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The compounds tricarbonyl(η5-1-iodocyclopentadienyl)manganese(I), [Mn(C5H4I)(CO)3], (I), and tricarbonyl(η5-1-iodocyclopentadienyl)rhenium(I), [Re(C5H4I)(CO)3], (III), are isostructural and isomorphous. The compounds [μ-1,2(η5)-acetylenedicyclopentadienyl]bis[tricarbonylmanganese(I)] or bis(cymantrenyl)acetylene, [Mn2(C12H8)(CO)6], (II), and [μ-1,2(η5)-acetylenedicyclopentadienyl]bis[tricarbonylrhenium(I)], [Re2(C12H8)(CO)6], (IV), are isostructural and isomorphous, and their molecules display inversion symmetry about the mid-point of the ligand C C bond, with the (CO)3 M(C5H4) (M = Mn and Re) moieties adopting a transoid conformation. The molecules in all four compounds form zigzag chains due to the formation of strong attractive IO [in (I) and (III)] or π(CO)–π(CO) [in (I) and (IV)] interactions along the crystallographic b axis. The zigzag chains are bound to each other by weak intermolecular C—HO hydrogen bonds for (I) and (III), while for (II) and (IV) the chains are bound to each other by a combination of weak C—HO hydrogen bonds and π(Csp 2)–π(Csp 2) stacking interactions between pairs of molecules. The π(CO)–π(CO) contacts in (II) and (IV) between carbonyl groups of neighboring molecules, forming pairwise interactions in a sheared antiparallel dimer motif, are encountered in only 35% of all carbonyl interactions for transition metal–carbonyl compounds.
One of the rapidly growing fields in metalloorganic chemistry is the synthesis of new materials. Examples include dendrimers (Tomalia et al., 1990 ; Stulgies et al., 2005 ; Astruc et al., 2008 ), staffanes (Kaszynski et al., 1992 ), Diederich’s carbon nets (Diederich & Rubin, 1992 ), and various novel electronic, photonic and magnetic materials (Barlow & O’Hare, 1997 ; Elschenbroich et al., 2005 ; Kinnibrugh et al., 2009 ). Because of the increasing interest in this area, we have focused our studies on structural investigations of the title compounds, (I)–(IV) (Figs. 1 and 2 ), which can be used as starting compounds for the construction of new materials (Sterzo et al., 1989 ). This work reports the first structural studies of the monohalogenated derivatives (η5-C5H4 X)M(CO)3 [for (I): M = Mn and X = I; for (III): M = Re and X = I] and the dinuclear [(CO)3 MC5H4]C C[C5H4 M(CO)3] compounds [for (II): M = Mn; for (IV): M = Re].
The mean values of the geometric parameters for compounds (I)–(IV) are in accordance with those previously reported (Table 1 ) for 89 monosubstituted cymantrenes and 27 (η5-C5H4 X)Re(CO)3 compounds, which were retrieved from the 2009 version of the Cambridge Structural Database (CSD; Allen, 2002 ) using ConQuest (Version 1.11; Macrae et al., 2006 ), as well as with the unsubstituted compounds C5H5 M(CO)3 (M = Mn and Re) (Fitzpatrick, Le Page et al., 1981 ; Cowie et al., 1990 ). The monosubstituted (η5-C5H4 X)M(CO)3 complexes (X = any atom; M = Mn and Re) were considered with the following search criteria: (a) three-dimensional coordinates and R < 0.10; (b) no errors; (c) no crystallographic disorder; (d) no polymer structures. The (O)C—Mn—C(O) angle is in accord with a tendency for decreasing the pyramidality of the M(CO)3 fragment with increasing π-donor capacity of the cyclic polyene (Fitzpatrick, Le Page et al., 1981 ): 88.22 (8)° for (C6H6)Cr(CO)3 (Rees & Coppens, 1973 ), 90.0 (2)° for CpRe(CO)3 (Fitzpatrick, Le Page & Butler, 1981 ), 92.02 (5)° for CpMn(CO)3 (Cowie et al., 1990 ), 95.6° for (C4H4)Fe(CO)3 (Hall et al., 1975 ) and 97.03 (3)° for (C4Ph4)Fe(CO)3 (Dodge & Schomaker, 1965 ). The M—C—O bond angles do not differ significantly from 180°.
The M(CO)3 (M = Mn and Re) fragment possess approximate C 3v symmetry, while coordination to the η5-C5H4 X ring lowers the molecular symmetry to C 1 (Fig. 3 ). Compounds (I)–(IV) possess different mutual dispositions of the carbonyl groups and η5-C5H4 X rings: the C6 O1 carbonyl group for each of (I) and (III) is in an eclipsed position relative to the substituted C atom of the η5-C5H4I ring, while the C7 O1 carbonyl group of each of (II) and (IV) is in the transoid position with respect to the substitutent-bearing C atom (Figs. 3 and 4 ).
Compounds (II) and (IV) crystallize with the molecules lying across crystallographic inversion centers. Each molecule consists of two identical [(CO)3 M(C5H4)C ] (M = Mn and Re) parts with the M(CO)3 moieties in transoid positions. We suggest that (II) and (IV) adopt the transoid structure due to the presence of strong attractive intermolecular π(CO)–π(CO) interactions in the sheared parallel packing motif (see below). In contrast, the only analogous compound found in the literature, viz. [(CO)3Mn(C5H4)C C(C7H5)Cr(CO)3]BF4, possesses a syn-facial (cisoid) conformation of M(CO)3 moieties, due to the formation of strong attractive intermolecular π(CO)–π(CO) interactions with a perpendicular packing motif (Tamm et al., 2000 ). The conformation of (CO)3 M(C5H4) moieties thus appears to depend, at least in part, on the type of π(CO)–π(CO) interactions formed.
