de Received 4th January 1999, Accepted 8th February 1999 The clusters [Cu32Se7(SenBu)18(PiPr3)6], [Cu50Se20(SetBu)10(PiPr3)10], [Cu73Se35(SePh)3(PiPr3)21], [Cu140Se70(PEt3)34] and [Cu140Se70(PEt3)36] were prepared from the reactions of CuCl, RSeSiMe3 and Se(SiMe3)2 (R = Ph, nBu or tBu) in the presence of phosphine ligands and their molecular structures were determined.The Se–Bu bond was cleaved more easily than the Se–Ph bond under the reaction conditions studied. Introduction The synthesis of transition-metal-containing complexes of selenium and tellurium has received1 less attention than that of the lighter chalcogen elements oxygen and sulfur. Over the past five years there has been increasing 2 interest in this area, partly due to the discovery of selenium in some enzymes,3 and the realisation that Se- and Te-containing compounds may have important applications, such as precursors for low-bandgap semiconductors, nanomaterials and window materials in solar cells.4 We are interested 2a in metal chalcogenide clusters both as potential nanoparticles and as intermediate structures between small molecules and bulk materials.We have previously developed 5–12 a general route to copper– selenide–phosphine clusters: CuX 1 nPR3 1 ��� Se(SiMe3)2 X = Cl or OAc [Cu2x 2 ySex(PR3)m] 1 Me3SiX (1) The driving force of the reaction is the elimination of Me3SiX. The formation of the cluster complexes depends very much on the nature of the phosphine. The reaction conditions, the solvents used for the synthesis and the ratio of Cu :PR3 also play a significant role in governing the structures of the products isolated, which crystallize under these conditions. A large number of complexes have been prepared with this method that cover a range of nuclearities.In order of increasing size, these include low nuclearity clusters such as [Cu12Se6(PR3)8] (R3 = Et2Ph5 or nPr3 or Cy3 6), ranging to [Cu20Se13(PEt3)12],7 [Cu26Se13(PCy3)10],6 [Cu26Se13(PEt2Ph)14],6 [Cu29Se15(PiPr3)12],8 [Cu30Se15(PR3)12] (R3 = iPr3 8 or tBu2Me9), [Cu31Se15(SeSiMe3)(PtBu2Me)12],10 [Cu32Se16(PPh3)12],11 [Cu36- Se18(PtBu3)12],8 [Cu44Se22(PEt2Ph)18],12 [Cu44Se22(PnButBu2)12],12 [Cu48Se24(PMe2Ph)20],10 [Cu52Se26(PPh3)16] 11 and [Cu59Se30- (PCy3)15],6 and finally to very large macromolecules such as [Cu70Se35(PEt3)22],7 [Cu70Se35(PiPr2Me)21],10 [Cu70Se35(PtBu2- Me)21],10 [Cu72Se36(PPh3)20] 11 and [Cu146Se73(PPh3)30].13 The last of these is one of the largest clusters characterised so far.We observe a systematic colour change from red (Cu12) through brown (Cu36) and dark brown (Cu70) to black (Cu146). Preliminary studies also show a relationship between size and conductivity.14 The above synthetic method has recently been modified 15,16 to create a route to mixed seleno–selenato and telluro–tellurato clusters by employing RESiMe3 or mixtures of E(SiMe3)2 and RESiMe3 (E = Se, Te). In this paper we describe the synthesis and characterisation of five novel clusters synthesized by the reaction of CuX (X = Cl or SCN) with mixtures of RSeSiMe3 (R = Ph or nBu or tBu) and Se(SiMe3)2 in the presence of alkyl phosphines PR3 (R3 = Et or iPr).Experimental Standard Schlenk-line techniques were employed throughout on a double-manifold vacuum line with high purity dry nitrogen. Solvents for reactions were distilled under nitrogen from appropriate drying agents prior to use. The compounds CuCl and CuSCN were purchased and CuCl was purified prior to use.The phosphines 17 and PhSeSiMe3 18 were prepared according to standard literature procedures. Syntheses RSeSiMe3 (1a R 5 nBu and 1b tBu). In an adaptation of the preparation of nBuTeSiMe3,16a grey selenium (63.0 g, 0.80 mol) was suspended in THF (700 mL) in a three-necked roundbottom flask (2 L) equipped with a water cooled condenser and dropping funnel. nBuLi (500 mL, 1.6 M in hexane) or tBuLi (500 mL, 1.6 M in pentane) was added dropwise to the rapidly stirred suspension at 0 8C, during which time the black Se gradually dissolved with the formation of a dark brown solution.After the addition was complete, stirring was continued for one hour to give a pale yellow