Arjun C. Sau

Synthesis and 1H NMR studies of some pentacoordinate tin(IV) complexes derived from triphenyltin halides

Abstract Several anionic—cationic and neutral pentacoordinate tin(IV) complexes were prepared by the reaction of triorganotin(IV) halides, R 3 SnX (R =Me and X =Cl; R =Ph and X =F, Cl, Br) with tetraalkylammonium halides and neutral ligands (pyridine, 4-(dimethylamino)pyridine, hexamethylphosphoramide and triphenylphosphine oxide). The complexes were examined in solution by 1 H NMR spectroscopy and characterized as having trigonal bipyramidal geometry around tin where the phenyl groups occupy the equatorial sites and more electronegative ligands are at axial positions. The 1 H NMR spectra of these complexes showed two distinct sets of aromatic multiplets arising from ortho -protons at low field, and meta - and para -protons at high field. A possible rationale has been offered for this observation. The upward shift of the tetraalkylammonium proton resonances in the phenyl-substituted complexes has been postulated to arise from shielding caused by the aromatic ring.

Convenient source of ‘naked’ fluoride: tetra-n-butylammonium chloride and potassium fluoride dihydrate

A mixture of tetra-n-butylammonium chloride and potassium fluoride dihydrate in acetonitrile can be used as a convenient source of active fluoride ion in place of tetra-alkylammonium fluoride or potassium fluoride–crown ether combinations.

Characterization of phenyl-substituted pentacoordinated compounds of main group elements by 1H NMR☆

Abstract Analysis of the aromatic region of the 1 H NMR spectra of some phenyl substituted pentacoordinated compounds of main group elements (Si, Pb, P, As, Sb, S, Te, I) revealed a characteristic low-field multiplet, assignable to ortho protons, separated from a more intense high-field multiplet, assignable to the meta and para protons. The data imply that an increase in the magnitude of the multiplet separation may be correlated with a decrease in electronegativity of the central atom and an increase in electronegativity of attached ligands. These effects are consistent with a delocalization of the aromatic π electron density into vacant d orbitals of the central atom as well as a strengthening of the central atom sigma bond. The enhanced mutiplet separation for equatorially oriented phenyl groups in a trigonal bipyramid or axially oriented ones in a rectangular pyramid is diagnostic in indicating the presence of the pentacoordinated state for main group element compounds in solution.

Synthesis of novel sulfur containing spirocyclic phosphoranes

Abstract The synthesis of new spirocyclic phosphoranes containing both sulfur and oxygen hetero atoms bonded to phosphorus is described.

A NEW GEOMETRICAL FORM FOR TIN. SYNTHESIS AND STRUCTURE OF THE SPIROCYCLIC COMPLEX [(CH3)4N][(C7H6S2)2SnCl] AND THE RELATED MONOCYCLIC DERIVATIVE [(C2H5)4N][(C7H6S2)Ph2SnCl]

Abstract The synthesis and X-ray structure of the tetramethylammonium chloride adduct of the spirobi(dithiolato)stannate(IV), [(CH3)4N]+[(C7H6S2)2SnCl]−, (2), provide the first example of a tin compound having a discrete rectangular-pyramidal geometry. The synthesis and X-ray structure of the related monocyclic derivative [(C2H5)4N]+[(C7H6S2)Ph2SnCl]− (4) shows tin to possess a trigonal-bipyramidal geometry. 2 crystallizes in the monoclinic space group Cc, with a = 14.126 (4), b = 11.485 (6) A, c = 14.609 (5) A, β = 100.37 (3)°, and Z = 4. 4 crystallizes in the monoclinic space group P21/c, with a = 12.344 (4) A, b = 11.975 (5) A, c = 19.120 (5) A, β = 96.41 (2)°, and Z = 4. Data for both compounds were collected on an Enraf-Nonius CAD 4 automated diffractometer out to a maximum 2θMoKα of 50°. The final conventional unweighted residuals were 0.039 and 0.048 for 2 and 4, respectively. It is shown that the 19mSn Mossbauer quadrupole splitting parameter is useful in distinguishing the square (or rectangular)...

SYNTHESIS AND MOLECULAR STRUCTURE OF SPIROARSORANES DIFFERING IN RING UNSATURATION. DISTORTION COORDINATES FOR FIVE-COORDINATED ARSENIC

Abstract The new compound 2-phenyl-2,2′-spirobi(1,3,2-naphthodioxarsole), (C10H6O2)2AsPh, 6, was prepared by reacting phenylarsonic acid and 2,3-dihydroxynaphthalene, similar to the preparation of the arsolanes (Me2C2O3)2AsPh, 5, and (C2H4O2)2AsPh, 7. The X-ray structures of 5-7, which were determined, varied from near trigonal bipyramidal (TBP), 5, to an intermediate geometry, 7, to rectangular pyramidal (RP), 6. For phenyl-substituted spirocyclic arsoranes containing like ring atoms directly bound to arsenic, the order of increasing displacement from the TBP toward RP parallels the order of increasing ring electron delocalization. It is found that the structures of arsoranes followed the C2v constraint of the Berry pseudorotational coordinate similar to that reported for phosphoranes. The “limiting” RP for arsoranes has a trans basal angle, θ, of 151.4° similar to that found for other main-group five-coordinated elements. Arsolane 5 crystallizes in the monoclinic space group C21c with a = 11.622 (3) A, ...

