The crystal and molecular structures of hydrogendi(bis-rc-cyclopentadienyl)-L-cysteinatomolybdenum-(IV) chloride (orthorhombic, a = 13"23, b = 15.90, c= 6.26/~, space group P2~212, linear diffractometer data 1785 reflexions, R = 0.038), hydrogendi(bis-rr-cyclopentadienyl)-L-Cysteinatomolybdenum(IV) hexafluorophosphate (triclinic, a = 15.94, b = 7.61, c = 6.19 A, ~ = 95.6, fl = 101.8, 7 = 90" 1 , space group P 1, four-circle diffractometer data 2205 reflexions, R= 0.119), bis-rc-cyclopentadienylglycinatomolybdenum(IV) chloride hydrate (monoclinic, a= 13"68, b= 16"65, c= 6.00/~,, 7= 105"8, space group P21/b, visually estimated photographic data 1819 reflexions, R = 0" 109) and bis-Tr-cyclopentadienylsarcosinatomolybdenum(IV) chloride methanolate (orthorhombic a=13-43, b=14.05, c=7.98 A, space group P21212,, linear diffractometer data 1140 reflexions, R = 0.072) have been determined by three-dimensional X-ray methods. In the bis-zr-cyclopentadienylmolybdenum groups the rings are staggered in the sarcosine and cysteine chloride complexes but eclipsed in the glycine and cysteine hexafluorophosphate. The mean length of the normals to the rings from molybdenum is 1.98 A and the mean angle between them is 133 °. The cysteine chelates through nitrogen and sulphur (Mo--N 2.256, Mo-S 2.446 A in the chloride) and the carboxylate groups are hydrogen bonded to form a typical acid carboxylate dimer (O-H..-O 2"46 A). The cysteine has different conformations in the PF6 and CI-complexes. In the glycine and sarcosine complexes the molybdenum is chelated through oxygen and nitrogen [Mo-N 2.24 (mean), Mo-O 2.10 A (mean)].