solution. After cooling the solution to 0 8C freshly distilled ClSiMe3 (100 mL, 0.80 mol) was added dropwise with vigorous stirring, during which time a white precipitate (LiCl) was formed. After complete addition, the mixture was stirred for one day at room temperature.The solution was filtered to remove LiCl and the solvent removed by distillation. Fractional vacuum distillation aVorded 1a; 80 g, 48%, bp 75–80 8C at 20 mmHg or 1b; 94 g, 56%; bp 77–80 8C at 20 mmHg. Both yellow liquids contained about 15% each of Se(SiMe3)2 and Bu2Se according to 1H NMR. Attempts to remove these impurities by further fractional distillation were unsuccessful. 1H NMR(C6D6): 1a d 2.38 (t, a-CH2), 1.55 (m, b-CH2), 1.29 (m, g-CH2), 0.80 (t, CH3), 0.30 [s, Si(CH3)3]; 1b d 1.44 (s, 3CH3), 0.37 [s, Si(CH3)3].[Cu32Se7(SenBu)18(PiPr3)6] 2. nBuSeSiMe3 (0.70 mL, 3.0 mmol) was added to a suspension of CuCl (0.25 g, 2.5 mmol) and PiPr3 (0.25 mL, 1.33 mmol) in Et2O (25 mL) at 0 8C with vigorous stirring. After two hours a clear dark red solution was1068 J. Chem. Soc., Dalton Trans., 1999, 1067–1075 Table 1 Crystallographic data Compound Empirical formula MF (000) Crystallized from Crystal size/mm Crystal system Space group Za /Å b/Å c/Å b/8 V/Å3 r (calcd.)/g cm23 T/K m(Mo-Ka)/mm21 q range/8 Index range Reflections collected Independent reflections Reflectopms observed Parameters refined Reflections refined R indices (obs.refl.) Goodness of fit 2 C126H288Cu32P6Se25 5996.66 5824 Diethyl ether 0.5 × 0.4 × 0.4 Monoclinic P2(1)/n 2 16.628(3) 29.937(6) 19.847(4) 101.79(3) 9671(3) 2.059 203(2) 8.222 2.25 to 25.99 216 < h < 19 236 < k < 19 216 < l < 24 11978 11283 (Rint = 0.12) 8792 (I > 2s(I)) 871 11278 R1 = 0.074, wR2 = 0.20 1.055 3 C69H160Cu25OP5Se15 3933.72 7568 Diethyl ether 0.4 × 0.4 × 0.3 Monoclinic C2/m 4 3399.8(7) 2016.0(4) 1992.3(4) 119.44(3) 11892(4) 2.197 203(2) 9.052 2.33 to 25.96 238 < h < 39 224 < k < 24 218 < l < 24 28803 11157 (Rint = 0.068) 8990 (I > 22s(I)) 430 11156 R1 = 0.068, wR2 = 0.19 1.034 4 C207H441Cu73P21Se38 11234.99 21688 Diethyl ether 0.4 × 0.3 × 0.3 Monoclinic P2(1)/c 4 38.460(8) 25.720(5) 36.310(7) 99.61(3) 35414(12) 2.107 203(2) 8.309 1.58 to 22.62 241 < h < 33 227 < k < 27 232 < l < 38 99014 43379 (Rint = 0.17) 12845 (I > 2s(I)) 1870 40709 R1 = 0.095, wR2 = 0.22 1.166 5 C204H510Cu140P34Se70 18439.90 34736 Diethyl ether 0.4 × 0.1 × 0.1 Monoclinic C2/c 4 34.116(7) 48.433(10) 30.942(6) 110.47(3) 47898(17) 2.557 203(2) 11.520 1.83 to 24.20 225 < h < 39 253 < k < 55 234 < l < 18 48996 29499 (Rint = 0.13) 8293 (I > 2s(I)) 1303 19169 R1 = 0.11, wR2 = 0.27 1.903 6 C226H540Cu140P36Se70 18796.30 177632 Pentane 0.3 × 0.2 × 0.2 Monoclinic P2(1)/m 2 31.650(6) 22.550(5) 37.840(8) 97.92(3) 26749(9) 2.334 203(2) 10.276 1.81 to 24.08 235 < h < 32 225 < k < 25 243 < l < 41 110121 42703 (Rint = 0.16) 12326 (I > 2s(I)) 1371 42694 R1 = 0.086, wR2 = 0.22 1.440 formed, which was allowed to stand at room temperature.Orange crystals grew within three days. Yield 80%. [Cu52Se20(SetBu)10(PiPr3)10] 3.tBuSeSiMe3 (0.62 mL, 2.6 mmol) was added to a solution of CuCl (0.25 g, 2.5 mmol) and PiPr3 (0.47 mL, 2.5 mmol) in Et2O (25 mL) forming a dark brown solution. The mixture was allowed to stand at room temperature. After one week a brown precipitate was filtered oV. A small amount of brown crystals grew within two weeks from the fil Yield 10%. [Cu73Se35(SePh)3(PiPr3)21] 4. PhSeSiMe3 (0.32 mL, 1.25 mmol) was added to a solution of CuCl (0.25 g, 2.5 mmol) and PiPr3 (0.94 mL, 5.00 mmol) in Et2O (25 mL) to give a clear yellow solution.This was cooled to 270 8C and Se(SiMe3)2 (0.16 mL, 0.64 mmol) was added. The mixture was then allowed to warm slowly to room temperature, during which time the colour changed from yellow, through brown to black. On standing at room temperature black crystals grew within several weeks. Yield 40%. [Cu140Se70(PEt3)34] 5. Method A. The procedure is the same as for 4, except PEt3 (0.50 mL, 3.2 mmol) was used. Black needle crystals were formed in one week together with a brown precipitate.Yield 30%. Method B. nBuSeSiMe3 (0.70 mL, 3.0 mmol) was added to a solution of CuSCN (0.32 g, 2.6 mmol) and PEt3 (0.50 mL, 3.2 mmol) in Et2O (50 mL) to give a brown solution. This was allowed to stand at room temperature. Black crystals grew within one week. Yield 90%. [Cu140Se70(PEt3)36] 6. nBuSeSiMe3 (0.62 mL, 2.6 mmol) was added to a solution of CuCl (0.25 g, 2.5 mmol) and PEt3 (0.82 mL, 5.2 mmol) in pentane (25 mL) forming a yellow solution.The solution was allowed to stand at room temperature. A small amount of black crystals grew within several weeks. Yield 10%. Crystal structure analyses Single crystal X-ray structural analysis of compounds 2 to 6 were performed using a Stoe-IPDS diVractometer (Mo-Karadiation) equipped with an imaging plate area detector and a rotating anode. Structure solution and refinement were carried out with SHELXS-8619 and SHELXL-9320 software by direct methods techniques.The weighting scheme applied was of the form w = 1/[s2(Fo 2) 1 (aP)2 1 bP] [a,b = refined variables, P = 1/3 max. (Fo 2,0) 1 2/3 Fc 2]. All calculations were performed on a Silicon Graphics INDY computer. Molecular diagrams were prepared using the SCHAKAL 97 program.21 Table 1 lists the summary crystallographic data for 2 to 6. CCDC reference number 186/1348. See http://www.rsc.org/suppdata/dt/1999/1067/ for crystallographic files in .cif format.Compound 2. Data were collected at 203 K in the q range 2.25 to 25.998 with a detector distance of 70 mm and 15 min radiation time per exposure; the f went step by step per exposure from 08 to 808 with the scan-step Df value of 0.58; 11978 reflections were measured of which 11283 were independent and 8792 were considered observed with I > 2s(I). The structure was solved by direct methods and refined by full-matrix leastsquares on F 2. All Se, Cu P and C atoms were refined anisotropically.Hydrogen atoms (except for one disordered nBu group) were placed in calculated positions. R = 0.074 with a goodness of fit value of 1.055. Parameters refined = 871. Compound 3. Data were collected at 203 K in the q range 2.33 to 25.968 with a detector distance of 70 mm with 12 min radiation time per exposure; the f went step by step per exposure from 08 to 72.58 with a scan-step Df value of 0.58; 28803 reflections were measured of which 11157 were independent and 8990 were considered observed with I > 2s (I).The structure was solved by direct methods and refined by full-matrix least-squares on F 2. All Se, Cu and P atoms were refined anisotropically, C atoms were refined isotropically. R = 0.068 with a goodness of fit value of 1.034. Parameters refined = 430. The asymmetric unit contains one quarter of a molecule. Within this unit six iPr groups of two phosphines and one tBu group are disordered. The disorder of the tBu group has been modelled using two sites related by rotation about the Se–C bond.A similar procedure involving rotation about the Cu–PJ. Chem. Soc., Dalton Trans., 1999, 1067–1075 1069 bond has been used to describe the disorder of the phosphine groups. This is a good model for P(1), but is less satisfactory for P(3). Compound 4. Data were collected at 203 K in the q range 1.58 to 22.628 with a detector distance of 90 mm with 20 min radiation time per exposure; the f went step by step per exposure from 08 to 1058 with a scan-step Df value of 0.38; 99014 reflections were measured of which 43379 were independent and 12845 were considered observed with I > 2s (I).The structure was solved by direct methods and refined by full-matrix least-squares on F 2. All Se, Cu and P atoms were refined anisotropically, C atoms were refined isotropically. R = 0.095 with a goodness of fit value of 1.166. Parameters refined = 1870. Three Cu atoms in the middle of the three face-shared octahedral holes formed by Se atoms (see structure description below) were considered to have a total population of 2 and each has a population of 0.67.Because the iPr groups are quite disordered, many of the C atoms have large thermal parameters and some of them could not be found. Compound 5. Data were collected at 203 K in the q range 1.83 to 24.208 with a detector distance of 80 mm and 30 min radiation time per exposure; the f went