Molecular structure of fluoro derivatives of anionic pentacoordinated germanium. A new geometrical form for germanium

Abstract The X-ray structures of tetraethylammonium bis(1,2-benzenediolato)fluorogermanate, [(C2H5)4N]+[(C6H4O2)2GeF]- (3), and the related monosolvate of methyltriphenylphosphonium bis(4methyl-1,2-benzenedithiolato)fluorogermanate, [(CH3)PPh3]+ [(C7H6S2)2GeF]-.CH3CN (4), lie along the Berry C 2t, coordinate connecting the idealized trigonal bipyramid with the rectangular pyramid. The structure of 3 is placed about 81% along this coordinate toward the rectangular pyramid and that for 4 is about 40% along this coordinate. 3 crystallizes in the monoclinic space group P21,/c with a = 12.886 (2) A, b = 14.870 (2) A, c = 10.912 (1) A, β = 100.29 (1)°, and Z = 4. 4 crystallizes in the monoclinic space group P21/n with a = 17.108 (6) A, b = 10.566 (3) A c = 20.630 (6) A, β = 114.01 (2)°, and Z = 4. The final conventional unweighted residuals were 0.035 and 0.058 for 3 and 4, respectively. The greater displacement of the pentacoordinated oxa compound 3 toward the RP is rationalized in terms of reduced electron-pa...

CRYSTAL STRUCTURES OF TWO PHENYL SPIROARSORANES. THE FIRST TRULY RECTANGULAR-PYRAMIDAL ARSENIC(V) COMPOUND

Abstract Single-crystal X-ray analysis of 2-phenyl-2,2′-spirobi(1,3,2-benzodioxarsole), (C6H4O2)2AsPh (5), and 2-phenyl-2,2′(3H,3′H)-spirobi(1,3,2-benzoxazarsole), (C6H2ONH)2AsPh (6), reveals, respectively, a rectangular-pyramidal structure and a trigonal-bipyramidal structure. 5 crystallizes in the monoclinic space group, P21/c, with a = 16.787 (5) A, b = 6.767 (3) A, c = 27.374 (6) A, β = 90.37 (2)°, and Z = 8. The structure was refined to R = 0.041, R w = 0.060 and showed two independent molecules per asymmetric unit. The displacement along the Berry coordinate for the two molecules, based on unit bond distances, is 99.2% and 94.8% from the trigonal bipyramid toward the rectangular pyramid. For 6, the orthorhombic space group, Pbca, is obtained with a = 10.933 (1) A, b = 10.726 (1) A, c = 26.710 (3) A, and Z = 8. The structure refined to R = 0.032, Rw = 0.043 and is displaced 22.9% from the trigonal bipyramid toward the rectangular pyramid. Comparisons between related group 5A pentacoordinated compound...

DISTORTION COORDINATE FOR NONRIGID FIVE- COORDINATED GERMANIUM. SYNTHESIS AND MOLECULAR STRUCTURE OF SPIROCYCLIC ANIONIC METHYLGERMANATES VARYING IN RING COMPOSITION′

Abstract Reaction of an organogermanium trichloride with a catechol or thiocatechol derivative in the presence of triethylamine, followed by a metathetical exchange, led to the isolation of the Et,N′ salts of the five-coordinated spirocyclic germanates [(C,H,0,),GeMe][Et,N] (1), [(MeC,H3S2_)2GeMe][Et,N] (2), [(C,CI,O,), GeMe][Et,N] (3), and [(C,H,S,), GePh][Et,N] (4). X-ray analysis showed that the geometry of 1 is close to a trigonal bipyramid, 2 is displaced about one-third toward the rectangular pyramid, and 3 is close to the rectangular pyramid. The low structural displacement for 1 is attributed to lattice effects. The structures of 2 and 3 are discussed in terms of ligand effects, the insertion of ring sulfur atoms in 2, and the electron-withdrawing effect of chlorine ring atoms in 3. The structures of these and related anionic germanates follow the local C2, constraint of the Berry pseudorotational coordinate with a trans basal angle, 0, for the “limiting” RP of 150.1°, similar to that for other ma...

A PSEUDOROTATIONAL COORDINATE FOR FIVE-COORDINATED SILICON. SYNTHESIS AND MOLECULAR STRUCTURE OF CYCLIC ANIONIC SILICATES ISOELECTRONIC WITH PHOSPHORANES

Abstract Hexamethylenediammonium bis[bis(1,2-ethylenediolato)phenylsilicate(IV)], [H3N(CH2,)6NH3]0.5-[(C2H4O2)2SiPh], 4, and tetraethylammonium bis(3,4,5,6-tetrachloro-1,2-benzenediolato)phenylsilicate(IV), [Et4N][(C6Cl4O2)2SiPh], 5, were synthesized and their X-ray structures established. 4 has a structure displaced 72% from a trigonal bipyramid (TBP) to a rectangular pyramid (RP). 5 is nearly a rectangular pyramid (RP) being 90% so displaced. A quantitative assessment of structural distortion for 4 and 5 and related anionic silicates shows that these pentacoordinated compounds form a continuous series of structures, similar to phosphoranes, between the trigonal bipyramid and square or rectangular pyramid along the Berry pseudorotational pathway. It is shown that the idealized RP geometry is approached when two five-membered unsaturated rings are present with like ligands in any one ring attached directly to silicon. The existence of this low-energy coordinate indicates the presence of nonrigid character...