{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,17]],"date-time":"2026-10-17T01:07:51Z","timestamp":1792199271292,"version":"4.4.0"},"reference-count":38,"publisher":"American Association for the Advancement of Science (AAAS)","issue":"5749","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Science"],"published-print":{"date-parts":[[2005,11,4]]},"abstract":"<jats:p>\n            Although in principle transition metals can form bonds with six shared electron pairs, only quadruply bonded compounds can be isolated as stable species at room temperature. Here we show that the reduction of {Cr(\u03bc-Cl)Ar\u2032}\n            <jats:sub>2<\/jats:sub>\n            [where Ar\u2032 indicates C\n            <jats:sub>6<\/jats:sub>\n            H\n            <jats:sub>3<\/jats:sub>\n            -2,6(C\n            <jats:sub>6<\/jats:sub>\n            H\n            <jats:sub>3<\/jats:sub>\n            -2,6-Pr\n            <jats:sup>i<\/jats:sup>\n            <jats:sub>2<\/jats:sub>\n            )\n            <jats:sub>2<\/jats:sub>\n            and Pr indicates isopropyl] with a slight excess of potassium graphite has produced a stable compound with fivefold chromium-chromium (Cr\u2013Cr) bonding. The very air- and moisture-sensitive dark red crystals of Ar\u2032CrCrAr\u2032 were isolated with greater than 40% yield. X-ray diffraction revealed a Cr\u2013Cr bond length of 1.8351(4) angstroms (where the number in parentheses indicates the standard deviation) and a planar transbent core geometry. These data, the structure's temperature-independent paramagnetism, and computational studies support the sharing of five electron pairs in five bonding molecular orbitals between two 3d\n            <jats:sup>5<\/jats:sup>\n            chromium(I) ions.\n          <\/jats:p>","DOI":"10.1126\/science.1116789","type":"journal-article","created":{"date-parts":[[2005,9,23]],"date-time":"2005-09-23T00:25:29Z","timestamp":1127435129000},"page":"844-847","source":"Crossref","is-referenced-by-count":565,"title":["Synthesis of a Stable Compound with Fivefold Bonding Between Two Chromium(I) Centers"],"prefix":"10.1126","volume":"310","author":[{"given":"Tailuan","family":"Nguyen","sequence":"first","affiliation":[{"name":"Department of Chemistry, One Shields Avenue, University of California, Davis, CA 95616, USA."},{"name":"Department of Chemistry, University of Missouri-Rolla, Rolla, MO 65409\u20130010, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Andrew D.","family":"Sutton","sequence":"additional","affiliation":[{"name":"Department of Chemistry, One Shields Avenue, University of California, Davis, CA 95616, USA."},{"name":"Department of Chemistry, University of Missouri-Rolla, Rolla, MO 65409\u20130010, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marcin","family":"Brynda","sequence":"additional","affiliation":[{"name":"Department of Chemistry, One Shields Avenue, University of California, Davis, CA 95616, USA."},{"name":"Department of Chemistry, University of Missouri-Rolla, Rolla, MO 65409\u20130010, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"James C.","family":"Fettinger","sequence":"additional","affiliation":[{"name":"Department of Chemistry, One Shields Avenue, University of California, Davis, CA 95616, USA."},{"name":"Department of Chemistry, University of Missouri-Rolla, Rolla, MO 65409\u20130010, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gary J.","family":"Long","sequence":"additional","affiliation":[{"name":"Department of Chemistry, One Shields Avenue, University of California, Davis, CA 95616, USA."},{"name":"Department of Chemistry, University of Missouri-Rolla, Rolla, MO 65409\u20130010, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Philip P.","family":"Power","sequence":"additional","affiliation":[{"name":"Department of Chemistry, One Shields Avenue, University of California, Davis, CA 95616, USA."},{"name":"Department of Chemistry, University of Missouri-Rolla, Rolla, MO 65409\u20130010, USA."