Molecular and Crystal Structures

The following section provides a brief summary of the molecular and crystal structures of the solid allotropes of sulfur mentioned in the Introduction. More specific details about the structures of most of the allotropes can be found in the cited literature. A conclusion concerning the characteristics of the molecular as well as of the crystalline structures of sulfur will be drawn at the end of this section. 

There are no crystalline forms known for the low atomic molecules S2 to S5 although these molecules are present in the gaseous and liquid phase [49, 59]. Since the cyclic molecules Sie, S17, S19, and S (n 21) have not yet been prepared, no molecular and crystal structure data are available. However, a mixture of large sulfur rings Sx( x s25) was observed as an unstable residue during the preparation of S12 (see above) [43]. The Raman spectrum of this mixture resembles that of a high pressure amorphous sulfur form as well as that of polymeric sulfur, often called (see the section on high-pressure forms of sulfur below). 

The packing of the molecules in crystalhne structures has only a sHght influence on the molecular geometry which is found typically in the range of a few percent variation of bond lengths and bond angles. 

A characteristic parameter to describe the conformation of sulfur molecules is the sign of the dihedral angle. For a sulfur chain or ring the order of the signs of the torsion angles is the so-called motif . Each of the molecular species shows a typical motif reflecting the molecular symmetry and shape. 

---

In contras t with dially lamines and their sulfonyl derivatives, IV-acy Idially lamines react with tellurium tetrahalides to give zwitterionic oxazolines 29 containing five-coordinated tellurium (85T1607). Molecular and crystal structures of one of this type of compound (29, R = Me, X = Cl) were studied by X-rays (85T1607). 

Molecular and crystal structures of the macroheterocycle 102 were studied by X-ray [96JCS(D)1203]. As for bis-imines of di(o-formylphenyl) telluride 106, [89MI1 91JOM(402)331] only one of two potentially possible intramolecular coordination N Te bonds exists in a molecule of the macrocycle 102, which, in... 

In closely related studies, the molecular and crystal structures of lithium, sodium and potassium N,N -di(p-tolyl)formamidinate and N,N -di(2,6-dialkyl-phenyl)formamidinate complexes have been elucidated. These showed the anions to be versatile ligands for alkali metals, exhibiting a wide variety of binding modes. ... 

Cyc/o-Undecasulfur Su was first prepared in 1982 and vibrational spectra served to identify this orthorhombic allotrope as a new phase of elemental sulfur [160]. Later, the molecular and crystal structures were determined by X-ray diffraction [161, 162]. The Sn molecules are of C2 symmetry but occupy sites of Cl symmetry. The vibrational spectra show signals for the SS stretching modes between 410 and 480 cm and the bending, torsion and lattice vibrations below 290 cm [160, 162]. For a detailed list of wavenumbers, see [160]. The vibrational spectra of solid Sn are shown in Fig. 23. 

Leciejewicz J, Alcock NW, Kemp TJ (1995) Carboxylato Complexes of The Uranyl Ion Effects of Ligand Size and Coordinat. Geometry Upon Molecular and Crystal Structure. 82 43-84... 

Thioamides and their use in the preparation of the heterocyclic compounds are widely reported in the literature. Also they attract considerable interests in peptide chemistry. Molecular and crystal structures of some thioamide derivatives have been confirmed by X-ray diffraction data.8 10 Lawesson s reagent or phosphorus pentasulfide (P4S10) is actively used for the synthesis of thio-carbonyl compounds. Their preparation methods, reactions, applications in the synthesis of heterocycles and biological effects are mainly described in this section. 

One learns from these molecular complexes that equivalent synthons can lead to virtually identical crystal structures. Synthons in, V and VI are chemically and geometrically equivalent though they originate from different molecules, a nitrile, an N-oxide and a nitro compound. These three synthons are used in crystal design in almost the same way. So, different molecules may yield similar crystal structures if they are capable of forming equivalent synthons. This is a powerful concept because it establishes a many-to-one correspondence between molecular and crystal structures. 

Three dimensional X-ray diffraction analysis has been employed to elucidate the molecular and crystal structure of Copper Phthalocyanine Blue ((3-modifica-tion). In all modifications, the planar and almost square phthalocyanine molecules are arranged like rolls of coins, i.e., in one dimensional stacks. The modifications vary only in terms of how these stacks are arranged relative to each other. One important aspect is the angle between staple axis and molecular plane. The a-phase features an angle of 24.7°, while the stacks in the -modification deviate by as much as 45.8° [13]. 

Eng-Wihnot DL, van der Hehn D (1980) Molecular and Crystal Structure of the Linear Tricatechol Siderophore, Agrobactin. J Am Chem Soc 102 7719... 

Molecular and Crystal Structures of Homocyclic Sulfur Allotropes.153... 

Molecular and crystal structures of the majority of matrine steroisomers have been discussed by Sadykov et al. 68-78). Three-dimensional structures of the following compounds were elucidated (+)-matrine (4) 68), (+)-matrine A -oxide... 

The field of organic conductors has been extensively reviewed (B-77MI1300, 78ANY25, B-78MI11300, 78MI11302, 79ACR79) and no attempt is made here to describe the synthesis and properties of known materials. Molecular conductors of the doped polymer type have been excluded since these are neither intrinsic conductors nor heterocyclic. A review of the principal requirements for the molecular and crystal structures as currently understood is presented as an introduction to the field of organic conductors. 

For the X-ray crystal structure determination, crystals were grown from methanol solution by slow evaporation at room temperature. Cell parameters and intensity data were derived from measurements on four-circle diffractometer Rigaku AFC5R. Molecular and crystal structures were determined by the direct... 

Molecular and crystal structure of DAD are shown in Figure 3 and 4. DAD crystallize in a triclinic system with the non-centrosymmetric space group P1. The direction of polarization of DAD in the molecular crystal is perfectly aligned in one dimension as shown in Figure 4. X-ray crystal analysis of DAD also shows the existence of two hydrogen bonds between adjacent molecules, 0 1--H... 

Molecular and crystal structures of the parent 1,3-ditellurole were studied by use of an X-ray diffraction method (85JA6298). Figure 6 displays the molecular geometry of 1,3-ditellurole. 

The homoleptic lanthanide(III) benzamidinates 20-23 can be regarded as analogues of the well known tris(cyclopentadienyl)lanthanide complexes (C5H5)3Ln [7, 8]. One of the most characteristic reactions of the homoleptic cyclopentadienyls is the formation of 1 1 adducts with Lewis bases such as ethers, nitriles, esters etc. [7, 8], Recently it was discovered that the homoleptic lanthanide benzamidinates [PhC(NSiMe3)2]3Ln (20) form similar adducts with THF and nitrile ligands such as acetonitrile or benzonitrile [59]. The molecular and crystal structures of two benzonitrile adducts (26g, h) have been determined by X-ray diffraction. Figure 8 depicts the molecular structure of the europium... 

---