Dibromo­diphenyl­stannane: isolated centrosymmetric dimers as a new structure motif for the inter­molecular association of diorganotin(IV) dihalides

In the crystalline state, the low-melting title compound [common name: diphenyl­tin(IV) dibromide], [SnBr₂(C₆H₅)₂], consists of distorted tetra­hedral mol­ecules with compressed halide and enlarged carbon opening angles of 102.741 (9) and 123.53 (8)°, respectively, and Sn—C and Sn—Br bond lengths of 2.109 (2)/2.113 (2) and 2.4710 (3)/2.4947 (3) Å, respectively. Inter­molecular Sn...Br inter­actions, typical for diorganotin(IV) dihalides, R₂SnHal₂ (with Hal = Cl, Br, I), and sterically less demanding organic groups lead to the formation of a hitherto unknown association pattern consisting of centrosymmetric dimers with an anti­parallel orientation of the dipole moments and two weak inter­molecular Sn...Br distances of 3.8482 (3) Å between one of the two Br atoms and its neighbouring Sn atom, and vice versa. The second Br atom is not involved in inter­molecular inter­actions and lies somewhat outside the association plane that, therefore, is not coplanar [inter­planar angle = 1.750 (2)°] with the tin–halide plane. The new structure motif of inter­molecular tin–halide inter­action can be classified as 2a_i, which indicates the number of mol­ecules (i.e. `2') composing the oligomer, the anti­parallel orientation (i.e. `a') of their dipole moments and the centre of symmetry (i.e. `i') giving rise to the association pattern.

A 2'-de­oxy­cytidine long-linker click adduct forming two conformers in the asymmetric unit

The title compound {systematic name: 4-amino-1-(2-de­oxy-[beta]-D-erythro-pentofuranosyl)-5-[6-(1-benzyl-1H-1,2,3-triaz­ol-4-yl)hex-1-yn­yl]pyrimidin-2(1H)-one}, C₂₄H₂₈N₆O₄, shows two conformations in the crystalline state, viz. (I-1) and (I-2). The pyrimidine groups and side chains of the two conformers are almost superimposable, while the greatest differences between them are observed for the sugar groups. The N-glycosylic bonds of both conformers adopt similar anti conformations, with [chi] = -168.02 (12)° for conformer (I-1) and [chi] = -159.08 (12)° for conformer (I-2). The sugar residue of (I-1) shows an N-type (C3'-endo) conformation, with P = 33.1 (2)° and [tau]_m = 29.5 (1)°, while the conformation of the 2'-de­­oxy­ribofuranosyl group of (I-2) is S-type (C3'-exo), with P = 204.5 (2)° and [tau]_m = 33.8 (1)°. Both conformers participate in hydrogen-bond formation and exhibit identical patterns resulting in three-dimensional networks. Inter­molecular hydrogen bonds are formed with neighbouring mol­ecules of different and identical conformations (N-H...N, N-H... O, O-H...N and O-H...O).

5-Ethynyl-2′-de­oxy­cytidine: a DNA building block with a `clickable' side chain

The title compound [systematic name: 4-amino-1-(2-de­oxy-β-D-erythro-pentofuranos­yl)-5-ethynylpyrimidin-2(1H)-one], C₁₁H₁₃N₃O₄, shows two conformations in the crystalline state. The N-glycosylic bonds of both conformers adopt similar conformations, with χ = −149.2 (1)° for conformer (I-1) and −151.4 (1)° for conformer (I-2), both in the anti range. The sugar residue of (I-1) shows a C2′-endo envelope conformation (²E, S-type), with P = 164.7 (1)° and τ_m = 36.9 (1)°, while (I-2) shows a major C3′-exo sugar pucker (C3′-exo-C2′-endo, ₃T², S-type), with P = 189.2 (1)° and τ_m = 33.3 (1)°. Both conformers participate in the formation of a layered three-dimensional crystal structure with a chain-like arrangement of the conformers. The ethynyl groups do not participate in hydrogen bonding, but are arranged in proximal positions.