step by step per exposure from 08 to 738 with a scan-step Df value of 0.38; 48996 reflections were measured of which 29499 were independent and 8293 were considered observed with I > 2s(I).The structure was solved by direct methods and refined by full-matrix least-squares on F 2. All Se, Cu and P atoms were refined anisotropically, C atoms were refined isotropically. R = 0.11 with a goodness of fit value of 1.903. Parameters refined = 1303. Many Et groups of PEt3 and the solvent molecules could not be found.Compound 6. Data were collected at 203 K in the q range 1.81 to 24.088 with a detector distance of 80 mm and 20 min radiation time per exposure; the f went step by step per exposure from 08 to 1108 with a scan-step Df value of 0.38; 110121 reflections were measured of which 42703 were independent and 12326 were considered observed with I > 2s(I). The structure was solved by direct methods and refined by full-matrix least-squares on F 2. All Se, Cu and P atoms were refined anisotropically, C atoms were refined isotropically.R = 0.086 with a goodness of fit value of 1.440. Parameters refined = 1371. Many Et groups of PEt3 and the solvent molecules could not be found. Results and discussion Synthesis Reactions among CuCl, PhSeSiMe3 and bidentate phosphine to produce some copper–seleno–phenylselenato clusters have been reported.14 However, the reactions of equimolar quantities of CuCl, PR3 (R3 = Et3, iPr3, tBu3) and PhSeSiMe3 in pentane produce only yellow solutions that remain unchanged over a period of a few months.This colour suggests that only lownuclearity copper–selenium molecules are present. Evidence for this was the isolation of [Cu2(SePh)2(PtBu3)2],22 which contains doubly-bridged phenylselenolate ligands and two terminallycoordinated PtBu3. As there was clearly little hope of isolating large clusters from these solutions, this line of investigation was not continued. We have observed that high nuclearity Cu–Se clusters often contain structural features similar to those found in copper selenide minerals.In order to facilitate the formation of similar motifs we have investigated reactions using a mixture of selenide sources. A combination of PhSeSiMe3 and Se(SiMe3)2 in a ratio of 2 : 1 has been used with a quantity of CuX chosen so that equal amounts of X and SiMe3 moieties were present. In order to avoid the formation of products containing only Se22, i.e. without RSe2, we first allowed the phosphine–copper salt mixture to react with PhSeSiMe3 before adding Se(SiMe3)2.Despite this most of the products we have characterised contain few or no PhSe2 fragments. The reaction performed in the presence of PtBu3 yielded the cluster [Cu36Se18(PtBu3)12],8 which was previously isolated from reactions employing Se- (SiMe3)2. When PEt3 was used we obtained [Cu140Se70(PEt3)34] 5. Although this compound contains no PhSe2 groups, it is diVerent from the material obtained from similar reactions in which Se(SiMe3)2 was the only selenium source, [Cu70Se35- (PEt3)22].7 From the reactions in which PiPr3 is present we obtain [Cu73Se35(SePh)3(PiPr3)21] 4, a markedly larger cluster than that obtained from only Se(SiMe3)2, [Cu30Se15(PiPr3)12]. The presence of a relatively small number of PhSe2 groups and the diVerence of these products from those obtained when only Se(SiMe3)2 is employed suggests that Se–C bond scission may accompany cluster growth.For a more comprehensive insight into this, we have synthesised the silylated reagents nBuSeSiMe3 and tBuSeSiMe3 from which we have been unable to remove the impurities Se(SiMe3)2 and SeBu2. We have used these reagents in a study of the CuX–PR3–BuSeSiMe3 system. The reaction of CuCl, PEt3 and nBuSeSiMe3 in diethyl ether produces the known compound [Cu70Se35(PEt3)22]. Replacement of CuCl by CuSCN leads to the new cluster 5 in high yield. It is possible that [Cu70Se35(PEt3)22] is an intermediate in the formation of 5 as it can be recognised as a fragment of the larger structure (see below).When pentane is used as the solvent for the reaction of CuCl, PEt3 and nBuSeSiMe3, cluster [Cu140Se70(PEt3)36] 6 is produced, which