Synthesis, Crystal Structure, and Magnetic Studies of Oxo-Centered Trinuclear Chromium(III) Complexes: [Cr 3 (μ 3 -O)(μ 2 -PhCOO) 6 (H 2 O) 3 ]NO 3 · 4H 2 O·2CH 3 OH, a Case of Spin-Frustrated System, and [Cr 3 (μ 3 -O)- (μ 2 -PhCOO) 2 (μ 2 -OCH 2 CH 3 ) 2 (bpy) 2 (NCS ) 3 ], a New Type of [Cr 3 O] Core