{"refrec":{"BRefID":209843,"RR":"<b>Regnier, P.; Lasaga, A. C.; Berner, R. A.; Han, O. H.; Zilm, K. W.</b> (1994). Mechanism of CO<sub>3</sub><sup>2-</sup> substitution in carbonate-fluorapatite: Evidence from FTIR spectroscopy, <sup>13</sup>C NMR and quantum mechanical calculations. <i>Am. Mineral. 79</i>: 809-818","BEntID":201815,"PublicFlag":1,"CheckedFlag":0,"wosflag":1,"vabbflag":null,"RefStringPartII":". <i>Am. Mineral. 79</i>: 809-818","DocTypID":8,"DocType":"Journal article","MarineFlag":0,"FreshFlag":0,"BrackishFlag":0,"TerrestrialFlag":0,"Authorstring":"Regnier, P.; Lasaga, A. C.; Berner, R. A.; Han, O. H.; Zilm, K. W.","OrigTitleTranslFlag":0,"Authorstringtrunc":"Regnier, P. <i>et al.</i>","Englishabstract":"The substitution of CO<sub>3</sub><sup>2-</sup> in carbonate-fluorapatite (“francolite”) has a destabilizing effect on the apatite structure that results in increased solubility. A commonly proposed substitution mechanism involves the replacement of a PO<sub>4</sub><sup>3-</sup> ion by CO<sub>3</sub>F<sup>3-</sup>, in which C is at the center of a tetrahedron and is surrounded by three O atoms and one F atom at the corners. However, no spectroscopic evidence exists for this hypothetical anion.We have investigated the microenvironment of CO<sub>3</sub><sup>2-</sup> in <sup>13</sup>C-enriched type B synthetic and natural sedimentary carbonate-fluorapatite samples by <sup>13</sup>C static and MAS NMR and FTIR spectroscopies. (True CO<sub>3</sub><sup>2-</sup> substitution in the apatite structure was ascertained by X-ray diffraction and FTIR.) The CO<sub>3</sub><sup>2-</sup> ion itself consists of an sp<sup>2</sup>-hybridized planar arrangement of three O atoms about the central C atom. If the CO<sub>3</sub><sup>2-</sup> geometry were changed to an sp<sup>3</sup> hybrid with F<sup>-</sup> ate one corner, the NMR chemical isotropic shift would change considerably, owing to the altered environment about the central C atom. Also, there would be an internuclear dipolar interaction between <sup>13</sup>C and <sup>19</sup>F.Simulated NMR spectra for <sup>13</sup>C-<sup>19</sup>F distances of 1.38 and 2.00 Å based on the sp<sup>3</sup> model are very different from those obtained on our apatite samples, which are instead characteristic of C in a planar sp<sup>2</sup> arrangement and no <sup>13</sup>C-<sup>19</sup>F dipolar coupling. No evidence from direct bonding between CO<sub>3</sub><sup>2-</sup> and F was found. This result is confirmed by ab-initio quantum mechanical calculations, which show that the hypothetical CO<sub>3</sub>F<sup>3-</sup> ion is unstable in an apatitic environment. Ab-initio results, as well as FTIR data, favor the existence of an interstitial position for F<sup>-</sup> if nonstoichiometric amounts of this element are present in apatite.","AbstractOtherLang":null,"BibLvlCode":"AS","StandardTitle":"Mechanism of CO<sub>3</sub><sup>2-</sup> substitution in carbonate-fluorapatite: Evidence from FTIR spectroscopy, <sup>13</sup>C NMR and quantum mechanical calculations","OrigTitleLangCode":"en","OrigTitleLangCodeExtended":"eng","OrigTitleLangID":15,"DateLastModified":{"date":"2024-12-10 01:33:17.368041","timezone_type":1,"timezone":"+01:00"},"UserAccessRight":null,"UserAccID":null,"AuthorKeywords":null,"OtherDescriptors":null,"Notes":null,"AnaPub":1994,"MonPub":null,"DateUpdate":"2011-11-23","DateCreate":"2011-11-23","SecASFANote":null,"ConfID":null,"PeerRev":1,"VlizCoreFlag":1,"WoScode":null,"VABBcode":null,"OpenAcc":0},"refs":null,"anarec":{"AnaID":209843,"PubliDate":1994,"Pagination":"809-818","XtraPublOfAnaID":null,"ISBN":null,"Volume":"79","Issue":null,"BRefMon":null,"BRefMonRR":null,"BRefXtra":null,"BRefXtraRR":null,"SerBRefID":42083,"SerRR":"American Mineralogist. 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