diVers from 5 only in the inclusion of two extra phosphine ligands. The smaller [Cu70Se35(PEt3)22] cluster may again be an intermediate. The similar reactions with the use of tBuSeSiMe3 lead invariably to [Cu70Se35(PEt3)22]. These reactions illustrate the profound influence of counter ion and solvent.The Se–Bu bond was cleaved in the reactions. For reactions in the presence of PiPr3 we observe a product dependance on the Cu :PR3 ratio in addition to the dependence on the RSeSiMe3 reagent used. From the reactions of nBuSe- SiMe3 the cluster [Cu32Se7(SenBu)18(PiPr3)6] 2 is obtained when half a molar equivalent of phosphine is used. For larger amounts of phosphine no crystalline product could be isolated.Reactions with tBuSeSiMe3 additionally show diVerent behaviour depending on which copper salt is used. For CuCl we obtain cluster [Cu50Se20(SetBu)10(PiPr3)10] 3 when one equivalent of phosphine is used, and cluster [Cu70Se35(PiPr3)21] when 1.5 to 4 equivalents of phosphine are used. With CuSCN as the starting material we isolate [Cu70Se35(PiPr3)21] when 1 to 3 equivalents of phosphine are employed. When this is increased to 4 equivalents of PiPr3 the known cluster [Cu30Se15(PiPr3)12] can be isolated.Structure description Compound [Cu32Se7(SenBu)18(PiPr3)6] 2 crystallizes from a diethyl ether solution in the monoclinic space group P2(1)/n and contains an inversion center at Se(10). Fig. 1 shows the molecular structure which consists of CuI, Se22, SenBu2 and PiPr3 ligands. The heavy atoms Cu and Se form the Cu32Se25 framework of the molecule. The six phosphine ligands are terminally linked to copper atoms [Cu(4), Cu(8), Cu(14) and their symmetry equivalents], each of which is doubly bridged by two SenBu2 ligands to give a trigonal-planar coordination. The corresponding Cu–Se bond lengths of Cu(4), Cu(8) and Cu(14) are similar to the other Cu–SenBu bonds, within a narrow range from 2.439(2) to 2.500(2) Å. 24 Cu atoms have trigonal-planar coordination geometry, of which six copper atoms [Cu(10), Cu(13) and Cu(15) and their symmetry equivalents] are each coordinated by three SenBu21070 J. Chem. Soc., Dalton Trans., 1999, 1067–1075 ligands, six Cu atoms [Cu(1), Cu(2) and Cu(9) and symmetry equivalents] by two SenBu2 and one Se22 ligand and the other twelve by one SenBu2 and two Se22 ligands.The related Cu–Se bond lengths for Se22 and SenBu2 ligands are in the range 2.381(2)–2.489(2) Å. The remaining two Cu atoms [Cu(12) and its symmetry equivalent] have ideal tetrahedral coordination formed by four selenide ligands. Accordingly the Cu–Se bond lengths are relatively long [2.600(2)–2.622(2) Å] in comparison to the other Cu–Se bonds.In contrast to the 18 SenBu2 ligands that are m3-bridging, the seven selenide ligands have greater connectivity. The selenide ligand Se(10) on the inversion centre coordinates to eight copper atoms with two long and six short Cu–Se bonds. The other six selenide ligands act as m5-bridges. The 25 Se atoms together form a regular triple-layer structure which corresponds to a cubic close packed arrangement as shown in Fig. 2.The middle layer has 9 Se atoms in a 3 × 3 rhombohedral arrangement. The other two layers each have one Se atom less. The location of the copper atoms can be explained with reference to this selenium grid. The six phosphine-bound copper atoms bind to two Se atoms of SenBu2 ligands and are located Fig. 1 Molecular structure of Cu32Se7(SenBu)18(PiPr3)6 2 (Cu: purple; Se22: dark red; Se–nBu2: light red; P green); Cu–Cu contacts and carbon atoms are omitted for clarity. Selected bond lengths (Å) in 2: Cu(4)–Se(1) 2.439(2), Cu(8)–Se(5) 2.500(2); Cu(9)–Se(1) 2.388(2), Cu(1)–Se(1) 2.489(2), Cu(1)–Se(13) 2.381(2); Cu(12)–Se(10) 2.600(2), Cu(12)–Se(11) 2.600(2), Cu(12)–Se(12) 2.622(2), Cu(12)–Se(13) 2.605(2), average Se–C 1.98(2); average Cu–P 2.240(4).Fig. 2 The Se packing of 2 (Se22: dark red; Se–nBu2: light red); nonbonding Se ? ? ? Se contacts are shown within 5.5 Å and the lines between Se atoms in the middle Se layer are drawn in violet (Se ? ? ? Se contacts between layers are omitted for clarity). on the periphery.Six