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"221","reference":[{"key":"e_1_3_1_2_2","doi-asserted-by":"publisher","DOI":"10.1126\/science.145.3638.1305"},{"key":"e_1_3_1_3_2","doi-asserted-by":"crossref","unstructured":"F. A. Cotton L. A. Murillo R. A. Walton Multiple Bonds Between Metal Atoms (Springer Berlin ed. 3 2005).","DOI":"10.1007\/b136230"},{"key":"e_1_3_1_4_2","doi-asserted-by":"publisher","DOI":"10.1038\/254503a0"},{"key":"e_1_3_1_5_2","doi-asserted-by":"publisher","DOI":"10.1021\/ic50171a003"},{"key":"e_1_3_1_6_2","doi-asserted-by":"publisher","DOI":"10.1021\/ic50171a004"},{"key":"e_1_3_1_7_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja00540a035"},{"key":"e_1_3_1_8_2","doi-asserted-by":"publisher","DOI":"10.1021\/cr00076a005"},{"key":"e_1_3_1_9_2","doi-asserted-by":"publisher","DOI":"10.1063\/1.481916"},{"key":"e_1_3_1_10_2","doi-asserted-by":"publisher","DOI":"10.1063\/1.480546"},{"key":"e_1_3_1_11_2","doi-asserted-by":"publisher","DOI":"10.1002\/qua.1539"},{"key":"e_1_3_1_12_2","doi-asserted-by":"publisher","DOI":"10.1021\/jp030146v"},{"key":"e_1_3_1_13_2","doi-asserted-by":"publisher","DOI":"10.1135\/cccc20030265"},{"key":"e_1_3_1_14_2","doi-asserted-by":"publisher","DOI":"10.1021\/jp027493"},{"key":"e_1_3_1_15_2","doi-asserted-by":"publisher","DOI":"10.1002\/qua.20254"},{"key":"e_1_3_1_16_2","doi-asserted-by":"publisher","DOI":"10.1002\/anie.199621501"},{"key":"e_1_3_1_17_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0065-3055(08)60619-X"},{"key":"e_1_3_1_18_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0010-8545(00)00317-9"},{"key":"e_1_3_1_19_2","unstructured":"The description \u201cquintuple bond\u201d is intended to indicate that five electron pairs play a role in holding the metal atoms together. It does not imply that the bond order is five or that the bonding is very strong because the ground state of the molecule necessarily involves mixing of other higher-energy configurations with less bonding character. This gives lower usually noninteger bond orders. Further discussion of bond order in transition metal complexes can be found in ( 2 )."},{"key":"e_1_3_1_20_2","unstructured":"All manipulations were carried out under anaerobic and anhydrous conditions. With rapid stirring a solution of {Cr(\u03bc-Cl)Ar\u2032} 2 [1.94 g 2 mmol synthesized in 70% yield from a [1:1] tetrahydrofuran (THF 30 mL) solution of CrCl 2 (THF) 2 and LiAr\u2032 ( 15 )] was added dropwise to a suspension of freshly prepared KC 8 (0.68 g 5.0 mmol) in THF (15 mL) being cooled with an ice bath. The resulting dark suspension in a red solution was stirred for 16 hours to ensure complete reduction. The volatile materials were removed under reduced pressure and a toluene (25 mL) extract of the solid was filtered reduced to \u223c15 mL and left for 2 days at 7\u00b0C after which 0.74 g (41% yield) could be isolated as dark red x-ray\u2013quality crystals with decomposition > 200\u00b0C. Ultraviolet (UV)\/visible (vis) [hexanes given as maximum wavelength (\u03bb max ) in nm and in parenthesis \u03f5 in mol \u20131 L cm \u20131 )] is 488 (3200). Infrared (nujol) frequency \u03bd = 1261s 1092s 1020s 867w 799s 493w cm \u20131 where s is strong and w is weak. Magnetic susceptibility \u03c7 M = 0.00112 emu\/mol Cr at 2 to 300 K combustion analysis (We found the following: C 80.72%; H 8.01%. Calculation for C 60 H 74 Cr 2 gave: C 80.14%; H 8.29%)."},{"key":"e_1_3_1_21_2","unstructured":"Crystal data for 1 \u00b7 2C 7 H 8 were obtained at 90(2) K with use of a Bruker SMART 1000 diffractometer and MoK \u03b1 radiation (\u03bb = 0.71073 \u00c5). The crystal data are as follows: a = 9.9982(15) \u00c5 b = 10.8869(16) \u00c5 c = 14.410(2) \u00c5 \u03b1 = 88.641(2)\u00b0 \u03b2 = 82.242(3)\u00b0 \u03b3 = 76.129(2)\u00b0 triclinic Z = 1 R 1 for 7931 [data intensity I > 2\u03c3( I )] data = 0.0320 w R 2 (all data) = 0.0939."},{"key":"e_1_3_1_22_2","unstructured":"For magnetic measurements the samples were sealed under N 2 in 2-mm quartz tubing. The sample magnetization was measured with use of a Quantum Design MPMSXL7 superconducting quantum interference device (SQUID) magnetometer. For each measurement the sample was zero-field cooled to 5 K and the magnetization was measured as a function of field to 2 T. The field was then reduced to 1 T and the magnetization of the sample was measured in 5-K increments to 300 K. The observed susceptibility was corrected for the 0.000374\u2013emu\/mol Cr diamagnetic contribution to the susceptibility a correction which was obtained from tables of Pascal constants. The extreme air sensitivity of 1 results in 2 to 6% contamination of all samples examined so far with paramagnetic impurities that involve Cr in higher oxidation states. It is also possible that the paramagnetic impurities could arise from incomplete or over reduction of {Cr(\u03bc-Cl)Ar\u2032} 2 . A plot of the molar magnetic susceptibility versus temperature for 1 is given in ( 37 )."},{"key":"e_1_3_1_23_2","unstructured":"A different type of quintuple bond which consists of three electron-pair bonds and four one-electron bonds has been calculated to exist in U 2 molecules ( 23 )."