The molecules in all four structures form zigzag chains due to the formation of strong attractive interactions. For (I) and (III), the zigzag chains along the crystallographic b axis involve strong attractive IO interactions [I1O2A(2 − x, − + y, − z) = 3.233 (2) Å and I1O2A—C7A = 112.1 (2)° for (I), and I1O2A(2 − x, − + y, − z) = 3.231 (4) Å and I1O2A—C7A 110.6 (3)° for (III)] (Fig. 5 ). The attractive nature of halogen–oxygen interactions is caused by electrostatic effects, polarization, charge transfer and dispersion contributions. The tendency to form short XE (E = O and N) interactions (X = I > Br > Cl) increases with the magnitude of their polarizabilities (Lommerse et al., 1996 ). The directionality of that type of interaction has been interpreted in terms of charge transfer between the highest occupied molecular orbital of E and the lowest unoccupied molecular orbital of X (Ramasubbu et al., 1986 ). The strength of halogen–carbonyl interactions has been characterized as a function of two geometric parameters, the halogen–oxygen distance (XO) and the halogen–oxygen–carbon angle (XO—C). The interaction energy of the most strongly bound system was found to be 2.39 kcal mol−1 (1 kcal mol−1 = 4.184 kJ mol−1) (iodobenzene–formaldehyde; IO = 3.2 Å and IO—C = 110°), of the same magnitude as those for C—HO hydrogen bonds (Riley & Merz, 2007 ). The observed interactions in (I) and (III) are consistent in geometry with these calculated strong interactions.
According to a systematic CSD analysis (Allen et al., 1998 ) of interactions between ketonic (C2—C=O) carbonyl groups, three types of interaction motifs were identified: a predominant slightly sheared antiparallel motif, a perpendicular motif, and a highly sheared parallel motif. For transition metal carbonyls, a higher percentage of the perpendicular motif has been reported (Allen et al., 2006 ). Compounds (II) and (IV) contain strong attractive antiparallel intermolecular π(CO)–π(CO) interactions between the carbonyl groups of neighboring molecules [O2C8A(2 − x, −y, z) = 3.138 (2) Å, C8—O2C8A = 105.00 (10)° for (II), and O2C8A(2 − x, −y, z) = 3.211 (6) Å and C8—O2C8A = 101.8 (3)° for (IV)], forming pairwise interactions in a sheared antiparallel dimer motif along the crystallographic b axis (Fig. 6 ). These antiparallel π(CO)–π(CO) interactions are a driving force for the formation of zigzag chains along the b axis. Comparison of the parameters obtained for (II) and (IV) with distances and angles reported for similar interactions in other transition metal carbonyls (2.95–3.60 Å/80–135°) indicates that the π(CO)–π(CO) interactions are relatively strong in (II) and (IV) (Allen et al., 2006 ). Also, intermolecular π(CO)–π(CO) interactions are not rare, and sheared antiparallel and perpendicular motifs can be found for 14 of the 89 hits for monosubstituted cymantrenes and for 3 of the 27 hits for (η5-C5H4 X)Re(CO)3 compounds in the CSD search (see above). The mean van der Waals radii used to identify intermolecular interactions and contacts were taken as C = 1.53 Å, O = 1.42 Å and I = 2.04 Å (Bondi, 1964 ).
The zigzag chains in (II) and (IV) are bound to each other by weak π(Csp 2)–π(Csp 2) and π(Csp 2)–π(Csp) stacking interactions between pairs of inversion-related molecules (CC distances ca 3.4 Å), leading to a ladder-type packing (Fig. 7 ).
Compounds (I)–(IV) were prepared according to the standard literature procedure of Sterzo et al. (1989 ). Crystals of (I) and (III) were obtained by slow evaporation of hexane solutions. Crystals of (II) and (IV) were grown by slow evaporation of chloroform solutions at room temperature.
All H atoms were positioned geometrically, with C—H = 1.00 Å, and included in riding mode, with U iso(H) = 1.2U eq(C).
For all compounds, data collection: APEX2 (Bruker, 2005 ); cell refinement: SAINT-Plus (Bruker, 2001 ); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.
Crystal structure: contains datablocks global, I, II, III, IV. DOI: 10.1107/S0108270109035902/sq3211sup1.cif
Structure factors: contains datablocks I. DOI: 10.1107/S0108270109035902/sq3211Isup2.hkl
Structure factors: contains datablocks II. DOI: 10.1107/S0108270109035902/sq3211IIsup3.hkl
Structure factors: contains datablocks III. DOI: 10.1107/S0108270109035902/sq3211IIIsup4.hkl
The authors are grateful to the NIH for support via the RIMI program (grant No. P20MD001104) and to the NSF for support via grant Nos. CHE-0832622, DMR-0120967 and DMR-0934212.
Supplementary data for this paper are available from the IUCr electronic archives (Reference: SQ3211). Services for accessing these data are described at the back of the journal.