copper atoms [Cu(2), Cu(15) and Cu(16) and their symmetry equivalents] are located approximately within the Se-layers and have trigonal-planar coordination geometry with normal Cu–Se bond lengths of 2.406(2)– 2.483(2) Å. The other 20 Cu atoms are located between the Se layers. Two of these [Cu(12) and its symmetry equivalent] have ideal tetrahedral geometry, while the others are shifted away from the centre of tetrahedral holes.Hence each of them has only three normal Cu–Se bonds with the fourth Cu–Se distance being relatively long (3.18 Å to 3.35 Å). The structure of the Se lattice in 2 is similar to that in the bulk material Cu2Se;23 however, most Se atoms in 2 come from SenBu2 ligands. Despite this, the similarity between the structure of 2 and the non-molecular Cu2Se suggests that a fragment of a bulk structure may be stabilised to nanosize by coating the surface with suitable groups.This tendency is also observed in three silver–seleno–selenolate clusters,24 [Ag112Se48(SenBu)32- (PtBu3)12], [Ag114Se46(SenBu)34(PtBu3)14] and [Ag172Se40- (SenBu)92{Ph2P(CH2)3PPh2}4]. Compound [Cu50Se20(SetBu)10(PiPr3)10] 3 (Fig. 3) crystallises in the monoclinic space group C2/m. The molecule contains an inversion centre and a mirror plane, so that the asymmetric unit consists of only a quarter of the cluster. Fig. 3 Molecular structure of Cu50Se20(SetBu)10(PiPr3)10 3 (Cu: purple; Se22: dark red; Se–tBu2: light red; P: green); Cu–Cu contacts and carbon atoms are omitted for clarity.Selected bond lengths (Å) and bond angles (8) in 3: Cu(4)–Se(5) 2.347(2), Cu(4)–Se(9) 2.370(2); Cu(10)–Se(8) 2.394(2); Cu(8)–Se(1) 2.386(2), Cu(2)–Se(2) 2.517(2), Cu(2)–Se(6) 2.353(2), Cu(2)–Se(10) 2.379(2); Cu(6)–Se(1) 2.573(2), Cu(1)–Se(2) 2.875(2), Cu(9)–Se(4) 2.718(2), Cu(12)–Se(4) 2.595(1), Cu(15)–Se(7) 2.715(2); average Se–C 2.03(2); average Cu–P 2.230(4); Se(5)–Cu(4)–Se(9) 136.67(7).Fig. 4 The Se packing of 3 (Se22: dark red; Se–tBu2: light red); non-bonding Se ? ? ? Se contacts are shown within 5.5 Å and Se ? ? ? Se contacts between layers are omitted for clarity.J. Chem. Soc., Dalton Trans., 1999, 1067–1075 1071 Fig. 5 Molecular structure of Cu73Se35(SePh)3(PiPr3)21 4 (Cu: purple; Se22: dark red; Se–Ph2: light red; P: green); Cu–Cu contacts and carbon atoms are omitted for clarity. Selected bond lengths (Å) in 4: Cu(8)–Se(6) 2.783(7), Cu(8)–Se(10) 2.628(7), Cu(8)–Se(32) 2.338(8), Cu(8)–Se(33) 2.674(8); Cu(51)–Se(6) 2.726(7), Cu(51)–Se(29) 2.458(6), Cu(51)–Se(34) 2.489(6); Cu(54)–Se(20) 2.480(6), Cu(54)–Se(27) 2.396(6), Cu(54)–Se(28) 2.473(5); Cu(73)–Se(6) 2.407(6), Cu(73)–Se(9) 2.498(6), Cu(73)–Se(33) 2.391(5); Se(36)–Cu(14) 2.401(8), Se(36)–Cu(16) 2.372(5), Se(37)–Cu(3) 2.398(9), Se(37)–Cu(19) 2.378(6), Se(38)–Cu(66) 2.357(6), Se(38)–Cu(70) 2.390(10); average Se–C 1.91(2).On the mirror plane lie ten Se atoms [Se(2), Se(3), Se(4), Se(6), Se(10) and their symmetry equivalents], ten Cu atoms [Cu(1), Cu(2), Cu(3), Cu(9), Cu(15) and their symmetry equivalents] and two P atoms [P(3) and its symmetry equivalent].The other Cu, Se and P atoms each have three symmetry-equivalent atoms within the molecule. The ten phosphine-bound Cu atoms [Cu(13), Cu(14) and Cu(15) and equivalents] are located on the periphery of the Cu50Se30 cluster core with two diVerent types of coordination.Cu(13), Cu(14) and their symmetry equivalents have a trigonalplanar coordination mode, and Cu(15) and its symmetry equivalent are tetrahedrally coordinated. As expeted, the Cu–Se bond lengths for Cu(13), Cu(14) and their symmetry equivalents [2.435(2)–2.584(2) Å] are significantly shorter than those for Cu(15) and its equivalent [2.630(2) and 2.715(2) Å], but the Cu–P bonds have a very small range [2.227(2)–2.233(2) Å]. The other 40 Cu atoms are coordinated exclusively by Se atoms with two types of coordination geometries.Four Cu atoms [Cu(4) and its symmetry equivalents] are bound by two Se atoms, one Se22 [Se(5)] and one SetBu2 [Se(9)]. They have short Cu–Se bond lengths [2.347(2) and 2.370(2) Å] and a bent Se–Cu–Se bond angle [136.67(7)8]. The remaining 36 Cu atoms are located in a distorted trigonal-planar