},{"key":"e_1_3_1_24_2","doi-asserted-by":"publisher","DOI":"10.1038\/nature03249"},{"key":"e_1_3_1_25_2","doi-asserted-by":"publisher","DOI":"10.1021\/ic50186a010"},{"key":"e_1_3_1_26_2","unstructured":"The secondary Cr\u2013C interaction involving a flanking aryl ring is due in part to the electron deficiency of the Cr center (12 electrons) and the electropositive character of the metal. It is also probable that the secondary Cr\u2013C interaction lengthens the Cr\u2013Cr bond because the \u201cextra\u201d Cr\u2013C interaction competes for the chromium orbitals thereby weakening the Cr\u2013Cr bonding. Furthermore all the Cr\u2013C interactions occur in one plane so that the Ar\u2032 ligands are eclipsed which increases steric congestion and causes the Cr\u2013Cr bond to lengthen. The existence of the eclipsed structure in 1 and its absence in the corresponding Ar\u2032FeFeAr\u2032 and Ar\u2032CoCoAr\u2032 species are consistent with the presence of \u03b4 bonding. The possibility that 1 featured bonds between chromium and hydrogen (i.e. an Ar\u2032-substituted Cr(II) hydride derivative) was also entertained. No evidence for a Cr-H moiety could be observed in the infrared (IR) or 1 H nuclear magnetic resonance (NMR) spectrum of 1 . X-ray data and computational studies ( 35 ) also supplied no indication of the presence of the hydrogens near Cr."},{"key":"e_1_3_1_27_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0277-5387(00)84393-4"},{"key":"e_1_3_1_28_2","doi-asserted-by":"publisher","DOI":"10.1021\/ic00281a023"},{"key":"e_1_3_1_29_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja00049a031"},{"key":"e_1_3_1_30_2","first-page":"2581","volume":"29","year":"2000","unstructured":"R. Clerac et al., Inorg. Chem.29, 2581 (2000).","journal-title":"Inorg. Chem."},{"key":"e_1_3_1_31_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0277-5387(00)86875-8"},{"key":"e_1_3_1_32_2","first-page":"447","year":"1987","unstructured":"D. R. Salahub, in Ab Initio Methods in Quantum Chemistry, Part 2, Advances in Chemical Physics, Vol. 69, K. P. Lawley, Ed. (Wiley, New York, 1987), pp. 447\u2013518.","journal-title":"Ab Initio Methods in Quantum Chemistry, Part 2, Advances in Chemical Physics, Vol. 69"},{"key":"e_1_3_1_33_2","unstructured":"Recent computational studies of dimetal species using several different functionals have shown that the calculated M-M distances can vary by as much as 0.24 \u00c5 ( 33 )."},{"key":"e_1_3_1_34_2","doi-asserted-by":"publisher","DOI":"10.1021\/jp0504468"},{"key":"e_1_3_1_35_2","doi-asserted-by":"publisher","DOI":"10.1039\/B1RP90011K"},{"key":"e_1_3_1_36_2","first-page":"355","year":"2005","unstructured":"F. Weinhold, C. R. Landis, Valency and Bonding (Cambridge Univ. Press, Cambridge, 2005), p. 355.","journal-title":"Valency and Bonding"},{"key":"e_1_3_1_37_2","unstructured":"The electronic structure of 1 was calculated using DFT at restricted level (B3LYP\/6-31*). Calculations were also performed using pure BP86 and BLYP functionals which yielded very similar results. Additional DFT calculations carried out on 1 using the unrestricted Kohn-Sham broken symmetry (UKS-BS) approach yielded a wave function corresponding to a singlet diradical ground state with antiferromagnetic coupling between the two electrons that occupy the HOMO orbital. Other details of the DFT calculations are reported in ( 35 )."},{"key":"e_1_3_1_38_2","unstructured":"Materials and methods are available as supporting material on Science Online."},{"key":"e_1_3_1_39_2","unstructured":"We are grateful to the donors of the Petroleum Research Fund administered by the American Chemical Society and NSF for financial support of this work. In addition we thank P. Klavins and L. D. Pham of the Department of Physics at the University of California Davis for recording the magnetic data and C. R. Landis and E. Sinn for useful discussions. Metrical data for compound 1 are freely available from the Cambridge Crystallographic Database Centre (CCDC \u2013 276888)."}],"container-title":["Science"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.science.org\/doi\/pdf\/10.1126\/science.1116789","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2024,1,10]],"date-time":"2024-01-10T02:08:46Z","timestamp":1704852526000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.science.org\/doi\/10.1126\/science.1116789"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2005,11,4]]},"references-count":38,"journal-issue":{"issue":"5749","published-print":{"date-parts":[[2005,11,4]]}},"alternative-id":["10.1126\/science.1116789"],"URL":"https:\/\/doi.org\/10.1126\/science.1116789","relation":{},"ISSN":["0036-8075","1095-9203"],"issn-type":[{"value":"0036-8075","type":"print"},{"value":"1095-9203","type":"electronic"}],"subject":[],"published":{"date-parts":[[2005,11,4]]}}}