coordination geometry. Four of them [Cu(10) and its equivalents] bind purely to SetBu2 ligands, ten [Cu(2), Cu(8), Cu(11) and their symmetry equivalents] are each coordinated by two Se22 and one SetBu2 ligand, and the other 22 Cu atoms [Cu(1), Cu(3), Cu(5), Cu(6), Cu(7), Cu(9), Cu(12) and their symmetry equivalents] are bound only to Se22 ligands.The Cu–Se bond lengths for Se22 and SetBu2 are similar and lie within the range of 2.353(2) to 2.595(2) Å. One exception is the bond Cu(1)–Se(2) 2.875(2) Å, which is relatively long and indicates that Cu(1) tends to be only doubly coordinated by Se atoms in a similar fashion to Cu(4).The ten SetBu2 ligands [Se(8), Se(9) and Se(10) and their symmetry equivalents] are located on the sides of the molecule and act as m3-bridging ligands, while the 20 Se22 ligands have1072 J. Chem. Soc., Dalton Trans., 1999, 1067–1075 Fig. 6 Molecular structure of Cu140Se70(PEt3)34 5 (Cu: purple; Se22: dark red); Cu–Cu contacts and carbon atoms are omitted for clarity. Selected bond lengths (Å) in 5: Cu(60)–Se(24) 2.426(6), Cu(60)–Se(36) 2.383(5); Cu(10)–Se(5) 2.456(6), Cu(10)–Se(7) 2.380(8), Cu(10)–Se(21) 2.756(7), Cu(10)–Se(25) 2.739(10); Cu(26)–Se(7) 2.577(8), Cu(26)–Se(9) 2.467(6), Cu(26)–Se(25) 2.577(8); Cu(59)–Se(1) 2.485, Cu(59)–Se(9) 2.462(5), Cu(59)– Se(10) 2.379(7); Cu(63)–Se(2) 2.489(9), Cu(63)–Se(15) 2.464(5), Cu(63)–Se(25) 2.310(9); average Cu–P 2.20(1).more neighbouring Cu atoms. 14 Se22 ligands [Se(1), Se(5), Se(6) and Se(7) and their symmetry equivalents] are each bound to five copper atoms, four [Se(3) and Se(4) and their symmetry equivalents] bridge between five Cu atoms and two Se atoms [Se(2) and its equivalent] act as m7 ligands.This variation in the bonding ability of the Se22 ligand is also demonstrated by the series of Cu–Se–cluster complexes mentioned above. The 30 Se atoms in 3 form approximately three layers (Fig. 4). The middle layer lies on the mirror plane and consists of ten Se atoms. The other two layers are symmetry equivalent and also contain ten Se atoms each.In contrast to the central layer these atoms do not form a strictly planar array. Not considering the eight out-of-plane Se atoms [Se(7) and Se(8) and their equivalents], the other 22 Se atoms show hexagonal close packing. This type of packing has been found in other Cu–Se macromolecules. The Cu atoms are positioned in the tetrahedral holes or sites relating to the octahedral holes of the Se lattice. Eight Cu atoms [Cu(5) and Cu(12) and their equivalents] are located in the tetrahedral holes with long Cu–Se distances, while ten Cu atoms [Cu(3), Cu(4) and Cu(7) and their equivalents] are not in the octahedral holes, but shifted strongly from the centre of the holes with only three Cu–Se bonds.This fragment of the structure is present in larger Cu–Se macromolecules indicating that 3 could be an intermediate in the formation of [Cu70Se35- (PiPr3)21],25 which is obtained by changing the ratio of Cu to PiPr3. Compound [Cu73Se35(SePh)3(PiPr3)21] 4 crystallizes in the monoclinic space group P2(1)/c with four molecules in the unit cell.Fig. 5 shows the molecular structure and the Se38-lattice, which is based on [Cu70Se35(PiPr3)21] with three additional CuSePh groups on the three corners. The structure of the [Cu70Se35(PiPr3)21] fragment is almost the same as that seen in the other Cu70 clusters.7,9,10 The structure of the new [Cu70- Se35(PiPr3)21] compound, also synthesised in this work, has not yet been completely solved.The Cu70 clusters have the common feature that the 35 Se atoms build a layer type structure. It contains three Se layers with 10, 15 and 10 Se atoms, respectively that form a hexagonal close packing. The copper atoms are positioned according to the Se lattice. The detailed structure of 4 is not given here due to the similarity to the known Cu70 clusters.7,10 Two of the three CuSePh groups are located on the same edge of the molecule, so that no symmetry is present.The linkage of the three CuSePh groups at corners indicates that the corners of the Cu70 clusters are capable of being altered. Another type of corner structure has been found in the very large cluster Cu146,13 which has four Se and six Cu atoms at each corner.J. Chem. Soc., Dalton Trans., 1999, 1067–1075 1073 Fig. 7 Molecular structure of Cu140Se70(PEt3)36 6 (Cu: purple; Se22: dark red); Cu–Cu contacts and carbon atoms are omitted for clarity. Selected bond lengths (Å) in 6: Cu(43)–Se(13) 2.588(9), Cu(43)–Se(33) 2.632(9), Cu(43)–Se(36) 2.617(9); Cu(60)–Se(13) 2.419(4), Cu(60)–Se(36) 2.435(4), Cu(60)–Se(41) 2.380(4); Cu(15)–Se(18) 2.585(4), Cu(15)–Se(22) 2.468(4), Cu(15)–Se(36) 2.531(4); Cu(62)–Se(22) 2.464(4), Cu(62)–Se(23) 2.457(4), Cu(62)–Se(41) 2.390(4); average Cu–P 2.20(1).The structures of [Cu140Se70(PEt3)34] 5 and [Cu140Se70(PEt3)36] 6 are very similar and diVer only by the presence of two extra phosphine ligands at the periphery (Figs. 6 and 7). In 6, all three corners have the same [Cu5Se2(PEt3)4] fragment. The corner with four PEt3 has approximate twofold symmetry as found in [Cu70Se35(PEt3)22].7 In 5 two of the corners only have three phosphine ligands. Owing to the similarities of the structures, only 5 is discussed below. The 70 Se atoms in 5 build a layer-type structure with 21, 28 and 21 Se atoms in the three layers. They are arranged in a hexagonal close packing structure (Fig. 8), which is characteristic for the Cu–Se macromolecules previously characterised.Except for the corner Se atoms, 36 Se atoms of both outer Se layers construct 36 tetrahedral holes together with the Se atoms of the middle layer. 25 Se atoms of the middle Se layer, excepting the three corner Se atoms, build 50 tetrahedral holes with the Se atoms of the outer ones. Some of these holes are open at the edges and become completed with the help of phosphine ligands. Thus, there are 86 tetrahedral holes in the Se70 lattice and 30 octahedral holes.One finds 15 pairs of octahedral holes sharing an Se triangular face. Besides the 15 Cu atoms at the three corners, the remaining 125 copper atoms are positioned according to the 86 tetrahedral holes and 15 pairs of octahedral holes of the Se lattice. The 86 tetrahedral holes are each found to be occupied by one Cu atom, although many copper atoms deviate from the center of the holes. However, the two positions in the middle of the molecule are actually found to be only partly occupied.These two positions are treated as one disordered copper atom [Cu(43)]. Hence there are 85 Cu atoms in the tetrahedral holes. The remaining 40 Cu atoms are found in the 15 pairs of octahedral holes. Six of these 15 pairs are bi-capped by two CuPEt3 groups and have the third Cu atom in the middle. The other nine pairs contain two or three Cu atoms. The structure of [Cu70Se35(PEt3)22] 7 can be seen as a substructure of 5 and they feature similar structural properties.The structure of 5 is also very similar to [Cu146Se73(PPh3)30],13 the diVerence between them being found in the corner regions. Conclusion This paper presents the synthesis and crystal structures of novel Cu–Se and Cu–Se–SeR clusters that are synthesized by employing mixtures of RSeSiMe3 (R = Ph or nBu or tBu) and Se(Si- Me3)2 in the presence of alkyl phosphines PR3 (R3 = Et or iPr). The formation of the products is strongly influenced by the1074 J.Chem. Soc., Dalton Trans., 1999, 1067–1075 Fig. 8 The selenium lattice of 5 (first layer: light red; second layer and the related Se–Se lines in the same layer: green; third layer: dark red); nonbonding Se ? ? ? Se contacts are shown within 5.5 Å. reaction conditions and the starting materials, mainly by the phosphine ligand itself. However, for the same phosphine ligand, products of diVerent cluster size and structure can be isolated through the variation of other conditions. It is not yet possible to predict the structure of the possible products when using a new phosphine ligand.The clusters presented herein show a layer-type structure of Se atoms as their common structural feature, which is often found in the non-molecular binary bulk materials. The Se substructure in 2 is cubic close packed, while the Se lattices in 3–6 are hexagonal close packed. 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